My PST CaK mod.
Re: My PST CaK mod.
Hi Bob,
I looked up that wikipedia page and I could see why you were a little unclear.
I have another site WWW.ray-optical.com this page belongs to Ray Williamson Consulting. On the page you will find Polarization Optics Tutorial. I think he does a better job explaining wave plates and polarization.
For what we want to do is get rid of secondary reflections. So we really have a broad range of 1/4 wave plates we can use.
If we start with unpolarized light and go through a linear polarizer. We get the standard( depending which school you went to P,S fast, slow, I,O ) two axis of light 90 deg apart.
Next
What is a 1/4 wave plate.
First they are usually not a 1/4 wave thick of the wavelength. They will be a multiple of the 1/4 wave or 3/4 wave to make them thick enough to work with.
The 1/4 wave plate rotates the wave 90 deg( let say counter clock wise). To keep it simple let say we are looking from the side. As the wave move forward. It would look like a the threads of a screw always rotating counter clock wise. If you looked from the end then it would look like it was going in a circle. Now when it hits a mirror it reflects back clock wise and when it get back to the 1/4 wave plate it is blocked because it is now in the wrong direction. So It stops the reflection from hitting the first mirror and reflecting back again.
The standard circulars Polaroids that 3M made, the 1/4 wave plate was design for around 560nm ( but depending how it was stretched it could be thicker or thinner, which means different wavelengths) . But they usually worked from 420nm-700nm for cutting out reflection. They came in gray, amber, red. The only difference was the color of the gel.
What we need is a UV circular polaroid. So it works the same. We placed the UV linear Polaroid axis on a piece of graph paper in the X axis and Y axis. Now the 1/4 wave plate will have its axis marked also. Now we place them 45deg from the X,Y axis. So we have a cross at 90 deg and another one at 45deg. The 1/4 wave plate will be on the back side.
Now come the practical problem. It would be best if this was all greased or laminated together with AR's on the outside windows.
I though about putting one together but I didn't have any AR's windows ( one sided) coated for 393nm. The least expensive AR would be a 1/4 wave of MGF2 at 393.4nm. It wouldn't be very broad band but it would work OK for that small range and we only care about around K-line(it would still be working at the H-line).
There is nothing new about this approach. Spectra Lab presented a paper in 1968 showing the difference between tilting and using circular Polaroids for reflection off two mirrored surfaces. They where using this approach back then with there own filters.
If you look at the ISOON diagram you will find a circular polariod between the etalons on that system.
Mark W.
I looked up that wikipedia page and I could see why you were a little unclear.
I have another site WWW.ray-optical.com this page belongs to Ray Williamson Consulting. On the page you will find Polarization Optics Tutorial. I think he does a better job explaining wave plates and polarization.
For what we want to do is get rid of secondary reflections. So we really have a broad range of 1/4 wave plates we can use.
If we start with unpolarized light and go through a linear polarizer. We get the standard( depending which school you went to P,S fast, slow, I,O ) two axis of light 90 deg apart.
Next
What is a 1/4 wave plate.
First they are usually not a 1/4 wave thick of the wavelength. They will be a multiple of the 1/4 wave or 3/4 wave to make them thick enough to work with.
The 1/4 wave plate rotates the wave 90 deg( let say counter clock wise). To keep it simple let say we are looking from the side. As the wave move forward. It would look like a the threads of a screw always rotating counter clock wise. If you looked from the end then it would look like it was going in a circle. Now when it hits a mirror it reflects back clock wise and when it get back to the 1/4 wave plate it is blocked because it is now in the wrong direction. So It stops the reflection from hitting the first mirror and reflecting back again.
The standard circulars Polaroids that 3M made, the 1/4 wave plate was design for around 560nm ( but depending how it was stretched it could be thicker or thinner, which means different wavelengths) . But they usually worked from 420nm-700nm for cutting out reflection. They came in gray, amber, red. The only difference was the color of the gel.
What we need is a UV circular polaroid. So it works the same. We placed the UV linear Polaroid axis on a piece of graph paper in the X axis and Y axis. Now the 1/4 wave plate will have its axis marked also. Now we place them 45deg from the X,Y axis. So we have a cross at 90 deg and another one at 45deg. The 1/4 wave plate will be on the back side.
Now come the practical problem. It would be best if this was all greased or laminated together with AR's on the outside windows.
I though about putting one together but I didn't have any AR's windows ( one sided) coated for 393nm. The least expensive AR would be a 1/4 wave of MGF2 at 393.4nm. It wouldn't be very broad band but it would work OK for that small range and we only care about around K-line(it would still be working at the H-line).
There is nothing new about this approach. Spectra Lab presented a paper in 1968 showing the difference between tilting and using circular Polaroids for reflection off two mirrored surfaces. They where using this approach back then with there own filters.
If you look at the ISOON diagram you will find a circular polariod between the etalons on that system.
Mark W.
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Re: My PST CaK mod.
Hi Mark
thank you very much for the wealth of information
thank you very much for the wealth of information
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Re: My PST CaK mod.
Thanks for all this info Mark, I need to do a lot of reading to get my head around what it's all on about!
In the meantime I bought a linear UV polariser; placing it between the 2 K-line elements and rotating the polariser relative to the elements has the effect of darkening the sky glow (which is a result of an out of focus ghost). I just haven't had clear skies for long enough to test this all properly and get things setup optimally, however you can see in this image I took first thing this morning the spicule ring and proms are much easier to see at the top half of the disk compared to the bottom half where we still have a ghost overlain.
cak-full-disk-large-bw by Mark Townley, on Flickr
This obviously has the effect of robbing me of some exposure time, but is all workable. Longer term i'm looking at alternatives to the blockers i'm using to get more light throughput. All in all positive results and a move in the right direction me feels...
In the meantime I bought a linear UV polariser; placing it between the 2 K-line elements and rotating the polariser relative to the elements has the effect of darkening the sky glow (which is a result of an out of focus ghost). I just haven't had clear skies for long enough to test this all properly and get things setup optimally, however you can see in this image I took first thing this morning the spicule ring and proms are much easier to see at the top half of the disk compared to the bottom half where we still have a ghost overlain.
cak-full-disk-large-bw by Mark Townley, on Flickr
This obviously has the effect of robbing me of some exposure time, but is all workable. Longer term i'm looking at alternatives to the blockers i'm using to get more light throughput. All in all positive results and a move in the right direction me feels...
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Re: My PST CaK mod.
Thank you very much for the link ( http://www.ray-optics.com/ ) and discussion Mark (W.) , a much better tutorial indeed!
Mark (T.) Very nice! - the double limb (again it is not a spicule ring -- it is the CaK chromopshere K2-K3 emission with photosphereic light leakage undernath as it were, just as in H alpha) is clearly visible all around the periphery of the disk, and good prominence detail. Do you attribute the improvement to the DS or use of the polarizer, or both? Have you tried the polarizer with a single stack to compare the results?
I'm getting the same type of "reflection" results, although in my case it must be coming from the use of the no. 2 filter (single stacked). On the other hand, I sometimes wonder if it might be due to some other effect -- perhaps camera-related -- as it always seems to be a "pulling" of light up & down the frame, as your image demonstrates, but usually more prominent is one direction verses the other. Is it possible there is some kind of excess UV leakage the camera is sensitive to that we are picking up and produces the "reflection" effect? Seems a little too consistent &/or coincidental in the location/orientation -- have you noticed this? I find it quite noticeable during the capture process.
Just food for thought (contrast adjusted to highlight effect):
Mark (T.) Very nice! - the double limb (again it is not a spicule ring -- it is the CaK chromopshere K2-K3 emission with photosphereic light leakage undernath as it were, just as in H alpha) is clearly visible all around the periphery of the disk, and good prominence detail. Do you attribute the improvement to the DS or use of the polarizer, or both? Have you tried the polarizer with a single stack to compare the results?
I'm getting the same type of "reflection" results, although in my case it must be coming from the use of the no. 2 filter (single stacked). On the other hand, I sometimes wonder if it might be due to some other effect -- perhaps camera-related -- as it always seems to be a "pulling" of light up & down the frame, as your image demonstrates, but usually more prominent is one direction verses the other. Is it possible there is some kind of excess UV leakage the camera is sensitive to that we are picking up and produces the "reflection" effect? Seems a little too consistent &/or coincidental in the location/orientation -- have you noticed this? I find it quite noticeable during the capture process.
Just food for thought (contrast adjusted to highlight effect):
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Re: My PST CaK mod.
Hi Mark
I was not aware that you are throwing LUNT CaK stacks on to the sun , you better bring them to switzerland
I was not aware that you are throwing LUNT CaK stacks on to the sun , you better bring them to switzerland
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Re: My PST CaK mod.
2 Mark T.
Before I buy a second CaK PST (for using it or DS), can you post some pairs of high resolution (as much as you do have) photos of the sun with SS vs DS photos
surace and prominences.
So, I will know exactly what I can expect from adding second main CaK filter (#1) to my CaK telescope train.
Thanks in advance.
Before I buy a second CaK PST (for using it or DS), can you post some pairs of high resolution (as much as you do have) photos of the sun with SS vs DS photos
surace and prominences.
So, I will know exactly what I can expect from adding second main CaK filter (#1) to my CaK telescope train.
Thanks in advance.
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Re: My PST CaK mod.
Hi All,
Sorry, slow to come back to the thread here...
Bob, must remember to call it the double limb - me bad! At the moment I haven't really had time (or the clear skies) to explore all the permutations that are possible with the elements in the filter. Certainly the double limb and the proms are much better seen when the filter unit is run double stacked and at f10. Much more contrast than single stack. The best thing to do Valery to look for comparisons is to have a look through the archives on my website. The whole 'CaK experiment' is documented on there often with more detail than I reflect with on here. The (linear) polariser does a decent job of removing some, but not all, of the reflections that make up the background glow in the sky. This background glow has the effect of losing contrast of proms and the double limb, you can see this effect well in the bottom of the image above compared to the top where the reflection isn't present.
In terms of the reflections i'm not sure why I get the outcome I do. I know If I hold the filter stack up to my eye and look to the sun I can see numerous ghost images. I guess this is attributed to the number of optical surfaces in the filter stack - 2x #1 CaK filters, a baader K-line (2 filters in this) and an EO 387/11nm filter.
When doublestacking the CaK filters the biggest issue you have is out of band blocking; In a single stack with 6% transmission (very nearly OD1) of filter #1 you can get away with just using a baader k-line, this combination works well. However doublestack 2 6% transmission filters and the transmission drops right down to 0.36% - about 1.5OD less, now, the transmission peak you're getting at 393nm is less than some of the out of band frequencies. So, to combat this you also then need to double stack the blockers... Problem then with all this is that the light throughput of the system drops, and with the increase of optical elements then also does the number of ghosts / reflections.
My current 'mission' with all this is to try and use different blockers than I have been using to let more light through and hopefully reduce the number of reflections; i'll let you all know how I get on...
Mark
Sorry, slow to come back to the thread here...
Bob, must remember to call it the double limb - me bad! At the moment I haven't really had time (or the clear skies) to explore all the permutations that are possible with the elements in the filter. Certainly the double limb and the proms are much better seen when the filter unit is run double stacked and at f10. Much more contrast than single stack. The best thing to do Valery to look for comparisons is to have a look through the archives on my website. The whole 'CaK experiment' is documented on there often with more detail than I reflect with on here. The (linear) polariser does a decent job of removing some, but not all, of the reflections that make up the background glow in the sky. This background glow has the effect of losing contrast of proms and the double limb, you can see this effect well in the bottom of the image above compared to the top where the reflection isn't present.
In terms of the reflections i'm not sure why I get the outcome I do. I know If I hold the filter stack up to my eye and look to the sun I can see numerous ghost images. I guess this is attributed to the number of optical surfaces in the filter stack - 2x #1 CaK filters, a baader K-line (2 filters in this) and an EO 387/11nm filter.
When doublestacking the CaK filters the biggest issue you have is out of band blocking; In a single stack with 6% transmission (very nearly OD1) of filter #1 you can get away with just using a baader k-line, this combination works well. However doublestack 2 6% transmission filters and the transmission drops right down to 0.36% - about 1.5OD less, now, the transmission peak you're getting at 393nm is less than some of the out of band frequencies. So, to combat this you also then need to double stack the blockers... Problem then with all this is that the light throughput of the system drops, and with the increase of optical elements then also does the number of ghosts / reflections.
My current 'mission' with all this is to try and use different blockers than I have been using to let more light through and hopefully reduce the number of reflections; i'll let you all know how I get on...
Mark
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Re: My PST CaK mod.
My single stack system is quite simple - 394nm Edmund Optics + #1 CaK PST - excellent contrast and a lot of light.
So, to DS the #1 CaK PST I just need to DS the 394nm EO filter as well. But I think that even OD 2 blocker will be enough to save
the same level of contrast.
So, to DS the #1 CaK PST I just need to DS the 394nm EO filter as well. But I think that even OD 2 blocker will be enough to save
the same level of contrast.
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Re: My PST CaK mod.
Hi Valery,Valery wrote:My single stack system is quite simple - 394nm Edmund Optics + #1 CaK PST - excellent contrast and a lot of light.
So, to DS the #1 CaK PST I just need to DS the 394nm EO filter as well. But I think that even OD 2 blocker will be enough to save
the same level of contrast.
Yes, that single stack system works perfectly. The important thing to realise here is when you double stack you are letting )approximately) OD1.5 less light through at 393.37nm, however the number one filter is pretty transparent with higher transmission across the rest of the spectrum, so you are not getting the same level of OD blocking here, and as such you need to compensate with more additional out of band blocking. Believe me, i've tried all this and speak from experience. My CaK filter works perfectly like your's in SS with the Baader K-line; I used it in this configuration for a couple of years, but, if you add in another #1 filter to double stack it doesn't work and the view is very washed out and lacking in contrast. The overall signal to noise ratio is worse which is why you need to add additional out of band blocking to get the contrast back. This is what is happening with Walter with his 'KLUNT' filter where he uses a Baader K-line with his Lunt CaK to get better contrast.
Mark
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Re: My PST CaK mod.
Mark,marktownley wrote:Hi Valery,Valery wrote:My single stack system is quite simple - 394nm Edmund Optics + #1 CaK PST - excellent contrast and a lot of light.
So, to DS the #1 CaK PST I just need to DS the 394nm EO filter as well. But I think that even OD 2 blocker will be enough to save
the same level of contrast.
Yes, that single stack system works perfectly. The important thing to realise here is when you double stack you are letting )approximately) OD1.5 less light through at 393.37nm, however the number one filter is pretty transparent with higher transmission across the rest of the spectrum, so you are not getting the same level of OD blocking here, and as such you need to compensate with more additional out of band blocking. Believe me, i've tried all this and speak from experience. My CaK filter works perfectly like your's in SS with the Baader K-line; I used it in this configuration for a couple of years, but, if you add in another #1 filter to double stack it doesn't work and the view is very washed out and lacking in contrast. The overall signal to noise ratio is worse which is why you need to add additional out of band blocking to get the contrast back. This is what is happening with Walter with his 'KLUNT' filter where he uses a Baader K-line with his Lunt CaK to get better contrast.
Mark
My idea was that for bringing the contrast back with #1 DS, one need additional blocker and this blocker can be OD = 2 or so. Such a filter will cost less and will have higher transmission at the 393nm wave length.
Am I correct?
BTW. Mark, I sent you the e-mail. Please, read.
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Re: My PST CaK mod.
I've obtained a second No. 1 CaK PST filter for some comparison trials.
Here's my optics chain: Orion (Skywatcher, etc.) ED100 F/9 refractor,
Baader Blue CDD filter (tilted) acting as a sub aperture ERF ~ 25 cm ahead of the CCD:
Baader CaK filter placed inside the PST filter housing acting as a bocking filter:
Then comes the original (still good!) No. 2 filter:
Then comes the original No. 1 filter in the PST housing (right), and the second No. 1, which is simply attached with silicone to the threaded ring (left):
This second No. 1 is screwed in behind the first, then placed in the existing DIY module, about 5 cm form the CCD (shown higher up in the adapter here for clarity):
Here are the identically processed images taken with my PGR Chameleon, generally poor conditions with nw winds @ 10-15 kph, temps in the mid to high 30's C:
Single stack @ 0.134 ms:
Double stack @ 0.438 ms:
Single stack @ 0.134 ms:
Double stack @ 0.438 ms:
Here's a full-disk DS mosiac taken under even worse seeing conditions. Some "scattering" remains evident; I will be exploring this more when better conditions prevail:
At this point I think it is a worthwhile addition, though nowhere near the improvement seen with DSing H alpha filters. Perhaps the waveplate/polarizer solution is in order for taming the scattering/reflection. A small enough set of filters would seem to be able to fit between the two No. 1 filters, and the use of "optical grease" per Mark Wagner might assist as well...
Best wishes,
Bob
Here's my optics chain: Orion (Skywatcher, etc.) ED100 F/9 refractor,
Baader Blue CDD filter (tilted) acting as a sub aperture ERF ~ 25 cm ahead of the CCD:
Baader CaK filter placed inside the PST filter housing acting as a bocking filter:
Then comes the original (still good!) No. 2 filter:
Then comes the original No. 1 filter in the PST housing (right), and the second No. 1, which is simply attached with silicone to the threaded ring (left):
This second No. 1 is screwed in behind the first, then placed in the existing DIY module, about 5 cm form the CCD (shown higher up in the adapter here for clarity):
Here are the identically processed images taken with my PGR Chameleon, generally poor conditions with nw winds @ 10-15 kph, temps in the mid to high 30's C:
Single stack @ 0.134 ms:
Double stack @ 0.438 ms:
Single stack @ 0.134 ms:
Double stack @ 0.438 ms:
Here's a full-disk DS mosiac taken under even worse seeing conditions. Some "scattering" remains evident; I will be exploring this more when better conditions prevail:
At this point I think it is a worthwhile addition, though nowhere near the improvement seen with DSing H alpha filters. Perhaps the waveplate/polarizer solution is in order for taming the scattering/reflection. A small enough set of filters would seem to be able to fit between the two No. 1 filters, and the use of "optical grease" per Mark Wagner might assist as well...
Best wishes,
Bob
Last edited by Bob Yoesle on Mon Jul 07, 2014 6:33 am, edited 1 time in total.
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Re: My PST CaK mod.
Hi Bob
very fine results, congratulations
very fine results, congratulations
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Re: My PST CaK mod.
Thanks a lot, Bob, for your excellent comparision between DS and SS. It seems, that I will need a second #1 CaK filter ASAP.
Valery.
Valery.
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Re: My PST CaK mod.
Thanks Walter and Valery,
I had some good seeing this morning and managed a good comparison image between continuum and CaK DS on AR 2109:
Bob
I had some good seeing this morning and managed a good comparison image between continuum and CaK DS on AR 2109:
Bob
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Re: My PST CaK mod.
Hi Bob
a very fine comparison
a very fine comparison
Only stardust in the wind, some fine and some less fine scopes, filters and adapters as well. Switzerland 47 N, 9 E, in the heart of EUROPE
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Re: My PST CaK mod.
Thank you Walter!
So looking at the reflection suppression issue, per Mark (W.) we seem to need a linear polarizer coupled to a 1/4 wave plate, and an optical coupling compound would be nice too.
Checking the usual suspects for such gear, the prices become a bit on the high side -- $500 to $1000 + USD minimum for the pair:
http://www.thorlabs.com/navigation.cfm?guide_id=8
http://search.newport.com/i/1/q1/produc ... pter/nav/1
Then I found a nice little article that opens the door to a possible and more economical solution:
http://www.bobatkins.com/photography/te ... izers.html
Thus photographic circular polarizers might be a possible solution, if of high enough quality -- they incorporate a linear polarizer and a 1/4 waveplate together in a single filter. I checked a bit on these and a couple of candidates in the appropriate sizes might be a B&W:
http://www.bhphotovideo.com/c/product/6 ... cular.html
or a Zeiss:
http://www.bhphotovideo.com/c/product/9 ... ilter.html
So I would like some advice or constructive critique - why would not these be worth a try? While likely not optimized for UV, not much else in the professional laser optics variety are either. It seems that a little "optical grease" of the "ecomomical option" -- http://www.logwell.com/tech/servtips/op ... rease.html
could be employed to make a CaK filter "sandwich" which might further reduce reflections... And there's this stuff as well, which is fairly cheap in a small quantity: http://www.advgauging.com/Merchant5/mer ... lectronics
Thoughts???
So looking at the reflection suppression issue, per Mark (W.) we seem to need a linear polarizer coupled to a 1/4 wave plate, and an optical coupling compound would be nice too.
Checking the usual suspects for such gear, the prices become a bit on the high side -- $500 to $1000 + USD minimum for the pair:
http://www.thorlabs.com/navigation.cfm?guide_id=8
http://search.newport.com/i/1/q1/produc ... pter/nav/1
Then I found a nice little article that opens the door to a possible and more economical solution:
http://www.bobatkins.com/photography/te ... izers.html
Thus photographic circular polarizers might be a possible solution, if of high enough quality -- they incorporate a linear polarizer and a 1/4 waveplate together in a single filter. I checked a bit on these and a couple of candidates in the appropriate sizes might be a B&W:
http://www.bhphotovideo.com/c/product/6 ... cular.html
or a Zeiss:
http://www.bhphotovideo.com/c/product/9 ... ilter.html
So I would like some advice or constructive critique - why would not these be worth a try? While likely not optimized for UV, not much else in the professional laser optics variety are either. It seems that a little "optical grease" of the "ecomomical option" -- http://www.logwell.com/tech/servtips/op ... rease.html
could be employed to make a CaK filter "sandwich" which might further reduce reflections... And there's this stuff as well, which is fairly cheap in a small quantity: http://www.advgauging.com/Merchant5/mer ... lectronics
Thoughts???
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Re: My PST CaK mod.
Hi Bob
thank you very much for your information. Very interesting I dive into it and visit the links
thank you very much for your information. Very interesting I dive into it and visit the links
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Re: My PST CaK mod.
Thanks, Bob, for your efforts in this project. Thoughts? My thought is that this is not so much necessary. If to use such a rig, then no necessity in fight against relections. B-CCD Baader ERF (also blocks geen and longer wave lengths) > K-line Baader > #1 CaK PST (both in the body of the #1 PST) > #1 PST (second one).Bob Yoesle wrote:Thank you Walter!
So looking at the reflection suppression issue, per Mark (W.) we seem to need a linear polarizer coupled to a 1/4 wave plate, and an optical coupling compound would be nice too.
Checking the usual suspects for such gear, the prices become a bit on the high side -- $500 to $1000 + USD minimum for the pair:
http://www.thorlabs.com/navigation.cfm?guide_id=8
http://search.newport.com/i/1/q1/produc ... pter/nav/1
Then I found a nice little article that opens the door to a possible and more economical solution:
http://www.bobatkins.com/photography/te ... izers.html
Thus photographic circular polarizers might be a possible solution, if of high enough quality -- they incorporate a linear polarizer and a 1/4 waveplate together in a single filter. I checked a bit on these and a couple of candidates in the appropriate sizes might be a B&W:
http://www.bhphotovideo.com/c/product/6 ... cular.html
or a Zeiss:
http://www.bhphotovideo.com/c/product/9 ... ilter.html
So I would like some advice or constructive critique - why would not these be worth a try? While likely not optimized for UV, not much else in the professional laser optics variety are either. It seems that a little "optical grease" of the "ecomomical option" -- http://www.logwell.com/tech/servtips/op ... rease.html
could be employed to make a CaK filter "sandwich" which might further reduce reflections... And there's this stuff as well, which is fairly cheap in a small quantity: http://www.advgauging.com/Merchant5/mer ... lectronics
Thoughts???
The pair K-line + #1 CaK PST has tilt in the cell and must be about 190mm from the camera - so the relection will not overlap the main sun disk image. This is important. Then a second #1 CaK PST should be in 50mm from the camera. All is about F/10 telescope.
When I do use very similar rig, I see no ghost image overlapped the Sun image. #2 PST > #1 PST > 140mm gap > Edmund Optics 11nm blocker.
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Re: My PST CaK mod.
Bob, Thanks for the detailed information. It will help with another project I am toying with.
Valery, thanks for the input on spacing etc.
Valery, thanks for the input on spacing etc.
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Re: My PST CaK mod.
Hi Joe, glad to help.
I've found another variation of the B+W circular polarizers -- the Kaesemann variant is stated to:
Bob
I've found another variation of the B+W circular polarizers -- the Kaesemann variant is stated to:
http://www.bhphotovideo.com/c/product/1 ... izing.htmlThe “high-end” polarizing foils of the Käsemann-type filters are neutral in color, they have a higher efficiency than conventional polarizing foils and they are cemented between high-grade plano-parallel optical glass. The resulting sandwich is then precision-polished again to achieve highly accurate plano-parallel surfaces. Subsequently they are edge-sealed to protect the foil against humidity... They are well suited for applications that require the highest possible imaging quality, especially with high-speed telephoto lenses and apochromatic lenses.
Bob
Last edited by Bob Yoesle on Thu Jul 10, 2014 4:45 pm, edited 1 time in total.
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Re: My PST CaK mod.
Hi Bob
thank you very much, more interesting stuff
thank you very much, more interesting stuff
Only stardust in the wind, some fine and some less fine scopes, filters and adapters as well. Switzerland 47 N, 9 E, in the heart of EUROPE
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Re: My PST CaK mod.
You're welcome Walter. I'm thinking some of my CaK scatter may be coming from my No.2 filter, and will try some images without it ASAP.
Also of note: Lunt appears to be implementing a similar method of using a polarizer between internal etalons to improve the performance of it's double stacking H alpha modules. Since these filters are available in sizes from 37 mm to over 100 mm, they might be worth checking out for the suppression on H alpha reflections between etalons as well.
http://www.bhphotovideo.com/c/product/1 ... izing.html
Bob
Also of note: Lunt appears to be implementing a similar method of using a polarizer between internal etalons to improve the performance of it's double stacking H alpha modules. Since these filters are available in sizes from 37 mm to over 100 mm, they might be worth checking out for the suppression on H alpha reflections between etalons as well.
http://www.bhphotovideo.com/c/product/1 ... izing.html
Bob
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Re: My PST CaK mod.
Hi Bob
an interesting thought
an interesting thought
Only stardust in the wind, some fine and some less fine scopes, filters and adapters as well. Switzerland 47 N, 9 E, in the heart of EUROPE
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Re: My PST CaK mod.
My findings as follow: the least scatter rig: Edmund Optics 11nm blocker > #1 PST CaK > 140mm gap> #2 PST CaK> 50mm gap > cameraBob Yoesle wrote:I'm thinking some of my CaK scatter may be coming from my No.2 filter, and will try some images without it ASAP.
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Re: My PST CaK mod.
Hi Valery, thanks for that ;-)
I ended up removing the No. 2 filter from my filter system, as it appears redundant and has a slight amount of cloudiness. This seems to have improved my imaging results.
Here's my "New" CaK module:
It now consists of the Baader Blue CCD filter (tilted) acting as a sub-aperture ERF > 205 mm gap > Baader CaK filter > 5 mm gap > PST No. 1 filter > 60 mm gap > PST No. 1 filter (tiltable) > 60 mm gap > CCD chip.
I'm utilizing a prototype Skybender tilt module: http://www.cloudynights.com/ubbthreads/ ... in/6403755 . It has a 1.25 inch nosepiece which is threaded for standard 1.25 inch filters; this is what the Badder CaK and piggybacked first No. 1 filter are attached to. Then it has an internal adjustable tilt filter holder to which I've attached the second No. 1 filter. I adjusted the tilt to produce the best contrast with the second No. 1 fiter, I don't think it's too far off from being normal to the optical axis. Here you can see the Baader CaK filter, and just below it is piggybacked a rotating 1.25 inch polarizer filter holder with the first No.1 filter. The second No.1 filter is similarly mounted in a standard 1.25 inch filter holder, attached to the internal tilt plate:
The Skybender system and filter holders shown above give me the ability to rotate the first and second No.1 filters with respect to each other, and tilt the soon to be purchased circular polarizer.
Here are my results from earlier today - Orion ED100 f/9 at prime focus in fair seeing:
Single stack No. 1
Double stacked No. 1's:
There is still some residual light scatter -- I'll be testing a circular polarizer in the tilt mechanism as shown in the ISOON telescope -- and placing the second No. 1 filter a bit closer to the CCD sensor... we'll see if this makes a significant improvement, or if tilting the second No. 1 filter alone is sufficient.
Again, pretty conclusive that just as with H alpha, we have less photosphere and more chromopshere detail with the DS CaK filter system.
Best wishes,
Bob
I ended up removing the No. 2 filter from my filter system, as it appears redundant and has a slight amount of cloudiness. This seems to have improved my imaging results.
Here's my "New" CaK module:
It now consists of the Baader Blue CCD filter (tilted) acting as a sub-aperture ERF > 205 mm gap > Baader CaK filter > 5 mm gap > PST No. 1 filter > 60 mm gap > PST No. 1 filter (tiltable) > 60 mm gap > CCD chip.
I'm utilizing a prototype Skybender tilt module: http://www.cloudynights.com/ubbthreads/ ... in/6403755 . It has a 1.25 inch nosepiece which is threaded for standard 1.25 inch filters; this is what the Badder CaK and piggybacked first No. 1 filter are attached to. Then it has an internal adjustable tilt filter holder to which I've attached the second No. 1 filter. I adjusted the tilt to produce the best contrast with the second No. 1 fiter, I don't think it's too far off from being normal to the optical axis. Here you can see the Baader CaK filter, and just below it is piggybacked a rotating 1.25 inch polarizer filter holder with the first No.1 filter. The second No.1 filter is similarly mounted in a standard 1.25 inch filter holder, attached to the internal tilt plate:
The Skybender system and filter holders shown above give me the ability to rotate the first and second No.1 filters with respect to each other, and tilt the soon to be purchased circular polarizer.
Here are my results from earlier today - Orion ED100 f/9 at prime focus in fair seeing:
Single stack No. 1
Double stacked No. 1's:
There is still some residual light scatter -- I'll be testing a circular polarizer in the tilt mechanism as shown in the ISOON telescope -- and placing the second No. 1 filter a bit closer to the CCD sensor... we'll see if this makes a significant improvement, or if tilting the second No. 1 filter alone is sufficient.
Again, pretty conclusive that just as with H alpha, we have less photosphere and more chromopshere detail with the DS CaK filter system.
Best wishes,
Bob
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Re: My PST CaK mod.
I've been absent from this thread for a while, time I jumped back in!
You've been doing some excellent comparisons there Bob, the last 2 comparison images really show the difference between single and double stack CaK very well. I've just not had the clear skies or the time lately to play around with my CaK rig as I would like but I have been making some inroads in reducing the scatter / reflections. I have recently been using some AR coated KG3 from Thor Labs in my setup, i'm fairly certain some of the scatter / sky brightening is caused by IR >1000nm causing noise on the camera chip, certainly with the KG3 in place it reduces, but does not completely eliminate the scatter. I've also been playing around with my Skybender and trying to work out which combination of filters works best in it. My findings echo yours Bob that the PST CaK filters like to be pretty much normal to the optical axis, i'm experimenting now with tilting the blocker in an attempt to throw reflections, though like I say the problem I am getting is finding the time and clear skies to get a good run at these experiments! I tried a linear UV polariser too, and while this shifted some reflection and scatter it never shifted it all, regardless of orientation of the polariser. Incidentally I tried one of the photographic circular polarisers when I was double stacking PST etalons last year, It got rid of the ghosts, but also significantly dimmed the image and also introduced a weird interference pattern both visible at the eyepiece and also when imaging - as such I abandoned this... I'm not surprised you get better results without the #2 filter in place, I ditched mine ages ago in favour of the baader K-line.
Mark
You've been doing some excellent comparisons there Bob, the last 2 comparison images really show the difference between single and double stack CaK very well. I've just not had the clear skies or the time lately to play around with my CaK rig as I would like but I have been making some inroads in reducing the scatter / reflections. I have recently been using some AR coated KG3 from Thor Labs in my setup, i'm fairly certain some of the scatter / sky brightening is caused by IR >1000nm causing noise on the camera chip, certainly with the KG3 in place it reduces, but does not completely eliminate the scatter. I've also been playing around with my Skybender and trying to work out which combination of filters works best in it. My findings echo yours Bob that the PST CaK filters like to be pretty much normal to the optical axis, i'm experimenting now with tilting the blocker in an attempt to throw reflections, though like I say the problem I am getting is finding the time and clear skies to get a good run at these experiments! I tried a linear UV polariser too, and while this shifted some reflection and scatter it never shifted it all, regardless of orientation of the polariser. Incidentally I tried one of the photographic circular polarisers when I was double stacking PST etalons last year, It got rid of the ghosts, but also significantly dimmed the image and also introduced a weird interference pattern both visible at the eyepiece and also when imaging - as such I abandoned this... I'm not surprised you get better results without the #2 filter in place, I ditched mine ages ago in favour of the baader K-line.
Mark
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Re: My PST CaK mod.
Hi Mark!
Good to hear form you - and some interesting points and observations.
I am not convinced the issue is one of reflections. But in the interest of thoroughness, I will get one of the best photographic circular polarizer filters seemingly available for a reasonable price: the B+W Käsemann circular polarizers:
Regarding the IR issue. How does IR longer than 1000 nm create noise on the chip, as the sensitivity curves indicate there should be no significant sensitivity beyond ~ 1000 nm? I'm using the Sony ICX445 chip:
Additionally, I'm using a Baader Blue CCD filter as an ERF, and it looks to suppress IR pretty well beyond 1000 nm, just as any normal IR/UV blocker would:
If the tiny amount of IR transmission shown in the curves above and the CCD sensors sensitivity in the IR to ~ 1000 nm or greater were responsible for the problem, I would expect it to look very different. IR would be coming mostly from the photosphere, and depending on how well the objective can focus this IR, it would appear different than the "scatter" -- or more accurately "smearing" we are seeing -- here's IR leakage in Ha -- note H alpha details are visible, and a greater intensity of out of focus photosphere sunspots. A simple IR filter (in this case a Baader Red CCD filter) cures it:
ADDENDUM:
I'm not seeing anything like this in your or my images. Thus I think we now may be left with UV leakage / verticle smearing:
See: http://www.ptgrey.com/support/kb/index.asp?a=4&q=88
Next on the shopping list will be a sub~380 nm UV blocking filter - if there is such a thing...
Again I'm hoping a good circular polarizer will rule out the reflection issue.
Best wishes,
Bob
Good to hear form you - and some interesting points and observations.
I am not convinced the issue is one of reflections. But in the interest of thoroughness, I will get one of the best photographic circular polarizer filters seemingly available for a reasonable price: the B+W Käsemann circular polarizers:
Transmission plot:Käsemann was an independent German company renowned for manufacturing some of the highest quality polarizer materialin the world. Schneider Krueznach purchased the company in 1989.
The quality and consistency of Käsemann material is uniform and neutral in color. In addition, the latest cementing technique used on these filters is guaranteed to prevent delamination. Moisture from humidity will destroy polarizing material if delamination occurs and this cementing technique protects the material by preventing delamination. Käsemann Polarizers are available in Linear and Circular. Note: The circular type comes with MRC (Multi-Resistant Coating) through 95mm.
Kaesemann-type filters feature greater optical efficiency than regular polarizing foils and are more neutral in color. The polarizing foils are cemented between plano-parallel optical glass layers, which are then precision-polished to achieve the most accurate plano-parallel surface. The Multi-Resistant Coating (MRC) is both an anti-reflection coating as well as a protective surface. It helps to increase light transmission by reducing reflections, scattered light, and ghosting.
Regarding the IR issue. How does IR longer than 1000 nm create noise on the chip, as the sensitivity curves indicate there should be no significant sensitivity beyond ~ 1000 nm? I'm using the Sony ICX445 chip:
Additionally, I'm using a Baader Blue CCD filter as an ERF, and it looks to suppress IR pretty well beyond 1000 nm, just as any normal IR/UV blocker would:
If the tiny amount of IR transmission shown in the curves above and the CCD sensors sensitivity in the IR to ~ 1000 nm or greater were responsible for the problem, I would expect it to look very different. IR would be coming mostly from the photosphere, and depending on how well the objective can focus this IR, it would appear different than the "scatter" -- or more accurately "smearing" we are seeing -- here's IR leakage in Ha -- note H alpha details are visible, and a greater intensity of out of focus photosphere sunspots. A simple IR filter (in this case a Baader Red CCD filter) cures it:
ADDENDUM:
I'm not seeing anything like this in your or my images. Thus I think we now may be left with UV leakage / verticle smearing:
See: http://www.ptgrey.com/support/kb/index.asp?a=4&q=88
Maybe we need to add some ND filters to the filter stew! Therefore perhaps it's an over-saturation issue related to the camera's sensor, which we can see from the above CDD sensor sensitivity graphs are sensitive to well below 300 nm. Or perhaps some inherent property of the No. 1 filter itself is causing the problem...Smear is often more noticeable when using very short (microsecond) shutter times. This is because the amount of charge collected in the light-sensitive area of the CCD varies based on exposure time, whereas the amount of charge that collects in the vertical transfer register is based on the sensor readout rate, which is a constant. With short exposures, the ratio of time integrating in the photosensor to time integrating in the vertical transfer is reduced. This reduced ratio may exacerbate smear.
Next on the shopping list will be a sub~380 nm UV blocking filter - if there is such a thing...
Again I'm hoping a good circular polarizer will rule out the reflection issue.
Best wishes,
Bob
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Re: My PST CaK mod.
Hi Bob
now that is an interesting point about the smear beeing related to the capture of UV light below 390nm. I doubt that it is an issue of the #1 filter as the LUNT stack showes the same problem
now that is an interesting point about the smear beeing related to the capture of UV light below 390nm. I doubt that it is an issue of the #1 filter as the LUNT stack showes the same problem
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Re: My PST CaK mod.
Good food for thought Bob!
Can't give you an answer regards IR >1000nm, I completely take on board and agree with what you're saying, when I get some clear skies for a half decent length of time i'll do some comparisons to show what I mean.
Maybe we do have a UV leak? The K line has a peak at ~340nm as can be seen in the graph, but this should still be way down in the noise floor, even with a pair of #1 CaK filters dropping the transmission at 393nm down considerably.
I have to say though, that CCD interline transfer smear does look remarkably similar to what we are seeing... More research to be done!
A good thread chaps!
Thanks
Can't give you an answer regards IR >1000nm, I completely take on board and agree with what you're saying, when I get some clear skies for a half decent length of time i'll do some comparisons to show what I mean.
Maybe we do have a UV leak? The K line has a peak at ~340nm as can be seen in the graph, but this should still be way down in the noise floor, even with a pair of #1 CaK filters dropping the transmission at 393nm down considerably.
I have to say though, that CCD interline transfer smear does look remarkably similar to what we are seeing... More research to be done!
A good thread chaps!
Thanks
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Re: My PST CaK mod.
Hi all, modders
I have added the SAFIX to my rig as a permanent optical part. The results are MUCH better than
without a SAFIX.
See here: http://solarchat.natca.net/viewtopic.ph ... 90#p123290
Bob and Mark, thanks for your input.
Valery.
I have added the SAFIX to my rig as a permanent optical part. The results are MUCH better than
without a SAFIX.
See here: http://solarchat.natca.net/viewtopic.ph ... 90#p123290
Bob and Mark, thanks for your input.
Valery.
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Re: My PST CaK mod.
Hi Valery, thanks for the update :-)
From my previous post:
I note in the above image that the smear is larger in diameter than the focused disk itself -- this could indicate the unfocused disk of the sun at the culprit wavelength. Also note that the smear is more triangular in shape above and below the sun's disk -- this may be due to limb darkening (horizontal brightness gradient) at the suspect wavelength, which would concentrate the smear more toward the center of the suns's disk, therefore intensifying the vertical smear towards the center of the disk.
Perhaps it's time to consult Point Grey for an expert evaluation...
Bob
From my previous post:
I've been thinking a bit more about this, and I'm more inclined than ever to attributing this scattered light effect to CCD smear of wavelengths which can't be focused well by the objective -- possibly IR, or more likely UV due to the cameras sensitivity in this region.On the other hand, I sometimes wonder if it might be due to some other effect -- perhaps camera-related -- as it always seems to be a "pulling" of light up & down the frame, as your image demonstrates, but usually more prominent is one direction verses the other. Is it possible there is some kind of excess UV leakage the camera is sensitive to that we are picking up and produces the "reflection" effect? Seems a little too consistent &/or coincidental in the location/orientation -- have you noticed this? I find it quite noticeable during the capture process.
Just food for thought (contrast adjusted to highlight effect):
I note in the above image that the smear is larger in diameter than the focused disk itself -- this could indicate the unfocused disk of the sun at the culprit wavelength. Also note that the smear is more triangular in shape above and below the sun's disk -- this may be due to limb darkening (horizontal brightness gradient) at the suspect wavelength, which would concentrate the smear more toward the center of the suns's disk, therefore intensifying the vertical smear towards the center of the disk.
Perhaps it's time to consult Point Grey for an expert evaluation...
Bob
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Re: My PST CaK mod.
Not too sure what it is. I had thought of the 'unfocused' disk as a possibility - same logic as you, it's larger than the actual disk...
Anyway, today I tried a new combination; KG3, PST#1, ~100mm gap, skybender with Baader K-line, ~30mm gap PST#1. Typically the clouds knew I was trying to test this out and so weren't obliging, but I did get this prom image, taken with the 40mm f10, 0.5x reducer and DMK31. I don't usually use the reducer, but today I wanted to get a quick snap of full disk with the proms. This setup is ruthless in showing up ghosts, but today we seemed to be free? Difficult I know with all that cloud but seems none too bad...
cak-prom by Mark Townley, on Flickr
I paid close attention to ensure the tilt of the elements in the K-line to make sure they aligned with the tilt axis on the skybender, by doing it this way and tilting the skybender I figured that any reflections should be deflected away from their point of origin and not interfere with the solar disk, well that was my theory...
Tomorrow morning is supposed to be properly clear - no clouds and blue skies, so will get up early in the morning and try some shots before work...
Mark
Anyway, today I tried a new combination; KG3, PST#1, ~100mm gap, skybender with Baader K-line, ~30mm gap PST#1. Typically the clouds knew I was trying to test this out and so weren't obliging, but I did get this prom image, taken with the 40mm f10, 0.5x reducer and DMK31. I don't usually use the reducer, but today I wanted to get a quick snap of full disk with the proms. This setup is ruthless in showing up ghosts, but today we seemed to be free? Difficult I know with all that cloud but seems none too bad...
cak-prom by Mark Townley, on Flickr
phpBB [media]
I paid close attention to ensure the tilt of the elements in the K-line to make sure they aligned with the tilt axis on the skybender, by doing it this way and tilting the skybender I figured that any reflections should be deflected away from their point of origin and not interfere with the solar disk, well that was my theory...
Tomorrow morning is supposed to be properly clear - no clouds and blue skies, so will get up early in the morning and try some shots before work...
Mark
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Re: My PST CaK mod.
Excellent Mark!
My full disk image was made from a six-pane mosaic - three vertical and two horizontal - so again it could be just a brightness gradient across the CCD, with the vertical smear.
Your images above seem to show a general scatter without a particular orientation... hmmm. Atmospheric scatter, ectoplasm, aether???
Looking forward to your additional images!
Best wishes,
Bob
My full disk image was made from a six-pane mosaic - three vertical and two horizontal - so again it could be just a brightness gradient across the CCD, with the vertical smear.
Your images above seem to show a general scatter without a particular orientation... hmmm. Atmospheric scatter, ectoplasm, aether???
Looking forward to your additional images!
Best wishes,
Bob
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Re: My PST CaK mod.
Hi Mark
that looks very good. Good luck in a hour
that looks very good. Good luck in a hour
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Re: My PST CaK mod.
While waiting for Mark's results, I decided to look at what I could do with my July 11th double stack image. Thanks to a suggestion from Valery, I picked up Astra Image for applying some deconvolution processing, and then added some color. Despite any of the preceding image issues, as Mark has noted (and as with H alpha) it appears that double stacking makes it easier to achieve a final result that shows both CaK prominence activity along with reasonable disk detail:
As an additional check on UV leakage, I was thinking about using this filter in the Skybender:
http://www.ebay.com/itm/Optical-Filter- ... 484266e4ba
Tilting it would seem to put it closer to being on-band @ 394 nm, and might further suppress UV leakage from the Baader CaK, and is a little bit cheaper alternative to the Edmund / Anchor 394 nm "experimental grade" filter: http://www.anchoroptics.com/catalog/product.cfm?id=567
Of course there is the Edmund 394 10 nm hard-coated bandpass filter that Valery is using instead of the Baader K line, which appears to have better UV suppression (but more IR transmission): http://www.edmundoptics.com.tw/optics/o ... ers/65-131
What are you seeing with your images Valery? - This could be a significant clue...
Bob
As an additional check on UV leakage, I was thinking about using this filter in the Skybender:
http://www.ebay.com/itm/Optical-Filter- ... 484266e4ba
Tilting it would seem to put it closer to being on-band @ 394 nm, and might further suppress UV leakage from the Baader CaK, and is a little bit cheaper alternative to the Edmund / Anchor 394 nm "experimental grade" filter: http://www.anchoroptics.com/catalog/product.cfm?id=567
Of course there is the Edmund 394 10 nm hard-coated bandpass filter that Valery is using instead of the Baader K line, which appears to have better UV suppression (but more IR transmission): http://www.edmundoptics.com.tw/optics/o ... ers/65-131
What are you seeing with your images Valery? - This could be a significant clue...
Bob
Last edited by Bob Yoesle on Mon Jul 14, 2014 10:07 pm, edited 4 times in total.
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Re: My PST CaK mod.
Good result Bob! I was clouded out, so will have to wait for another day to see how it's looking... DS CaK is definitely a good thing
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Re: My PST CaK mod.
Hi Bob
a great result using Astra Image
a great result using Astra Image
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Re: My PST CaK mod.
Watching with interest. I get the same vertical smearing on the Lunt B1800 ss. I would love to see that go away.
Look Up!
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Re: My PST CaK mod.
Hi Bob,
I would suggest you to use the EO 11nm filter because of it's very high transmission at the 393nm - somewhat higher than 90%. You need these 25% saving with your DS CaK !!!
In my opinion, the best blocker will be two EO 11nm filters. They both will supress all the continuum dawn to zero (for camera) and still deliver more than 70% transmission at the CWL.
K-line is the combo of two filters. And two EO 11nm 393nm hard coated filters will cost more than K-line, but also transmits more at the CWL and supress the continuum better.
Valery.
I would suggest you to use the EO 11nm filter because of it's very high transmission at the 393nm - somewhat higher than 90%. You need these 25% saving with your DS CaK !!!
In my opinion, the best blocker will be two EO 11nm filters. They both will supress all the continuum dawn to zero (for camera) and still deliver more than 70% transmission at the CWL.
K-line is the combo of two filters. And two EO 11nm 393nm hard coated filters will cost more than K-line, but also transmits more at the CWL and supress the continuum better.
Valery.
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Re: My PST CaK mod.
On a last note, I need to underline that CaK imaging is challenging vs Ha or white light imaging and therefore, if possible, we don't have
to allow too many compromises. Better to save longer, but buy the best components. Later then we will thanks ourselves for such a
principal position concerning compromises.
My next purchases will be a second #1 CaK filter and a second EO 394nm filter. And my CaK rig will looks as follow:
ERF > EO 394nm > EO 394nm > #1 CaK PST > SAFIX > Barlow (if needed) > #1 CaK PST> camera.
First EO 394nm should have a tilt directly opposite to the tilt of the second EO 394 which it has in the native cell coupled with a #1 CaK.
Such a directly opposite tilt will nullify the astigmatism and move the ghost reflected image out of the primary solar disk image.
Valery.
to allow too many compromises. Better to save longer, but buy the best components. Later then we will thanks ourselves for such a
principal position concerning compromises.
My next purchases will be a second #1 CaK filter and a second EO 394nm filter. And my CaK rig will looks as follow:
ERF > EO 394nm > EO 394nm > #1 CaK PST > SAFIX > Barlow (if needed) > #1 CaK PST> camera.
First EO 394nm should have a tilt directly opposite to the tilt of the second EO 394 which it has in the native cell coupled with a #1 CaK.
Such a directly opposite tilt will nullify the astigmatism and move the ghost reflected image out of the primary solar disk image.
Valery.
Last edited by Valery on Tue Jul 15, 2014 11:21 am, edited 3 times in total.
"Solar H alpha activity is the most dynamic and compelling thing you can see in a telescope, so spend accordingly." (c) Bob Yoesle.
Largest full size 185 - 356mm Dielectric Energy Rejection Filters (D-ERF) by ARIES Instruments.
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Re: My PST CaK mod.
Chaps, don't know if you picked up on this that Mark Wagner said in another CaK thread a couple of days ago http://solarchat.natca.net/viewtopic.ph ... 25#p123184 Certainly something to think about...
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Re: My PST CaK mod.
Mark,marktownley wrote:Chaps, don't know if you picked up on this that Mark Wagner said in another CaK thread a couple of days ago http://solarchat.natca.net/viewtopic.ph ... 25#p123184 Certainly something to think about...
Using two filters ( EO 394nm and #1 CaK PST) divided with 190mm gap, I was not able to detect any ghost image which overlap the main sun image even when I pushed the camera
to the highest gain and increase the exposure to that value I use for prominences imaging of even more in duration. I see only overall noise caused by continuum leackage through
the EO 394nm blocker. Adding #2 CaK filter solves this problem, but I now see the ghost image near the main sun image - as the result of the reflection between #1 and #2 filters
mounted in the one cell with a small tilt, which is enough to bring the ghost image out to not overlap with the main image. However this works only at 200m distance between these
filters and focal plane and 400mm FL. If the distance is shorter or the FL is shorter or both, the image will overlap by the ghost.
The best solution, IMHO is to tilt two(!) EO filters at larger angle than in the original cell and in directly opposite directions - so, the reflections will be out of FOV and no astigmatism will
be in the final image. Any other solutions will have more disadvantages and more optical elements involved.
Last edited by Valery on Tue Jul 15, 2014 11:23 am, edited 2 times in total.
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Re: My PST CaK mod.
All more things to try Valery! We will solve the CaK reflection issue for sure, i'm sure.
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Re: My PST CaK mod.
Hi ValeryValery wrote:On a last note, I need to underline that CaK imaging is challenging vs Ha or white light imaging and therefore, if possible, we don't have
to allow too many compromises. Better to save longer, but buy the best components. Later then we will thanks ourselves for such a
principal position concerning compromises.
My next purchases will be a second #1 CaK filter and a second EO 394nm filter. And my CaK rig will looks as follow:
ERF > EO 394nm > EO 394nm > #1 CaK PST > SAFIX > Barlow (if needed) > #1 CaK PST> camera.
First EO 394nm should have a tilt directly opposite to the tilt of the second EO 394 which it has in the native cell coupled with a #1 CaK.
Such a directly opposite tilt will nullify the astigmatism and move the ghost reflected image out of the primary solar disk image.
Valery.
what sort of ERF are you using?
Only stardust in the wind, some fine and some less fine scopes, filters and adapters as well. Switzerland 47 N, 9 E, in the heart of EUROPE
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Re: My PST CaK mod.
Hi Walter,swisswalter wrote:
Hi Valery
what sort of ERF are you using?
I now use a B&W 80A blue filter. Then the EO 11mm filter reflects enough light to be not too much heated in a 100mm telescope.
However I already ordered two ERF - a blue glass with narrower transmission in blue-violet and zero at red and IR
and also I ordered a B-CCD filter from Baader.
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Re: My PST CaK mod.
hi Velry
thank you very much. All these ERF's in 100 mm Diameter ?
thank you very much. All these ERF's in 100 mm Diameter ?
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Re: My PST CaK mod.
No, the B-CCD Baader is 2" filter - can be used as an internal ERF and the blue-violet glass I found only in 93x93mm squire,swisswalter wrote:hi Velry
thank you very much. All these ERF's in 100 mm Diameter ?
so it can be cut down to about 88mm diameter and must be installed internally not too far from the 100mm objective.
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Re: My PST CaK mod.
OK fellas, the sun came out this afternoon and I was able to play 'ghost hunting' - I found them, I videoed them, but how do we get rid of them?
I used the 40mm f10 scope with a reducer to give me somewhere in the region of 300mm fl to get it on the chip of the DMK31. You can see the main ghost - he is about 3/4 degree away from the sun, and i'm not too bothered about him, but, watch as I move the sun around the field of view - our problematic ghost is hiding straight behind the sun when we have the disk mid chip on the ccd, but, as the image is moved around it reveals our ghost who moves in a 'reflective' way the opposite the main image does.
Check out the vids...
I'm wondering if it is a reflection off the back of the objective lens?
Time to start looking at that quarter waveplate me thinks...
What are you guys thoughts?
I used the 40mm f10 scope with a reducer to give me somewhere in the region of 300mm fl to get it on the chip of the DMK31. You can see the main ghost - he is about 3/4 degree away from the sun, and i'm not too bothered about him, but, watch as I move the sun around the field of view - our problematic ghost is hiding straight behind the sun when we have the disk mid chip on the ccd, but, as the image is moved around it reveals our ghost who moves in a 'reflective' way the opposite the main image does.
Check out the vids...
phpBB [media]
phpBB [media]
phpBB [media]
I'm wondering if it is a reflection off the back of the objective lens?
Time to start looking at that quarter waveplate me thinks...
What are you guys thoughts?
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Re: My PST CaK mod.
Hi Mark
thank you very much for the demonstration. Now I see that I have at least tree ghosts. A circular one I can't get rid off, a near by the disk and a far away of the disk one. The one which bothers me is the circular one, wich I showed in an earlier pic.
thank you very much for the demonstration. Now I see that I have at least tree ghosts. A circular one I can't get rid off, a near by the disk and a far away of the disk one. The one which bothers me is the circular one, wich I showed in an earlier pic.
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Re: My PST CaK mod.
Hi Mark - fantastic videos! I think you may have nailed it...
I had already ordered an economical circular polarizer (i.e. a linear polarizer with integrated quarter wave plate) photo filter that I believe might fit a standard filter thread, or if not, the filter element itself should fit in a standard 1.25 inch filter holder, which I'll plug into the Skybender for tilting. It shipped yesterday:
http://www.amazon.com/Tiffen-28CP-Circu ... B0000AIS1K
It may not be the best, but I figured it would give an indication of how well a photo CP filter would work if the artifact was indeed a reflection phenomena -- without the increased expense of the B+W Kaesemann series. If it does what I hope it will, this 49 mm seems to be the cheapest size of the B+W Kaesemann series:
http://www.amazon.com/Kaesemann-Circula ... +Kaesemann
Again Mark, thanks for a great effort and telling results!
Bob
I had already ordered an economical circular polarizer (i.e. a linear polarizer with integrated quarter wave plate) photo filter that I believe might fit a standard filter thread, or if not, the filter element itself should fit in a standard 1.25 inch filter holder, which I'll plug into the Skybender for tilting. It shipped yesterday:
http://www.amazon.com/Tiffen-28CP-Circu ... B0000AIS1K
It may not be the best, but I figured it would give an indication of how well a photo CP filter would work if the artifact was indeed a reflection phenomena -- without the increased expense of the B+W Kaesemann series. If it does what I hope it will, this 49 mm seems to be the cheapest size of the B+W Kaesemann series:
http://www.amazon.com/Kaesemann-Circula ... +Kaesemann
Again Mark, thanks for a great effort and telling results!
Bob
Diagonally parked in a parallel universe.
Curiosity is the father of knowledge; uncertainty is the mother of wisdom.
Dark-Sky Defenders
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Curiosity is the father of knowledge; uncertainty is the mother of wisdom.
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