My PST CaK mod.

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Re: My PST CaK mod.

Post by marktownley »

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.

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Re: My PST CaK mod.

Post by Bob Yoesle »

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:
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.
Transmission plot:
B+W Kas C-POL MRC 72 mm.jpg
B+W Kas C-POL MRC 72 mm.jpg (43.57 KiB) Viewed 6530 times
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:
pgr-qe-comparison1.png
pgr-qe-comparison1.png (59.85 KiB) Viewed 6530 times
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:
Baader_RGB_transmission.jpg
Baader_RGB_transmission.jpg (156.84 KiB) Viewed 6530 times
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:
IR leak.jpg
IR leak.jpg (218.44 KiB) Viewed 6530 times
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:
CCD interline transfer smear.jpg
CCD interline transfer smear.jpg (16.12 KiB) Viewed 6530 times
See: http://www.ptgrey.com/support/kb/index.asp?a=4&q=88
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.
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...

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.

Post by swisswalter »

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


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Re: My PST CaK mod.

Post by marktownley »

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.
Ba-K-log.gif
Ba-K-log.gif (135.08 KiB) Viewed 6526 times
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.

Post by Valery »

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.


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Re: My PST CaK mod.

Post by Bob Yoesle »

Hi Valery, thanks for the update :-)

From my previous post:
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):
CaK full disk enhanced.jpg
CaK full disk enhanced.jpg (91.5 KiB) Viewed 6512 times
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.

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.

Post by marktownley »

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...

Imagecak-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...

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Re: My PST CaK mod.

Post by Bob Yoesle »

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


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Re: My PST CaK mod.

Post by swisswalter »

Hi Mark

that looks very good. Good luck in a hour


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Re: My PST CaK mod.

Post by Bob Yoesle »

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:
July 11, 2014 CaK jpg SM clr.jpg
July 11, 2014 CaK jpg SM clr.jpg (196.73 KiB) Viewed 6486 times
As an additional check on UV leakage, I was thinking about using this filter in the Skybender:
400BP.GIF
400BP.GIF (10.34 KiB) Viewed 6483 times
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
Edmund 394 10 nm HC Bandpass log.jpg
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.

Post by marktownley »

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.

Post by swisswalter »

Hi Bob

a great result using Astra Image


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Re: My PST CaK mod.

Post by sullij1 »

Watching with interest. I get the same vertical smearing on the Lunt B1800 ss. I would love to see that go away.


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Re: My PST CaK mod.

Post by Valery »

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.

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Re: My PST CaK mod.

Post by Valery »

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.
Last edited by Valery on Tue Jul 15, 2014 11:21 am, edited 3 times in total.


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Re: My PST CaK mod.

Post by marktownley »

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.

Post by Valery »

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...
Mark,

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.

Post by marktownley »

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.

Post by swisswalter »

Valery 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.
Hi Valery

what sort of ERF are you using?


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Re: My PST CaK mod.

Post by Valery »

swisswalter wrote:
Hi Valery

what sort of ERF are you using?
Hi Walter,

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.

Post by swisswalter »

hi Velry

thank you very much. All these ERF's in 100 mm Diameter ?


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Re: My PST CaK mod.

Post by Valery »

swisswalter wrote:hi Velry

thank you very much. All these ERF's in 100 mm Diameter ?
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,
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.

Post by marktownley »

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...

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.

Post by swisswalter »

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.


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Re: My PST CaK mod.

Post by Bob Yoesle »

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


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Re: My PST CaK mod.

Post by marktownley »

Thanks guys, i hope it is 'just' a reflection off the back of the objective. I'll have a try this afternoon with the linear polariser if the storms stay away and the skies remain blue...


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Re: My PST CaK mod.

Post by Bob Yoesle »

Following up on some experiments:

I tried the photographic circular polarizer (reversed on the near side of the SkyBender tilt plate) between the two PST no. 1 filters without success. An interesting finding was that reversing the Baader CaK filter greatly improved the separation of the major reflections, some of which are seen in Mark's videos on the preceding page. Alas however, the smearing reflection that overlies the primary image was still there.
R_194104 LR Decon JPG sm SM.jpg
R_194104 LR Decon JPG sm SM.jpg (375.11 KiB) Viewed 2501 times
R_194104 LR Decon adj sm.jpg
R_194104 LR Decon adj sm.jpg (285.57 KiB) Viewed 2501 times
21/08/14 @ 19:41 UTC

I also noticed only the first filter of the Baader CaK is tilted, the second one is normal to the optical axis. I'm beginning to think the best solution is the obvious one -- needing to tilt every component slightly ~ 1/2 to 3/4 a degree to minimize the reflections without shifting the filter passbands too much...

Bob


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Re: My PST CaK mod.

Post by swisswalter »

Hi Bob

thanks for sharing that information


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Re: My PST CaK mod.

Post by marktownley »

I've got a lot I need to add to this thread, I will be doing a big addition to it soon...


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