Is a C8 and a PST mod really usable?

Frankenscope? Let's see it!***be advised that NOTHING in this forum has been safety tested and you are reading and using these posts at your own peril. blah, blah, blah... dont mess around with your eyesight when it comes to solar astronomy. Use appropriate filtration at all times...
Post Reply
User avatar
marktownley
Librarian
Librarian
Posts: 42269
Joined: Tue Oct 18, 2011 5:27 pm
Location: Brierley Hills, UK
Has thanked: 20424 times
Been thanked: 10242 times
Contact:

Re: Is a C8 and a PST mod really usable?

Post by marktownley »

Great looking mod there!


Image
http://brierleyhillsolar.blogspot.co.uk/
Solar images, a collection of all the most up to date live solar data on the web, imaging & processing tutorials - please take a look!
bart1805
Almost There...
Almost There...
Posts: 636
Joined: Mon Feb 06, 2017 9:04 pm
Location: The Netherlands
Been thanked: 1 time

Re: Is a C8 and a PST mod really usable?

Post by bart1805 »

Hi langleif, looks nice! Don't understand completely what you are saying.
- there is no difference between a 180mm f/10 refractor and a C8 when you look at the light cone. That the light cone is bigger than the etalon means that you are not able to see the whole of the sun. Not that you are using just 6 inch when using a magnification of 200 times or a ASI290MM.
- when imaging you could try without the ITF but with a UV/IR block or the Baader 35nm H-alpha.
- what do you mean with the H-alpha layer on a BF of a PST? Don't you mean the other filter you cab find on top of the black box?
AOK made me an adapter to mount the etalon directly to an Intes M703: http://solarchatforum.com/viewtopic.php ... 64#p238164
If asked he would surely be willing to make one for you.
Looking forward to images you made with the ASI! Bart.


AndiesHandyHandies
Way More Fun to Share It!!
Way More Fun to Share It!!
Posts: 1444
Joined: Fri Mar 30, 2018 6:46 am
Location: Derbyshire UK
Has thanked: 3292 times
Been thanked: 1887 times

Re: Is a C8 and a PST mod really usable?

Post by AndiesHandyHandies »

Hi,

Does the PST with the original black box on the back reach focus on the C8? If so how far is the eyepiece field stop back from the C8?

The optimum back focus on the C8 for no spherical abberation is 5" 127mm. The PST Collimator needs to be 200mm inside the original telescopes focus to collimate properly. You may need to move the Collimator out of the PST and up inside the focus tube or diagonal. So that the PST etalon can go after the Celestron output port with a short adapter. The lens fits in a Celestron/Skywatcher plastic Moon filter. So that the C8 and PST are used optimally. Whilst you can get a focus where its not in the optimal position there will be abberations from the C8 and/or PST if both not used optimally.

The 30mm is the whole beam and probably vignetted. I asked what the fully illuminated field was for a similar Meade LX200 on CN and Don Pensack said 23mm, and thats at the output. I worked out for someone on CN the fully illuminated field with a diagonal on and I said he only needed to use 0.96" old eyepieces. Say 20mm field stop? Daystar say the clear aperture of the PST is 18mm.

The focal length of the C8 is 2035mm so the suns size at focus is about 21mm so you will not quiet have a full Sun.

You need to have the PST Collimator lens 200mm in front of the telescopes focus to use the full F10. But it will be vignetted as the beam there is the focal plane size of 21mm plus the light cone needed for full illumination. 200mm x 200mm / 2035mm = 20mm. So at 40mm you will have some vignetting for a 30mm output. Only the centre of the image will be fully illuminated.

Most front DERFs seem to pass about 40% of the light through at best.
Astrograph uses 2" Baader 35nm filters as an internal ERF up to 6" on refractors. He says the light coming through is 'cold'.
So a 1.25" one will work up to 4" and I use one on a 110mm Maksutov without a problem. It should then work on the C8 with the DERF you have. I use bits of flocking to tilt the filter in its holder, double for the 2". Two on one side about 15mm apart and one opposite so it sits in a triangle.
Put the Baader up the focusser till its fully illuminated. I use a 48mm to 43mm step down ring on the front of a 2" Baader 35nm in my 127mm refractor to act as a baffle for the rest of the focus tube beyond it.
The Baader 35nm on my 110mm has the ambient temperature on the outside of its holder.

I use a Beloptik UV-IR KG3 in the eyepiece for visual to block the far IR the Baader 35nm lets through. For imaging you could put the KG3 after the Baader.

Andrew


bart1805
Almost There...
Almost There...
Posts: 636
Joined: Mon Feb 06, 2017 9:04 pm
Location: The Netherlands
Been thanked: 1 time

Re: Is a C8 and a PST mod really usable?

Post by bart1805 »

Hi langleif, luckily vignetting and aperture loss are not the same. If you use the etalon in a 100mm f5 telescope and position the etalon at minus 20cm of the focal point, then there is aperture loss. The systems functions as a 50mm f/10. When using a small etalon on a big f/10 scope, yes there is vignetting, but no aperture loss. You can see lots of images here that are made with bigger telescopes than a C8 and the resolution is a lot better. If your way of thinking was right there would be no difference.
Can't answer your other questions. The C8 is a great instrument to use as a mod, look for example at the pictures allhoest posted recently. I use a Intes Alter M703. It has the advantage that the back focus is a lot bigger than that of a C8.
CS! Bart.


AndiesHandyHandies
Way More Fun to Share It!!
Way More Fun to Share It!!
Posts: 1444
Joined: Fri Mar 30, 2018 6:46 am
Location: Derbyshire UK
Has thanked: 3292 times
Been thanked: 1887 times

Re: Is a C8 and a PST mod really usable?

Post by AndiesHandyHandies »

Hi

Well theory and practice may not differ so much.
Many people run Telecentric Daystars at F16 to F20 for seeing when F30 is optimum for the telecentric.

How did you measure the temperature? A thermometer in the beam?

The Baader will reflect most of the energy outside of its 35nm passband, and let some long IR through, over 1100nm.

What it reflects has passed through the DERF once so it should pass back through.

Because the Baader is reflecting a narrowing cone it will focus it back up the telescope to a point as far in front of it as the focus is behind it. Need to avoid its reflected focus being in corrector lenses or the DERF.

Interesting to know the temperature after the Baader is added, and also if the Beloptik KG3 is than added after the Baader.

Cheers. Andrew.


bart1805
Almost There...
Almost There...
Posts: 636
Joined: Mon Feb 06, 2017 9:04 pm
Location: The Netherlands
Been thanked: 1 time

Re: Is a C8 and a PST mod really usable?

Post by bart1805 »

If you can measure the distance of the focus of the incoming lightcone that is reflected in the 35nm filter you know how far you are from the real focus point of the C8. Optimal distance to the focus point for the front lens of the etalon is 20cm, anything less means that there is substantially more heat entering the etalon.


User avatar
Valery
Way More Fun to Share It!!
Way More Fun to Share It!!
Posts: 4059
Joined: Sun Nov 18, 2012 3:13 pm
Has thanked: 156 times
Been thanked: 893 times

Re: Is a C8 and a PST mod really usable?

Post by Valery »

langleif2 wrote: Thu Aug 22, 2019 6:32 pm What I did, the Baader filter was in place up front the PST mod at the exit of the C8 (The focus is measured when I see a sharp image with the PST mod and binoviewer in place, because that's where it's usable). I then removed the mod and measured the distance to focus point (the sharp image) albeit it was not exact. To my logic that must be the distance (heat) reflected by the filter from where it is located and then entering the telescope. But math isn't really my thing ;-) or I do not quite understand optics.

But I don't use the Baader filter up front any more because of the possible heat development. And I'll use what I think would be safe for the etalon and block filter and that's the UV/IR cut on KG3 glass. I will not allow 70 deg C entering the etalon device. By the way, I have used this setup for a while now and never had any issue with heat build up in the PST mod. Not so sure about the 35nm filter I used in a short period. I recall some heat tube currents or was it just bad seeing. Whatever, I don't use it up front anymore. I'll do otherwise if told, though.
Use a 35nm Baader or UV/IR in front of the PST etalon for absolute safeness and the BF10 at the end. No more is required.

Valery


"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.
User avatar
marktownley
Librarian
Librarian
Posts: 42269
Joined: Tue Oct 18, 2011 5:27 pm
Location: Brierley Hills, UK
Has thanked: 20424 times
Been thanked: 10242 times
Contact:

Re: Is a C8 and a PST mod really usable?

Post by marktownley »

Thanks for the update Leif


Image
http://brierleyhillsolar.blogspot.co.uk/
Solar images, a collection of all the most up to date live solar data on the web, imaging & processing tutorials - please take a look!
User avatar
daslolo
Ohhhhhh My!
Ohhhhhh My!
Posts: 62
Joined: Fri Feb 07, 2020 1:17 am
Has thanked: 4 times
Been thanked: 3 times

Re: Is a C8 and a PST mod really usable?

Post by daslolo »

What ERF do you use at the entrance of this C8?


PST on its way to modding heaven
Quark + Orion 120mm + beloptik
LX65 8" ACF
User avatar
marktownley
Librarian
Librarian
Posts: 42269
Joined: Tue Oct 18, 2011 5:27 pm
Location: Brierley Hills, UK
Has thanked: 20424 times
Been thanked: 10242 times
Contact:

Re: Is a C8 and a PST mod really usable?

Post by marktownley »

daslolo wrote: Sun Feb 16, 2020 8:18 pm What ERF do you use at the entrance of this C8?
Aries DERF


Image
http://brierleyhillsolar.blogspot.co.uk/
Solar images, a collection of all the most up to date live solar data on the web, imaging & processing tutorials - please take a look!
User avatar
daslolo
Ohhhhhh My!
Ohhhhhh My!
Posts: 62
Joined: Fri Feb 07, 2020 1:17 am
Has thanked: 4 times
Been thanked: 3 times

Re: Is a C8 and a PST mod really usable?

Post by daslolo »

marktownley wrote: Thu Feb 20, 2020 8:55 am
daslolo wrote: Sun Feb 16, 2020 8:18 pm What ERF do you use at the entrance of this C8?
Aries DERF
got it! so
450$ for the pst used
about 200$ for the various extensions to get proper focus
about 1600$ for the filter and mount (off memory)
2300$ to turn an 8" solar


PST on its way to modding heaven
Quark + Orion 120mm + beloptik
LX65 8" ACF
Post Reply