H-alpha telescope with Omega Optical filters

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Re: H-alpha telescope with Omega Optical filters

Post by p_zetner »

Hi Mark.

I'm not that familiar with the PST optics but, if the front lens is used to collimate, then replacing it with a telecentric will truly mess things up. A collimator, in effect, produces a final image at infinity (parallel beams output). The telecentric is designed for an image plane located at finite distance (converging beams output). Totally different optical requirements.

If you have access to just the PST etalon by itself (no additional focusing optics) then you could consider placing it in the image space of a telecentric. That might be interesting! (Is that what you're proposing?)

Cheers.
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Re: H-alpha telescope with Omega Optical filters

Post by marktownley »

If you have access to just the PST etalon by itself (no additional focusing optics) then you could consider placing it in the image space of a telecentric. That might be interesting! (Is that what you're proposing?)


Yes, this is what I was proposing, would it work, and if so how to do it??? :)


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Re: H-alpha telescope with Omega Optical filters

Post by p_zetner »

Hi Mark.

That's good! The 1st step would be to determine how much back focus (distance from final lens surface in telecentric to image plane - ccd) you want. You'd have to fit the PST etalon within this back focus distance and have room for your camera. If you want to try a single (positive) achromat lens for the refocuser then the back focus would simply be the focal length of this refocuser lens. For lens groups (2 or more) this calculation becomes more complicated and more difficult to explain unless you have some background in paraxial optics.

Once you establish the necessary focal length of the refocuser, the required focal length of the (negative) collimator lens is determined by the magnification you want the telecentric system to achieve. A factor of 2x , for example, requires the collimator to have half the focal length of the refocuser (only negative). If we call the refocuser L3 and the collimator L2 then the magnification is simply: mag = -f3/f2.

Telecentricity of the L2, L3 system requires a specific separation between L2 and L3. The separation between these lenses is determined by f2, f3 and the objective focal length through the formula for d2 in the notes I attached above.

So, you'll have to make some calculations, but relatively simple ones.

Hope this helps.

Peter.


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Re: H-alpha telescope with Omega Optical filters

Post by GreatAttractor »

Thank you, Peter, I might give it a try at some point. Though for now I like how the prominences come out and I'll work to maximize the sweet spot with a single etalon.


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Re: H-alpha telescope with Omega Optical filters

Post by GreatAttractor »

Peter,
I'm considering using the telecentric configuration. As you said, the telecentric beam, in which the etalon will be located, should be at least f/30. Since I don't want to have an oversampled image (Chameleon's pixels are well-matched to rather f/13-f/16), I'd need to use a focal reducer after the etalon. Can you offer any advice on that?

I've once tried a cheap, no-name 1,25" 0.5x reducer (screws into camera nosepiece) in Mak 180 (native f/15), quite narrowband (Solar Continuum - 8 nm), and outer 50% of image was distorted (that is, on Chameleon's small 1/3" sensor). Perhaps a longer f.l. achromat or a plano-convex lens, or positive meniscus, like something from Surplus Sched? (This is of course for narrowband only, H-alpha or continuum green light).


My software:
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ImPPG — stack post-processing and animation alignment
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SW Mak-Cass 127, ATM Hα scopes (90 mm, 200 mm), Lunt LS50THa, ATM SSM, ATM Newt 300/1500 mm, PGR Chameleon 3 mono (ICX445)
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Re: H-alpha telescope with Omega Optical filters

Post by GreatAttractor »

Nevermind, I got a whole load of Surplus Shed lenses (incl. achromats) and will try different combinations.

Here's the picture of the latest (and probably the last) improvement to the old mod:
adapt1b600.jpg
Now it's all coaxial and rigid. B600 diagonal's nose is held in a 1,25"/2" reduction borrowed from a 2" diagonal. There is also a Borg T2 non-rotating focuser and the camera is mounted close to the blocking filter with a custom T2/C-mount rotating adapter.


My software:
Stackistry — an open-source cross-platform image stacker
ImPPG — stack post-processing and animation alignment
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SW Mak-Cass 127, ATM Hα scopes (90 mm, 200 mm), Lunt LS50THa, ATM SSM, ATM Newt 300/1500 mm, PGR Chameleon 3 mono (ICX445)
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Re: H-alpha telescope with Omega Optical filters

Post by swisswalter »

Hi Filip

that looks good, does it produce fine pics ?


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: H-alpha telescope with Omega Optical filters

Post by GreatAttractor »

Yup, everything from last week :)


My software:
Stackistry — an open-source cross-platform image stacker
ImPPG — stack post-processing and animation alignment
My images

SW Mak-Cass 127, ATM Hα scopes (90 mm, 200 mm), Lunt LS50THa, ATM SSM, ATM Newt 300/1500 mm, PGR Chameleon 3 mono (ICX445)
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Re: H-alpha telescope with Omega Optical filters

Post by swisswalter »

Hi Filip

thank you. Oh I wasn't aware of it


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 :)

from 7 am - 7 pm http://www.nanosys.ch

from 7.01 pm - 6.59 am http://www.wastronomiko.com some times vice versa ;)
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Re: H-alpha telescope with Omega Optical filters

Post by p_zetner »

Hi Filip.

Sorry, I haven't been checking this forum regularly. It seems like you have the optics under control. The prominence animations are great.
Some optics configurations I've been using (telecentric and focal reducers) can be found below.

Original designs for the Omega Optical filters:
http://www.pbase.com/p_zetner/opticsdesign1

Latest designs for the Daystar filter:
http://www.pbase.com/p_zetner/configurations

They're based on Edmund Optics / Surplus Shed achromats (with additional camera lenses for the FR).

Cheers.
Peter.


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Re: H-alpha telescope with Omega Optical filters

Post by swisswalter »

Hi Peter

thanks for the details


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 :)

from 7 am - 7 pm http://www.nanosys.ch

from 7.01 pm - 6.59 am http://www.wastronomiko.com some times vice versa ;)
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