Optical performance of Mak 90 mm f/16, 200 mm f/15 and 200 mm f/10 in near UV

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christian viladrich
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Optical performance of Mak 90 mm f/16, 200 mm f/15 and 200 mm f/10 in near UV

Post by christian viladrich »

Hello,
I've just uploaded a webpage on the optical performance of Mak telescopes in near UV and blue light, according for Ca K & H and G-band.
Indeed, Mak telescopes are easily available in 90 mm to 150 mm apertures, and quite compact too.

http://astrosurf.com/viladrich/astro/in ... ak/Mak.htm

- The small 90 mm f/16 Mak-Gregory is doing good, even in Ca K. I think the current design of the ETX 90 mm is no longer f/16 but f/12 ?

- The 200 mm Mak-Gregory 200 mm f/15 is no good is near UV and blue. Mak-Gregory version means than the secondary mirror is indeed the central part of the back of the meniscus, which is coated to reflect light.

- The 200 mm Mak-Rumak 200 mm f/10 is excellent from UV. The Rumak version has a separed secondary mirror, which allows a much better correction. I am afraid Rumak are now quite rare. Years ago, Intes manufactured Rumak in 180 mm, 200 mm and 250 m apertures.

Christian


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MalVeauX
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Re: Optical performance of Mak 90 mm f/16, 200 mm f/15 and 200 mm f/10 in near UV

Post by MalVeauX »

Interesting, thanks! Mirrors without corrector plates that sabotage near UV are probably best for near UV as you've shown here.

I'm curious what do you think attributes the better near UV performance on the Rumak compared to other two designs?

And do you think its worth it on these designs at these apertures vs just using a long focal-ratio newtonian reflector for the same job, say, F6 at the fastest?

And with either, do you think it would require specific focal length amplification to not negatively influence the optical performance with a barlow or telecentric barlow, etc?

Very best,


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Re: Optical performance of Mak 90 mm f/16, 200 mm f/15 and 200 mm f/10 in near UV

Post by marktownley »

Thanks Christian. I found my meade etx90 awful in cak and got rid of it for that reason.


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Re: Optical performance of Mak 90 mm f/16, 200 mm f/15 and 200 mm f/10 in near UV

Post by vineyard »

This is v useful to know, thanks (I have an old STF7 f/10 Rumak :) 180mm aperture). Have you ever had a chance to run an ETX125 f/15 through its paces?


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Re: Optical performance of Mak 90 mm f/16, 200 mm f/15 and 200 mm f/10 in near UV

Post by christian viladrich »

I've just included the simulation of the 150 f/15 Mak originaly designed by John Gregory in 1957 :

http://astrosurf.com/viladrich/astro/in ... ak/Mak.htm

Back then, the design looked interesting for ATM because all surface were spherical. But now, it is difficult to find much interest in the Mak-Gregory version.


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Re: Optical performance of Mak 90 mm f/16, 200 mm f/15 and 200 mm f/10 in near UV

Post by christian viladrich »

MalVeauX wrote: Sun May 29, 2022 2:33 pm Interesting, thanks! Mirrors without corrector plates that sabotage near UV are probably best for near UV as you've shown here.

I'm curious what do you think attributes the better near UV performance on the Rumak compared to other two designs?

And do you think its worth it on these designs at these apertures vs just using a long focal-ratio newtonian reflector for the same job, say, F6 at the fastest?

And with either, do you think it would require specific focal length amplification to not negatively influence the optical performance with a barlow or telecentric barlow, etc?

Very best,
Hello Marty,
The Rumak is better because the curvature of the secondary mirror is different than the curvature of the rear surface of the meniscus. This is an additional degree of freedom for the correction of aberation.

An f/6 Newton vastly outperforms a Gregory-Mak. However the Mak-Rumak is quite interesting in term of field coverage.

I have'nt investigated the combination with a Barlow lens.


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Re: Optical performance of Mak 90 mm f/16, 200 mm f/15 and 200 mm f/10 in near UV

Post by christian viladrich »

marktownley wrote: Sun May 29, 2022 4:45 pm Thanks Christian. I found my meade etx90 awful in cak and got rid of it for that reason.
Very interesting, and not completely surprising.


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Re: Optical performance of Mak 90 mm f/16, 200 mm f/15 and 200 mm f/10 in near UV

Post by christian viladrich »

vineyard wrote: Sun May 29, 2022 9:09 pm This is v useful to know, thanks (I have an old STF7 f/10 Rumak :) 180mm aperture). Have you ever had a chance to run an ETX125 f/15 through its paces?
You have to keep it preciously ;-)

I have not checked a ETX 125 f/15.


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Re: Optical performance of Mak 90 mm f/16, 200 mm f/15 and 200 mm f/10 in near UV

Post by vineyard »

christian viladrich wrote: Tue May 31, 2022 6:17 pm
You have to keep it preciously ;-)
I do! I've never looked through any other scopes of this (or bigger) aperture so can't really compare, but this is so well made, even the finder is a joy. Wonderful on the moon, I'm waiting for Mars this year :)

Cheers.


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Re: Optical performance of Mak 90 mm f/16, 200 mm f/15 and 200 mm f/10 in near UV

Post by RomanH »

Thanks for very interesting info!


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