What is better, f5.9 or f6.9, to use with a Quark filter

Use this section to discuss "standard" Baader/Coronado/ Lunt SolarView/ Daystar, etc… filters, cameras and scopes. No mods, just questions/ answers and reviews.
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shadowchaser
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What is better, f5.9 or f6.9, to use with a Quark filter

Post by shadowchaser »

I'm considering purchasing an 81mm aperture refractor telescope to use with my Quark Chromosphere filter in order to achieve a wider field of view compared to my Sky Watcher Evostar 150.
I have two telescopes in mind: the William Optics Zenithstar 81 (doublet) with an f6.9 focal ratio, and the William Optics GT81 (triplet) with an f5.9 focal ratio. I am inclined towards the GT81 due to its shorter focal length, but I'm unsure if its f5.9 ratio would have a negative impact on the performance of the Quark filter.

Thank you very much in advance!

Eduardo Schaberger Poupeau


Dennis
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Re: What is better, f5.9 or f6.9, to use with a Quark filter

Post by Dennis »

Go for the f / 6.9 one. You want to achieve at least something like f30 at the etalon. Short focal length refractors are not a thing when it comes to contrasty h-alpha. f/35-40 is even better for the etalon performance.


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shadowchaser
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Re: What is better, f5.9 or f6.9, to use with a Quark filter

Post by shadowchaser »

Dennis wrote: Thu May 25, 2023 9:48 pm Go for the f / 6.9 one. You want to achieve at least something like f30 at the etalon. Short focal length refractors are not a thing when it comes to contrasty h-alpha. f/35-40 is even better for the etalon performance.
Thanks a lot for the advice, Dennis! I really find it super helpful!


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Re: What is better, f5.9 or f6.9, to use with a Quark filter

Post by marktownley »

The f6.9 scope will deliver a more contrasted view with the Quark


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