Solar mod - masking down

[Andrew*]

Okay, I need a quick answer please, because the success of my project depends on this, and there's a patient seller waiting for confirmation!! I've been getting contradicting answers to this question and need to be certain.

A PST etalon performs optimally in an f/10 light cone. My ED120 is f/7.5, but if I stop it down to 90mm, it will, in effect, become f/10, right? Therefore, it will be at the optimal ratio for the etalon?

I can't see any reason why this would not be the case, but I'm very new to this, so please set me straight.

Cheers

Andrew

[Merlin66]

Yes is the answer!

by stopping down the aperture you'll end up with f10 beam

Ken