Clear aperture

Question for the group.What constitutes a 22mm or a 26mm clear aperture in a binoviewer and by extension how big do the prisms have to be to achieve the stated clear aperture.
Thanks,Scotty

Hello again Glen, why don't you say what you have in mind here, save me drawing triangles around circles anyhow.
Scott.

Theres a lot to be said on this subject. Some specific questions would help. My personal hand crafted 1.25" units have a 25mm bottom prism aperture with a 27mm opening but I have always rated them as a 22mm unit. Why? It is alway better to understate the aperture then to overstate it. I love these little gremlins. This is Michelin Tire's philosophy. Many other tire companies overstate it knowing you will come back to buy new tires to cash in on your prorate. Years ago I was service manager at a Firestone. So I know this firsthand. Now, there is bottom clear aperture, internal clear aperture, and eyepiece socket clear aperture. Which is most important? I won't go into that, but even in SCT's which are the most forgiving with regards to light cone, you start getting restrction under 29mm's at the bottom of the bino. This would reduce overall brightness. Here even a difference of 2mm's makes a big difference. The right corrector can help this problem a lot in refractors and dobs and even SCT's. But if you use an SCT without a corrector, the larger the bottom aperture the better. Clear apertures in different locations are important for different reasons. More later.

Harry Siebert