identify Max F stop

[Steve M Hostetter]

Hello,,

I have a 16" barrel lens with a front diameter of 4-1/8" ... What would be the maximum F stop ??


Thank you
steve

[goamules]

The diameter will give you a "close" Fstop, but you really need to measure the circle of light you can see, looking into the front. There may be internal restrictions, so it's not about just measuring the glass.

But the formula is Focal Length divided by "apparent aperture" equals Fstop.

So 16 / 4.125 = F 3.8

[Steve M Hostetter]

goamules,, Yes I see what your saying and I do see a inner rim near the fstop slot which is maybe in an 1/8th .. hence f4.0

thank you
steve

[Steve M Hostetter]

Guess I'm gonna shoot this beast tomorrow morning.. She weighs in at 8 lbs but I've tested it with my Korona and after bending the rail sliders in tight (makes for stiff focus) but they can now handle the weight ..
Wish me luck.
steve