Randy
23-Jun-2011, 15:59
I am sure this has come up before but I can't seem to find what I need to know. I calculated waterhouse stops for an old brass lens a couple years ago with the help of Galli, but that was then, this is now :( and I forgot...and I suck at cipher'n.
I have an uncoated 18" f/10 Wollensak Process Velostigmat.
I unscrewed the front cell and taped a 12" coated meniscus to the front. Infinity focus is now 12" with the rear cell still in place.
I want to calculate the aperture at wide open, all the way up to f/64 on the existing aperture dial.
Here are my measurements:
FL - 12" (300mm)
Front element diameter - 65mm
Aperture openings:
f/10 - 44mm
f/16 - 29mm
f/22 - 20mm
f/32 - 12mm
f/45 - 9mm
f/64 - 7mm
I guess what I need to figure out is what the aperture actually is when set wide open (f/10 on the dial), and what each succeeding f/stop actually is. I am guessing f/10 on the dial is probably more like f/8, f/16 on the dial is probably closer to f/11, and so on.
If someone could give me some instructions to at least get me started, or offer a web page that might give instructions, I would be grateful. I am anxious to give this lens concoction a try on 5X7.
I have an uncoated 18" f/10 Wollensak Process Velostigmat.
I unscrewed the front cell and taped a 12" coated meniscus to the front. Infinity focus is now 12" with the rear cell still in place.
I want to calculate the aperture at wide open, all the way up to f/64 on the existing aperture dial.
Here are my measurements:
FL - 12" (300mm)
Front element diameter - 65mm
Aperture openings:
f/10 - 44mm
f/16 - 29mm
f/22 - 20mm
f/32 - 12mm
f/45 - 9mm
f/64 - 7mm
I guess what I need to figure out is what the aperture actually is when set wide open (f/10 on the dial), and what each succeeding f/stop actually is. I am guessing f/10 on the dial is probably more like f/8, f/16 on the dial is probably closer to f/11, and so on.
If someone could give me some instructions to at least get me started, or offer a web page that might give instructions, I would be grateful. I am anxious to give this lens concoction a try on 5X7.