I have gotten a vintage brass lens. Not a genuine antique with a famous name and waterhouse stops. It is unsignerd or unbranded and has a modern-ish looking rting set diaphragm with aperture numbers that do not correspond to modern f-stop numbers.
The focal length seems to be about 300mm. Getting it mounted on a lens board just now and when it comes back it will go on my 8x10 to see what coverage it has. Howe is the actual the focal length best measured?
Getting a more accurate focal length will help in determining the f-stops.
How may I determine the aperture wide open . . .and how may this be done for the other diaphragm settings? I'd like to be able to create a conversion chart relating the lens' numbers to modern f-stop numbers.
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