hello,
I have a very old Darlot Paris Single View lens that has a rotating disc of stops but no markings on them at all. How could I determine what f/stops these holes represent?
thanks
hello,
I have a very old Darlot Paris Single View lens that has a rotating disc of stops but no markings on them at all. How could I determine what f/stops these holes represent?
thanks
If you can measure them and if you know the focal length of the lens, you can work it out mathematically. Even approximate values would be helpful, I imagine.
I might be wrong, but I would start by going on the assumption that each hole allows half as much light as the next.
Kent in SD
In contento ed allegria
Notte e di vogliam passar!
Find your size lens here on page 17!
http://www.antiquecameras.net/1890lenscatalogue.html
It will give the real focal length.
Devide this figure by the diameter of "holes" and you have the F-value for each. When there are only 4 or 5 hole, the apertures may not follow the usual sequence.
Last edited by Steven Tribe; 29-Mar-2017 at 00:51.
thanks so much for the helpful ideas!
Terence,
I am collecting old brass lenses and often face the same problem. It is always helpful to check literature, when you can find it. But I feel more reassured if I can combine or double check it with some experimental procedure. I usually take pictures of front element with different stops and then measure the entrance pupil (not the hole size) comparing sizes in pixels. This is just a procedure to measure something that is not accessible, that is an image. I describe the method here: https://apenasimagens.com/en/measuring-lens-aperture/. In case you don't know the focal length, I also prepared a routine that takes several sets of image size, subject size and lens trip (up to 12). Then a linear regression is made in order to show the focal length. I like that because it gives you an idea of consistency of data through a simple statistical algorithm. I have that here: https://apenasimagens.com/en/measure...-focal-length/. You have to be in the mood of doing this home lab work. I understand that the quick way is just about installing the lens in your camera, focus your subject and shoot.
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