How do you estimate exposure when shooting a film SLR with no lens attached?
Asked 8/19/2021
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If a 35mm film SLR is used with no lens mounted, what effective f-number should be assumed to estimate exposure? The goal is not a sharp image, just a very blurred field of color/tones. How can shutter speed be chosen for a roughly proper exposure in this setup?
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
4y ago
2 Answers
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You can use pinhole camera calculations. It doesn't really matter that it is a terribly made/designed pinhole camera.
The distance that the lens mount opening (pinhole lens) is in front of the image/film plane is the camera's focal length. And the opening's diameter in relation to the focal length is it's f-ratio/f#. For the Nikon F mount SLR/DSLR's w/o a lens it is 46.5mm flange distance ÷ 44mm lens mount opening = f/1.06
Of course, you still need a measure of the light intensity, and know the film's sensitivity, in order to determine an appropriate SS (at least approximately).
Originally by user70370. Source · Licensed CC BY-SA 4.0
user70370
4y ago
0
Generated from our catalog & community — verify before relying on it.
With no lens attached, you can treat the camera as a very poor pinhole-like system. The effective f-number is approximated by:
f-number ≈ flange distance ÷ mount opening diameter
For example, one answer gives Nikon F as about 46.5mm ÷ 44mm ≈ f/1.06, which is effectively about f/1.0. So as a practical estimate, meter as if you were shooting around f/1.
Then choose shutter speed the normal way for your film speed and scene brightness: use a light meter or the camera meter if it can meter without a lens. One contributor reports some cameras effectively default to maximum aperture around f/1.0 and can give usable exposure that way.
This is only approximate because there is no lens forming a proper image, and the camera body opening limits the acceptance angle in a non-ideal way. But for your stated goal—very blurry, mostly solid-color frames—assuming roughly f/1 to f/1.1 is a reasonable starting point.
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