Does crop factor change light meter readings or exposure settings?
Asked 3/19/2018
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I’ve read that crop factor can make a lens seem “equivalent” to a different focal length or even a different aperture when compared to 35mm/full frame. For example, a camera with an f/3.2 lens might be described as having a wider “equivalent” aperture in full-frame terms.
When using a light meter, do I need to convert the f-number based on crop factor, or do meter readings stay the same regardless of sensor/film size?
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
8y ago
2 Answers
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No, the light meter reading (for example, ISO 100, f/11, 1/200 second) already applies to any camera, any sensor size, any crop factor. That''s the beauty of the "f/stop" numbering system.
Crop factor might apply to focal length and sensor size situations, but Not to exposure.
Originally by user38978. Source · Licensed CC BY-SA 4.0
user38978
8y ago
0
Generated from our catalog & community — verify before relying on it.
No—crop factor does not change light meter readings or the exposure you set.
An exposure reading like ISO 100, f/11, 1/200s is valid regardless of sensor or film size. That’s exactly what the f-stop system is for: f-numbers describe the light intensity reaching the image plane, so the same f-number and shutter speed give the same exposure on full frame, APS-C, medium format, etc., assuming the same ISO.
Crop factor only changes how much of the lens’s image is captured. A smaller sensor uses a smaller central portion of the image circle, which narrows the field of view compared with full frame. The lens itself does not change its actual focal length or transmission just because a smaller sensor is behind it.
So when using a light meter, use the actual aperture marked on the lens. Do not convert the f-number for crop factor when setting exposure.
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