Does a full-frame f/2.8 lens become slower on a crop-sensor body?
Asked 1/11/2016
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If I mount a full-frame lens on a crop-sensor camera, does it need more light or effectively change aperture? For example, does an f/2.8 full-frame lens behave like f/4.2 on a 1.5x crop body, or does it stay f/2.8?
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
10y ago
2 Answers
9
The amount of light passed through the lens stays the same, the lens will still be a F/2.8 lens.
Since the smaller sensor only crops out a different area from the illuminated circle, the exposure related properties of the image taking process will stay the same, regardless of the crop-factor.
Originally by user45637. Source · Licensed CC BY-SA 4.0
user45637
10y ago
0
Generated from our catalog & community — verify before relying on it.
No. An f/2.8 lens stays f/2.8 on both full-frame and crop-sensor cameras.
The lens passes the same light per unit area at a given f-number regardless of sensor size, so exposure settings do not change just because the sensor is smaller. If a scene is correctly exposed at 1/100s, f/2.8, ISO 100 on full frame, it will also be correctly exposed at 1/100s, f/2.8, ISO 100 on a crop body.
What changes is the sensor only records the center part of the image circle, so the result looks like a crop of the full-frame image. That means:
- field of view becomes narrower (e.g. 50mm looks like 75mm equivalent on 1.5x crop)
- exposure stays the same at f/2.8
- depth of field, compared at the same framing, is similar to using about f/4.2 on full frame
So the aperture does not actually become f/4.2. Only the full-frame equivalent look for framing/depth of field changes.
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