What changes when using equivalent focal lengths on APS-C and full-frame cameras?
Asked 4/20/2012
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If a 35mm lens on an APS-C/DX camera gives about the same field of view as a 50mm lens on a full-frame camera, what stays the same and what changes between those setups? Specifically, how do perspective, exposure, depth of field, and background blur/bokeh compare when shooting the same scene, especially if both lenses are used at the same f-number?
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
14y ago
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Assuming the same scene and focal lengths chosen to match field of view:
Perspective will be the same, as it is a function of subject distance.
Exposure will be the same for he same f-stop.
Depth of field will be different for the same f-stop, as it is a function of absolute aperture size, 50/2.8 is a bigger quantity than 35/2.8, so the 50mm lens will have shallower depth of field.
Bokeh in the strictest sense is dependant on the lens design and construction so there is no overall trend.
The larger format will in general resolve more detail.
Originally by user1375. Source · Licensed CC BY-SA 4.0
user1375
14y ago
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Generated from our catalog & community — verify before relying on it.
For the same framing, a 35mm on APS-C and a 50mm on full frame are only “equivalent” in field of view.
What stays the same:
- Perspective: same, if camera position/subject distance stays the same. Perspective depends on where you shoot from, not sensor size.
- Exposure: same at the same shutter speed, ISO, and f-number.
What changes:
- Depth of field: not the same at the same f-number. The 50mm on full frame will give shallower depth of field than the 35mm on APS-C when framing is matched.
- Background blur: generally greater on full frame with the longer lens at the same f-number.
- Total captured detail/light over the whole image: the larger format generally gathers more total light and can resolve more detail.
About bokeh:
- Bokeh quality is mainly a lens-design characteristic, so there is no universal “APS-C vs full frame” bokeh look apart from the depth-of-field/background-blur difference.
A useful rule: equivalence applies to both focal length and f-number for matching look. So roughly, 35mm f/1.8 on APS-C behaves similarly to about 50mm f/2.7 on full frame for field of view and depth of field.
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