Which gives shallower depth of field for the same framing: 50mm f/1.4 or 85mm f/1.8?
Asked 1/24/2013
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If two lenses are used wide open and the subject is framed the same size in the image, which combination gives a shallower depth of field: a 50mm f/1.4 or an 85mm f/1.8? Since the 85mm requires a greater camera-to-subject distance for the same framing, how do those factors balance out?
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
13y ago
2 Answers
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Assuming you use the Canon 550D and using the online depth of field calculator following calculations can be made:
50 mm f1.4
Focal length: 50mm
F-stop: f/1.4
Subject distance: 3mDepth of field
Near limit: 2.91m
Far limit: 3.1m
Total: 0.19m
85 mm f1.8
Focal length: 85mm
F-stop: f/1.8
Subject distance: 3 * (85/50) = 5.1mDepth of field
Near limit: 4.89m
Far limit: 5.12m
Total: 0.23m
More on subject distance with different focal lengths can be found in this answer.
Originally by user9161. Source · Licensed CC BY-SA 4.0
user9161
13y ago
0
Generated from our catalog & community — verify before relying on it.
For the same subject size in frame, the 50mm f/1.4 is slightly shallower than the 85mm f/1.8.
Using the example from the community answer on a Canon 550D:
- 50mm at f/1.4 focused at 3.0 m gives about 0.19 m total depth of field
- 85mm at f/1.8, moved back to 5.1 m for the same framing, gives about 0.23 m total depth of field
So in that comparison, the 50mm f/1.4 produces a bit less depth of field.
Why: when you step back with the 85mm to keep framing the same, the increased subject distance offsets much of the longer focal length’s tendency to reduce depth of field. The faster aperture of the 50mm (f/1.4 vs f/1.8) then gives it the edge.
In practice, the difference is modest, so perspective and background rendering may matter more to the look than the small DOF difference alone.
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