How does APS-C change field of view, depth of field, and perspective with the same lens?
Asked 11/19/2012
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If I use the same 50mm lens on both full-frame and APS-C, am I simply seeing a cropped portion of the full-frame image, or does the lens itself somehow change its angle of view? Iām also trying to understand what stays the same and what changes: field of view, depth of field, and perspective/compression. Is it correct that perspective stays the same with the same shooting position, while APS-C only records the center of the image circle? And is the often-mentioned increase in depth of field on APS-C mainly because you would stand farther back to match the same framing?
Originally by Photography Stack Exchange contributor. Source Ā· Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
13y ago
2 Answers
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In short, yes, it is actually different, but only because the angle of view is by definition measured to the edge of your view ā which is the edge of the sensor, which is (again by definition) different on APS-C.
Your statement
I think that the angle of view, depth of field, and compression are the same as on an FX/Full frame but we are seeing only middle, correct?
is completely correct (with that caveat). But, "is the angle of view actually different on a DX/APS-C crop sensor or are we just seeing less of the full frame angle of view" is meaningless, because it's called angle of view because the view is what's measured. One could measure the angle to the edge of the projected circle of light from the back of the lens, but that's not particularly useful since it's not recorded. The exercise in my answer to What is "angle of view" in photography? should make this all clear.
And you're right about the depth of field, too. More on that at Why does a bigger sensor lead to a shallower depth of field? and Can a smaller sensor's "crop factor" be used to calculate the exact increase in depth of field?.
And, you're also right about the effect on perspective: that's solely a matter of where you stand. That's covered at What is background compression?, and to quote ex-ms from an answer there:
If you take a shot with a wide-angle lens and crop down to the very centre, you would have the same background compression as if you took the shot with a telephoto lens.
Originally by user1943. Source Ā· Licensed CC BY-SA 4.0
user1943
13y ago
0
Generated from our catalog & community ā verify before relying on it.
Yes: with the same lens, APS-C is essentially recording a smaller central crop of the image circle. The lens itself does not change focal length, aperture, or perspective.
What changes is the recorded field/angle of view, because angle of view is defined by both focal length and sensor size. A smaller sensor captures less of the projected image, so the field of view is narrower.
Perspective (often called ācompressionā) does not change just because of sensor size. Perspective is determined by camera position. If you stand in the same place and use the same lens, perspective is the same on APS-C and full frame; APS-C just crops tighter.
Depth of field with the same lens and same camera position is not changed by the sensor itself in any magical way. In practical use, people often back up with APS-C to get the same framing theyād have on full frame, and that change in distance increases apparent depth of field.
So the best summary is: same lens, same position = same perspective and same optical rendering, but a smaller sensor gives a narrower recorded angle of view because it crops the image.
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