Do DX/APS-C lenses use their actual focal length, and do you still apply crop factor?
Asked 3/26/2016
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I shoot Nikon APS-C (DX) and have a 50mm f/1.8 FX lens plus a 35mm f/1.8 DX lens. I understand that focal length is printed in millimeters, but I’m confused about whether DX lenses are labeled with their true focal length or with a 35mm-equivalent view.
Is the Nikon 35mm DX lens really 35mm, or should I think of it as roughly 52.5mm equivalent on DX? Do I still apply the 1.5× crop factor to DX lenses the same way I do with FX lenses when comparing field of view? Also, would a 35mm FX lens on full frame give the same view as a 35mm DX lens on APS-C?
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
10y ago
2 Answers
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35mm is the true focal length. You still need to multiply it by 1.5 to get the equivalent focal length.
If you would put it on FF Nikon body, it would show vignetting (because it was designed to cover just the DX sensor).
If you were to use the more expense FF version of the 35mm lens on a DX camera, it would look the same (apart of course for differences due to lens quality) as the DX lens on the DX body.
Originally by user48268. Source · Licensed CC BY-SA 4.0
user48268
10y ago
0
Generated from our catalog & community — verify before relying on it.
Lens markings show the lens’s actual focal length, not an “effective” one. So a Nikon 35mm DX lens is truly a 35mm lens, just like a 35mm FX lens is truly 35mm.
What changes on DX is the field of view, because the sensor is smaller. To compare with full-frame/35mm view, you still apply the 1.5× crop factor to both DX and FX lenses when used on a DX body. So a 35mm lens on DX gives a field of view similar to about 52.5mm on full frame, and a 50mm lens on DX is similar to about 75mm on full frame.
DX vs FX does not change focal length; it mainly changes image-circle coverage. A DX lens is designed to cover the smaller APS-C sensor, so on full frame it may vignette heavily. An FX lens covers full frame and also works on DX.
A 35mm FX lens on a full-frame camera will not look the same as a 35mm DX lens on a DX camera. But a 35mm FX lens on DX and a 35mm DX lens on DX should give essentially the same framing.
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