Why do APS-C and full-frame 50mm lenses have the same field of view on my APS-C camera?
Asked 6/3/2017
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I use a Sony a5100 (APS-C) and compared two 50mm lenses on it: a Sony E 50mm f/1.8 made for APS-C and a manual Minolta MC Rokkor-PG 50mm f/1.4 made for 35mm film/full-frame, mounted with a simple non-optical adapter. I expected the full-frame 50mm to behave more like an 80mm APS-C lens because of crop factor, but both lenses appear to give the same angle of view. Why?
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
9y ago
2 Answers
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Here's what you are missing: The crop factor multiplier only applies if you want to compare the same focal length lenses on two different cameras with different sensor sizes.
Used on the same camera, any lens with a 50mm focal length will give the same field of view (assuming both lenses cast an image circle large enough to completely cover the sensor). That is because focal length is a property of the lens, not of the size of the sensor. Angle of view is a property of both the focal length and the size of the sensor.
For more, please see these existing questions here at photography.stackexchange:
Why do Full Frame lenses and crop body lenses exhibit the same crop factor when used on a crop body camera?
Does my crop sensor camera actually turn my lenses into a longer focal length?
Does an APS-C lens label itself with effective or true focal length?
Shooting 50mm EF vs EF-S
What is crop factor and how does it relate to focal length?
What is "angle of view" in photography?
Is an EF 50mm f/1.4 the same as 50mm with an EF-S lens on a Canon 550D?
Will a 50mm EF lens give the same result as a 50mm EF-S lens?
What does 'Equivalent to 1.6x the focal length of the lens' mean?
FX glass on DX body
Why don't lens manufacters just label their lenses in 35mm equivalent terms?
Why are crop lenses indicated with focal lengths they don't have?
How does "designed for APS-C" affect focal length?
Originally by user15871. Source · Licensed CC BY-SA 4.0
user15871
9y ago
0
Generated from our catalog & community — verify before relying on it.
Because both lenses are 50mm, and you’re using them on the same APS-C camera.
Crop factor does not change a lens’s focal length. It only helps compare the field of view of the same focal length on different sensor sizes. On your a5100, any true 50mm lens will give essentially the same field of view as any other 50mm lens, as long as the lens covers the sensor and the adapter has no optics changing magnification.
What changes between APS-C and full-frame lenses is mainly the size of the image circle they project, not the focal length itself. A full-frame 50mm projects a larger image circle, but your APS-C sensor still only records the central APS-C-sized portion. An APS-C 50mm is designed to cover a smaller image circle, but the captured field of view is still determined by 50mm focal length plus your APS-C sensor size.
So on APS-C:
- 50mm APS-C lens ≈ same field of view as
- 50mm full-frame lens
Both are roughly equivalent to an 75–80mm field of view compared with full frame.
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UniqueBot
AI9y ago
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