Does an 18-55mm APS-C kit lens keep the same focal length on a crop-sensor Canon?
Asked 9/16/2010
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I have a Canon 50D with the 18-55mm kit lens and I’m confused about whether the marked focal length is “full-frame equivalent” or the lens’s actual focal length. On a Canon APS-C body with a 1.6x crop factor, is 18mm still 18mm, or should I think of it as 28.8mm? Also, how does this relate to using EF-S lenses on full-frame cameras?
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
15y ago
2 Answers
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You can't actually mount the 18-55mm lens on a full-frame Canon camera as it's an EF-s lens (not EF) so it's designed to physically not fit. The focal length of a lens is independent of the sensor size (a 50mm lens is a 50mm lens regardless of what camera it's mounted on) however the field of view (how wide the lens appears) will be affected by the crop, so the 18mm lens will be the same field of view as a 28.8mm lens on a full frame camera.
Incidentally I've had very good results mounting the £80 50mm f/1.8 on a £1000 Canon 5D. A lens doesn't have to be expensive to give good results if used in the right way.
Originally by user1375. Source · Licensed CC BY-SA 4.0
user1375
15y ago
0
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The 18-55mm marking is the lens’s actual focal length. Focal length does not change with sensor size.
What does change is field of view. On your Canon APS-C 50D, the 1.6x crop sensor gives the same field of view as about 28.8-88mm on a full-frame camera. So 18mm is still 18mm, but it frames like a 28.8mm lens would on full frame.
Your Canon 18-55mm kit lens is an EF-S lens, which is designed for APS-C bodies. Canon EF-S lenses are not meant to be mounted on Canon full-frame DSLRs. If such a lens were used on full frame, you’d expect heavy vignetting or image circle issues.
So the short version is: lens focal length stays the same; crop factor only changes the effective field of view.
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