Canon EF-S lens focal length on APS-C Body?

Started 6 months ago | Discussions thread
AndreaV
Regular MemberPosts: 126
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Re: Canon EF-S lens focal length on APS-C Body?
In reply to kbdkbd, 6 months ago

kbdkbd wrote:

Can someone please explain the resultant focal length of a Canon EF-S lens on an APS-C body such as Rebel t4i?

I think I know that to figure out the resultant focal length of an EF lens on an APS-C would be to multiply by 1.6 so for instance a 50mm EF would be 80mm equiv focal length on APS-C.

I thought that if I used an EF-S lens on the t4i designated as let's say 18-135mm that it would give a resultant image equiv to 18mm on the wide end and 135mm on the tele end. But what I have read lately seems to indicate that this is not the case.

I would like to steer away from EF-S for the eventual move to full frame, but it seems difficult to get wide angle zooms (starting in 10-15mm wide) from EF type lenses (also taking into consideration non-Canon) on an APS-C body. Now I'm thinking even if I do get an EF-S 10-22mm that I'm still not getting 10-22mm but rather 16-35.2mm on the APS-C body.

This is very confusing.

Hi. So, the issue is not if the lens is a Canon EF or EF-S. The equivalent focal length is only dependent on the sensor size. In your particular case an APS-C sensor is 1.6 times smaller than a full frame one, therefore a 50mm lens on an APS-C sensor gives an angle of view equivalent to a 50mm*1.6=80mm on a full frame sensor.

Note that the "equivalent" is referred only to the angle of view, not to the lens itself, that doesn't change its focal length depending on which camera you mount it. So your 18-135mm lens mounted on an APS-C camera will generate the same angle of view that a 28.8-216mm lens would generate on a full-frame camera.

The Canon EF-S 10-22mm used on an APS-C camera is therefore equivalent to the Canon EF 16-35mm on a full frame from angle of view.

The main difference between EF-S and EF lens is that the EF-S are not able to fully cover a sensor as big as a full frame, and that's why you can mount an EF lens on a APS-C camera but not a EF-S lens on a FF camera.

I hope I was not too confusing!

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