Relationship between camera sensor size and lens focal length

Question

I am choosing a camera and lens.

I want to buy a Canon EOS 650D, as this camera seems to be a good point of entry into the world of SLR.

My question is in the following:

The EOS 650D has a cropped sensor, so as I understand if I use Canon 50mm f/1.8 lens, the behavior will be quite different on a smaller sensor in comparison to full-frame sensor.

What is the relation between cameras sensor size and lens focal length?

Hi Alex. Basically with a smaller sensor, any lens is effectively 1.5-1.6 times what you'd get on a full frame. So 50mm on a 650D is like a 75-80mm lens on a full frame camera. Have a look at these: focal length and crop factor and Does my crop sensor camera actually turn my lenses into a longer focal length? — MikeW, Mar 31 '13 at 07:13
And this - How can I get the same image with the same 50mm lens on both FF and APS-C? - Those links should explain how it all works. Basically a 35mm lens on a 650D is similar to a 50mm lens on full frame. 50mm is stil fine on a crop sensor, but if you're say indoors, you may find you don't have as much working room as you would with full frame — MikeW, Mar 31 '13 at 07:14

score 3 · Accepted Answer · answered Mar 31 '13 at 07:39

The 650D has a "crop factor" of 1.6 so a 50mm will have about the same field of view of 50*1.6=80mm on a full frame.

This does not change the lens's focal length (or any other optical property) you get a "zoom in" effect because you only looking at the center of the image projected by the lens, that center part of the image is exactly what you would see with a full frame camera in the same exact situation if you cropped the picture in post processing and kept only the center area.

Relationship between camera sensor size and lens focal length

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