FF lenses on APS-C sensor cameras

Started May 4, 2012 | Discussions thread
sherwoodpete
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Re: FF lenses on APS-C sensor cameras
In reply to thejohnnerparty, May 4, 2012

thejohnnerparty wrote:

I am confused. Do we or don't we get 1.5 x magnification when we put FF lenses on APS-C sensor body cameras?

Yes. At the simplest level, it doesn't matter whether or not the lens was designed for full-frame or APS-C. (Though the optical characteristics of the lens may differ). This applies if both the full-frame and APS-C cameras have a similar number of pixels.

Or, do we just get a narrower field of view because of the smaller sensor in the camera?

If the full-frame camera has the same number of MP as the APS-C camera, then cropping the full-frame image to give a similarly reduced angle of view would result in a substantially lower resolution image (because of the lower number of pixels). This lower-resolution image would not allow printing to such a large size as the APS-C image.

It's important to realise that digital camera images, just like those from a film camera, undergo two stages. First, the lens produces a reduced-size image on the sensor or film. When the image is printed or displayed, this small image is enlarged.

The image from the smaller-sensor camera will be enlarged more than that from a large-sensor camera, to produce a print of the same size. This is where the difference arises.

Similarly, a compact camera with a 50mm (actual) lens can deliver an image which would require a 300mm lens on full-frame.

The lens does not operate in isolation. It can give different degrees of enlargement depending upon what sensor it is used with, and how closely-packed the pixels are.

Of course there are trade-offs made, such as increased noise, or diffraction effects. Any lens defects, such as chromatic aberration, may appear worse with this extra degree of enlargement. That's why it's generally a good idea to use a lens with an optical design which is optimised for that particular sensor size.

Regards,
Peter

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