Current 40D owner contemplating upgrade

Started Nov 25, 2012 | Discussions thread
oss Regular Member • Posts: 270
Re: Current 40D owner contemplating upgrade

Y Hafting wrote:

About EFS lenses:

When it comes to the 17-55 f2.8 you should remeber that the equivalent FF lens is 27-88 f4.5, shot at 1.6 times higher iso than you would use on a non FF. And as long as the resolution of a FF lense is not worse to an EFS counterpart than 1/1.6 (in terms of lines per picture height) tested on the same camera- the FF lense will resolve more on a FF system than the EFS lense. So even a 24-105 f4 on a FF system beats the 17-55 f2.8 hands down when it comes to resolution.


This is not correct a 17-55 f2.8 lens appears to be a 27-88 f2.8 on APS-C, the f number does not change, put an EF lens on an APS-C body and the f number remains the same, the same light per unit area falls on the sensor from the same lens, you are simply sampling a smaller area of the image, it is still the same image projected from the lens as you would get on a full frame camera.

Only thing is that changes is the apparent focal length simply because you are looking at a smaller section of the image.

edit: sorry I should have made it clear that I meant if you had a 17-55 EF lens it would appear to be a 27-88 on APS-C, such a lens does not exist in the Canon range the closest would be the 17-40 L. the principle still applies f number does not change.

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