EF and EF-S Focal Lengths

[ma5ter5]

Hi,

I've been doing lots of research on new bodies and lenses as I'm looking to invest in more camera gear. I've got a simple question, but I fear that I've done so much research that I can't think clearly to answer it. I currently shoot on a 40D, and am looking to get a 5D at some point. Thus, I know I want to stick with EF lenses only. However, for my crop sensor, will the image be the same between EF and EF-S lenses? I.e., if I have the EF 17-40 and EF-S 17-55, at 17mm both images will be the same.

I understand the other benefits of EF-S lenses on crop sensors, but didn't know if they would convert the focal length back down to those of full frames.

Thanks,

Steve

[Rentham]

Focal lengths can't be converted. 17mm is 17mm is 17mm. The physical properties of a lens are the same no matter what body it occupies. What does change is the interplay between the sensor and the lens. 17mm on your 40D will look to have the field of view of around 28mm. Putting that same lens on a 5D will show you the full 17mm and, hence, look wider.

I never got into EF-S lenses, but my guess is the 17mm-55mm lens is a rough analog for the EF 24-70 lens on crop bodies.

[inkista]

Yes, 17mm, whether EF or EF-S will look the same on the same body (assuming the sensor is covered by the image circle of the lens).

The EF/EF-S difference is not one of focal length, but of the size of the image circle projected by the lens.

My basic advice is if you don't need an ultrawide, then go for only EF lenses, but if you do need an ultrawide, go ahead, break down, and get an EF-S/DX/Di II/DC crop lens if your full frame purchase is not imminent. You aren't going to find anything that works for full frame that will give you an ultrawide field of view on a crop body, and it won't be nearly the same price as an ultrawide for full frame would cost. You can always sell it and recoup the majority of what you paid, and in the meantime, you'll have an actual ultrawide to play with.

The EF-S 17-55/2.8 IS USM is a walkaround for a crop.

The EF 17-40 f/4L USM is an ultrawide for full frame.