Is a 17-85mm EFS lens still a 25.5-127.5mm on a Canon Rebel XSi?


TPF Noob!
Jan 27, 2012
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Southern California
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Since EFS lenses only work on cameras with an APS-C sized image sensor, do they take the magnification into account when labeling the mm? What I'm asking is, does a 17-85mm EFS lens shoot at 25.5-127.5mm on a Rebel XSi because of the 1.5x magnification, or is it labeled the mm that it shoots at on the sensor that it is made for?
It has the Field of View of 27.2 to 136 ( canons are 1.6 Crop Factor)

Hi to So Cal from So Cal
Don't the EF-S lenses take into account the crop factor? I thought they did...

IE: A 50mm EF-S = 50mm x 1.6

Whereas a 50mm EF = 50mm

Thats what I was told anyway... I am probably in left field.
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Focal length is never ever changed by the crop factor of the camera body nor the crop factor of the lens. A 50mm is always a 50mm lens no matter if its built for a crop sensor DSLR or if its built for a medium format camera.

However the angle of view that you get with different sensors will change how the resulting images appear when you shoot. 35mm (full frame) is the "norm" most people with a background in film shooting are familiar with and is the one most people compare to. However if you've never shot on 35mm the idea of crop factor on a sensor smaller than 35mm is a moot point since you've not that history of experience.

In general though the only difference that the EFS lenses have over their regular EF is that they are smaller in size because they only cast the area of the image circle that the crop camera can see - the edge areas which are not seen are simply not included (which is why if they were to be fitted to a fullframe body* they would have a large black ring around them)

* most EFS lenses will not physically fit to a fullframe body and if they are modified can cause damage.
Overread: - Thank you for the description that -finally- got it right in my head. Although I sort of figured it was as you described, it's easy to assume that putting an EF 17-55 on a crop body would be the same as putting a 1.6 extender (eg, multiplier) lens on it with a ff body. In truth, it's the ANGLE OF VIEW that gets reduced to that of a higher focal length lens when on a crop body, not an increased focal length.

It's like concentric circles. Consider a lens that projects a 12" diameter circular image. It needs a rectangular "sensor" that is 11.99" diagonally measured (ef, full frame) to 'see' the full picture. Put the same lens on a crop body, with a 7.99" diagonally measured sensor, what the camera 'sees' is only a portion of the full image projected by the lens. By comparison, an EF-S lens projects an 8" diameter circular image. The 7.99" crop body sensor would get the full picture as projected. Putting the EF-S lens on a full-frame body (if possible), there would only be an 8" picture in a 12" area, thus a black area around the projected picture.

I've only had a DSLR since last May. With all the discussion here and elsewhere of 1.6 crop multiplier, it's easy to think it was like having an tele-extender built in, which it is not. Us old geezers will "get it" eventually...maybe tomorrow, next week, next year...

I think I understand it now...
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