True 17-40mm

[Brianbar]

I have a question on the Canon 17-40mm L Lens.
Is it a true 17-40mm or do will still convert by using x1.6 = 27.2- 64 ?
When I use it a 17mm it appears much wider than 27.2.

Brian

[Tom W]

Both - the actual focal length of the lens is 17-40 mm, AND you have to use the 1.6 multiplier to calculate the equivalent field-of-view of full-frame 35 mm film.

So the lens is 17-40 mm in actual measurement, and it gives the equivalent field of view that a 27-64 mm lens would provide on a full-frame sensor or 35 mm film.

[sGu]

if you use on a 10D/300D or any digital SLR with a focal length multiplier, then yes, you'll need to do the math, unless it's a 1Ds or the Kodak full frame sensor one, or film cameras, then it's real 17-40mm.

[petiot]

just to make things a bit more complicated, with a 17-40 on a 10D you will end up with a field of view equivalent to the one given by a of 17*1.6=27mm lens, but you will have the same perspective as a 17 mm lens.

the 1.6* is a crop factor (crop of a photo taken at 17 with a full frame camera), but does not change the focale (and therefore does not change the perspecive) of the lens. that is why many people dont think, for instance, that a 50 mm lens on a 10D is a good portrait lens, since it still provides the perspective of a 50mm lens, despite the pseudo 80 (50*1.6) mm field of view.

huuuu am i correct? ... yes i think so.

Dan

[topeju]

just to make things a bit more complicated, with a 17-40 on a 10D you will end up with a field of view equivalent to the one given by a of 17*1.6=27mm lens, but you will have the same perspective as a 17 mm lens.

Not quite. Perspective depends only on the distance from the subject, not on focal length. Try it: take a photo of the same subject from the same location at 17 mm and another at 40 mm, then crop the 17 mm photo to cover the same view as the 40 mm image - the photos should be identical in terms of perspective.

Depth of field, however, ...

[drisley]

I agree with petiot.
If you do what topeju said, you will get different dof and distortion.
I think perspective would also be different.

[petiot]

I agree with petiot.
If you do what topeju said, you will get different dof and distortion.
I think perspective would also be different.

sorry Drisley (and everybody who read me).... :( i was wrong:
http://jamesmskipper.tripod.com/jamesmskipper/photo_perspective.html

in fact the 1.6 factor really transform your lens into a longer lens. and since the perspective does not depend on the lens inherent physical characteristics (as the link proves, there are other if you google : lens perspective focale), the 1.6 factor realy allows you to keep more distance beteen the subject and you and therefore allows you to control the perspective better (as with a longer lens).

Well. we learn by doing mistakes, and this forum is great because you can always find someon more knowledgeable than you!!!
thanks Topeju

Dan

[petiot]

this link is more explicit

http://www.reasonableexpectations.com/Photo_Myths/Perspective/perspective.htm

[Volatile]

In other words, you get the "angle of view" of 27mm and the "depth of focus" of 17mm.

[Persian-Rice]

BrianBar,

As long as you are using almost any Dslr, other then some of the mentioned full frame sensor cameras such as the 1Ds, there will be crop factor of some sort.

Crop factor is not a thing crontrolled by the lens, its a part of the camera.
It doesnt matter if you buy the 17-40 or the 1200..............there will be a crop factor regardless.

There is a huge upside to the fact that you get a lot more reach, its like having a built in teleconverter without any optical degredation. The downside to this is that no, you wont get a true 17mm shot, which in turn, makes it harder to get very wide angle shots unless you have a very very short focal length or a fish-eye.