full frame lens on a crop senser

[Bootsy]

after deciding to stay with my 40D for a while and change my EFS kit for EF lens.with eye on going full frame in the future.now i already have a nifty 50 1.8 and a 70 -200 F4 and i'm looking to spend most of my budget on a EF 24-70mm f/2.8 L USM.but for the wide end i was considering a 17-40 f/4 as cant afford 16-35 f/2.8 as well.but i've read on the net that there are issues using the 17-40 f/4 on a crop sensor.user's complain that its soft across the frame and not just the corners when use on a crop sensor. does anyone on here use the 17-40 f/4 on full frame or on crop sensor how do you get on with it.basically i dont wont to buy a lens that only good as and when i go full frame.
cheers

[Manfred M]

I have used full-frame lenses on crop sensors for almost as long as I owned my DSLR. If someone is reporting issues with softness on a crop frame, chances are the lens is bad and will perform even less well on a full-frame sensor. If anything the lens should give better results on a crop frame.

The bulk of the distortion that we see from lenses tends to be when they are wide open, and light is distorted near the outside edges of the lens. The reason that we get better lens performance when we stop down is that as the iris stops down, we get more light coming throught the centre part of the lens. This continues to improve until the diffraction limit is hit, at which point the small diameter iris is working against you.v When you put a full frame lens on a crop frame sensor body, you are essentially only using the centre part of the lens, i.e. the part that gives you better image quality.

[Scott Stephen]

Like Grumpy says, you are using the best part of the lens and throwing away the bad part. In particular, you won't get any fall-off (vignetting) on the cropper, as that is, well, cropped off.

[Dave Humphries]

Can't improve on Manfred's post

[pnodrog]

I will back Manfred up. When I shifted from SLR film (Nikon F90x) to DSLR (Nikon D200) I simply continued using the lenses I had. Subsequently I purchased a Sigma 15-30 and recently a Nikon 28-300 because like you I want to maintain full frame compatibility with any lens purchase. All the lenses perform to my expectations.

[rpcrowe]

Any 1.6x crop Canon DSLR camera will accept any auto focus Canon Lens, be that lens an EF or EFS model.

My hangup with using the 17-40mm f/4L IS on a crop camera is that the lens is not really wide angle when shooting with a 1.6x crop camera.

Instead, it is more like a mid-range zoom. In that capacity it lacks the following:

40mm is not really long enough for me to use on a crop camera as a mid-range zoom. 64mm equivalent is quite lukewarm.

f/4 without IS assistance is too slow for me to use as a mid-range zoom.

The gap between 40mm and 70mm is quite annoying to me.

If I bought a lens specifically as a wide angle or ultra wide angle, I would want a lens that started somewhere between 10mm and 12mm. The 10-22mm Canon, 11-16mm Tokina or 12-24mm Tokina would be among the candidates. I personally will never buy another Sigma lens (but that is a completely different staory).

If I wanted a lens which will match up well with the 70-200mm f/4L; I would consider the Canon 17-55mm f/2.8 IS lens as my first chice. The focal length is better suited for a mid range zoom since 55mm is an equivalent 88mm which can be a decent portrait length. I don't miss the 55mm to 70mm gap anywhere as much as I missed the gap between the 40mm and 70mm focal lengths. The constant f/2.8 aperture allows shooting in lower light conditions and the efficient IS capability adds to the low light efficiency. The only problem with this lens is that it is fairly expensive. A less expensive alternate might be either of the 17-50mm f/2.8 Tamron lenses: the VC or the non-VC.