If you compare the frame you get on your 450D between the two lenses, the frame you get should be the same at any given focal length. The difference is that the EF lenses have a wider field of view than the EF-S lenses, so they can be used on a full frame or 35mm body as well. If you expect up upgrade to a full frame camera in the future, then buying EF lenses will mean you can also use them on the full frame model.
The x1.6 crop factor is simply comparing the relative field of view an EF lens mounted on camera like your 450D as compared to a full frame model. Because the sensor is smaller, the view is cropped compared to the camera with a larger sensor.
This screenshot I did a while back may help illustrate it, though it is actually showing the difference between an APS-C sensor like your 450D has, (the full image) and a compact camera sensor (the highlighted crop box) at a given focal length.
This was shot at 28mm with my Tamron 28-300 lens on my EOS350D. The crop box shows what a small sensor compact camera (Such as my Powershot S5) would see at 28mm.
This is why the focal lengths are sometimes given in 35mm equivalents. It's supposed to make is easier to comapre apples to apples, but it seems to actually complicate the issue more.
Photanswers.co.uk has some very good field guides that you may find helpful. The issue on using your lenses has a very good explanation and a comparison of the same scene with full frame and APS-C sensor cameras.
Message edited by author 2009-07-24 20:33:28. |
