Here’s a comparison of pros and cons of the Canon 50D and the camera it replaces, the Canon 40D.
Canon EOS 50D Advantages
Viewfinder coverage: Coverage is at 95%, with a 0.97x magnification. This is slightly better than on the 40D which has the same coverage but slightly lower magnification of 0.95x.
Higher-resolution rear LCD: The image preview experience as well as navigating the menus will be much better on the VGA-standard rear LCD that comes with the 50D. Resolution is rated at 640 x 480 pixels while the one that’s on the 40D is only at 320 x 240 pixels.
In-camera vignetting (Canon calls it “Lens Peripheral Illumination Correction”) correction: This added convenience on the 50D means you don’t have to run your photos through similar post-editing in order to remove the artifacts. Imaging Resource’s review of the 50D says:
… works by default with 26 of Canon’s most common EF-mount lenses. Data can be stored in the EOS 50D body for up to a maximum of 40 lenses at once, while Digital Photo Pro ships with data for 82 lenses that can be added to the camera via the EOS Utility software as needed. Canon has even gone as far as to include some lens models that are no longer available at retail, a boon for those with old lens collections. The Lens Peripheral Illumination correction function will work for any focal length, f-stop, or focus distance.
User-adjustable AF (autofocus) fine-tuning: There are times when certain lenses just don’t seem to AF properly with the camera, blame this on manufacturing tolerances. With the 40D, you’d have to send in your camera and lenses to Canon Service for AF calibration if such a situation arises. The 50D on the other hand, allows you to fine-tune the AF yourself, ensuring that each of your lenses can focus as close to perfection as possible wih the camera.
Canon 40D Advantages
Slightly higher burst speed: The 40D manages to squeeze off bursts at 6.5 fps (frames per second) at maximum resolution and image quality, while the 50D manages 6.3 fps. Consideration must be given to the fact that the 50D has a much higher resolution, so image processing bandwidth is actually much larger on the 50D. The almost insignificant difference between the burst speed of both cameras means this 40D advantage shouldn’t be listed at all, but it is an advantage, nevertheless.