I have often wondered about the difference in quality between a prime and a zoom. I decided to start testing the differences and this page contains the first results. I decided to compare my 28-105 3.5-4.5 USM and 50 1.8 MKI. The 28-105 is considered a better, consumer zoom. The 50 1.8 is a cheap lense but like most 50mm primes, is considered sharp.

I realize there are a lot of things I left out of this test, like testing the lenses wide open, etc.

Besides scanning the images and comparing the scans, I looked at the images using an 8x loupe on a light table, and through a microscope at 40x and 100x. My conclusion from those tests are that only minor differences are detectable using even the microscope. The 50mm image appears to be slightly sharper and to have slightly better contrast. The fact that the exposure is slightly different may account for some of the percieved differences. Further testing will be necessary.

Test Conditions:
The pictures were taken around 11am.
The direction of the picture is opposite the sun, so flare is not a factor.
No filters on either lense.
Pictures were taken with an EOS 650.
Fuji Velvia rated at 50 was used.
Bogen 3001 tripod with 3025 Head.
Selftimer was used for shutter release.
The images were scanned using a Minolta Dimage Dual at 2438DPI.
Both images are unaltered except by a slight but equal increase in brightness using the scanning software.
The large images were resized to 640x427 using Photoshop, they were saved using a JPEG compression setting of 8
The small images are 1:1 from the original scan and were saved using a JPEG compression settion of 10 (maximum)

Note: I did not use the same FStop for both pictures because I estimated that the 50mm would have peak sharpness at a larger fstop than the 28-105.

While you are here you might want to check out some of my more interesting photographs.