Thought I'd post some crops comparing between the Tamron 17-50 and 28-75 lenses. I used the 28-75 first and was thrilled with the results from day 1. Received a copy of the 17-50 on Thursday and wanted to compare it with its big brother.
Test conditions:
Tamron 17-50 mounted on Pentax Kx
Tamron 28-75 mounted on Canon Xti (400D) - a 10 MP camera
Both cameras tripod mounted. Pentax output DNG. Canon output RAW (CR2).
All images loaded into Photoshop CS3 and processed with default parameters with exception of WB and exposure. To equalize the brightness in images, I adjusted the exposure. The Canon Xti AWB sucks so I had to adjust WB manually in Photoshop.
Focus on the Pentax was done through Liveview and MF via magnification. Sorry, the Canon Xti has no LiveView, and the viewfinder is just too small and dark for accurate MF so I just used AF. Focus point was the right red cheek on the sunshine toy.
So yes, we are dealing with two different cameras, but when you see the results, IMHO the resolution differences between the two cameras was not a major factor in the results. Feel free to disagree.
Please ignore the colour differences...the WB was probably the reason for the difference.
First, here is the overall scene from where the crops were made: