I have a lot of infrared aerial photos printed onto transparent film with dimensions 24cm x 26cm. They should really be scanned with a scanner incorporating a light source, but we unfortunately are not able to outsource that task. I want to use my Olympus E-420 DSLR to capture the images in the best resolution possible whilst maintaining all the colour information. I have a light table, tripod, remote control, and the DSLR.
Which and focal setting would be best to avoid distortion as these photos will be referenced in a geographic information system to be used as basemaps for environmental agencies.
I have done a few tests and found that only the middle of the photos are really sharp and the outer edges are blurred. Is there any way to reduce this perpective-blurring? I really need to retain the colours as well, as these colours give meaning the photos regarding vegetation density and type.