Originally posted by emalvick I would say that looking at the 100 and 200 may limit you just a bit. The 200 was quite similar to the k10d with a few limitations (I think it might have only had one dial and a little less customizability). I would probably just focus on the K10d, K20 or even K30 or K50.
IMHO, the main limitations of the K200D are the pentamirror viewfinder and the single control wheel. Otherwise, it's a great camera. Given what the OP mentioned about vision concerns, I would definitely suggest avoiding bodies with the pentamirror viewfinder because they are dimmer.
My own recommendation would be to take advantage of the current deals on a K30 or a K50 ( they are almost identical ). There's something to be said for getting a newer camera with a warranty. These cameras are solid performers, with most of the features of the flagship bodies including weather sealing, etc.
If you think you might want to use some of your older lenses on your new DSLR, the focus peaking feature of the K30/K50 might be VERY useful to you. I wish I could get more mileage out of it, but I'm usually shooting in bright light that washes out the LCD screen, and I'm rarely using a tripod.
( note: when in live view mode, the camera is displaying your view "live" on the rear LCD screen. Focus peaking is a feature which highlights what's in focus on the screen so that you can see exactly what's in focus and what isn't. It is a handy feature for manually focusing. But it requires that you use live view and look at the rear LCD rather than the 'normal' mode of using the viewfinder. )
If your shooting style is a bit slower and more patient than mine, and you can make better use of the focus peaking, it might be a big help to you in terms of your vision issues. To deal with the problem of sunlight washing out the rear LCD, you can get a sort of hood to shade it. There are a couple of different styles - one is a collapsible one that shades light from the top and sides, there's another that's more of a loupe arrangement that turns the rear screen into a big viewfinder. Either of those options will make your camera a bit bigger, but if they make the rear LCD more usable, and allow you to take advantage of the focus peaking, it may be a good option for you.
Installing a split-prism focus screen is another option, but probably more expensive compared to using the focus-peaking feature build into the camera body. I believe the K30/K50s are the cheapest DSLR bodies with the focus peaking feature.