Quote:
Originally Posted by
aizan 
yeah. the current prosumer options aren't mature yet, being only first or second generation products. while the nikon d700 has unbeatable low light performance and almost everything a professional could wish for, the megapixel count is a comparatively low 12mp. meanwhile, the sony a900/a850 and canon 5dmkii are 24mp and 21mp, respectively. the bad news is that sony doesn't have a comprehensive system of lenses yet, and canon is dragging its heels when it comes to things like top of the line build quality and autofocus.
the d3100's high iso performance is at the top of its class, so no worries there. i just wouldn't buy the more expensive and specialized lenses, which is basically anything with a depth-of-field scale (the little window). one of the best things about full frame is using fast prime lenses, so i would highly recommend getting the small, fast 35/1.8 dx to see if you like them.
some aps-c and full frame dslrs may share a lens mount, but they're really best considered as semi-separate systems. if you start buying (expensive) cropped sensor lenses now, they're not going to cover full frame later. going in the other direction, full frame lenses are not exactly ideal when you put them on a cropped sensor body.
I have a D700 and am pretty happy with it. The full frame sensor is noce for shooting in low light, but I really like it for the bright, full size viewfinder. Also, being able to use the full range of Nikon lenses is great. One of my favorites is a manual focus 85mm F1.4. It is a joy to use such a mechanical jewel and at $4-600 used, it is a cheap joy.