Doug,
You'll find a large part of this (ad nauseum?) topic on a thread comparing lenses, that gradually moved on to the 1Ds/10D issue because someone suggested in oder to discern any difference between the two lenses in question you would need a 1Ds. A 10D would not be up to the job. The link is below.
http://www.luminous-landscape.com/cgi-bin....3;t=280Michael is probably going to stay clear of this issue because in that thread, he provided some really eye-opening information about relative pixel sizes of the two cameras. Trouble is, the information related to the D30 and the 1Ds, with only an implication that the extremely small pixel size of the D30 also applied to the D60 and 10D.
In short, the pixel pitch of the 1Ds is 8.8 microns and that of the 10D 7.4 microns. However, the pixel (or photosite) size of the 1Ds is also close to 8.8 microns, whereas that of the 10D might be as small as 5.25 microns, which is the size of the D30's pixels. In other words, the 1Ds pixels are packed like sardines whereas the 10D pixels have big spaces between. For a unit area of sensor there are more 10D pixels than 1Ds pixels (by my calculation about 4.5M for the 1Ds in the same area as the 10D's 6M). In that sense, the 10D has greater pixel density and one would expect is therefore capable of higher resolution in terms of lines per mm.
However, the 1Ds pixels (packed like sardines) cover about 97% of the sensor area (according to Michael), whereas the 10D pixels cover, possibly, only 25% of the sensor area.
If this is true, and I certainly have no inside information on this apart from what Michael has written, it would seem to me this fact alone will affect the relative performance of these two cameras using the same lens.
For example, let's imagine what happens when photographing a target with fine grain, say texture on a wall. Some of those particles will be as small as 5 microns from the camera's perspective. Because the 1Ds photosites are so tightly packed, the light from a 5 micron particle cannot avoid illuminating one or more of the 1Ds pixels. If the lens is good enough and the target contrasty enough, some 5 micron particles will probably (possibly?) be recorded as 8.8 micron particles. Some will straddle two or more photosites and become irrelevant (not enough photons to matter).
In the case of the 10D, if it's true we have only 25% coverage of the sensor, a large percentage of the 5 micron particles will be essentially lost in the spaces. However, the light from at least some of those particles will hit a 10D photosite square on, and when it does, we will have a more accurate representation of that 5 micron particle.
This is how I see it. I hope I haven't oversimplified matters to the point of error
