Hi Bob The Canon EOS Utility allows one to control focussing remotely using a laptop or other computer. If you select fine focussing, do you have any idea how far forward or back the plane of focus moves for one click? I have started to come to terms with focus stacking and I am advised that altering focus using the lens is better than moving the camera using a focussing rail. Regards Ken Lindup
Sorry Ken, I don't know. One way you could test this would be to have a stepped (or slanted) focus target and see how many "clicks" it takes to move from one focus point to a second focus point a known distance behind (or in front of) the original focus point. It will depend on focus distance. I assume it's stepping the focus by a fixed number of focusing motor "steps". Those steps will correspond to larger changes in subject distance for more distant subjects than for close subjects.
It's possible that each lens may be different too. Telephoto lenses require much more focus travel than wideangle lenses. It's hard to guess at how the EOS Utility's focus algorithms would handle this, along with the influence of subject distance. I guess that ideally you'd like a constant increase in the spot size (= degree of defocusing) for each click on the adjustment, no matter what focus distance or focal length. As long as the lens reports back the focal length and focus distance, it should be possible to do that, but whether of not Canon did it that way I don't know.
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