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T's right. At f/2, your critical focus zone is going to be in the order of 8.8 microns, which is bordering on the realms of impossibility as far as focusing by hand goes (consider that my Takahashi FSQ-106N has a CFZ of just 55 microns and I had to purchase a RoboFocus unit to do the focusing for me -- the thickness of a human hair is 100 microns). The slightest change in temperature is going to change focus.
H
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