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Why the images are so sharp is that I can now adjust focus as the temperature of the lens body changes without disturbing anything. The stepper motor focuser I built needs to be adjusted by one thousand steps for every degree change in temperature of the lens body. One thousand steps corresponds to 0.1 mm linear movement of the focus ring. So even over a long series of images (or night) I can change focus between each exposure to keep accurate perfect focus.
This also shows why these lenses cost an arm and a leg and a torso,they are so close to perfect that a 0.1mm movement in the focus ring is noticeable and only at the pixel level. The other thing is the lens wide open at F2.8 is almost as good at the corners as it is in the centre.
Bert
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