Focusing
The difference between an excellent and an “OK” focus position may only be ten microns. The effect on the image is often far greater.
In earlier chapters the importance of accurate focusing was discussed at some length, as well as the need for good mechanical robustness in the focus mechanism. Here, we will look at the various focusing aids and their reliability, along with a few considerations that may catch you out during an imaging session. It assumes that any conventional astrophotography optic is fitted with a motorized focuser (preferably computer controlled) and that conventional shorter focal-length photographic optics are focused by hand.
fig.1 This is the focus control panel from Maxim DL 5, showing a completed ...
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