Using Canon lenses for astro work

[wingeing Pom 774]

I have given misleading/incorrect information about using Canon lenses for astrophotography. If you look at the focus indicator window on a Canon lens, you will see at the infinity point a vertical bar (indicating infinity). At the bottom of this vertical bar is a horizontal bar off to the right. This bar indicates the amount of movement the lens has BEYOND INFINITY. So when connecting this lens to your camera you must use the correct back focus distance and you will find there is enough movement beyond the infinity point for FocusMax to do its stuff. If you operate the lens INSIDE the correct back focus distance in order to "free up" some movement beyond infinity, all you will do is increase the star FWHM values above what they should be at correct focus.

Greg