I know the Duncan mask has been discussed in the past on this forum and am interested to get some first hand experience of its use. Does it do anymore than centre the secondary mirror as does a very defocused star? I get confused by owners publishing collimation as simply centering the secondary mirror shadow in the defocused star and that’s it , done and dusted without going to the next stage of observing a star at high magnification and centering it in the airy disc. Something that with poor eyesight and poor conditions I find difficult . Thus the question of the Duncan mask. Artificial stars are also cited and used at distances where the artificial star can be resolved? And always the suggestion that you have to fine tune on a real star. Any comments , experience and suggestions appreciated.
Regards philip
