Focussing with Hartmann Mask

[peterthebike]

I am correct in thinking it is better to use a star to focus on with a Hartmann Mask, as opposed to a planet?

With Venus available when I have started to image, I used that to focus on as it is an easy target. But thinking about it I guess a smaller object allows tighter focussing.

[barkis]

A star is preferable, as it is a point source, whereas a planet is an extended object, and although you may think you have good focus, it may well not be perfect.

Stay with a star, and why not use Polaris as your target, it's first magnitude star, and quite adequate for the task.

Ron.

[peterthebike]

Thanks Ron, fingers crossed I can put it into practise as we are forecast clear skies for the early part of this evening.