Quote:
Originally Posted by robbo4
P.S.
The focal length of my mirror is f5.7.
It has a slight T.D.E. and a small hill in the middle.
I have tried Photographing to give me an idea of how
it is shaping but have found it very difficult to place the reflection.
I shall next try to use a small scope to look at the Mirror and if that fails
I shall have a go with making a Bath Interferometer
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Rob
Can I recommend to you as your mirror is reasonable 'slow' - a simple null test will be much easier to use . If you can use a ronchi grating on a star it will make interpretation very simple- you are just aiming for straight lines . John Dobson used to use trap door style back ends to his telescopes do he could quickly take mirror in and out for testing. This can be good for final testing / tweaking and the comparative ronchi test ( Google Mel Bartels ) good for rough figuring . Knife edge testing can be notoriously difficult for the beginner . I guess it really depends if you are after a usable mirror soon or alternatively `the journey is the goal ' ..