Wanting more info on Mr. Kennedy's new auto-collimator.
What is that?
I have no experience in mirror-making.
The autocollimation or double pass null test is well regarded and widely used in professional optical shops for testing parabolic mirrors.
Like the Ross and Dall tests it is a null test so the ideal parabolic mirror shows straight bands when use with a Ronchi ruling or is seen to darken uniformly when viewed with the knife edge.
However, the test is twice as sensitive as the other null tests as light is reflected off the test optic twice, this makes it a very powerful test. The price to pay for this sensitivity is that the test set up requires a high quality optical flat at least as big as the mirror under test, such an item is difficult to make and very expensive to buy.
With the autocollimation test the mirror is tested at it’s focus unlike the Ross and Dall tests which are at the centre of curvature.
You can read more info at: