[ATM] Star testing with a ronchi test to quantify a TDE

[Raphaël GUINAMARD <rguinamard@infonie.fr>]

The star testing of my mirror shows a Turned Down Edge.
It doesn't seem very big but I think I 'm going to put an annular mask to avoid the image degradation.
I've also seen this TDE using a ronchi grating, and if I take a picture of the image, I think I could mesure where the TDE is starting -at least on the picture itself-.
My question is : 
I know the ronchi test is not very sensitive with fast scope (mine is a 24" f/3.3) so is the measure of the TDE on the picture would be a good approximation of the TDE on the real mirror?
I mean, if I measure for example on the image that the 2% outer part of the image has a TDE, does this mean I could confidently make a mask for the 2% outer part of the mirror?
Maybe the low sensitivity of the ronchi test could show a 2% outer TDE with a 4 % outer TDE mirror? no? 
I know I could try different annular width and star test with each, but my question is to go as quickly as I could to the solution
Thanks in advance
Raphaël
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