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I intended to finish this project before the end of the year but things got in the way as usual..
At least I managed to get the Mangin out of the way. I just have to do some coatings now and will be ready for preliminary assembly over the coming weeks.
The front surface of the Mangin is the fastest surface I ever tested with a Ronchi setup. Amazingly my light source was able to illuminate it evenly, despite the f/1.29 ratio. The lines looked very straight on both sides of focus, however I don't think that is due to my wonderful skills and perfect polishing lap, but rather has to do with the lack of sensitivity of the Ronchi test as this sort of extreme f-ratio.
For the back surface I also used the Ronchi tester, through the front surface. Due to the near concentricity of the two surfaces the Ronchi lines were nearly straight. The longitudinal focal spread, according to ray tracing, was only 0.25mm and it was very difficult to measure even though I 3D printed a zonal mask for it.
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