Well my ronchi test stand for checking what this mirror is was even more scrappy. cardboard box, duct tape, books for adjusting height and shuffle it back and forth, using a duct-tape covered red bike led with the lens removed for light.
The bands are dead straight - it's spherical. diameter 200mm, RoC 1500, so f=3.75. Although terrible in terms of a practical sort of mirror (since an f6 or so would be much easier to figure and still be a very easy handling scope, I think it is actually good since it means I have some challenging figuring work to do but on a small scale. Since I have bought a big 550mm diameter (22") piece of glass from Stephen, I am going to need the practice.
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Originally Posted by sopticals
Hi Hamish, most probably the mirror will be spherical. To perform satisfactory it would require parabolizing. However a simple Ronchi test would confirm that. I have a spare 85 lpi grating which I could let you have,(PM me). The test is easy to set up and gives an immediate visual profile of the mirrors figure. Pic of my Ronchi tester made of scrape materials.
Best regards
Stephen
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