The tube’s come up well. Before you put finish on it, wipe down with turpentine over it. This will help you see if there is still any glue in the wood that needs removing. The tube might then need a quick rub with fine sandpaper as the turps may raise the grain.
Wow, haven't posted here in ages!
So I spherise the mirror, fixed the tde and started parabolizing. I'm very close now, like 1/4 wave!
Tube had to be redone because the polyurethane didn't dry. Almost ready to star test!
Lot of figuring, and finally the mirror is done!!! Can't wait to use it!
Left : outside roc Ronchi, right: Ross null image
I'll get interferometry data soon too!
Good effort Logan, but don't forget that these tests are not very sensitive at this sort of f ratio. You may be surprised if the interferometric test shows a half wave raised zone near the edge.
Most of that astigmatism is probably caused by your interferometer. I'm using a tiny lens and prism to minimise the displacement between the two beams. My spacing is something like 6mm. How much is on yours?
Anyway you have to make 5 sets of measurements, rotating the mirror 72 degrees between the sets, then average each set, derotate each set and combine for a valid final result. A big undertaking.
Looking at stars, passes the snap focus test nicely! clear point where it's in focus!!
With 5% uncoated reflectivity, it reminds me of views through a 60mm frac!