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  #61  
Old 22-12-2018, 12:07 PM
Rod
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Hi Logan

The tubeís 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.

Rod
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  #62  
Old 22-12-2018, 03:48 PM
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Lognic04 (Logan)
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Thanks Rod!
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  #63  
Old 26-01-2019, 05:18 PM
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Lognic04 (Logan)
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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!
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  #64  
Old 14-03-2019, 08:02 AM
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Lognic04 (Logan)
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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!
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  #65  
Old 14-03-2019, 08:26 AM
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Atmos (Colin)
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That’s looking pretty darn good Logan!
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  #66  
Old 14-03-2019, 09:02 AM
Rod
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Congratulations Logan.

A lot of work and good on you for persevering through some frustrating experiences. How is the star test appearing to you?

Looks like you might need to mask off a little at the edge but thatís no big deal.

It will be great to see it under a dark sky one day.

Rod
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  #67  
Old 14-03-2019, 02:13 PM
Stefan Buda
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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.
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  #68  
Old 14-03-2019, 03:25 PM
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Hi Stefan, we will have to wait and see.
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  #69  
Old 14-03-2019, 03:26 PM
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This is by far the closest and smoothest it has been so far, with an average conic of -1.02 so far from igrams which is pretty good
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  #70  
Old 14-03-2019, 11:09 PM
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Still having trouble with astigmatism being induced by air currents, but the main point here is the smooth, uninterrupted -0.99 conic!
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  #71  
Old 15-03-2019, 10:48 AM
Stefan Buda
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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.
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  #72  
Old 15-03-2019, 03:47 PM
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Thanks Stefan. For now I disable the astigmatism Zernike. The mirror might need some smoothing unless the ke says otherwise
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  #73  
Old 15-03-2019, 09:19 PM
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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!
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