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Old 14-11-2019, 09:05 AM
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alistairsam
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Mirror Testing

hi

I have a 10inch F4 Orion optics standard grade primary mirror and wanted to know if there are any options in DIY testing to get a general idea of the quality of the mirror? or are there any testers in AU that can do the testing?

I came across these
http://www.astrofox.nl/contents/en-u...g-mirrors.html
https://www.instructables.com/id/Opt...bolic-Mirrors/

https://www.teleskop-express.de/shop...th-a-star.html


Thanks
Alistair
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Old 14-11-2019, 09:52 AM
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An easy test you can do is to use a Ronchi grating (https://en.wikipedia.org/wiki/Ronchi_ruling) and observe either an artificial star or a real star reasonable high up.
Any distortions in the observed lines could indicate a problem - either in collimation or the mirror.
http://www.ronchiscreens.com/screens.php
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Old 14-11-2019, 10:47 AM
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Thanks
will this one do as I have this. its 10lines per mm.

https://www.teleskop-express.de/shop...th-a-star.html

Can I use an artificial star to test as well and do I observe the lines at focus?

Thanks
Alistair
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Old 14-11-2019, 11:00 AM
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Yes,
works with an artificial star (I use the Hubble torch https://www.bintel.com.au/product/hu...v=6cc98ba2045f ) as far as you can position it from the scope...
I use the hallway which is pretty long!
Near to focus, get four or five lines visible and then work closer from there.
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Old 11-04-2020, 02:22 PM
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hi

I took some pics with a 10L/mm grating on a fairly bright star, anyone able to interpret these? they were taken afocal with an iphone.

Thanks
Alistair
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Old 11-04-2020, 02:30 PM
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Looks good, but it would be worthwhile getting fewer lines by moving the grating.
Not sure about the feature lower right. Have you got something in the light path?
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Old 11-04-2020, 02:35 PM
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I agree...not too bad but you need an image closer to focus (four or five lines visible)
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Old 11-04-2020, 02:46 PM
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hi

had a few more pics

not too sure about that feature, seems to shift between pics.
the curved line is my secondary heater wire.

i'll try and setup the artificial star test, but would that help?

This is a standard grade 10inchF4 Orion Optics mirror I got 5 to 6 years ago.

Thanks
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Old 11-04-2020, 03:42 PM
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It could be atmospheric distortions..
There’s definitely something in the light beam around 4 o’clock, shows between the secondary and the edge - camera strap??
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Old 13-04-2020, 12:03 PM
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He's already said it's his secondary heater wire.

Could do with a couple of pics on the other side of focus
but overall looks pretty good. The distortions in the lines move
in each pic so I would say they're atmospheric as opposed to rough
optics. If this scope is used for imaging you could take some video
and do some stacking to take out the seeing effects.
Dave
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Old 13-04-2020, 01:36 PM
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Ahhh, missed that!
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Old 06-06-2020, 04:39 PM
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looks ok to me. maybe a tiny hint of hooked in ends on one or two of the pictures, but so subtle that it might be nothing. looks fine to me.





as far as testing, if you are in melbourne, Logan Nicholson has been making some pretty tricky mirrors (as fast as f3 i think). But from experience, I highly recommend that you build yourself a foucault test rig and learn to test foucault, ronchi at radius of curvature, and star test.
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