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Making my 14" f/3.85 mirror.

  • DaveGrennan
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Making my 14" f/3.85 mirror. was created by DaveGrennan

Those who know me on facebook will know that I have been annoying the heck out of everyone about a piece of glass I've been working on for the past few months. That piece of glass a 14" f/3.85 mirror came back from the alumising plant today.

www.webtreatz.com/images/stories/mirror/mirror1.jpg
www.webtreatz.com/images/stories/mirror/mirror2.jpg
www.webtreatz.com/images/stories/mirror/mirror3.jpg

I also wrote up quite a detailed article on the process of grinding, polishing, figuring and testing this mirror

www.webtreatz.com/resources/Grinding_a_14inch_mirror.pdf

I probably went a bit overboard int he amount of detail but hopefully some may find it useful.

The mirror is going into a carbon fibre tube which is due to arrive in the next week or so. More pics of the scope as it develops.

Regards,

Dave.
Regards and Clear Skies,

Dave.
J41 - Raheny Observatory.
www.webtreatz.com
Equipment List here
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8 years 10 months ago #98141

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Replied by philiplardner on topic Re: Making my 14" f/3.85 mirror.

Dave - that's a work of art! Well done on a really great surface. I can't wait to see the first images to come out of that new baby!!

Nice job on the Bath interferometer too... but a 40MW lazer??? holy cow! :bigshock:

Phil.
8 years 10 months ago #98153

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Replied by martinus on topic Re: Making my 14" f/3.85 mirror.

I'm sure I'll not be the only person with the opinion that you cannot go into too much detail.

I'm putting this on my to-read list. Thanks for going to the effort of documenting it all, Dave. :)
8 years 10 months ago #98154

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  • DaveGrennan
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Replied by DaveGrennan on topic Re: Making my 14" f/3.85 mirror.

Nice job on the Bath interferometer too... but a 40MW lazer??? holy cow! :bigshock:


Yes that was really the crux of my problem. With such a fast mirror, the beam needed to be expanded to a large size over a short distance. It turns out that most laser dots are not round but either rugby ball shaped or even flatter still. This was a problem. without the beam being round, it lead to uneven illumination of the mirror and very bad contrast fringes around the edges. It was impossible to get a good analysis. I ended up taking a stab and picked up a few different types of laser module from ebay. The 40Mw laser wasn't so much for the wattage, it was the one I found with the closest approximation of a round beam to evenly and fully illuminate the mirror.
Regards and Clear Skies,

Dave.
J41 - Raheny Observatory.
www.webtreatz.com
Equipment List here
8 years 10 months ago #98160

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Replied by martinus on topic Re: Making my 14" f/3.85 mirror.

Surely that's a small m (milliwatt)?

Lasers rated in MegaWatts are evil genius or US military constructions:
en.wikipedia.org/wiki/Advanced_Tactical_Laser
8 years 10 months ago #98165

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Replied by derek0207 on topic Making my 14" f/3.85 mirror.

Just read your article. Interesting read. I made an 8.5" mirror 20 years ago (still in school!) I like the idea of the diamond disk to hog out the curve. Will do that if I ever make a mirror again.
D

BTW there is a typo in the article, page 5, 'arse pits'. sorry LOL.
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8 years 4 months ago #99775

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