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Old 07-07-2019, 12:00 PM
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mental4astro (Alexander)
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12"-ish, f/7-ish primary mirror.

Hi all,

This is a real stab in the dark, Hail Mary request!

Might anyone have kicking around a 12" f/7 primary mirror?

I have a 12" f/5 scope, but I'm wanting to push the envelope with a more specialized planetary scope, hence the slower f/ratio. I'm going Old School here!

Doesn't need to be exactly 12", a little smaller or a little larger is worth considering. Same with a little variation in the f/ratio. Only thing is its figure needs to be outstanding. If the coating needs refreshing thats ok too.

Let me know if you have something like this, or if you know of someone who might.

Thanks for looking,

Alex.
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Old 07-07-2019, 08:13 PM
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Scope

This is old school 10" F/6

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  #3  
Old 12-07-2019, 08:40 PM
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Quote:
Originally Posted by mental4astro View Post
Hi all,

Only thing is its figure needs to be outstanding.

Alex.
Hi Alex ' what minimum size mirror / focal ratio & surface wave spec's do you require .

Cheers
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Old 13-07-2019, 09:30 AM
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mental4astro (Alexander)
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Hi Bob,

I already have a 10" f/5 Parks mirror. So if a 10" mirror is offered, f/6 is just too similar. I really want something closer to 12". Surface specs 1/8 wave or better.

Cheers

Alex.
  #5  
Old 13-07-2019, 12:17 PM
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scope

Understand Alex' I did have an old 12.5 F/7 many years back that would have suited you , I just about gave it away as it was a pain to set up , this was in the days before dobs & the only light it saw was when the shed doors got opened !

Hope you get what your looking for soon

Cheers
Bobby .
  #6  
Old 14-07-2019, 09:24 PM
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Wave specs

Quote:
Originally Posted by mental4astro View Post
Surface specs 1/8 wave or better.

Cheers

Alex.
Hi again Alex ,
That 1/8 surface spec could be interpreted as 1/4 wavefront giving a Strehl ratio of .82 or the Rayleigh limit , not a top mirror .

Now is saying that I might be getting it wrong' but Id'e be be looking for a .92 or above Sterhl ratio mirror .

Have heard a perfect 1.0 Strehl mirror is not possible .

Regards
Bobby.
  #7  
Old 16-07-2019, 08:38 AM
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mental4astro (Alexander)
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Bob,

Yes, 0.92 Strehl or better is what I'm after. 0.998 is ideal... might have to be made from Unobtainium

I'm also working on making Ronchi and Foucault set of bench testers. I'm gathering the bits and pieces at the moment.

Alex.
  #8  
Old 18-07-2019, 11:01 AM
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Quote:
Originally Posted by mental4astro View Post
Bob,

Yes, 0.92 Strehl or better is what I'm after. 0.998 is ideal... might have to be made from Unobtainium

I'm also working on making Ronchi and Foucault set of bench testers. I'm gathering the bits and pieces at the moment.

Alex.
Do hope you get a ripper Alex ' you will need one made out of ' unobtainium ' for Strehl 0.998

Good to hear your making the bench testing gear .

Bobby .
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Old 18-07-2019, 05:50 PM
Wavytone (Nick)
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Could take a 17 f4.5 and cut it down to size
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Old 18-07-2019, 08:59 PM
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Ooh, that'll be work...
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Old 18-07-2019, 09:21 PM
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Good numbers are not what they seem !

Alex I should start another thread after this .

There was a time when the numbers from various optical tests were the ultimate criterion of what I though real !

Mirrors with top number tests were sort after ..

Then I was shocked to read this article from Carl Zambuto site .

https://zambutomirrors.com/zambutoopticalce.html


My thoughts of the only True simple way to test a mirror will need it's own thread .
Including the secondary .

Bobby.
 

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