TheSkySearchers

I may end up having a Newtonian made. If I go this way I need to source a really nice mirror. It'll probably be an 8", F/6.

I've not even looked at who makes such mirrors in recent years. Ideally it would be something which is effectively off-the-shelf. I know that GSO makes decent mirrors but I am looking for a very good mirror and that means finding a premium mirror maker.

So I'm hoping folk might have good ideas as to who makes the mirrors which would be appropriate.

Interestingly, I did look up Lockwood but they don't make a sufficiently small mirror. Same thing for Hubble Optics (which normally does pretty good mirrors and I like their cooling system).

I don't know about the cost effectiveness of things better than GSO. Nevertheless there are always:

Zambuto: https://zambutomirrors.com/whyzambuto.html

and

Royce: (OOOOPS! he's retired! Yikes!)

and

Lightholder: http://www.lightholderoptics.com/index.htm

and

Pegasus: https://pegasusoptics.com

One strategy might be to start with a GSO set and have Pegasus refigure it if need be.

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I've got this one, unused, 8.25" diameter. Don't know speed. Yours for postage.
Wrong style?

Those sources are greatly appreciated!

If Pegasus is fast, I already have a couple of old mirrors which could be refigured. The problem is that they are probably thicker than need by modern standards (better mirror cells).

And the mirror offer is greatly appreciated! But yeah, if it happens it'll be a standard Newtonian - just very nicely made.

OleCuss wrote: ↑Thu Jun 13, 2019 10:14 am
If Pegasus is fast, I already have a couple of old mirrors which could be refigured.

Do I detect the possibility of a binocular set up at some stage?

I am a sucker for big bino scopes... I'd love to put one together...
That might be a retirement project. Sorry, not to derail the thread...

JimMinCT wrote: ↑Sun Jun 16, 2019 12:07 am I am a sucker for big bino scopes... I'd love to put one together...
That might be a retirement project. Sorry, not to derail the thread...

I think that might have been me derailing the thread. .

A binoscope would be cool.

And if you keep your eyes open you can sometimes get something rather inexpensively. I also have a 20" F/5 mirror. Two problems with that, however:

1. I don't have the time to build it out.
2. It is really too thick at 4" so the thing would take most of the night to cool down. I think there is someone who will cut mirrrors into thinner ones. With modern mirror cells you could cut it to about 1.5" and end up with the mirror and a mirror blank.

That 20" mirror may or may not have been a good purchase. But maybe eventually it will turn out well.

OleCuss wrote: ↑Sun Jun 16, 2019 11:26 am A binoscope would be cool.

And if you keep your eyes open you can sometimes get something rather inexpensively. I also have a 20" F/5 mirror. Two problems with that, however:

1. I don't have the time to build it out.
2. It is really too thick at 4" so the thing would take most of the night to cool down. I think there is someone who will cut mirrrors into thinner ones. With modern mirror cells you could cut it to about 1.5" and end up with the mirror and a mirror blank.

That 20" mirror may or may not have been a good purchase. But maybe eventually it will turn out well.

and there is an interesting possibility for the forum. Would there be any members willing / capable of grinding / polishing a mirror of that size?

mcolbert wrote: ↑Sun Jun 16, 2019 9:10 pm

OleCuss wrote: ↑Sun Jun 16, 2019 11:26 am A binoscope would be cool.

And if you keep your eyes open you can sometimes get something rather inexpensively. I also have a 20" F/5 mirror. Two problems with that, however:

1. I don't have the time to build it out.
2. It is really too thick at 4" so the thing would take most of the night to cool down. I think there is someone who will cut mirrrors into thinner ones. With modern mirror cells you could cut it to about 1.5" and end up with the mirror and a mirror blank.

That 20" mirror may or may not have been a good purchase. But maybe eventually it will turn out well.

and there is an interesting possibility for the forum. Would there be any members willing / capable of grinding / polishing a mirror of that size?

At that size I think they'd need a grinding machine so who has one?

notFritzArgelander wrote: ↑Sun Jun 16, 2019 9:29 pm

mcolbert wrote: ↑Sun Jun 16, 2019 9:10 pm

OleCuss wrote: ↑Sun Jun 16, 2019 11:26 am A binoscope would be cool.

And if you keep your eyes open you can sometimes get something rather inexpensively. I also have a 20" F/5 mirror. Two problems with that, however:

1. I don't have the time to build it out.
2. It is really too thick at 4" so the thing would take most of the night to cool down. I think there is someone who will cut mirrrors into thinner ones. With modern mirror cells you could cut it to about 1.5" and end up with the mirror and a mirror blank.

That 20" mirror may or may not have been a good purchase. But maybe eventually it will turn out well.

and there is an interesting possibility for the forum. Would there be any members willing / capable of grinding / polishing a mirror of that size?

At that size I think they'd need a grinding machine so who has one?

can we put this out into public circulation on the board in some way? Maybe in announcements? Or is there somewhere better suited to grab people's attention?

mcolbert wrote: ↑Sun Jun 16, 2019 10:07 pm

notFritzArgelander wrote: ↑Sun Jun 16, 2019 9:29 pm

mcolbert wrote: ↑Sun Jun 16, 2019 9:10 pm

and there is an interesting possibility for the forum. Would there be any members willing / capable of grinding / polishing a mirror of that size?

At that size I think they'd need a grinding machine so who has one?

can we put this out into public circulation on the board in some way? Maybe in announcements? Or is there somewhere better suited to grab people's attention?

There is a "vendor" area where folks equipped for such enterprises could be invited to post.

Well, it hasn't been tested, but that 20" mirror is figured/polished/whatever to F/5. What's more, it is a NASA mirror so it is likely very nicely done (no expense spared).

It came out of a LIDAR unit. It appears likely that the LIDAR unit never worked well and was thus sold off as scrap. The reason I believe this is that the entire unit was effectively intact and we dismantled it so that I could get out the mirror and the diagonal mirror - and a defect was found.

The diagonal mirror appears to be attached to its support by something like silicon. The thing is, the diagonal mirror is not aligned with its support - it appears to have slipped on the support quite significantly.

So to me it appears the diagonal mirror slipped and the unit was giving poor results. Rather than take it apart to figure out what was wrong and determine whether it could be fixed - they scrapped it.

So I've a perfectly good F/5 primary mirror and the corresponding rather large secondary mirror.

Likely the only problem is that the mirror is too thick to be practically useful.

This means it may be technically possible to cut the mirror roughly in 1/2 and have a finished mirror and a blank. However, there is a shallow chip on the back (about 1/4" deep) so it might be best to cut it into three parts. Probably about 1.5" for both the finished part, 1.5" for a blank, and knock off about 1" to take out the flawed back of the thing.

One would hope that someone could do the cutting with a water jet so that there would be no significant heating and thus no need to go back and re-do the finished mirror surface.

I don't think that water jets can cut sufficiently deeply to make this actually work. So this might mean that cutting the blank to a reasonable thickness could heat the blank and/or introduce strain in some other manner. The thing might require annealing and re-figuring.

My starting point when I'm about ready to go would be Optic Wave Laboratories/OSI. Carey has machine tools, re-figures mirrors, and has the ability to coat a mirror of that size. I'm not sure, however, that he has the machines/tooling for cutting down the thickness of a mirror of that size. For that matter, he could test it to see just how well-figured it really is before we decided to consider tearing into the thing. If the mirror is more poorly done than I suspect NASA would accept, then if it is going to have to be re-done I might try for somewhat faster optics (even at F/5 I'd expect the OTA to be more than 8 feet tall).

But it is a bit early to pursue this very much. I've not the time to build the OTA around it and I have to develop more ATM experience as well.

I'd probably first try building out one of the 8" mirrors or maybe the 13.1" mirror.

The 20" is just a bit too far out right now.

Thinning a mirror as you require seems to have a lot of potential risks. It's certainly not SOP. Good luck.

notFritzArgelander wrote: ↑Sun Jun 16, 2019 10:11 pm

mcolbert wrote: ↑Sun Jun 16, 2019 10:07 pm

notFritzArgelander wrote: ↑Sun Jun 16, 2019 9:29 pm

At that size I think they'd need a grinding machine so who has one?

can we put this out into public circulation on the board in some way? Maybe in announcements? Or is there somewhere better suited to grab people's attention?

There is a "vendor" area where folks equipped for such enterprises could be invited to post.

it just needs the word to spread - perhaps as a sub heading on the vendor forum heading? Who do we need to contact?

well at least you have started an interesting conversation and raised possibilities for others here on the forum.

mcolbert wrote: ↑Mon Jun 17, 2019 2:15 am

notFritzArgelander wrote: ↑Sun Jun 16, 2019 10:11 pm

mcolbert wrote: ↑Sun Jun 16, 2019 10:07 pm


can we put this out into public circulation on the board in some way? Maybe in announcements? Or is there somewhere better suited to grab people's attention?

There is a "vendor" area where folks equipped for such enterprises could be invited to post.

it just needs the word to spread - perhaps as a sub heading on the vendor forum heading? Who do we need to contact?

I'd suggest that individuals invite folks to post in the vendor area. The only one out of my list I ever corresponded with was Royce and he's retired. So if you know someone....

I'm thinking of inviting the SV folks to post.

ATMers, no not that I know of. I was more thinking about about those with expertise but not necessarily professionals or involved in the retail side of things. Enthusiasts who spend time on different sites. There does seem to be a lot of expertise out there. I'll PM Roger and see if he can suggest something that fits with the forum as a whole.

oops! Roger????? I meant Gordon.