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Where to find a *good* optically flat mirror?

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Pete Rimmer23/02/2021 17:13:13
1008 forum posts
57 photos

I put an advert on homeworkshop for an optically flat mirror but as yet have had no responses to it. These things seem to be thin on the ground and very expensive, if you buy the mounted ones.

I'm looking for 'thinking out of the box' suggestions as to where I can find a decent fractional-wave first surface mirror to use as a reflector for an autocollimator I am picking up shortly. I can make the sled to carry it and I'm confident that I can make a mount but I need to first buy the mirror itself.

I know that there are a few members interested in telescopy and other optical interests so I'm hoping that someone can suggest a source for a reasonably priced mirror. It must be flat, and first-surface, and fractional waveength, so half-wave or better.

I'm not a tightwad but I don't want to pay newor crazy ebay prices. Hopefully there will be someone here can point me in the direction of a decent mirror or a device or instrument where they re used so I can look for a surplus one.

Pete,.

Michael Gilligan23/02/2021 17:34:36
avatar
18349 forum posts
872 photos

Have a look at SurplusShed : **LINK**

https://www.surplusshed.com/index.php

Fred is a very honourable chap, and will accept an order cancellation if you don’t like his shipping rate.

MichaelG.

old mart23/02/2021 18:59:39
3197 forum posts
201 photos

You need to post the maximum and minimum diameters that would be useful to you.

Pete Rimmer23/02/2021 20:03:17
1008 forum posts
57 photos

Well Mart, they come in all sizes but realistically I am expecting to find one between 1" and 3" diameter.

John Haine23/02/2021 20:09:12
3952 forum posts
227 photos

A surplus scanner?

DC31k23/02/2021 20:10:26
506 forum posts
1 photos

There is a US site, firstsurfacemirror.com where they have an online calculator. I do not know if their products are suitable for your application so apologies in advance if this is misdirection.

Robert Atkinson 223/02/2021 20:24:29
avatar
1018 forum posts
20 photos

I have some first surface mirrors that should suit. send me a PM.

Robert G8RPI. (Cambridge UK)

Dave S23/02/2021 21:28:12
146 forum posts
27 photos

You could try comar optics - comaroptics.com

They list 25mm dia 1/4 wavelength for what seems a reasonable £36.

We used them for custom optics when I worked in precision non contact metrology.

Dave

Clive Hartland23/02/2021 22:26:16
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2691 forum posts
40 photos

Pete, if you are going to mount a surface mirror it needs adjustment in x and y planes. The ones I used had three adjusters. The mirror mount was mounted on 1 ball bearing and the adjustment screws held the mount onto the ball. The best were made from Titanium, solid, about 15mm thick. Not glass but polished up very well and of course flat.

I surveyed a damaged ships engine bed after a con rod bent which from the survey ended up bent like a banana. I measured at 300mm intervals and drew it out and it had 230 Thou. droop at both ends and 180 thou in the middle.

Pete Rimmer23/02/2021 23:55:47
1008 forum posts
57 photos

Thanks for the replies and suggestions. It's given me a lot to go on.

Comar optics do a 63mm 1/10 mirror which would be ideal except it's £120 plus vat. I was hoping to avoid quite that much expense but if I don't find a suitable mirror for less I will have to stump up the cash for that.

Pete.

Lainchy24/02/2021 07:05:48
avatar
271 forum posts
103 photos

Have a look at Orion optics in Crewe.

Clive Hartland24/02/2021 07:57:55
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2691 forum posts
40 photos

Pete, could you give us what application/use you have in mid for the collimation work. I have some experience in collimation etc.

Pete Rimmer24/02/2021 08:35:54
1008 forum posts
57 photos

Clive yes I am buying an autocollimator for checking surface plates and machine alignment. It will only be used over short distances so I can suffer a bit of error in the mirror. I've got a couple of plates that I need to renovate, one is quite bad the other quite good. I've got a lapping plate and I've made a repeat-o-meter and found this instrument, now I need a good mirror to use with it.

John Baron24/02/2021 09:02:54
avatar
471 forum posts
186 photos
Posted by Pete Rimmer on 23/02/2021 17:13:13:

I put an advert on homeworkshop for an optically flat mirror but as yet have had no responses to it. These things seem to be thin on the ground and very expensive, if you buy the mounted ones.

I'm looking for 'thinking out of the box' suggestions as to where I can find a decent fractional-wave first surface mirror to use as a reflector for an autocollimator I am picking up shortly. I can make the sled to carry it and I'm confident that I can make a mount but I need to first buy the mirror itself.

I know that there are a few members interested in telescopy and other optical interests so I'm hoping that someone can suggest a source for a reasonably priced mirror. It must be flat, and first-surface, and fractional waveength, so half-wave or better.

I'm not a tightwad but I don't want to pay newor crazy ebay prices. Hopefully there will be someone here can point me in the direction of a decent mirror or a device or instrument where they re used so I can look for a surplus one.

Pete,.

Hi Pete,

There are usually a number of different size first surface mirrors in a laser printer head unit !

Martin Connelly24/02/2021 09:17:30
avatar
1790 forum posts
190 photos

The disk in a scrap hard drive may be useable. If you have one to take apart the disk is aluminium so easily cut. Don't know how well it will work for your application but it may be a suitable stop gap until you get exactly what you want.

Martin C

Anthony Knights24/02/2021 09:21:21
533 forum posts
230 photos

Sheer speculation-how flat is a hard drive disk?

Martin Kyte24/02/2021 10:19:14
avatar
2462 forum posts
40 photos

I've used this lot in the past for telescope optics.

**LINK**

regards Martin

Michael Gilligan24/02/2021 10:45:26
avatar
18349 forum posts
872 photos

I’m sure you know all this, and more, Pete ... or you wouldn’t have started this thread

But for general reference, there are some useful diagrams here: **LINK**

https://www.taylor-hobson.com/-/media/ametektaylorhobson/files/product-downloads/autocollimators/autocollimators-en.pdf?dmc=1&la=en

MichaelG.

noel shelley24/02/2021 11:47:27
639 forum posts
18 photos

Coventry gauge and tool at their Gt Yarmouth plant made optical measuring instruments that used mirrors that were polished at the plant back in the late 60s. They used the name Kandux and the machines were optical comparetors. The mirrors were quite a few inches in diameter - it might be worth looking for an old unit, as I expect most have gone now but the mirrors might have survived. I worked there. Noel.

Dave S24/02/2021 12:16:37
146 forum posts
27 photos
Posted by Anthony Knights on 24/02/2021 09:21:21:

Sheer speculation-how flat is a hard drive disk?

According to this **LINK** - lambda/100

or Very Very Flat

might be a cheap alternative

Dave

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