Where to find a *good* optically flat mirror?

[Pete RimmerParticipant @peterimmer30576]

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,.

[Pete RimmerParticipant @peterimmer30576]

[Michael GilliganParticipant @michaelgilligan61133]

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 martParticipant @oldmart]

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

[Pete RimmerParticipant @peterimmer30576]

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

[John HaineParticipant @johnhaine32865]

A surplus scanner?

[DC31kParticipant @dc31k]

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 2Participant @robertatkinson2]

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

Robert G8RPI. (Cambridge UK)

[Dave SParticipant @daves59043]

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 HartlandParticipant @clivehartland94829]

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 RimmerParticipant @peterimmer30576]

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.

[LainchyParticipant @lainchy]

Have a look at Orion optics in Crewe.

[Clive HartlandParticipant @clivehartland94829]

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

[Pete RimmerParticipant @peterimmer30576]

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 BaronParticipant @johnbaron31275]

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 ConnellyParticipant @martinconnelly55370]

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 KnightsParticipant @anthonyknights16741]

Sheer speculation-how flat is a hard drive disk?

[Martin KyteParticipant @martinkyte99762]

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

**LINK**

regards Martin

[Michael GilliganParticipant @michaelgilligan61133]

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 shelleyParticipant @noelshelley55608]

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 SParticipant @daves59043]

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

[Bob WorsleyParticipant @bobworsley31976]

Found a front silvered mirror off of a H&W shadowgraph? Also thought I had one of the mirrors you pictured but so far can't find it.

[Pete RimmerParticipant @peterimmer30576]

If you do find the mounted one Bob please let me know. What size and thickness is the shadowgraph mirror?

[Clive HartlandParticipant @clivehartland94829]

Hello Pete, had a look through all my bits and peces and found two round mirrors, one is 28mm dia. but has slight surface marks. the second is pristine and is a stepped body of about 65 mm dia and the mirror part at 55mm. This body is about 20mm thick.

PM me if you are interested.

[Pete RimmerParticipant @peterimmer30576]

Thanks Clive, I've sent you a message. That one does sound just about ideal.

Pete.

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