A little bit of DIY mirror re figuring.

[RAC]

About mid 2013 I decided I wanted to build a really nice imaging scope but I wanted to get away from the standard flat back mirror for this type of scope so I would never have to think about the mirror shifting around the cell or collimation changing. I looked around and the only real option was a Royce conical mirror and he had a really good reputation to go with it so I placed an order for a 10" f4 conical mirror.

Now I had never heard a bad word spoken about his mirrors and the claims on his website put little doubt in my head as to how good the mirror will be when it arrived. It took about 9-10 months to arrive, this gave me time to build the rest of the scope.

I've been using the scope ever since and I've been happy with it but I did notice that visually and when planetary imaging the mirror was better with an edge mask so that's how I left it. I still thought this must be as good as it gets for a commercial mirror so I just used it as anyone would.

Late last year I started making my own mirrors as I wanted a larger planetary imaging scope and there was no way I was going to be able to afford to buy the mirror I wanted, this started with an 18" f3.3 mirror that turned out very well(after a lot of learning) and then there was a 20" f3.8 for a wheel out dob and then a 25" f3.8 but this one wasn't for myself.

Now as I am fairly proficient at looking at Ronchi and Foucault test images I though it would be interesting to have a look at my Royce 10" f4 mirror and I must say I expected it to be good!

Needless to say I was a little bit disappointed to see this. There are too many problems with this to point out, it's just plain bad!

And here is a Foucault showing the terrible surface quality.

And a Figure XP surface profile.

In my opinion fixing it myself was going to be the only way I was going to get what I wanted and that was a really good mirror.

Anyway two days work is what it took, I took it back to a sphere and then re figured it and it turned out every bit what i wanted.

So here's the new mirror.

And a shot of the new surface. These Foucault images are stacked HDR images and show very fine small scale surface details.

Figure XP surface profile.

In my opinion a simple Ronchi and Foucault image can tell you a lot and is what every mirror should come with because I can tell you this mirror would NOT have been sent out if that was the case!

[barkis]

Pretty bad as you said. I don't know how anyone could turn out a piece of work  like that.

Certainly in a different class now though. Lovely sight.

Fine Job there.

It used to be that  test reports was supplied with mirrors at one time, but even so, Images and reports could be doctored by an unscrupulous supplier.

I wholeheartedly agree on the  Foucault being used in the testing phases, Ronchi Data  is great, but I too love to see the delicate shadows at different radii changing under the knife edge.

Ron.

[Mick J]

Interesting work Raymond,  have you the mirror back in the scope yet ?   also how easy/difficult are these tests and producing the pictures, (a quick & simple answer to that one if it's possible).

[Cozzy]

Mick's already asked but 'hey' no harm in asking twice.

Very nicely refigured. So well done to you and your skills.

 I find this fascinating and would love to see how my budget explorer 200mm measures up.

Please could you explain how you achieve the images you have in (really really easy to understand terms) for a complete and absolutely clueless person on this topic like myself.

Tim  

[Stu]

Excellent result on the re figure, 0.997 Strehl is not to be sniffed at!!

Did you send your results to Royce?

[RAC]

Excellent result on the re figure, 0.997 Strehl is not to be sniffed at!!

Did you send your results to Royce?

I was thinking about it but I wouldn't know what to say other than I am little more than disappointed in his work.

[Stu]

I was thinking about it but I wouldn't know what to say other than I am little more than disappointed in his work.

Well, if nothing else I think they should find it interesting that such poor quality is coming out of an outfit promoting precision optical components.

Did they quote a minimum accuracy when you ordered? I can't see any references on their site.

[RAC]

Thats the funny bit as his specs get a bit vague below f4.5.

Making an f4 mirror should be a walk in the park for someone who has made so many. It's clear to see it was all done on a machine and not by hand looking at the swirl marks.

[RAC]

Mick's already asked but 'hey' no harm in asking twice.

Very nicely refigured. So well done to you and your skills.

 I find this fascinating and would love to see how my budget explorer 200mm measures up.

Please could you explain how you achieve the images you have in (really really easy to understand terms) for a complete and absolutely clueless person on this topic like myself.

Tim  

I'll try.

Buy a grating from here. I like a 133lpi for just about all mirrors. Get an LED( I like a white one ) Shine the LED through the Ronchi grating, the led is up close to the grating and they are both at the mirrors radius of curvature(about two times the focal length), the return beam(reflection) is then viewed again through the grating. When you move the led and grating back or forward the bands on the mirror will change.

You can use this online calculator to know what the bands should look like for your mirror.

[Cozzy]

I'll try.

Buy a grating from here. I like a 133lpi for just about all mirrors. Get an LED( I like a white one ) Shine the LED through the Ronchi grating, the led is up close to the grating and they are both at the mirrors radius of curvature(about two times the focal length), the return beam(reflection) is then viewed again through the grating. When you move the led and grating back or forward the bands on the mirror will change.

You can use this online calculator to know what the bands should look like for your mirror.

Thanks for the links, your gent.

cheers

Tim

[Astrobits]

Nice one. At least it is now.

Nigel

[RAC]

Here's a little update on this.

A few star test images and an image of the Orion nebula in HA as a test.

Orion ha test by Raymond Collecutt, on Flickr

[SnakeyJ]

Very disappointing to see such poor work on the original figure given the Royce reputation and price - though it's good to see a good bit of quartz turned around.

Is it noticeably harder to work than borosilicate?

[RAC]

It's just a pyrex conical mirror.

[Ajohn]

I suspect the problem with suppliers and faster mirrors is time and wondering just how long it might take to reach perfection and maybe seeing them as just being light buckets for nebulae etc where as planets ideally need perfection.

Great work again Raymond and thanks for including a link to your flickr pages. There are some shots on it using equipment I have wondered about on smaller scopes especially barlows.

There is a shot of the eagle nebula that might interest Tim  - 8" Skywarcher. Looks like you have a lot of skill in the astro photo area too Raymond.  Something I am not sure I will enjoy gaining. If I can. Ordinary photography was bad enough.

I've noticed that GW on youtube sometimes has a hole in the back of mirrors. I had wondered if this was to get it central on the table but maybe it's for location in the scope.

John

-

[RAC]

Yeah I think a big problem is the amount of orders. One man can only do so much. Doing it by hand it took me two full days so if you think about that then these mirrors are too cheap if you include the blank and the rest of the grinding and polishing, all I did was take it back to a sphere and figure it from there, I couldn't just figure it from where it was as there was a turned edge I wanted to fix.

[RAC]

I think the hole in the back was a left over from the quartz blank as it was to be used in the semiconductor industry. I think they where seconds but perfectly ok for mirrors.

[Astrobits]

It's just a pyrex conical mirror.

I think the hole in the back was a left over from the quartz blank as it was to be used in the semiconductor industry. I think they where seconds but perfectly ok for mirrors.

???

Is it Pyrex or Quartz?

Can't make a Pyrex mirror from a quartz blank.

Nigel

[RAC]

I was talking about this quote from John about something he noticed on Gordon Waite's youtube channel.

"I've noticed that GW on youtube sometimes has a hole in the back of mirrors. I had wondered if this was to get it central on the table but maybe it's for location in the scope."

[Astrobits]

Apologies and thanks for the clarification.

Nigel

[mapstar]

Interesting stuff Raymond and good to see you've turned it into a very nice looking mirror.  The images are superb of the Ronchi and Foucault 

The star test images you've put up have a very stable look to them. If it was our atmosphere they would look terrible.

I must admit I really fancy starting another mirror but at present I just don't have the time as I'm still tinkering with getting the build for the last one finished. 

[barkis]

Interesting stuff Raymond and good to see you've turned it into a very nice looking mirror.  The images are superb of the Ronchi and Foucault 

The star test images you've put up have a very stable look to them. If it was our atmosphere they would look terrible.

I must admit I really fancy starting another mirror but at present I just don't have the time as I'm still tinkering with getting the build for the last one finished. 

Damian, what's the story on your mirror, is it finished now then, I didn't get to see the end of your thread ?

I should have a look to see what transpired. I did see the bit where John had done some work on the surface for you,

but not the conclusion. 

Must be fine if you are engaged in the build of the enclosure for it.

[mapstar]

Damian, what's the story on your mirror, is it finished now then, I didn't get to see the end of your thread ?

I should have a look to see what transpired. I did see the bit where John had done some work on the surface for you,

but not the conclusion.

Must be fine if you are engaged in the build of the enclosure for it.

Hi Ron it is complete just the shell to post here:-

http://stargazerslounge.com/topic/237343-the-22-mapstar-mirror/page-44

[RAC]

Interesting stuff Raymond and good to see you've turned it into a very nice looking mirror. The images are superb of the Ronchi and Foucault

The star test images you've put up have a very stable look to them. If it was our atmosphere they would look terrible.

I must admit I really fancy starting another mirror but at present I just don't have the time as I'm still tinkering with getting the build for the last one finished.

Those star test pics are stacked images done with a planetary camera.

Making a small mirror is nothing like making the mirror you did.

[mapstar]

Aaaah right I suppose I'm just showing my lack of knowledge with photography equipment as I didn't think of that?

I learnt a lot from the last outing and shouldn't waste the experience by not trying again.

Well done but I still can't believe how bad it was to start with!