61 replies to this topic

[CanaryMax]

I did not know these threads, read them carefully, thank you.

 

Martin: Attached the mirror test, few conclusions I get it, you?

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[glend]

 

I will follow this with interest, having just completed a 10" imaging newt using carbon fibre struts with plywood rings. 

Planning on posting some info on your build?

 

Alex, it has been posted before but I have sent you a PM with the info.

glend

[CanaryMax]

Hello:
I am no expert in valuing a mirror through the test, the numbers seem right, but I'm friend of evaluating under good sky. All that wonder of this test is to see the raised edge as shown in red on the image above to the right of the test.
If that test is made using all the mirror surface, it appears that by making a small mask few millimeters could eliminate all the red area, thereby improve the PV value.
I do not know, if it corresponds to the curve of the parabola or a TUE.

Regards

Maximo

[fjh]

Hi Maximo,

Thanks for sharing the details of your project. It's impressive to say the least!  I'm very interested in these mirrors. Herr Rohr provides a very detailed report. I have two questions.

Does the report talk about the smoothness of the mirror? If so, what does it say and where in the report is it communicated?

I see from the photos that your mirror has threaded tube/pipe attached to the back. Did that come with the mirror? Is it permanently attached? Did you get it from a third party?

Thanks

Edited by fjh, 22 October 2015 - 09:39 AM.

[CanaryMax]

Hello fjh:

Thanks, it's been a very fun and entertaining project.
The core values that show the softness and quality are the mirror, the Peak to valley, RMS and Strehl, and the MTF curve, you have them in the above test. However, we know that the test does not coincide with reality, because they eliminate astigmatism, coma, and to not use it in the real sky few conclusions can be taken.

 

I'm making the cell and the mirror is fixed to it by a nut and if I find that a spring diameter 63mm.

[fjh]

Maximo, I think you may be discounting the test prematurely. There has been a lot of discussion regarding the interpretation of his tests. Clearly some folks think his test are meaningless because the report has astigmatism and coma turned off. I believe this is a misunderstanding of his testing method.

 

As I understand  his  method he uses a special test for astigmatism before he goes to any other test. This test identifies the high and low order astigmatism in the figure of the mirror. Once he has determined that the astigmatism is inconsequential he proceeds with the other tests.

 

In these later tests astigmatism can enter from other sources such as the temporary mirror supports, air currents or uneven temperature. Since he has already determined the amount of astigmatism from the first test he does not need to look for it in the later tests. He is free to remove astigmatism from these later tests. He is merely making sure that astigmatism from extraneous sources does not distort the later tests. The testing for coma follows a similar logic. Since coma is inherent is a parabolic newtonian, it makes sense to eliminate it from the later tests.

 

Simply stated. Once you know what you need to about astigmatism and coma, quit looking for it. Don't let it

interfere with the later tests.

 

This approach makes perfect sense to me. Each of his three tests are optimized for what is being tested. Sorry for the long post.

Thanks

[Rohr]

Dear Maximo,

 

These testing procedure just belongs for testing parabolic mirrors:

01. The main problem is, what causes the astigmatism you can observe.

- is it the seeing of the testing setup ?

- is it the storage of the mirror ?

- is it the Bath Interferometer ?

- or is it just the astigmatism of the mirror itself?

And just the last one you can consider to the mirror itself. So I think, you should

investigate for the astigmatism just of the mirror itself. And this is my first step.

 

02. You can subtract coma from your result, because there is no coma if you test

a parabola on optical axis !

 

03. So I test a parabolic mirror in two steps:

a) is there a significant astigmatisms or not? (the first step)

b) what about the spherical Aberration? (the second step)

 

04. But don't forget the elliptical flat. This one can introduce a lot of optical errors

to the Newton System.

 

I hope I could explane my way testing  parabolic mirrors.

And don't forget: We test optical Systems for astronomical observers and not

for long aloof discussions for theoreticians.

[fjh]

Herr Rohr,

Thank you for explaining and correcting my misstatements and misunderstandings.

 

Thank you

[CanaryMax]

Hello:

 

Thank you very much Mr. Rohr for stopping to answer, I do not intend to publish the test have an everlasting theoretical discussion, I published it because I was asked and I think may be of interest.
Glad to know before you take the test evaluates astigmatism and that this is negligible in my mirror. I am sure that I will have a good performance.

 

I finished the cell and lack of aesthetic touches and place the second dovetail the lower case is finished.

The mirror comes with a large screw 63 or 64mm metric I'm not sure, I could not find a nut of this measure and I've had to make, in carbon fiber course ;-) using the screw as a negative mold.

They can be seen in the cell, side screws in the center of the cell, which serve to center the mirror. I've placed gaskets between the mirror and the clamping nut not like it just because the mirror moves with the inclination, I think I will remove those gaskets, the central nut and the side screws will suffice.

 

Regards
Máximo Suárez

 

Edit: More images in http://canaryastro.w...lbumid=15819330

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Edited by CanaryMax, 28 October 2015 - 12:15 PM.

[Rohr]

Hello,

 

here you can read an additional report testing a 250/1250 Parabola:

http://r2.astro-fore...wo-times-tested

 

My problem: I just can respect the astigmatism value of the tested mirror itself.

[CanaryMax]

More images of the cell.

 

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[fjh]

Maximo, are making these parts using vacuum bagging or some other method? Do you have any pictures of your fabrication set up?

 

Thanks,

[CanaryMax]

Hello:

As I said in the first message the technique I use is bulk molding compound (BMC) is obviously a home scale, both in size and in the media.

I use resin curing at room temperature, and chopped carbon fiber, pressure applied manually by the clamps. It may seem that the pressure is low but I can assure that it is enough to remove the excess resin and eliminate air bubbles inside.
Being careful to mix the resin and fiber is well wet resin, the finish of the pieces is very good, it depends more on the quality of the mold.

 

My method is very rudimentary and easily upgradeable but if I stand in better, never finish making my telescope that is my goal.

 

I have a vacuum pump and everything you need to place vacuum bag but honestly the results without it seem as good and much cheaper costs and manufacturing time.
The whole process should take less than 60min... Little time to stop and take pictures of the process, with gloved hands, face masks, and all dirty resin and fiber, some I've taken.

 

After 24h in the mold under pressure, you can unmold and start work cut burrs, depending on size can be done with a cutter, dremmel, or milling machine in an open and well ventilated site, and using masks dust and gases, it is very dangerous to breathe.

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[fjh]

Maximo,
Thanks for the response and great pictures. Now I have even more questions:
1 - What brands of BMC and chopped carbon fiber are you using?
2 - What supplier are you getting it from?
3 - How much is required for the whole scope?
4 - What's the cost of the BMC and carbon fiber for the whole scope?
5 - How much space is between the male and female moulds?
6 - Is it hard to get consistent thickness for multiple parts.
7 - How hard is it to make multiple parts?

Thanks in advance

[polaraligned]

I would be curious to know what the density and Young's modulous is, of this material.

[CanaryMax]

Hello:

 

1-2-4, http://shop1.r-g.de/item/210137.

 

3, My telescope have 2.4Kg aprox  chopped carbon fiber. Fiber tubes are more expensive.

 

5, The space between the male and female moulds is about 1mm, the thickness of the saw.

 

6. It is one of the problems, get a good distribution of mass in the short time available before it hardens. The mass is introduced into the mold by hand trying to maintain a uniform distribution, when pressed first with a spatula and then with strong pressure eventually distribute it fairly well. The pressure can be performed in stages to achieve better compaction, mass distribution, and consistent thickness.
I could do some test looking for the center of gravity of a piece and check if it matches the theoretical, honestly for my taste differences will be negligible.

 

7. For small parts, the release is much easier and the mold can be reused more times. Large rings I could do with a single mold, the release took some more, but nothing that can not be taking the opposite pressure and cleaning especially well burrs excess resin before hardening.

I've assembled for the first time the entire structure. Weighs 11Kg total, + 8,9Kg primary, Add the secondary weighing, focuser, the finderscope and nylon fabric cover, I hope not exceed 23Kg.

 

Sorry for the quality of the photos, my phone does not have very good camera, I'll get better quality when I have finished.

 

 

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[CanaryMax]

Hello Polaraligned:

 

The density of my pieces is 1450Kg/m3 Ratio fiber/resin is 55/45% aprox.

I would also like to know the Young´s modulous, might send pieces to my university to make test but that costs money. Or do some flexure test at home and compare it with known materials, that are in the mountain of pending experiments do.
 

Please, I do not want to turn the thread in a theoretical struggle whether it is better wood, aluminum or fiber, each ATM maker has excellent reasons to work at what likes, want, or can... I would appreciate it if you want to discuss this, another thread that I will participate in with what I can contribute thanks.

 

Regards

Maximo

[fjh]

The pictures are great. Thanks for all the info. What cure rate hardener are you using?

Thanks again,

[CanaryMax]

Hello fjh

 

See here:

 

http://www.cloudynig...rall/?p=6442055

[fjh]

Sorry Maximo, I've read the entire thread multiple times. I didn't remember that you already posted that info. I'm not the only one forced to deal with my faulty old memory.

[Raginar]

So, you make a template... put the carbon fiber into it and then use pressure to make it into a sheet?  For the small parts you're making, are you cutting those out of a bigger sheet or do you still make the template for each piece?

 

Pretty cool.

[careysub]

Hello Polaraligned:

 

The density of my pieces is 1450Kg/m3 Ratio fiber/resin is 55/45% aprox.

I would also like to know the Young´s modulous, might send pieces to my university to make test but that costs money

 

Chopped CF filled epoxy usually has a modulus of 2-2.5 million psi, compared to 1.5 million psi for baltic birch. So it should out perform wood in modulus (but not specific modulus) even on favorable axes, and is isotropic to boot. Also no moisture related dimensional changes, and the advantage of being molded to arbitrary shapes.

 

In my work with CF telescope components I have also found vacuum bagging to be (so far) unnecessary - flat clamping, and stretch plastic wrapping give good results.

[Ishtim]

_{Any updates CanaryMax?  I am looking at building my own and we like to see your progress.}    

 

_Cheers!

[CanaryMax]

Hello Ishtim:

I had some delay in receiving the secondary mirror and very little free time to complete it, it is very close to finish and that at least is fully functional. In a few days I hope to upload the images.

 

Raginar: Sorry, I did not pay attention to your question, small parts are also made of a mold, only the support rods were initially made in one piece and then cut.

 

Cheers

Maximo Suarez

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[CanaryMax]

Hello:
After more time than I would have liked the telescope is operational, unfinished for lack of many details but since I could first use.

I had many problems with holding the primary mirror, the threaded tube inserted into the center is fastened with a very soft silicone and the mirror moved losing collimation depending on the position of the telescope, really bad solution by the manufacturer using such silicone.

The first night I could only make collimation, make a star test, the result is excellent showing good quality mirror and observe the M42 noting color tones in the nebula, and trapeze E and F components with a 24mm ES 68. Then came the clouds and keep waiting for them to leave since ...

Thank the Astronomical Association of Gran Canaria the possibility of using its observatory and EQ8 mount and Antares Optics for sending a much better than I had asked secondary mirror.

 

Regards

Maximo

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Edited by CanaryMax, 09 February 2016 - 08:03 AM.