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StarStructure Telescopes / LARGE APERTURE SCOPES

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#1 michael

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Posted 24 August 2013 - 01:40 PM

Hi all,
Have a few big boys in the making...Including a 36" and 34".
I am building two each with the second structure available.

In addition to the 36 and 34, I also have most major components fabricated for a 30", 28" two 26"'s a 24" and two 20" sizes.

All are the new Horizon design and can have any focal length up to F3.6. Smaller size are also available.

Please contact me directly if interested.

Thanks for looking,

Mike

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#2 skyward_eyes

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Posted 25 August 2013 - 10:50 AM

Wow, excellent work. I love this new design you have done. Would be quite a treat to have a scope of that size. Gotta start saving.

#3 michael

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Posted 27 August 2013 - 06:11 PM

Thanks Skyward,

I'm building a 36" now and it's quite the beasty...here is a pic of the mirror cell in progress.

Mike

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#4 michael

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Posted 27 August 2013 - 06:11 PM

Pic of the altitude bearings...

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#5 Sky-Watcher USA

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Posted 27 August 2013 - 06:23 PM

Where is the first 36" heading to?

#6 michael

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Posted 27 August 2013 - 06:37 PM

The first 36 is heading to Canada.

Mike

#7 Sky-Watcher USA

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Posted 28 August 2013 - 12:12 PM

Wow thats huge. Awesome stuff. A 36" is no small scope.

#8 Bob S.

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Posted 28 August 2013 - 01:02 PM

Michael, That is really neat how you have attached the alt bearings to top of the mirror box and then integrate them into the whole mirror box structure. As you have previously reported, there is no other commercial scope maker that is making them in the sizes you are making that overall have as small a footprint as your Horizon's have. Good job. Bob

#9 MDavid

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Posted 28 August 2013 - 01:24 PM

Hi all,
Have a few big boys in the making...Including a 36" and 34".
I am building two each with the second structure available.

In addition to the 36 and 34, I also have most major components fabricated for a 30", 28" two 26"'s a 24" and two 20" sizes.

All are the new Horizon design and can have any focal length up to F3.6. Smaller size are also available.

Please contact me directly if interested.

Thanks for looking,

Mike


Do you have an eyepiece height estimate for the 20" f/3.6? or at f/4.5? How about the approximate total weight?
The scope looks amazing.

#10 michael

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Posted 28 August 2013 - 06:59 PM

Hi,
Focal lengths on the Horizon design typically run focal length -3 so a 20" F3.6 would be about 69" / 20" F4.5 about 87".

Weight of a 20" 3.6 would be about 125 with a 1.6" thick primary.

Thanks,
Mike

#11 michael

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Posted 28 August 2013 - 07:00 PM

Thanks Bob.

Mike

#12 michael

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Posted 29 August 2013 - 05:28 PM

Here are a few pics of the 36" mirror cell. Note that this is a custom sandwitch mirror.

This picture showing the mock-up mirror blank.

Mike

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#13 michael

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Posted 29 August 2013 - 05:31 PM

Showing side profile of 5.75" thick mirror

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#14 michael

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Posted 29 August 2013 - 05:31 PM

Here is a face on shot of the cell. Both inner and outer frames.

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#15 michael

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Posted 29 August 2013 - 05:33 PM

Close-up of the 16 point floating edge support.

The pads shown are for spacing only and will not be on the finished cell.

Mike

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#16 Jarad

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Posted 30 August 2013 - 08:51 AM

Hi Michael -
I suspect that with those sandwich mirror the number of support points on the back is less critical. The front plate is essentially supported by the posts between the plates, small deformations of the back plate probably aren't transmitted through.

Not that having 27 points will cause a problem, but I bet that 6 would work just fine.

Jarad

#17 Howie Glatter

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Posted 30 August 2013 - 09:20 AM

". .small deformations of the back plate probably aren't transmitted through."

If the mirror is monolithic, why wouldn't back plate deformations be transmitted to the front through the spacer posts in between?

#18 michael

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Posted 30 August 2013 - 11:04 AM

Hi Howie and Jarad,
I think you both have valid points.
I've gone through many of them in my head as well.

Truth is...it's a big unknown.

Another twist to the equation is that both front and back plates are slumped the same amount. So the back of the optic is curved, same as the front. This pretty much takes away all conventional cell point theory.

With that said...All the specs for the cell have been provided by the owner, both cell points and edge support. I am building the cell to spec and take no responsibility for the performance of the optics. It was the only way I agreed to build the scope.

The second 36” I building with this one is designed for a conventional 2.25” thick primary.

Mike

#19 Jarad

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Posted 30 August 2013 - 01:01 PM

If the mirror is monolithic, why wouldn't back plate deformations be transmitted to the front through the spacer posts in between?



Because it's not monolithic. I have made a crude drawing below. The big black circle are the two mirror plates (we are looking straight down). The blue squares are the posts between the plates (and there are probably more in the real thing, but I got tired of drawing them...). The 6 red circles are the 6 cell supports.

So let's say that the back plate is deformed upward by say a full wave by the 6 cell supports. The deformation at the nearest post will not be nearly as large, and would mostly be a pull towards the cell point on the order of a fraction of a wave. The deformation transferred to the front plate would be a product of the angle of the tiny sideways movement of the base of the plate over the length of the post (fraction of a wave divided by inches).

Michael, of course you are doing what the customer asks. I think this would be more a job for the mirror maker to test. I suspect that cellular designs can handle much simpler cells than monolithic mirrors can. It should be easy enough for the mirror maker to do a test (I presume he has testing equipment for making the mirror anyway). Put the mirror on a 27 point cell, take an interferogram, then put it on a 6-point cell and repeat.

From the mirror maker standpoint, simpler cell requirements could be a selling point, and partly offset the additional cost of the cellular blank with savings on the cell.

Jarad

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#20 Howie Glatter

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Posted 30 August 2013 - 01:29 PM

Hi Jarad,

I think monolithic means one piece, so after the pieces of the blank are fused together, it is a monolithic blank.
Your explaination assumes the back support points will be placed between, and as far away as possible from the support posts; which is a good design idea, but it may not be so in a particular implementation.

#21 Jarad

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Posted 30 August 2013 - 01:49 PM

I suppose I think of monolithic as meaning a single, solid piece. I think of all the sandwich or honeycomb designs as "not-monolithic".

Anyway, the definitive answer will only come from actually testing it. I suppose someone could set up a finite-element model of a sandwich design, but just testing one on a couple of cells would be the best way to see.

Jarad

#22 Relativist

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Posted 31 August 2013 - 11:52 AM

Interesting that both sides are slumped, reminds me of what Mel describes on his 13" f/3 zip dob page:

http://www.bbastrode...Dob/ZipDob.html

Under "Meniscus, the Superman Mirror"

I agree that a good place for the responsibility of the number and location of the supports for a non standard mirror should probably be the mirror designers.

Hi Howie and Jarad,
I think you both have valid points.
I've gone through many of them in my head as well.

Truth is...it's a big unknown.

Another twist to the equation is that both front and back plates are slumped the same amount. So the back of the optic is curved, same as the front. This pretty much takes away all conventional cell point theory.

With that said...All the specs for the cell have been provided by the owner, both cell points and edge support. I am building the cell to spec and take no responsibility for the performance of the optics. It was the only way I agreed to build the scope.

The second 36” I building with this one is designed for a conventional 2.25” thick primary.

Mike



#23 michael

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Posted 03 September 2013 - 08:11 AM

I agree that a good place for the responsibility of the number and location of the supports for a non standard mirror should probably be the mirror designers.



Hi,

Yes...In a case like this, you'd be crazy to do it any other way.

Pic shows the begining of the mirror box assembly with the outer cell frame in place.

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#24 michael

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Posted 03 September 2013 - 08:20 AM

A nice feature of the Horizon design is that I can make the altitude bearing as thick as I want without increasing the width of the scope. The picture shows the 4” thick altitude bearing.

I probably won’t use all 4” but it’s nice to have. This way I can play with the Teflon / FRP width for smooth altitude operation.

Mike

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#25 michael

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Posted 03 September 2013 - 04:53 PM

Here is a shot with the cell assembly with sim mirror in the mirror box.

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