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Equipment Discussions >> Reflectors

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David PavlichAdministrator
Transmographied
*****

Reged: 05/18/05

Loc: Mandeville, LA USA
Sky Watcher 18" prototype
      #6202171 - 11/18/13 05:45 PM

We spoke with the guy that's doing the work on this reflector and it's still in its rough stages, but you get an idea in which direction they're headed:

[image][/image]

[image][/image]

[image][/image]

[image][/image]

[image][/image]

This is Steve (Watermaster)in the picture for scale. He's over 6' tall.

[image][/image]

Note that there are no clips on the top side of the mirror holding it in place. The Teflon "clamps" actually protrude into the gaps between the mirror, the cells and the base to keep the mirror from shifting. Pretty novel approach!

David


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dvb
different Syndrome.
*****

Reged: 06/18/05

Loc: Vancouver, Canada
Re: Sky Watcher 18" prototype new [Re: David Pavlich]
      #6202388 - 11/18/13 07:38 PM

Wow - I hope they get the mechanicals right; that is, nice smooth bearing movements.

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David PavlichAdministrator
Transmographied
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Reged: 05/18/05

Loc: Mandeville, LA USA
Re: Sky Watcher 18" prototype new [Re: dvb]
      #6202734 - 11/18/13 10:37 PM

Actually, the movement isn't bad now. What they are working on is gaining more rigidity. This is going to be a nice scope if they get a few of the rough spots fixed. They will be offering a shroud.

David


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Starman1
Vendor (EyepiecesEtc.com)
*****

Reged: 06/24/03

Loc: Los Angeles
Re: Sky Watcher 18" prototype new [Re: David Pavlich]
      #6202808 - 11/18/13 11:25 PM

A few things I noticed:
--no altitude stop (yet) so the scope can continue down until it comes off the bearing. I'm sure they'll add one in production.
--curved focuser board. I don't know why no one else thought of this. It really improves the rigidity of the focuser mount.
--All-metal ball/socket (similar to Moonlite) pole connectors with no-tools fasteners. Nice.
--1.25" poles (a lot more rigid than 1" in this size.
--Sandwich-construction mirror. Is this really lighter than a thin solid mirror?
Bottom supports were blocks at 90 degrees apart--better than a sling for this style of mirror.
--All metal construction. How light will overall scope be?
--secondary mirror looked to be over 4", perhaps 4.5", so they've paid attention to not making secondary too small.

Overall, a fairly impressive prototype. It'll create waves, I bet. If it comes in under $5K (ballpark estimate), it WILL create waves. And it'll pack in a very small car.


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skyward_eyes
Vendor - Sky-Watcher USA
*****

Reged: 12/12/06

Loc: California
Re: Sky Watcher 18" prototype new [Re: Starman1]
      #6203296 - 11/19/13 09:30 AM

Don,

It was nice meeting you at the show and thank you for the input. It was very helpful to refine this scope into something people really want.

The primary mirror is 20 pounds for the 18". This is much light then standard 2" thick mirrors. We plan to have this technology for this new line of large dobs. I will be talking to the factory about the shroud and altitude stop. For the mirror cell, Howie Glatter has been a major help with its side mounting blocks. We use three of them to hold the mirror in place. The nice this is that the clips mount between the back and rear elements of the primary so there are no clips obstructing the mirror at all.

We are very excited about this scope. We hope to have a production model for next year. Once the 18 is done its onto the 20!


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dvb
different Syndrome.
*****

Reged: 06/18/05

Loc: Vancouver, Canada
Re: Sky Watcher 18" prototype new [Re: skyward_eyes]
      #6203527 - 11/19/13 11:19 AM

Very encouraging that Skywatcher is listening to people like Howie Glatter and Don Pensack in its designs!

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Starman1
Vendor (EyepiecesEtc.com)
*****

Reged: 06/24/03

Loc: Los Angeles
Re: Sky Watcher 18" prototype new [Re: skyward_eyes]
      #6203850 - 11/19/13 02:09 PM

Quote:

Don,

It was nice meeting you at the show and thank you for the input. It was very helpful to refine this scope into something people really want.

The primary mirror is 20 pounds for the 18". This is much light then standard 2" thick mirrors. We plan to have this technology for this new line of large dobs. I will be talking to the factory about the shroud and altitude stop. For the mirror cell, Howie Glatter has been a major help with its side mounting blocks. We use three of them to hold the mirror in place. The nice this is that the clips mount between the back and rear elements of the primary so there are no clips obstructing the mirror at all.

We are very excited about this scope. We hope to have a production model for next year. Once the 18 is done its onto the 20!



I really appreciated the bottom edge support design. Most sandwich mirror designs have suffered from improper support of the "bread" in the sandwich, inducing noticeable astigmatism. Your support should do a good job of solving that problem--an elegant solution.
I forgot to ask how many points of support there were for the primary mirror and whether you used a computer program like PLOP to design the support point locations.


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Roy McCoy
Pooh-Bah
*****

Reged: 10/13/05

Loc: Glendale, AZ
Re: Sky Watcher 18" prototype new [Re: Starman1]
      #6203899 - 11/19/13 02:39 PM Attachment (82 downloads)

Nine. Don't know if plop was used.

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Markovich
professor emeritus
*****

Reged: 05/22/07

Loc: Central Ohio
Re: Sky Watcher 18" prototype new [Re: Roy McCoy]
      #6204017 - 11/19/13 03:37 PM

Ok, looking the picture above, I don't get something:
The 18" scope weighs 150 lbs?? Goodness, an 18" Obsession Classic weighs much less than that! Where is the weight coming from?


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cpr1
professor emeritus
*****

Reged: 03/24/12

Loc: Louisiana
Re: Sky Watcher 18" prototype new [Re: Markovich]
      #6204334 - 11/19/13 06:26 PM

Maybe it is made with steel instead of aluminium? Since it is a prototype. Hope they can lose the counterweights when the production model is done.

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bob irvin
sage


Reged: 03/22/11

Loc: Greater Los Angeles, CA
Re: Sky Watcher 18" prototype new [Re: David Pavlich]
      #6204346 - 11/19/13 06:29 PM

It would be nice to have an alternative to the Obsession.

bob


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David PavlichAdministrator
Transmographied
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Reged: 05/18/05

Loc: Mandeville, LA USA
Re: Sky Watcher 18" prototype new [Re: Starman1]
      #6204392 - 11/19/13 06:52 PM

Quote:

A few things I noticed:
--no altitude stop (yet) so the scope can continue down until it comes off the bearing. I'm sure they'll add one in production.
--curved focuser board. I don't know why no one else thought of this. It really improves the rigidity of the focuser mount.
--All-metal ball/socket (similar to Moonlite) pole connectors with no-tools fasteners. Nice.
--1.25" poles (a lot more rigid than 1" in this size.
--Sandwich-construction mirror. Is this really lighter than a thin solid mirror?
Bottom supports were blocks at 90 degrees apart--better than a sling for this style of mirror.
--All metal construction. How light will overall scope be?
--secondary mirror looked to be over 4", perhaps 4.5", so they've paid attention to not making secondary too small.

Overall, a fairly impressive prototype. It'll create waves, I bet. If it comes in under $5K (ballpark estimate), it WILL create waves. And it'll pack in a very small car.




Well shoot! I wish I would have run into you, Don.

David


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GeneT
Ely Kid
*****

Reged: 11/07/08

Loc: South Texas
Re: Sky Watcher 18" prototype new [Re: Markovich]
      #6204887 - 11/19/13 11:18 PM

Quote:

Ok, looking the picture above, I don't get something:
The 18" scope weighs 150 lbs?? Goodness, an 18" Obsession Classic weighs much less than that! Where is the weight coming from?




Good question.


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Markovich
professor emeritus
*****

Reged: 05/22/07

Loc: Central Ohio
Re: Sky Watcher 18" prototype new [Re: bob irvin]
      #6205210 - 11/20/13 07:52 AM

Quote:

It would be nice to have an alternative to the Obsession.

bob




No argument there, but for a minimalist design and a sandwich mirror, one would expect it to be lighter, not significantly heavier than a comparable size from Obsession, or Webster,et al.....


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drago
sage


Reged: 01/11/08

Loc: Latvia
Re: Sky Watcher 18" prototype new [Re: Markovich]
      #6205214 - 11/20/13 07:58 AM

how about mirror in various temperatures?
i be reading, a synta 14" sandwich type mirror in low temperatures (0 to -30 celsium) get an out of "right" figure, and produce terrible images...?


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Fireball
professor emeritus


Reged: 03/24/06

Re: Sky Watcher 18" prototype new [Re: drago]
      #6205291 - 11/20/13 09:13 AM

I am getting excited. I am looking for a reasonably priced dob in the 20" range with minimized design and weight (hopefully) to eventually replace my trusty 12" Lightbridge

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Starman1
Vendor (EyepiecesEtc.com)
*****

Reged: 06/24/03

Loc: Los Angeles
Re: Sky Watcher 18" prototype new [Re: drago]
      #6205383 - 11/20/13 10:11 AM

Quote:

How about the mirror in various temperatures?
I've been reading that a Synta 14" sandwich type mirror in low temperatures (0 to -30 Celsius) gets an out of "right" figure, and produces terrible images...?



This would be true of any mirror that is still cooling. And once cooled, the sandwich mirror shouldn't perform any worse than it would 50C higher.

But my question concerns the cylinders between the upper and lower thin solid sections: they are filled with air which expands and contracts with temperature. Does that internal pressure change affect the surface figure of the mirror above the cylinders? The mirror could be perfect at +20C. Does it appear dimpled at -20C?


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skyward_eyes
Vendor - Sky-Watcher USA
*****

Reged: 12/12/06

Loc: California
Re: Sky Watcher 18" prototype new [Re: bob irvin]
      #6205485 - 11/20/13 11:09 AM

The 150 pound weight came from factory. This scope is entirely made of metal so the weight might be a bit higher as the Obsession uses wood. Once the scope arrives from the show I will be able to weigh it.

The scope is a 9 point flotation cell.


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Howie Glatter
Vendor


Reged: 07/04/06

Re: Sky Watcher 18" prototype new [Re: Roy McCoy]
      #6205519 - 11/20/13 11:31 AM

"Nine. Don't know if plop was used."

Don mentioned the edge supports. They are pivoted lever blocks, pivoted in the plane of the mirror's center of mass. That way the support force is divided over the two disks, and also, the mirror will not loose collimation when pointed low because there will be no tendency to tip forward or back.
Mike Zammit used something similar, but more elaborate with good reason, for a 32"(if I remember correctly)Horizon scope with a sandwich mirror. It's in the vendor forum.

I believe the mirror cells are individually vented by holes in the back plate, otherwise it would become a barometer read by Pickering.

Update: the below poster shows us that the cells are vented by cuts in the glass rings. I was wondering about that, because there were holes in the backplate on the
prototype mirror at NEAF this year, and I didn't see them on this one.

Edited by Howie Glatter (11/20/13 04:17 PM)


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Roy McCoy
Pooh-Bah
*****

Reged: 10/13/05

Loc: Glendale, AZ
Re: Sky Watcher 18" prototype new [Re: Starman1]
      #6205541 - 11/20/13 11:40 AM Attachment (67 downloads)

Quote:

But my question concerns the cylinders between the upper and lower thin solid sections: they are filled with air which expands and contracts with temperature. Does that internal pressure change affect the surface figure of the mirror above the cylinders? The mirror could be perfect at +20C. Does it appear dimpled at -20C?




Don,

I noticed that there were small Vs in the bottom of the cylinders which I assume were needed during the fusing process. These openings should help mitigate the temperature differential a little.


Regards,

Edited by Roy McCoy (11/20/13 12:45 PM)


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