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Zambuto vs Royce Conical for 11" STS.

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#1 dscarpa

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Posted 22 January 2013 - 11:13 AM

I was sure about going with the Zambuto but after spending some time on Royce's site am not so sure now. The mounting system of the Royce looks like it would make for a faster cooling mirror as most of the cell is set back from it. That's not a big deal for me. I've got a IM-715 mak and hardly ever have to run the fan and the STS has one if I need it. Of much more importance to me is it looks like the Royce would hold collimation better as the mirror is bolted onto the cell. You can see how it's done on Teeter's site in the STS scope log in the gallery shots of the 11" F/5 with the Royce mirror. Teeter told me he thought the Royce was very close to the Zambuto optically. In the review of a Royce Conical 8" on this site the reviewer says Zambuto himself recommended Royce. The Zambuto is less expensive because Royce has to shave down a 12.5" blank to make an 11". David

#2 eric moerman

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Posted 22 January 2013 - 12:06 PM

Hi,


i did have a royce 12.5F7 conical mirror and now i have a zambuto 12.5 F5.6 mirror.
I did compared them to eachother and i have to say that it was very close.
The only difference i could see was that the zambuto gave a litle bit more contrast.Buth it was very close.Maybe the newer coating made the difference.
So i think you cant go wrong with any of the 2 very good mirror makers.
My to (euro)cents ;-)
Hope this helps.

Greetings,eric

#3 Mirzam

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Posted 22 January 2013 - 03:00 PM

I have a 12.5" Royce conical in my Cassegrain, which is held in place by the baffle tube and a clamp. This is not the greatest arrangement because the hole in the mirror is a bit irregular and thus careful shimming of the mirror against the baffle tube was needed to eliminate side to side shifting. You don't want to clamp down too hard for the same reasons that you don't want to use mirror clips that are too tight.

I'm not sure from the photos how the conical mirror is held in the case of the STS. Is there one central support point or multiple (3) points? Is the mirror glued on the supports? If it is glued I would hate to worry about how to get it off when the time comes for re-coating.

I think that the cooling benefit of conical mirrors is overrated. The central part of the mirror is full thickness and will hold a ton of heat.

My vote would be for a Zambuto mirror, as thin a possible, and ideally made of quartz. My 14" travel scope has a thin quartz mirror from Mark Cowan and it is terrific.

JimC

#4 dscarpa

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Posted 22 January 2013 - 03:35 PM

The 12.5" Conicals and down are held in place by single nut inside the center of the mirror that has resin around it and a bolt threaded into it. The bolt goes through a hole in the cell and is held in place by a nut on the other side. Mirrors bigger than 12.5" have a hole in the center. David

#5 Bob S.

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Posted 22 January 2013 - 03:45 PM

David,
If you ever go to resell the scope, it is likely that the Zambuto mirror will fetch a higher resale value. Royce mirrors are great and I have owned a couple of them and are built to a certain level of quality (I think Royce guarantees .96 Strehl?). Zambuto mirrors are great and seem to be built to the highest levels of quality that can be put into a mirror? I recently sold an 11" f/4.3 Zambuto to a vendor friend in Germany who had it tested my Wolfgang Rohr. This was the second or third Zambuto that Rohr has tested on his Zygo Interferometer and each time, he raves about the quality of Zambuto mirrors. They are apparently about the smoothest mirrors he has ever seen and Carl Z. prides himself in reducing micro-ripple to a small value. The ZOC mirrors tend to test out in the .98-99 Strehl range which arguably we shouldn't be able to see much of a difference between Strehls that are that high. Royce mirrors have tested well on his equipment but not quite at the same level as Zambuto's IIRC. You need pretty good seeing nights to see any difference but I have had an opportunity to have owned two 8" scopes with one Royce mirror and one Zambuto mirror and myself and several others on a shootout slightly preferred the performance of the Zambuto. The differences were very, very, subtle but there was a discernible difference that three people were able to independently see at the same time in excellent, steady, Florida skies. I found my old post from February 2011 here on CN: "I had an 8" f/5.5 Zambuto/Portaball and an 8" f/6 Royce/UTI and myself and others found the Zambuto-mirrored scope to have just a tad more contrast. It would not have even been noticeable if we did not have them side-by-side and using equilevant (sp?) magnification. The difference was detectectable but very slight. Also, the structures were different and there is no way to tell if that was making a difference? Both mirrors were superb!" There are only a few opticians work that I have encountered/owned whos mirrors seem to provide a level of contrast that is off the chart. Names that come readily to mind are Zambuto, Lockwood, Harry and Spooner. Bob

#6 johnnyha

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Posted 22 January 2013 - 07:25 PM

Of much more importance to me is it looks like the Royce would hold collimation better as the mirror is bolted onto the cell.


Is there a problem with collimation on the Zambuto STS's?

Also, does the bolted-on Royce use the new mirror cell Rob has been raving about?



#7 steveyo

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Posted 22 January 2013 - 07:34 PM

To get an 11" Royce conical, one must pay the price for the 12.5, as noted above, which is $1650, vs, Zambuto 12.5 at $1960. HOWEVER, and it's a really big "however", the 10" Royce conical is $850, compared to 10" Zambuto @ $1400.

Bottom line: the 11" Royce is $800 more than the 10" Royce. Whoa.

I just ordered a Teeter STS11 (solid tube 11" Dob) with a 10" f/5 Royce conical mirror. A slightly slower system than the 11" f/4.5, and the extra space around the mirror should provide better temperature equilibrium. Another bonus, the OTA will be little lighter weight.

Best of all, the 10" Royce mirror is only a $200 bump up in Teeter's price structure for the "regular" STS11.

#8 Bob S.

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Posted 22 January 2013 - 07:48 PM

To get an 11" Royce conical, one must pay the price for the 12.5, as noted above, which is $1700, vs, Zambuto 12.5 at $1960. HOWEVER, and it's a really big "however", the 10" Royce conical is $850, compared to 10" Zambuto @ $1400.

So I just ordered a Teeter STS11 (solid tube 11" Dob) with a 10" f/5 Royce conical mirror. A slightly slower system than the 11" f/4.5, and the extra space around the mirror should provide better temperature equilibrium. Another bonus, the OTA will be little lighter weight.

Best of all, the 10" Royce mirror is only a $200 bump up in Teeter's price structure for the "regular" STS11.


Steve, That sounds like a very sweet option. Increased cooling and a premium mirror that is lighter to move around for very little extra money. Good job! Bob

#9 dscarpa

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Posted 22 January 2013 - 09:41 PM

A 10 wouldn't do it for me as I've got a very good C-9.25. I just talked to Rob and he said with the new cell and the Zambuto being siliconed on the Conical doesn't have an advantage holding collimation. He said the Royce is used with the old wood cell. The Royce would have come in a lot sooner and I'm sure it's a great optic but I just put a deposit on a Zambuto! Hopefully this year. David

#10 johnnyha

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Posted 23 January 2013 - 05:23 AM

Good luck! I just got my 14.5" Zambuto, it took about 10 months, and definitely worth the wait. I know CZ intends to start coating mirrors in-house soon with some super high-tech machines, so yours will probably be one of the new breed. :cool:

#11 Jitou

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Posted 23 January 2013 - 05:38 AM

Juste a comment about Zambuto new coating facility, they announced they will plan a testing run next Spring and they expect to start production this summer. In the meantime Galaxy or OMI will do the job.

http://tech.groups.y...p/message/13614

#12 NHRob

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Posted 23 January 2013 - 07:33 AM

Is Zambuto still doing thin quartz mirrors?

#13 Mirzam

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Posted 23 January 2013 - 08:03 AM

They show a range of thicknesses for 11" mirrors of 28-35 mm. If available, the 28 mm sounds like a very nice option. 10/1 Thickness ratio. Not sure about quartz other than the 20" mirrors that they make for Starmaster.

JimC

#14 Jarad

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Posted 23 January 2013 - 08:07 AM

He's doing one now for his personal scope.

http://tech.groups.y...p/message/13567

Jarad


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#15 Alan A.

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Posted 23 January 2013 - 02:42 PM

Is Zambuto still doing thin quartz mirrors?


Relatively recently I received a 10" 0.7" thick quartz mirror from Carl, its like looking through an APO.

#16 iluxo

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Posted 24 January 2013 - 07:00 AM

I've been thinking about building a 12-14" dob with either a zambuto or Royce mirror - and I have one concern. Coatings don't last forever despite SiO overcoating, and the time will come when a Royce mirror has to be recoated. If the mirror is epoxied to a support, or has a central bolt oxide in place, I would expect this must be removed before the mirror can be recoated - otherwise the epoxy will outgas in the vacuum chamber.

Thoughts ?

#17 Jeff Morgan

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Posted 24 January 2013 - 04:18 PM

The Royce conical has another interesting point for the ATM - it mounts very easily. One does not need to get a commercial floatation cell which is both heavy and expensive.

If you're trying to build a light-weight telescope, most of the mass is located in the mirror box. A welded steel cell is a great place to start getting rid of dead weight. While my Aurora Precision cell is a work of art, it does weigh 15 pounds all by itself. (I should have asked about having it made it aluminum. Next time.)

In the end I guess I would go with cost and availability. You won't go wrong either way.

I've bought four Royce mirrors, and all have been excellent. My first Zambuto mirror is awaiting First Light, perhaps next week. A conical would have been a little better weigh and cost wise, but I was curious to see what all the fuss is about with Zambuto optics.

#18 btom

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Posted 02 February 2013 - 09:17 AM

This is very interesting. I have just purchased the first production 11" STS from it's original owner. It uses an 11" meniscus mirror figured to F/4.5 by Gordon Waite from 1" thick pyrex. I also have a 10" F/5 Royce conical mirror originally intended for an ATM solid tube. The one thing about the 11" STS that I'm concerned about is the 11" mirror in an 11 7/8" ID tube that is powdercoated and insulated only with felt. That seems like a recipe for tube currents but the STS does have a fan so maybe it's all good. If there are problems, I could use the 10" Royce conical in the same tube and have plenty of room to add the protostar tube liner for insulation but then I'd give up an inch in aperture. Another option is to add a baffle above the 11" mirror that slightly infringes the 100% illumination cone and add the tube liner above that, maybe I'd end up with a 10.75". But hopefully it'll work like a charm out of the box...

#19 Mirzam

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Posted 02 February 2013 - 09:28 AM

I'm in agreement that a fan will likely solve most if not all tube current issues. Just wait and see how things work out with the current arrangement. Would it be possible to use a larger ID tube if tube currents or vignetting appear to be problematic?

No way would I give up using the 1" thick meniscus mirror unless the figure was poor (unlikely). I'm curious to know how the mirror is mounted.

JimC

#20 btom

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Posted 02 February 2013 - 10:44 AM

I agree 100%. After thinking about this - I would maybe play around with Mauro Da Lio type baffle that doesn't infringe on light cone or if so very minimally to see if that helps scrub the mirror surface and helps eliminate any currents. The mirror is mounted with 3 dobs of silicon adhesive to a birch plywood plate. The scope is due to arrive today or Monday so I'll know more then. For what it's worth Gordon Waite and Rob Teeter both say this mounting is totally fine for this type mirror - this is the only STS with a meniscus. Rob only moved to the 6 point flotation cell to address issues with the thin flat back mirrors that are used in most other STS. Anyway, I did a bit more research on meniscus primaries and that agrees with what I've found including some info at Mel Bartel's site. The Royce conical is of course fine with a single point attachment to the birch plate using it's center mounting bolt.

#21 ccaissie

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Posted 02 February 2013 - 05:17 PM

If the mirror is epoxied to a support, or has a central bolt oxide in place, I would expect this must be removed before the mirror can be recoated - otherwise the epoxy will outgas in the vacuum chamber.Thoughts ?


I used a 12.0" Conical blank on a project, and epoxied in a 5/8" nut in a recess I bored. I put the nut in to aid in grinding /tooling fixtures. When finished, I extracted the nut to eliminate the epoxy/outgassing issue (screwed a very hot threaded rod into the nut and used another nut/tube etc. to pull the warmed/softened epoxy out) and I chipped the back recess. It did not ruin the blank, cosmetic only. I contacted Cary at OWL and learned that I should have left it in, as the outgassing issue is "overblown" in his opinion.

Check with your coater, but I've heard from an expert it's not an issue.

#22 jpcannavo

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Posted 04 February 2013 - 07:03 AM

Of much more importance to me is it looks like the Royce would hold collimation better as the mirror is bolted onto the cell.


Is there a problem with collimation on the Zambuto STS's?

Also, does the bolted-on Royce use the new mirror cell Rob has been raving about?

As someone who has owned and tested Zambuto and Royce 16s...
1) Collimation shift is minimally due to mirrors wobbleing/teetering in the cell, and far more due the cell and the rest of the mechanical structures, shifting flexing etc. Moreover, that having been said, the base of a conical is far smaller than a standard blank and therefore would be MORE prone to such wobble were it to occur at all. This was precisely the case with my 16. I solved this problem by literally molding the cell to the mirror base with a non adherent layer of epoxy putty. BTW for pics of that cell (epoxy layer not visible though):
Royce16cell
2) As for quality, my 16 ZOC tests to a strehl of .96-.97 - outstanding for a 16 - with an essentially perfect edge. The Royce did not test as well.






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