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Celestron Omni XLT 102 and 102 GT objectives

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#1 skyglow78

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Posted 25 November 2012 - 04:50 PM

Does anyone know if the Celestron Omni XLT 102 and the Celestron Nexstar 102 GT use the same objective lens? They are both f 9.8 achromats, so I am assuming that they are the exact same lens, but does anyone know if that is not the case?

Second, but related question. I have an old C102HD that I used years ago (before I got the APO fever) and it performed quite well. The C102HD is listed as an f/10 though. This might not be a relevant question since manufacturing specs and QC often change over time, but is this really the same objective too? The reason for the questions is that I am researching beginner 102mm scopes and only have experience with the C102HD, and not the other 2 listed above.

Thanks!

#2 Zamboni

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Posted 25 November 2012 - 05:23 PM

They are in face the exact same synta objective and are very good. The only difference between the two OTAs is the lens cell and dew shield. The lens cell in the Nexstar GT is non-collimateable and the lens dew shield is plastic, compared with an adjustable cell and metal dew shield on the Omni. If you have to collimate the Nexstar you have to shim the focuser.

These ARE in fact the same optics as the old C102 HD. Some production runs rounded the focal ratio up to f/10 on the labels, but all of them have the exact same focal length of 1000mm. Skywatcher 102/1000 refractors are also the same optics.

#3 csrlice12

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Posted 25 November 2012 - 06:14 PM

Also the XLT lenses are hand matched, so the quality is a little better overall, whereas the GT were just mated up as they came out of the machine

#4 Zamboni

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Posted 25 November 2012 - 07:18 PM

I have it on good authority that the hand matching is done on all of the 102 syntas these days. Celestron just calls attention to it in their product lit for the Omnis to make them sound more "premium" than they really are.

#5 Meadeball

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Posted 25 November 2012 - 07:55 PM

I just looked into the objective end of my 102GT and there appears to be a plastic ring or "cover" pressed down against the objective cell. Is it possible that the objective is collimatable and has the required screws, but this plastic ring is covering them up (potentially to keep newbies from messing up their scopes)? It would seem counter-productive to manufacture an entirely new cell for one telescope, especially one with not a lot of profit margin. Note that the dewcap is different too ... possibly this ring is the "end" of the dewcap and it press-fits into the objective end of the tube, over the objective cell?

This pic from the classifieds shows what I'm talking about. It appears that the featureless, plastic ring is actually part of the dewcap; could sliding off the dewcap reveal collimation screws? If you look closely, there appears to be a metal cell behind the plastic ring, and if you look closely behind the objective itself, at 3 o'clock and 6 o'clock, there appears to be something there.

102GT objective

Meade

#6 Starhawk

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Posted 25 November 2012 - 10:11 PM

Meade,

That's an interesting observation. Considering the way the dew shield is built more like an impact guard, it's possible they wanted this to be a "guaranteed positive experience" telescope. And so, they made it as rough, tough, and mishandling resistant as possible.

-Rich

#7 Starhawk

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Posted 25 November 2012 - 10:13 PM

After I wrote that, I had a forehead-smacking DUH! Moment- these are for Costco to sell. They know they're done in that channel if they turn out to be a huge problem for the seller.

-Rich

#8 Jon Isaacs

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Posted 26 November 2012 - 12:17 AM

I am curious to know how it is that one can be so certain that these are the exact same objectives, that they pass the same QC tests, that they have the same coatings, etc... It seems to me that Synta could have different standards for the various products..

:question:

Jon

#9 Zamboni

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Posted 26 November 2012 - 12:40 AM

Having seen both, the coatings look identical. I don't think the coatings are different since Synta uses the same dark green coatings across the board on all of the achromats from the shorttube 80 to the CR-6.

Last week a friend with a C102HD (and an excellent sample at that) bought the GT and compared the two. Star tests came out identical and bench tests didn't show any differences either. Also, wouldn't it be more expensive for synta to have two different manufacturing standards and processes for two different 4" f/9.8 optical systems? They have the 4" achomats down to a science because they've been producing the same system for nearly 14 years now. Doesn't make much sense to start making a different set of optics at different standards to the same overall specs when they have the infrastructure already in place.

I've read about 12 or 13 reports on the optics of the Costco scopes and all of them have come out pretty well identical to the Omni / C102HD. I find it EXTREMELY unlikely that these are somehow a completely different set of optics.

#10 Meadeball

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Posted 26 November 2012 - 02:25 AM

Doesn't make much sense to start making a different set of optics at different standards to the same overall specs when they have the infrastructure already in place.


That's what I'm thinking. Naturally there's no way I can be certain of this, but like he said, it would seem counterproductive to retool an entire line (or devote another lab routine, change line settings, create new stock area and catalog custom parts) in what's probably a 99-percent automated factory), especially for a line of inexpensive entry-level telescopes that has very little markup to recoup these expenses.

Meade

#11 Jon Isaacs

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Posted 26 November 2012 - 07:08 AM

They have the 4" achomats down to a science because they've been producing the same system for nearly 14 years now. Doesn't make much sense to start making a different set of optics at different standards to the same overall specs when they have the infrastructure already in place.



It doesn't take retooling or making a different set of optics, it could be a simple as changing the QC specs or sorting them based on quality...

Synta Optical is huge and is making large quantities, there lines are probably computerized, often such companies make changes based on vendor specs.

My point though, if one really knows they are they are identical, then it is reasonable to say they are identical. But if one is making an educated guess that they are identical, then it is best to qualify any statements appropriately.

Jon

#12 csrlice12

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Posted 26 November 2012 - 09:04 AM

Talked with the folks at S&S Optica. The Omni XLT has collimateable front cells, the 102GT version does not. There was another thread here where somebody took off the dew shield and apparently the dew shield holds the lens assembly in place and the lenses use spacers. Apparently, in removing the dew shied, he noted he "rotated slightly" one of the objective lenses when he put it back in and had problems. So, while the glass may be the same, the contstruction is better in the Omni serieds.

#13 Zamboni

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Posted 26 November 2012 - 12:13 PM

Sounds a lot like the plastic cell in the first generation C102HD before they switched to the non-adjustable aluminum.

#14 BoriSpider

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Posted 27 November 2012 - 11:17 AM

My C4-R has a collimateable aluminum cell.

#15 Tim J K

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Posted 15 January 2013 - 11:20 AM

I see that OPT has the 102mm Nexstar GT optical tubes for $119.95 shipped.






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