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What does XLT stand for?

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#1 Pyrodav

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Posted 09 December 2018 - 10:37 AM

Can somebody tell me what the "XLT" stands for and what makes it better than the regular "Starbright" coating.  



#2 Richard O'Neill

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Posted 09 December 2018 - 10:41 AM

From the horses mouth.   https://www.celestro...ptical-coatings

 

https://www.cloudyni...re-they-really/


Edited by Richard O'Neill, 09 December 2018 - 10:45 AM.


#3 CHASLX200

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Posted 09 December 2018 - 11:45 AM

My C8 has the XLT coatings.



#4 RalphMeisterTigerMan

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Posted 09 December 2018 - 12:15 PM

I believe "Extra Light Transmission" or something very similar.

 

RalphMeisterTigerMan


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#5 TOMDEY

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Posted 09 December 2018 - 01:06 PM

Yep, thanks for that, this from your second ref >>> "According to Celestron:  "The average system transmission for StarBright coatings is 72%, while the average system transmission for StarBright XLT is 83.5%. StarBright uses soda lime glass correctors, whereas StarBright XLT uses water white glass, which improves the corrector throughput dramatically."

 

The good news is that the newer coatings are better... GOOD! But it's still in the incremental class... nice, but not profound. It's a 16.5% overall loss, vs the earlier 28%... which is Great. I'm surprised they didn't explicitly call it "New and Improved!"  And previously never touted, "Transmits 72%!" So, we're looking at a legit improvement, as "filtered through" the Marketing Department.

 

A good Newt, with enhanced coatings, probably loses around 10%, and has a Much smaller central obstruction.    Tom


Edited by TOMDEY, 09 December 2018 - 01:08 PM.


#6 Pyrodav

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Posted 09 December 2018 - 08:08 PM

Thank you for the responses. I guess my old Nexstar c11 OTA is outdated. I deforked it to put on my cgx-l for planetary imaging. Now I’m questioning my decision



#7 mclewis1

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Posted 10 December 2018 - 08:49 AM

You normally cannot see a difference between Starbright and XLT scope images, the actual difference in the areas where our eyes are most sensitive is less than 10%. Spectrographic work with a sensitive camera does show a difference between XLT and non XLT scopes but for DSO and planetary imaging you won't be able to tell the difference.

 

For planetary imaging it is much more important to have a scope with good/great optical figure (and be in as close to perfect alignment as possible) than to worry about small differences in the optical coatings.

 

As for the comments about Newtonians ... well there's are a number of reasons that some of the best amateur planetary images (taken by Christopher Go and Damien Peach who arguably good use virtually any scope) are taken with large SCTs.


Edited by mclewis1, 10 December 2018 - 08:50 AM.

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#8 dscarpa

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Posted 10 December 2018 - 12:56 PM

Sadly collimation is the issue with newts. There is no reason this needs be so given the right structure. Unless it received a fairly hard wack the SCT is going to retain collimation and is easy to collimate if needed.  I've got a 11" Tetter STS tube newt with Zambuto that goes out of collimation if carefully moved from table to mount. There is hope for it after putting spacers and stiffer springs in the cell .  I've got a last of the made in the USA C9.25 XLT and it's a great scope. David 



#9 photoracer18

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Posted 10 December 2018 - 04:15 PM

When Meade and Celestron both upgraded their coatings, Celestron Starbright to Starbright XLT and Meade from EMC to UHTC (Meade had another name for their standard coating that they upgraded but it was just the EMC with a new name).
But the coatings are not the most important thing as mentioned above. Heck Celestron Field Models in the early days had uncoated correctors that dropped the throughput to around 61% and it was not that easy to tell. They both also tried silver coatings, which were better than anything else at the time. However they never licked the silver tarnishing problem no matter what kind of protective coating they put over it. So both stocked using it after a couple of years.

Edited by photoracer18, 10 December 2018 - 04:15 PM.


#10 jallbery

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Posted 11 December 2018 - 09:35 AM

 

A good Newt, with enhanced coatings, probably loses around 10%, and has a Much smaller central obstruction.    Tom

 

Thank you for the responses. I guess my old Nexstar c11 OTA is outdated. I deforked it to put on my cgx-l for planetary imaging. Now I’m questioning my decision

 

A Much smaller central obstruction?

 

Hmm...

 

The OP has a c11.   34% central obstruction.  It has an OTA that is 24" long and weighs 27 pounds.

 

A 10" F/4 Newt has a tube (picking the GSO solid tube as an example) has an OTA that is 38" long and weighs 34 pounds.  And we have a secondary with 88mm minor axis against a 250mm aperture.   That's 35% with only taking in account the mirror.

 

Now go to F/5. and we can get the obstruction down to 25-28%, but now we have a tube that almost 4 feet long.

 

Try a 12" at F/4 and we have an OTA that weighs in at almost 50 pounds and is almost four feet long, and we most likely still have an obstruction larger than 30%.

 

Sure, an 8" F/6 Newt has significantly smaller obstruction than an 8" F/10 SCT.  But in larger sizes, Newts get challenging to mount if you want/need a tradition equatorial mount. You can somewhat mitigate this by moving to faster focal ratios, but then Newts no longer have a substantial advantage in central obstruction design.  That's not to say that large fast newts don't have their advantages, too (e.g., wider fields of view).  But a C11 is a great planetary imaging scope.

 

As for the Starbright XLT vs the earlier plain Starbright coatings.  I wouldn't worry about it.  Certainly, if everything else were equal, I'd take the improved coatings.  But I doubt you could visually tell the difference.   In terms of light transmission, we are talking about roughly the difference between an 11.5" and a 11" scope, with no improvement in resolution.

 

And as far as the question about what "XLT" stands for, my guess is that "XLT" doesn't actually stand for anything, .   A made-up combination of letter can be registered as a trademark, and so these sorts of brand labels often have no official definition (trademarking a phrase is more difficult).  The marketers responsible probably hoped to evoke the word "excellent," or perhaps  "eXtra Light Transmission," but I doubt it has an official meaning.  Whatever Celestron's marketing intentions, "XLT" just looks like "extra large, tall" to me.


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#11 TOMDEY

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Posted 11 December 2018 - 12:26 PM

A Much smaller central obstruction?

 

Hmm...

 

The OP has a c11.   34% central obstruction.  It has an OTA that is 24" long and weighs 27 pounds.

 

A 10" F/4 Newt has a tube (picking the GSO solid tube as an example) has an OTA that is 38" long and weighs 34 pounds.  And we have a secondary with 88mm minor axis against a 250mm aperture.   That's 35% with only taking in account the mirror.

 

Now go to F/5. and we can get the obstruction down to 25-28%, but now we have a tube that almost 4 feet long.

 

Try a 12" at F/4 and we have an OTA that weighs in at almost 50 pounds and is almost four feet long, and we most likely still have an obstruction larger than 30%.

 

Sure, an 8" F/6 Newt has significantly smaller obstruction than an 8" F/10 SCT.  But in larger sizes, Newts get challenging to mount if you want/need a tradition equatorial mount. You can somewhat mitigate this by moving to faster focal ratios, but then Newts no longer have a substantial advantage in central obstruction design.  That's not to say that large fast newts don't have their advantages, too (e.g., wider fields of view).  But a C11 is a great planetary imaging scope.

 

As for the Starbright XLT vs the earlier plain Starbright coatings.  I wouldn't worry about it.  Certainly, if everything else were equal, I'd take the improved coatings.  But I doubt you could visually tell the difference.   In terms of light transmission, we are talking about roughly the difference between an 11.5" and a 11" scope, with no improvement in resolution.

 

And as far as the question about what "XLT" stands for, my guess is that "XLT" doesn't actually stand for anything, .   A made-up combination of letter can be registered as a trademark, and so these sorts of brand labels often have no official definition (trademarking a phrase is more difficult).  The marketers responsible probably hoped to evoke the word "excellent," or perhaps  "eXtra Light Transmission," but I doubt it has an official meaning.  Whatever Celestron's marketing intentions, "XLT" just looks like "extra large, tall" to me.

Sure! My 36-inch Newt has a 17% (diam) obstruction, and my (sold) 29 has 17%, enhanced coatings all, and no need for the other lossy elements... the Window Glass Plate and Star Diagonal, used on SCTs.  Used in domes... weight, set-up, travel time, etc. drop to near-zero.  Isaac Newton and John Dobson were a lot smarter than we realize!  Ummm... I'll admit, 987 square inches of pupil also brightens things up, a wee bit.   Tom

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#12 Hugh Peck

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Posted 11 December 2018 - 12:48 PM

Thought this was about the meaning of XLT.



#13 jallbery

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Posted 11 December 2018 - 02:08 PM

Sure! My 36-inch Newt has a 17% (diam) obstruction, and my (sold) 29 has 17%, enhanced coatings all, and no need for the other lossy elements... the Window Glass Plate and Star Diagonal, used on SCTs.  Used in domes... weight, set-up, travel time, etc. drop to near-zero.  Isaac Newton and John Dobson were a lot smarter than we realize!  Ummm... I'll admit, 987 square inches of pupil also brightens things up, a wee bit.   Tom

Sure...  a giant fast Newtonian will have a relatively smaller obstruction.   And a slower Newt will have a relatively smaller obstruction as well.  I never said anything to the contrary.  I was just pointing out that in the 10-12" range (the size of the OP's SCT), particularly if you want something at least somewhat portable that can be mounted on a tracking mount, it is not a foregone conclusion that Newtonians are going to have a substantially smaller obstruction.  But I was not in any way denouncing Newtonians. I'd love to have an observatory with a giant Newtonian.  

 

My larger point was that a NexStar 11 OTA is hardly an inferior scope to either the current CPC 1100 or a Newtonian of similar bulk.  The Nexstar 11 OTA is not out-dated.  While it may not have the latest coatings, that carbon fiber tube has its merits as well.  In terms of optical quality, there is probably more variance in performance between individual C11s of either era than there is between CPC-era C11s  and Nexstar 11 GPS-era C11s in general.  I'd take an exceptional (or even very good) 12-17-year-old C11 over a randomly selected brand new XLT C11 (even though current quality control is supposed to be very good).   


Edited by jallbery, 11 December 2018 - 02:10 PM.

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#14 Hugh Peck

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Posted 11 December 2018 - 05:18 PM

extra lettuce and tomato


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#15 Reid W

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Posted 11 December 2018 - 06:59 PM

I have no clue how old my C11 is.  It produces superb planetary views.  Binoviewer is a perfect match.  Deep sky is good too. 

 

In it's prior life, it was a Nexstar.

 
20181211 174832


#16 Spikey131

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Posted 11 December 2018 - 09:44 PM

Thought this was about the meaning of XLT.

Apparently, it means that newtonian scopes are better than SCTsconfused1.gif


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#17 MortonH

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Posted 12 December 2018 - 07:24 AM

Thought this was about the meaning of XLT.

It was, and that was answered in post #2.  Everything else is additional/educational if you want to read it.  If not why did you read past #2 in the first place? wink.gif



#18 SandyHouTex

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Posted 12 December 2018 - 10:15 AM

When Meade and Celestron both upgraded their coatings, Celestron Starbright to Starbright XLT and Meade from EMC to UHTC (Meade had another name for their standard coating that they upgraded but it was just the EMC with a new name).
But the coatings are not the most important thing as mentioned above. Heck Celestron Field Models in the early days had uncoated correctors that dropped the throughput to around 61% and it was not that easy to tell. They both also tried silver coatings, which were better than anything else at the time. However they never licked the silver tarnishing problem no matter what kind of protective coating they put over it. So both stocked using it after a couple of years.

I give up.  How does an uncoated corrector drop the throughput to 61%?  A polished, uncoated optical surfaces only reflects 5%.  Glass absorbs like 2% per inch of thickness, so for a 3/8 inch corrector that equals about 2/3%, and then the last surface of the corrector another 5%.  So it should allow 89 1/3% through.


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#19 Traveler

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Posted 12 December 2018 - 11:54 PM

When (approx) did Celestron came out with their XLT-SCT's?



#20 jallbery

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Posted 13 December 2018 - 12:28 AM

When (approx) did Celestron came out with their XLT-SCT's?

July, 2003


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#21 EJN

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Posted 13 December 2018 - 12:38 AM

XLT = Extra Large Tomatoes


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#22 Hugh Peck

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Posted 13 December 2018 - 05:38 PM

XLT = Extra Large Tomatoes

I like my definition better. grin.gif 



#23 Pyrodav

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Posted 16 December 2018 - 10:50 AM

Very informative....Thank you



#24 Joe Bergeron

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Posted 20 December 2018 - 12:03 PM

Extra Light Transmission.
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#25 SeattleScott

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Posted 20 December 2018 - 10:45 PM

I give up. How does an uncoated corrector drop the throughput to 61%? A polished, uncoated optical surfaces only reflects 5%. Glass absorbs like 2% per inch of thickness, so for a 3/8 inch corrector that equals about 2/3%, and then the last surface of the corrector another 5%. So it should allow 89 1/3% through.


I think the 61% is cumulative. 72% less 11% for the uncoated corrector basically.

Scott


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