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"StarBright XLT" Coatings. How much better are they really?

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#1 thornhale

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Posted 12 March 2016 - 02:38 PM

Hi community,

 

The choice of telescopes is mind-boggling. Every maker has some fancy term that sets it apart from the rest. For the Celestron SE series, it is this "StarBright XLT" coating. I have no experience with these telescopes, but I am wondering. How much better are these coatings compared to other coatings out there (from Meade or Orion or even the Celestron SLE series)? Does anyone have any experiences with "StarBright XLT" coated and "normally" coated telescopes? I am utterly confused on what these coatings "buy" you.

 

Any insights would be appreciated!


 

#2 jeff gill

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Posted 12 March 2016 - 03:04 PM

The coatings pushed as extras are better, they transmit more light to the eyepiece, and in some comparisons it is quite a big difference, i have an old 10" meade sct and because of the coatings loss on the corrector it would appear that mathematically at least the reduction in light transmission makes it the equivalent of an 8" with modern coatings.


 

#3 jrcrilly

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Posted 12 March 2016 - 03:14 PM

Meade's UHTC is comparable to Starbright XLT. In a compound telescope like an SCT the losses on the various surfaces add up so transmission is noticeably better (15% or more) with the upgrade coatings.  In Newts and refractors the differences don't accumulate as much, even with multiple surfaces in a refractor  (antireflective coatings on lenses are pretty efficient anyway)


 

#4 thornhale

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Posted 12 March 2016 - 03:27 PM

That's really interesting, jrcrilly, and jeff! I had no idea that this makes such a big difference!

 

So do the "StarBright XLT" coatings on the 4SE make up for a 1" aperture reduction in an Orion Starseeker IV 127mm Mak-Cas without the "StarBright XLT" coatings?

 

Similarly, is a 5SE telescope with StarBright XLT brighter than the Orion Starseeker IV 127 mm Mak-Cas?


 

#5 junomike

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Posted 12 March 2016 - 03:35 PM

IME, the difference is less noticeable as the aperture increases. In my Starbright C11 I noticed no real difference from one set up beside me that had XLT.

I'm sure on certain targets it may account for something, but the difference to me wasn't drastic.

 

Mike


 

#6 Jon Isaacs

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Posted 12 March 2016 - 04:57 PM

That's really interesting, jrcrilly, and jeff! I had no idea that this makes such a big difference!

 

So do the "StarBright XLT" coatings on the 4SE make up for a 1" aperture reduction in an Orion Starseeker IV 127mm Mak-Cas without the "StarBright XLT" coatings?

 

Similarly, is a 5SE telescope with StarBright XLT brighter than the Orion Starseeker IV 127 mm Mak-Cas?

 

The difference in brightness between a 4 inch scope and a 5 inch scope at he same magnification is 55%, that is significant.  A difference of 15% in brightness by comparison is relatively small,  they say experienced observers can see a difference of 10%.  That's about 0.1 magnitudes, quite small.

 

If one is comparing a refractor to a Mak or SCT, the differences can be more significant.  A 5 inch Mak or SCT with XLT coatings will have about 85% transmission (according to Celestron) but there is an addition loss due to the area lost to the secondary mirror. That's a loss of 16%, the scope transmits about 70% of the light, a quality refractor will transmit nearly 100% of the light.  That all means that a 5 inch refractor would be about 40 % brighter than the SCT or Mak.

 

Newtonians fall in the middle and cover a wider range, premium coatings are available, the secondary can very small and there is no need for a diagonal.  

 

That's the short story..  

 

Jon


 

#7 39.1N84.5W

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Posted 13 March 2016 - 12:30 AM

Saving the money on not buying these coatings and instead buying the very best eyepieces is a sound investment.
 

#8 Redbetter

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Posted 13 March 2016 - 02:14 AM

It would seem doubtful that there would be a large upgrade in system transmission with Starbright XLT vs. UHTC, but Celestron's old marketing (with test curves) made a claim of 6% overall for visual for XLT vs. UHTC.  https://www.optcorp....OPT/EDU/xlt.pdf    I don't know if Meade has changed their UHTC since then, or if the original test was accurate or representative.    There was some substantial improvement from Celestron's original Starbright that preceded the XLT, again per graphs.  http://www.celestron...-coating-system  My old 8" is of the older Starbright coating type, so for a similarly figured SCT with the newer XLT I could calculate taking a hit (16% claimed, or an effective difference of 2/3 of an inch of aperture--note that it wouldn't impact resolving power but instead the ease with which lower surface brightness/dimmer objects could be detected.)

 

As others have noted, if you are considering the differences in light transmission you should also consider the other parts of the optical train including whether or not a diagonal will be used (e.g. a refractor, SCT, etc.) and what type. Of course, buying a better quality diagonal than what comes stock can also improve light transmission to the eyepiece.  Eventually, for a given scope one is likely to upgrade to 2" diagonals from 1.25" stock to allow use of 2" eyepieces.  So there is substantial cost to consider there as well with only a minor improvement in overall reflectivity.  One advantage of the newest/highest transmission diagonal coatings is their durability.  If looking at a Newtonian you are set if it has a 2" focuser...unless you plan on a coma corrector.

 

Then as others have noted if you are still comparing light transmission you can calculate how much is lost to the central obstruction of each type.  This diameter can typically be found in specs posted somewhere, although not always.  Sometimes only secondary mirror diameter is given without accounting for the holder.  

 

Having said all that, I'm not sure why anyone would complain about the higher quality coatings now available (standard?) on the same scope type.  :confused:  You can get the same tube with better coatings now for about the same price as 20 years ago.   

 

Really what is likely to matter more to you is which type and size of scope best fits your needs for portability, travel, visual/photography, physical storage, Goto, etc.  Length, bulk, and mounting systems are often limiting factors in the end choice for any given user.  There is so much to learn that it is probably best to start by describing how you plan to use it and then soliciting some suggestions and comparisons. 


 

#9 Jeffmar

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Posted 13 March 2016 - 07:33 PM

I have two C11's. The newer one is a one year old Edge and the older one is between 27 and 30 years old. I believe the older one predates XLT coatings. The difference is profound. It was as if someone had added three inches or more to my newer 11 inch. I have heard that mirror coatings on SCT scopes are better protected and do not degrade as much as an open reflector. If that is true then the newer coating are way better. I don't recall how many times reflective surfaces and lens coatings have been improved in Celestron SCT scopes. Two or three times? More than that? :confused:  


 

#10 jrcrilly

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Posted 13 March 2016 - 07:46 PM

Starbright coatings were a major upgrade from the original single layer coatings on your older model. From Starbright to Starbright XLT was a more recent and smaller step.


 

#11 orion61

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Posted 15 March 2016 - 11:44 AM

To put it more simply, on a SCT the difference between standard coatings and Starbright is being able to see something straight on compared to the need of averted viewing, Srarbright to XLT is again just about the same thing.

One thing I have noticed is, Jupiter looks better to me with standard coatings. due to the glare.


 

#12 petert913

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Posted 04 July 2018 - 05:30 PM

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."


 

#13 Ken Sturrock

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Posted 04 July 2018 - 06:47 PM

Interesting resurrection. If Thornhale comes back this year and needs it, we'll unlock it.


 


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