SCT coating specs, take with a grain of salt?

Seems like I remember both Celestron and Meade
claiming in the 1980s and 1990s that their mirrors
on their SCTs were enhanced coated, providing at least
92-96% reflectivity at each mirror surface.
Now, Meade claims their standard coatings consist of
only regular aluminum on the mirrors (88% reflectivity
per surface) and mag-fluoride (98.5% transmission at
each surface) on the correctors. Where did the "enhanced
aluminum" go? Total system transmission of incoming light
is only 75% by those numbers.

Meanwhile, Celestron claims their standard coatings
provide 91% transmission at the corrector and 91%
reflectivity at the mirrors for a system total of
72%. The figure is lower than for Meade's 75% because
Celestron uses soda lime glass for their correctors
with standard Starbright versus water white glass for
their correctors when Starbright XLT coatings are used.
Soda lime glass apparently absorbs some of the light.

Was the claim for enhanced aluminum mirrors a past lie on
Meade's part, or are they only now claiming they use
plain aluminum in their standard coatings in order to
have the most impressive spread between their standard
coatings and new UHTC coatings group?

Here is their current claim on standard coatings:

"Meade Standard Coatings: The optical surfaces of all Meade telescopes
include high-grade optical coatings fully consistent in quality with
the precision of the optical surfaces themselves. These
standard-equipment coatings include mirror surfaces of highly purified
aluminum, vacuum-deposited at high temperature and overcoated with
silicon monoxide (SiO), and correcting lenses coated on both sides for
high light transmission with magnesium fluoride (MgF2). Meade standard
mirror and lens coatings equal or exceed the reflectivity and
transmission, respectively, of virtually any optical coatings
currently offered in the commercial telescope industry."

To me, this is:
Each mirror = 88% reflectivity
Each corrector surface = 98.5% transmission.
Which = 75% system throughput.


I remember seeing Meade correctors in the past with
a clear glass look, no colour tinge that would indicate
any coatings.

Does anyone remember Meade's MCOG (Multi-coated Optics Group)
or MCSO (Multi-coated Silver Optics Group-which failed)?
My question is this:
When did Meade (and Celestron) dispense with multicoatings or enhanced
mirror coatings and adopt only aluminum on the mirrors and
single-layer mag-fluoride on the correctors? How can Celestron and
Meade have used the terms, "Starbright" and "Multi-coated" to refer
what are now their standard optical coatings groups if they
were nothing more than overcoated aluminum and single-layer
mag-fluoride at best, based on system transmissions?

The new Celestron XLT and Meade UHTC coatings are another issue
altogether and I didn't want to include them in the post at all.
-Rich

RichA wrote:

Seems like I remember both Celestron and Meade
claiming in the 1980s and 1990s that their mirrors
on their SCTs were enhanced coated, providing at least
92-96% reflectivity at each mirror surface.
Now, Meade claims their standard coatings consist of
only regular aluminum on the mirrors (88% reflectivity
per surface) and mag-fluoride (98.5% transmission at
each surface) on the correctors. Where did the "enhanced
aluminum" go?

sacrificed to health cost inflation - and bridge realty.

Total system transmission of incoming light
is only 75% by those numbers.

Meanwhile, Celestron claims their standard coatings
provide 91% transmission at the corrector and 91%
reflectivity at the mirrors for a system total of
72%. The figure is lower than for Meade's 75% because
Celestron uses soda lime glass for their correctors
with standard Starbright versus water white glass for
their correctors when Starbright XLT coatings are used.
Soda lime glass apparently absorbs some of the light.

Was the claim for enhanced aluminum mirrors a past lie on
Meade's part

who knows. who could prove anything.

, or are they only now claiming they use
plain aluminum in their standard coatings in order to
have the most impressive spread between their standard
coatings and new UHTC coatings group?



who knows...

Here is their current claim on standard coatings:

"Meade Standard Coatings: The optical surfaces of all Meade telescopes
include high-grade optical coatings fully consistent in quality with
the precision of the optical surfaces themselves. These
standard-equipment coatings include mirror surfaces of highly purified
aluminum, vacuum-deposited at high temperature and overcoated with
silicon monoxide (SiO), and correcting lenses coated on both sides for
high light transmission with magnesium fluoride (MgF2). Meade standard
mirror and lens coatings equal or exceed the reflectivity and
transmission, respectively, of virtually any optical coatings
currently offered in the commercial telescope industry."

To me, this is:
Each mirror = 88% reflectivity
Each corrector surface = 98.5% transmission.
Which = 75% system throughput.

I remember seeing Meade correctors in the past with
a clear glass look, no colour tinge that would indicate
any coatings.

Does anyone remember Meade's MCOG (Multi-coated Optics Group)
or MCSO (Multi-coated Silver Optics Group-which failed)?
My question is this:
When did Meade (and Celestron) dispense with multicoatings or enhanced
mirror coatings and adopt only aluminum on the mirrors and
single-layer mag-fluoride on the correctors? How can Celestron and
Meade have used the terms, "Starbright" and "Multi-coated" to refer
what are now their standard optical coatings groups if they
were nothing more than overcoated aluminum and single-layer
mag-fluoride at best, based on system transmissions?

The new Celestron XLT and Meade UHTC coatings are another issue
altogether and I didn't want to include them in the post at all.
-Rich

good thing you didnt - we are depressed enough.

The new Celestron XLT and Meade UHTC coatings are another issue
altogether and I didn't want to include them in the post at all.
-Rich

good thing you didnt - we are depressed enough.

Hi:

Who's this "we"? You got a mouse in your pocket? ;-)

Instead of speculating without data, why not check out some of the sites of
folks who've actually analyzed these coatings' performance, like
http://www.arksky.org/index.htm?


Peace,
Rod Mollise
Author of _Choosing and Using a Schmidt Cassegrain Telescope_
Like SCTs and MCTs?
Check-out sct-user, the mailing list for CAT fanciers!
Goto http://members.aol.com/RMOLLISE/index.html

On 02 Nov 2004 11:47:58 GMT, (Rod Mollise) wrote:

The new Celestron XLT and Meade UHTC coatings are another issue
altogether and I didn't want to include them in the post at all.
-Rich

good thing you didnt - we are depressed enough.

Hi:

Who's this "we"? You got a mouse in your pocket? ;-)

Instead of speculating without data, why not check out some of the sites of
folks who've actually analyzed these coatings' performance, like
http://www.arksky.org/index.htm?

Do you know where on that page that info might be?
Thanks
-Rich

RichA wrote in
:

Do you know where on that page that info might be?

type "coatings" in the search box.

http://arksky.org/uhtc_compare.htm


--
Pierre Vandevenne - DataRescue sa/nv - www.datarescue.com
The IDA Pro Disassembler & Debugger - world leader in hostile code analysis
Saving the net is our business.

On Tue, 2 Nov 2004 21:19:21 +0000 (UTC), Pierre Vandevenne
wrote:

RichA wrote in
:

Do you know where on that page that info might be?

type "coatings" in the search box.

http://arksky.org/uhtc_compare.htm


Thanks very much! Well, despite some things in the report
that were questionable, the UHTC coatings IMO do point out
that Meade's recent (at least) SCTs without the UHTC only
use standard aluminum on the mirrors and single-layer
mag-fluoride on the corrector. So I'm back to,
"When did Meade discontinue multicoatings on their standard
scopes and did they ever really use anything other than
standard aluminum and single-layer mag-fluoride?"

http://arksky.org/uhtc_compare.htm

Thanks!
Peace,
Rod Mollise
Author of _Choosing and Using a Schmidt Cassegrain Telescope_
Like SCTs and MCTs?
Check-out sct-user, the mailing list for CAT fanciers!
Goto http://members.aol.com/RMOLLISE/index.html

Thanks very much! Well, despite some things in the report
that were questionable

Hi Rich:

What? If Clay Sherrod says it, you can usually take it to the bank.

Peace,
Rod Mollise
Author of _Choosing and Using a Schmidt Cassegrain Telescope_
Like SCTs and MCTs?
Check-out sct-user, the mailing list for CAT fanciers!
Goto http://members.aol.com/RMOLLISE/index.html

What? If Clay Sherrod says it, you can usually take it to the bank.

He did mention something in his report that is not accurate. You cannot use a
spectrophotometer to measure the transmission efficiency of an optical system
like an SCT. It would have been more accurate if actual CCD images were taken
of some reference star and compared the peak pixel readings. Only problem with
using a star is that the peak reading is highly influenced by seeing and focus.
The two instruments would have to be set up next to each other and carefully
tweaked. In any case, small variations on the order of 10% would probably be
lost in the noise.

Roland Christen

You can get rid of the problems of using peak pixel reading by
using an aperture and setting the radius to many times
the seeing radius. Should be able to do much better than a percent for
stars much brighter than the sky.


D.



Chris1011 wrote:
What? If Clay Sherrod says it, you can usually take it to the bank.


He did mention something in his report that is not accurate. You cannot use a
spectrophotometer to measure the transmission efficiency of an optical system
like an SCT. It would have been more accurate if actual CCD images were taken
of some reference star and compared the peak pixel readings. Only problem with
using a star is that the peak reading is highly influenced by seeing and focus.
The two instruments would have to be set up next to each other and carefully
tweaked. In any case, small variations on the order of 10% would probably be
lost in the noise.

Roland Christen