RESULTS OF COMPARTATIVE TESTING
by: P. Clay Sherrod
Meade UHTC Enhanced Coating Group vs. Standard Coatings (....and similarly offered enchanced coatings groups by other manufacturers)
Many of you have been asking for some side-by-side comparisons and/or testing of the new optical coating groups offered by Meade Instruments for their entire telescope line (as well as from other manufacturers). Because of the odd timing of the announcement of availability of these coatings (only two weeks after the release of hundreds of new LX 200 GPS scopes for customers who had been waiting months...), and the lack of supporting information, I have been quite hesitant to recommend these coatings, either on a NEW telescope being ordered, or as a RETROFIT for those poor souls who received their telescopes after the announcement had been made as to the availability.
In a nutshell:
1) THE COATINGS ARE EXACTLY AS MEADE SUGGESTS THEY ARE....they are excellently done and WILL indeed, enhance limiting magnitude....object brightness.....color saturation....wavelength penetration (particularly in the emission spectra of red objects) and by FAR: CONTRAST in lunar, planetary and deep sky object viewing.
2) THEY ARE VERY SENSITIVE TO CLEANING AND NEED SPECIAL PRECAUTIONS, just as I had suspected and alerted users to from the advent of this announcement.
A - MEADE SPECIFICATIONS:
Emission Line Wave-length Transmission:
Group nm old% new% Increase
Hydrogen-alpha 656 76.9 93.1 21%
Hydrogen beta 486 75.3 85.8 14
Oxygen III 496 76.5 85.4 12
Oxygen III 501 77 85.4 11
Helium II 496 72.5 86.1 19
Helium I 588 79.5 93.5 18
Nitrogen II 655 77 93.2 21
Nitrogen II 658 76.7 92.8 21
Sulfur II 673 75.7 91.8 21
MEADE STATEMENT: "....transmission is increased by 21%. Averaged over the entire visible spectrum (450nm. to 700nm.), total light transmission to the telescope focus increases by about 20%"
B. RESULTS OF TESTING
(results of two tests in controlled optical bench environment, using photodensitometer and spectrophotometer on LX 200 12" "classic" telescope, still new in box (standard coatings) and LX 200 10" GPS with UHTC coatings. NOTE: allowance for difference in surface area is accounted for and NOT part of the testing parameter results).
After initial testing, the 10" UHTC telescope was compared outdoors with one of the observatory's 10" LX 200 classic telescope with standard coatings that has provided optimum performance and a limiting visual stellar magnitude of 15.2 at the dark sky site.
My test was NOT done in each wavelength of light, although the reported sensitivity into the red (nebular) region was checked and verified. The test was done at the AVERAGE wavelength specified by the Meade statement (about 575 to 600 nm).
** Test Bench Results (two tests) **
- Meade Reported Light increase for entire spectral range:
- Tests by ASO actual light increase measured with UHTC group:
** NOTE: NO DIAGONAL IN TESTED SYSTEMS! THESE TESTS ARE DONE FOR COMPLETE SYSTEM TRANSMISSION....this includes light passed through the corrector plate, light reflected from both surfaces of primary and secondary mirror but DOES NOT include a prism or mirror diagonal in the system! I do not have access to Meade's new enhanced coated diagonal and did not want to skew test results with the introduction of any of many available diagonal systems.
C. DARK SKY TESTS (in moonlight.....)
This series of tests was my most critical and done on March 28, 2002, with very clear and dark skies, but with a near-100% moon in the sky. Both telescopes were Meade 10" LX 200s with perfect collimation and as-new optics.
1. Planetary images - astounding. The colors on Jupiter with the UHTC were absolutely breathtaking, even in less-than-steady conditions. No planetary glare was visible in 250x (10mm Radian) nor 132x (19mm Panoptic) and there was no secondary imaging. Fainter satellites of Saturn were clearly MORE visible in the UHTC coated telescope. Images of both Saturn and Jupiter were visibly brighter with the UHTC coated instrument.
2. Stellar images - bright star; diffraction pattern and assessment. No difference at all, although the very bright stars of YELLOW intrinsic coloration did exhibit perhaps a bit more blue false color with the standard coatings than without.
3. Deep Sky contrast - here is the main difference in my opinion (although I was still reeling from the beautiful colors of Jupiter). Using Messier 65 and 66 and M-81 and 82 as targets as well as the proverbial Messier 42, I found a considerable gain in contrast between the moon-soaked sky and the deep sky object with the UHTC group. In addition, M-65 and 66 were very near the full moon and the GLARE that was exhibited with the standard coated unit was very much absent with the UHTC group.
4. Limiting magnitude - again, full moon is hampering, but the Pleiades star field (see "Guides" for limiting magnitude here on the ASO website) was used with the standard magnitude test stars. The faint 14th magnitude pair within the small easy-to-spot "triangle" of stars in the test field (14.4 and 14.8)were NOT visible in the moonlight with the standard 10".....they were CLEARLY visible with the UHTC-coated group. Turning the scopes to the variable star fields in the Orion Nebula also revealed considerably more faint stars embedded in the nebula with the new coatings.
5. Resolution - theoretically there "could" be a relationship with greater light transmission and better resolution, but in actual use, this is either doubtful or negligible. If anything REDUCTION OF GLARE will increase angular resolution and this perhaps is where the UHTC coatings have a slight edge.
a) planetary resolution: the same fine delineation of detail was seen in both telescopes, although a contrast enhancement via the UHTC coatings clearly made what fine details was visible much more obvious. Saturn's Encke division was used as a critical test on this and could be seen "coming and going" in both instruments. The color contrast however on Saturn was very impressive in the UHTC group which gave "the impression" of increased fine detail, when in actuality none was there.
b) stellar resolution: out-of-focus star images presented a very well defined Airy disk and pattern in both instruments; no visible difference in extra-or intra- focus could be detected. IN FOCUS, there was clearly a third diffraction ring encircling the star Procyon seen in the UHTC scope which was most definitely NOT visible in the standard coatings. This is believed entirely due to the remarkable cut-down on the glare of bright objects, which in itself makes this option worth the price.
6. Imaging with UHTC - no tests have yet been done with either film, digital nor CCD with these coatings. I expect similar results with imaging, although I suspect that when imaging in the reddish end of the spectrum, users will see remarkable gains in nebulae, comets and other such objects.
D. SUMMARY AND RECOMMENDATIONS:
1) These coatings do everything that Meade has claimed and in my opinion: "more." They are absolutely fantastic when clean and clear of debris and film.
2) In spite of the fact that there are thousands of Meade telescopes out there that CANNOT be retrofitted with these coatings, I HIGHLY RECOMMEND THE UHTC coatings as a major advance in amateur viewing and imaging.
3) Cleaning - THIS IS THE BIG BUG IN THESE COATINGS. Meade Tech Support has suggested that using the standard cleaning solution of 1/4 alcohol to 3/4 cup distilled water with a touch of Ivory Liquid is suitable for these coatings. NO. These coatings have a "surface tension film" that is totally unlike that of polished glass....they "hold onto" film and debris almost in static fashion.
TO CLEAN UHTC COATINGS:
[NOTE: remember, your mirror surfaces (*including your mirror diagonal!) should NEVER be cleaned, short of dusting off debris with a soft artists' paint brush and ONLY when necessary at that!] Cleaning procedures ONLY apply to the corrector plate.
FIRST: IF POSSIBLE, THROW OUT THE KLEENEX AND GO TO A MEDICAL SUPPLY STORE! Invest in 4" x 4" "surgical swabs" which are 100% cotton and totally lint free....they allow very fine buffing of the finished cleaned surface. Kleenex will do fine for the initial swabbing of solution onto the corrector plate, but not for final polishing!!
SECOND: See My NEW cleaning protocol and innovative streak-free cleaning solution posted Summer 2002 under the "Guides" sections of the ASO site (go to the ASO home page, www.arksky.org and click onto "Guides" in the directory). Use ONLY this solution for cleaning....it is quick, effective and streak free when done properly and slowly.
Smears will be a BIG problem on these new coatings....use a moist (with above solution) Kleenex or sterile surgery pad (these have NO lint and I prefer them over tissue!) to polish out smears ever-so gently as described in great detail under "ASO Guides."
The materials out of which these coatings are comprised:
[per meade: "....aluminum enhanced with a complex stack of multi-layer coatings of titanium dioxide (TiO2) and silicon dioxide (SiO2). The thickness of each coating layer precisely controlled to within +/-1% of optimal thickness."]
[per Meade: "...multiple layers of aluminum oxide (Al2O3), titanium dioxide (TiO2), and magnesium fluoride (MgF2)"]
suggest to me that - if properly maintained and cared for (see below) - the coatings should remaing at near peak for at least several years. These combinations seem to have been selected as optimum transmission (corrector) and reflectance (mirrors) while MAINTAINING a minimal rate of ambient air oxidation. This proves to be an excellently durable mix.....
Only TIME and use will play this factor out into reality.
This is my assessment of the new Meade Enhanced Coatings group....and a very honest and fair one.
I was highly sceptical when first touted to increase transmissions into the 20% range, but I am absolutely convinced that - IF YOU KEEP THEM CLEANED PROPERLY - these coatings will provide marked increases in limiting magnitude, color and contrast and imaging response.
NOTE: I will not make comments further than this study publicly nor privately. Reproduction of this report is prohibited and will represent a serious infringement of applied copyright. Few, if any, requests for permission to reproduce will be considered as this represents a private and independent study here at ASO.
Arkansas Sky Observatory
copyright March 31, 2002
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