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The Baader BBHS-Sitall Silver Diagonal

by: William A. Paolini, February 13, 2016

Fig 1: LEFT - Baader 2" BBHS Silver; CENTER - Astro-Physics 2" MaxBright Dielectric; RIGHT - Baader 2" Zeiss Prism.


1. Overview


The new Baader Broadband Hardened Silver (BBHS) diagonal, available as both non-T2 (pictured) and T2-threaded in 2" and as T2 in 1.25" sizes, promises to bring Silver back to the mainstream for diagonal mirrors.  Silver has always been an excellent coating for mirroring surfaces, better than aluminum having higher reflectance across the visual spectrum with better transmission in the red color spectrum over aluminum.  In addition, both silver and aluminum are easier to maintain a flat wave front since they have less layers compared to full dielectrics (even the tightest coating tolerances can become problematic when 100 or more layers are deposited as with dielectric mirrors).  The disadvantage of silver however is that it is subject to tarnishing if not protected very well from moisture; but the new BBHS technology purportedly overcomes the tarnishing issue through the use of a dielectric overcoat to create a durable protective layer for the silvered mirror.  With this dielectric overcoat the BBHS silver diagonal is purported to have the same life expectancy as high quality protected aluminum when cleaning is performed with the same care and attention recommended for all precision optical surfaces.


In addition to the use of silver for the mirroring, the Baader BBHS also uses Sitall glass for the mirror's substrate.  Sitall is a crystalline glass-ceramic possessing ultra-low thermal expansion properties and a coefficient of thermal expansion of only 0±1.5 x 10−7/°C in the temperature range -60 to 60°C.  Sitall has been used in the making of primary mirrors for the Russian Maksutov telescopes, was selected by Lytkarino Optical Glass Factory (LZOS) for the manufacture of the 91 primary mirror segments of the Southern African Large Telescope (SALT), and was used for the primary and secondary mirrors of the VLT Survey Telescope.


Baader claims their BBHS diagonals offer peak reflectivity over a much extended spectrum compared to conventional dielectrics.  The typical premium-level dielectrics, like the Astro-Physics MaxBright diagonal and Baader Maxbright star diagonal, claim peak reflectivity in the visual spectrum from approximately 400nm to 700nm.  The new BBHS technology claims extending that performance far into the infrared with peak reflectivity extending further into the visual spectrum past 700nm to far outside the visual up to 2000nm.





Reflectivity Claim

Wave Front Claim

Body Build

Baader BBHS


Silver Mirror

Not specified

Not specified

Diecast and CNC Machined Magnesium

Astro-Physics MaxBright






CNC Machined

Baader Zeiss Prism


Zeiss Specification** Prism

Not specified, (Baader Phantom Group Coatings)

Not specified

CNC Machined

Fig 2: Comparative diagonal features.

* -    Marketing on AP website makes no wave front claim.  Reference to 1/10 to 1/20 wave over the portion of the mirror in the light path apparently based on forum conversations.  No specification in these claims if this is before or after dielectric coating.

** -   Per Baader Planetarium, many production divisions of the former government owned Carl Zeiss Jena have been privatized.   The Zeiss core enterprise today concentrates on production of finished ultra-high end optical and medical devices.  Many of the thousands of standard components are delivered to Jena "just in time" like any car factory works today.  The opticians and skilled people that once made up the company are still alive (and kicking) and as a result many highly capable optical companies have developed in this region, still producing optics in the old Zeiss tradition.  Baader has people employed who formerly worked at Zeiss Jena and they still use their contacts to existing optical shops there for the production of their prisms and all optical components for the Mark V binocular,  all produced to the original exacting Zeiss specifications and processes.



2. Build, Form Factor and Features


The Baader BBHS diagonal's all metal construction, which is magnesium for lighter weight and faster thermal acclimation, feels robust with excellent fit and finish.  The 2" nose has a very shallow and narrow undercut and at no time did I experience any difficulties when removing it from the focusers on the Takahashi, Vixen, or APM/Lunt telescopes I used for testing.  The Baader Clicklock mechanism provided outstanding operation, easily proving to be the most ergonomic method I have ever used to secure eyepieces into a diagonal.  With a very short twist of the Clicklock mechanism eyepieces were securely held or effortlessly released. 


      Fig 3: Bottom view.


From a weight perspective, all three diagonals had a similar heft.  I did not have a precision scale to do exact weightings, but their feel was very close with the Zeiss prism perhaps being slightly heavier than the other two.  Internally, the Baader BBHS diagonal uses flat black micro baffling for light suppression in the nose piece, with side walls in the interior housing smooth and flat blackened.


Fig 4: Top view of the Baader BBHS diagonal


The BBHS diagonal I used for this test was not their T-2 version, but what they call the BBHS-Sitall Zenith Mirror diagonal (Baader product # 2456115).  It comes standard with the 2" Clicklock mechanism at the eyepiece end and a 2" nosepiece for the focuser.  While the nosepiece unscrews and uses threading like their other T-2 diagonals, the 2" Clicklock adapter does not attach using T-2 threads but is held in place by six small hex key set screws that secure themselves to a non-threaded housing.


Fig 5: Disassembled for cleaning.


Light path measures reveal the Baader BBHS, as configured, was the longest of the three diagonals (note that its light path length is approximately the same as the Baader Maxbright Dielectric as measured in my 2014 article: "Mirror vs. Dielectric vs. Prism Diagonal Comparison").  While longer, observationally I encountered no issue with running out of infocus using any eyepiece or with binoviewers with the optical corrector accessory (OCA) attached.



Measured Light Path (mm)

Baader Zeiss 2" Prism


Astro-Physics 2" MaxBright Dielectric


Baader 2" BBHS


Fig 6: Diagonal light path measures.

3. Observational Field Tests


Fig 7: Baader BBHS diagonal on Lunt 152 ED-Apo with Pentax 30mm XW eyepiece.


Observational testing was conducted in a suburban location in Northern Virginia, west of Washington, D.C., where the light pollution level varies, depending on the particulates and water vapor in the atmosphere, between light to moderate. Limiting magnitudes at this location vary on Moonless nights from magnitude 4 to magnitude 5.5.  For this review the diagonal was tested in three telescopes over the course of several months:

  • Lunt152 f/7.9 ED-Apochromat refractor
  • Takahashi TSA-102 f/8 Super Apochromat refractor
  • Vixen 81S f/7.7 Apochromat refractor


In the above telescopes, the primary eyepieces used for observing were the Pentax XW line and the Baader Morpheus line.  The Baader Zeiss prism diagonal and the Astro-Physics MaxBright dielectric diagonal were included for comparison purposes as these two diagonals were used in the original diagonal comparison report in 2014 of twelve different diagonals, Mirror vs. Dielectric vs. Prism Diagonal Comparison


3a. Thermal Acclimation


Since my tests were conducted in the winter, my initial tests were related to thermal acclimation time.  In my 2014 comparison of various diagonals, I noted that some diagonals exhibited astigmatism while they were cooling to the ambient outdoor temperatures.  With a temperature delta of 28º F (i.e., indoor temp of 74º F and outdoor observing temp of 36º F), the time to acclimate where the on-axis image showed no levels of astigmatism were as follows:



Time to Acclimate


Baader 2" BBHS


Baader 2" Zeiss Prism


Astro-Physics 2" MaxBright Dielectric


Fig 8: Diagonal thermal acclimation times for a 28º F temperature delta.

When the diagonals showed astigmatism while cooling, stars could not be brought to precise focus and the slightly defocused star showed the characteristic oval that changed orientation by 90º when defocusing between slight in-focus to slight out-focus.  With its magnesium construction and virtually zero-expansion Sitall mirror, the BBHS showed the quickest cool down characteristics of the three diagonals.  Interestingly, the amount of astigmatism during cool down was also comparatively small in the BBHS and Zeiss prism compared to the Astro-Physics MaxBright dielectric.  As a result, both the BBHS and Zeiss prism showed the least amount of star point deformation during cool down.  Of course, all scopes were fully acclimated showing perfect star points and airy disk patterns with no diagonals in the train before this test was conducted.


3b. Stray Light Control and FOV Illumination


As noted in my 2014 test of various diagonals, not all diagonals maintain a fully illuminated field of view (FOV) when using a 2" eyepiece that has a field stop that renders the maximum true field of view (TFOV) capability of the 2" barrel.  For this test, I used the Pentax 40mm XW with a field stop of 46.5mm.  All diagonals presented a visual FOV that appeared well illuminated with no detectable vignette of the FOV or dimming near the field stop.  The field stop also showed sharp and distinct with all diagonals.  At no time were any stray light artifacts observed during the testing.


3c. Scatter


In my 2014 diagonal comparison, I assessed that the Baader Zeiss prism diagonals tested and the Vernonscope Silver diagonal were the ones that showed a markedly less amount of scatter compared to the dielectrics and aluminized diagonals tested.  While the premium dielectrics like the Astro-Physics MaxBright and Baader Maxbright dielectrics were better relative to scatter than other dielectrics, they still showed more scatter than the Baader Zeiss prisms and Vernonscope silver.  Using the same Astro-Physics MaxBright diagonal from that test in this current test, the Baader BBHS visually showed a level of scatter that was slightly less.  However, the Baader Zeiss 2" prism diagonal still slightly less scatter than the BBHS.  As example, scatter halos around stars and planets showed slightly less extent and slightly less brightly in the BBHS compared to the dielectric.  This difference was close, but still visually detectable.  And where the scatter difference apparently had more impact was in observing close double stars.  Using the 81mm Vixen 81S Apo with a low power eyepiece so the split of Rigel was more difficult, through the dielectric the separation was just observable with a very slim line of gray-black separating the two stars.  With the BBHS the visual of the split appeared very different, with the gray-black region between the stars being more fully black and also thicker, making the split observation all the easier. Moving to some closer doubles in Orion, the results were consistently similar.  One one double in Orion that was too close to split at the magnification I was using so that it appeared as just a non-descript elongation of a single mass through the dielectric, with the BBHS this same double showed instead as two distinct touching balls.  This improved performance was very exciting to see.  My presumption is that this performance difference was due to narrow angle scatter differences nearest the stars, but it could very well be other factors that are involved.  Regardless of what the main driver for the difference is, scatter or some other attribute, what was important was that the BBHS was more effective at splitting close doubles and provided a more enjoyable observation as a result.


3d. Faintest Stars and Nebula


For this test I approached it two ways: first I observed clusters with faint stars to see if any of the faintest threshold stars showed in one diagonal any better than another, and secondly I observed the greatest extent of nebula that were visible (i.e., did any diagonal show nebula extending to a further extent).  Many amateurs in casual discussions usually refer to differences like this as being due to transmission differences.  However, although transmission may indeed be a player, it must be realized that other factors can also contribute, such as contrast and scatter.  So rather than getting bogged down in trying to determine the optical or manufacturing drivers behind any observation outcome difference, it is best in my opinion to just focus on the observations.


Looking for faintest stars, I observed the Double Cluster, the Orion Nebula, and the open clusters in Auriga.   I was not expecting much of any differences relative to seeing faintest stars as all the diagonals were top shelf equipment.  To my surprise however, I discovered differences immediately.  When observing the Double Cluster, the faintest stars that were at the threshold of vision and only detectable with adverted vision in the BBHS and Zeiss prism, were completely invisible in the Astro-Physics dielectric!  This performance difference was repeated observing other open clusters and was repeatedly encountered when observing the Trapezium in M42, where the F component remained illusive in the dielectric but was plainly visible in the BBHS and to a slightly lesser extent in the Zeiss prism. 


Moving to M42 and M43 to observe any differences in the extent of their nebulosity, the BBHS and Zeiss prism both showed more of the wings of M42 extending into the distance, and more pronounced and brighter nebulosity around M43.  The caveat relative to nebulosity though is that when the magnification was lower and exit pupils larger, all three diagonals appeared to perform the same.  So it was only when more magnification was employed that the performance differences presented themselves.  In the case of the Orion observation, the nebula looked visually the same when operating at an exit pupil of 1.25mm using a 10mm XW eyepiece (120x in the Lunt 152 and 82x in the TSA-102).  However, when I switched to a 5mm XW with a resulting 0.63mm exit pupil in both refractors, the nebulosity of M42 extended notably further when observed through the BBHS or Zeiss prism than through the Astro-Physics dielectric.  The Zeiss prism showed the furthest extent of the nebulosity, but it was only very slightly more.


3e. Rendition of Colors


Initially I had not planned for any testing of how colors were portrayed by any of the diagonals.  My presumption was that they should all be relatively the same so I doubted there would be any notable differences to warrant a test.  This all changed when I began my planetary testing observing Jupiter.  On my first evening out observing Jupiter, I used the Astro-Physics dielectric diagonal first. The observation was excellent with Jupiter giving up a ton of details through the Lunt 152 Apo.  The GRS was also well in view in all its swirling glory.  When I switched to the BBHS diagonal, I was shocked as the view was obviously different, and the GRS appeared markedly more saturated displaying a beautifully bright and rich red-pink color!  This richer color of the GRS was not slight at all, making it appear surprisingly more contrasted and colorful against its surroundings.  In comparison through the dielectric, the GRS looked lackluster and pale in comparison and much less contrasted to its surroundings.   I switched diagonals several times, and repeated the observations on other evenings and the difference remained.  The BBHS silver mirror was definitely showing colors more vividly than the dielectric, and even a little better than the prism as well.  After seeing this performance relative to colors, on other evenings I decided to observe several clusters that contained orange-red stars, like those within M37 as example.  Now attuned to look for how vividly colors are shown, it was apparent that the silver diagonal was doing an exceptional job compared to the dielectric as all the clusters I visited showed their orange and red stars much more vividly.  Seeing all these star colors so much better then reminded me of a quote from Vincent van Gogh where he said, "The night is even more richly coloured than the day…  If only one pays attention to it, one sees that certain stars are citron yellow, while others have a pink glow or a green, blue and forget-me-not brilliance. And without my expiating on this theme, it should be clear that putting little white dots on a blue-black surface is not enough."  Sometimes we get so caught up in the details, we forget about the colors.  Using the BBHS definitely reminded me just how colorful many targets can be when all components of the optical train are up to the task.


3f. Image Crispness


My final tests were relative to how sharp or crisp the views were between the diagonals, and if there were any differences readily visible between them.  For these tests I limited them to lunar and planetary (Jupiter) observing only to make the assessment.  Overall, all three diagonals produced what I felt were equally sharp and distinct views with no notable differences.  Aside from differences in contrast and color saturation, all diagonals showed sharp and crisp views from low to higher magnifications of approximately 250x.


4. Conclusion


Fig 9: Image inset: Jupiter; NASA, ESA, and A. Simon (Goddard Space Flight Center)


The purpose of this evaluation was to test the performance of this latest offering from Baader relative to the diagonals I previously tested in my 2014 report, Mirror vs. Dielectric vs. Prism Diagonal Comparison.  In that previous comparison there was a silver diagonal that proved to be exceptional, but with a prohibitive cost, the Vernonscope 1/20th wave quartz star diagonal.  The new Baader BBHS technology was therefore intriguing as it promised the performance of silver without the purported longevity worries and at a price commensurate with the non-silver competition.


Overall, all three diagonals provided superlative results with earned reputations.  However, the Baader BBHS dielectric protected silver diagonal distinguished itself by pulling in fainter stars, showing minimal scatter, and presenting colorful stars and planetary features more richly colored, with its silver technology besting the defacto standard for high performance dielectric diagonals.  Its Clicklock mechanism provided a level of ergonomic ease far surpassing other locking technologies I have used.  It clearly demonstrated low levels of perceived scatter, the ability to bring into view the dimmer of stars in clusters than the other diagonals, the ability to make more authoritative double star splits, and the ability to show the faintest extents of nebula.  All these attributes were highly welcomed and they clearly enhanced my observations.  Most surprising however, was how brightly and vividly the BBHS technology portrayed the colors of stars and of planetary features, showing colors more richly saturated and more beautifully bright than even the best dielectric technology diagonal could muster.  The views through the BBHS of brightly colored stars accentuated in familiar clusters, and of a richly colored GRS coursing its way across Jupiter were nothing less than truly memorable. 

~ ~ ~

About the Author

William "Bill" Paolini has been actively involved in optics and amateur astronomy for 45 years, is author of the desk reference on astronomical eyepieces: Choosing and Using Astronomical Eyepieces which is part of the Patrick Moore Practical Astronomy Series published by Springer of New York, has published numerous product reviews on major online amateur astronomy boards, and volunteers with public tours at a famous vintage Clark refractor site.

Bill's professional background is as an officer in the U.S. Air Force and as a computer scientist, holding a Bachelor’s degree in Computer Science and a Master of Science in Education. He has worked for the U.S. Department of Defense, the U.S. Department of Commerce, the Federal Trade Commission, the Federal Reserve, the World Bank, and a variety of commercial corporations in the information technology, information technology security, and telecommunications industries.

Bill has been observing as an amateur astronomer since the mid-1960's, grinding mirrors for homemade Newtonian telescopes during the 1970's and eventually owning, using, and testing several hundreds of eyepieces in a wide variety of telescopes from Achromatic and Apochromat refractors to Newtonian, Maksutov-Cassegrain, and Schmidt-Cassegrain designs. Today he enjoys observing and testing new equipment from his suburban home west of Washington, D.C., where his primary amateur astronomy pursuits are lunar, planetary, bright nebula, open cluster, and globular cluster observing.



This article is placed in the public domain with no use restrictions when presented in its entirety.  Quoted excerpts are permitted without request with the citation: "William Paolini, The Baader BBHS-Sitall Silver Diagonal".

Images without credits are by the author and © William Paolini, 2016.  All rights reserved.

Please direct all questions or requests for permission to use images to the author at wapaolini@hotmail.com.

  • doctordub, cwright, roadi and 16 others like this




So, what are the chances this diagonal will fare better than Lumicon's silvered diagaonals and Meade's MCSO telescopes, both of which saw their silver coatings rot off?

That's the 64,000 dollar question, well maybe the 479 dollar question.  Always looks good up front but what about looong term.



I believe the vendor is claiming that longevity will be the same as protected aluminum.  They are very well aware of the longevity of Silver using the older protective technologies and processes like the ones you mention.  What they are using now is supposed to overcome all those issues.  So should not be any issues.  Time will be the ultimate teller of the story though.  FWIW, I have zero worries on the issue and am rather enjoying the vibrancy it brings to colors. :D


As long as the coating isn't porous, it should keep out the acid and the sulfur that occur in the air in some environments.  The problem with precision diagonals is that they (at least, TeleVue) don't offer repairs, only new mirrors.  Don't know about Baader.

    • Procyon likes this



Please provide a link for Baader Silver Diagonals & prices.





Link to info about Baader diagonals:


    • A6Q6 likes this



Please pardon my ignorance, but why would silver's higher transmission of red have an effect on the reflectance of a mirror? I seemed to have learned that all wavelengths are reflected back from the surface but maybe that was too rudimentary (rereading your article, that notion of reflection is now obviously simplistic).


Also, I wonder if this new technology could be used in any flat fold mirror--such as Newtonian secondaries?


Fascinating report.



    • Procyon likes this

Of course it could be used in secondary mirrors, and primaries.

Aluminum is used because it costs less, tarnishes very slowly, and is moderately easy to remove.

Silver isn't a panacea--it does have lower transmission at short wavelengths than aluminum.

Having a flat response into the infrared isn't critical for most scotopic viewing since scotopic vision

is largely blind above 600-650nm.

There are other materials with better spectra of reflection in the visible spectrum but they suffer from either the inability

to be removed from the glass, or quick tarnishing, or the tendency to clump when coating.

Over a hundred years of aluminum-on-glass and it's still the most practical coating.



Not all wavelengths are reflected with equal strength. Some are not reflected by the material (at those wavelengths, aluminum is essentially flat black) while, at other wavelengths, reflection is strong.

Aluminum, overcoated with a few layers of transparent dielectrics, can reflect in the visible range with quite high percentages.

Silver has a flatter spectrum of reflectance above about 500nm, but poorer transmission from 400 to 500nm than aluminum.

That would accent the longer wavelengths more with a silver coating, producing stronger reds and oranges, but weaker violets and blues.

Aluminum has a flatter spectrum in the visible 400-700nm range.

    • jrbarnett, Neptune, Procyon and 1 other like this



 C9.25 Edge HD unit's corrective optics, however, are scarcely an inch inside the rear aperture, and there is no stop.


Wow.  That's amazing!  Thanks for the info.


I have often toyed of getting a 9.25 to replace my 10" Dob as it is a rarely used instrument and I like the smaller form factor of course.  Would be for DSO only.  From what I read little difference off-axis between the Edge and Non-Edge of the 9.25, so would probably go with the non-Edge anyway.


True.  Non-edge avoids the issue of corrector-diagonal contact, and also allows use of Lymaz coolers.


But the VB on the rear of the standard unit is small like a C8, so you are looking at either an extension 2" adapter or an SCT-style thread on connector where you lose ease of diagonal rotation, with the standard C9.25.  The rear port on the Edge C9.25 is larger like on the C11 and C14.


Trade-offs either way, really, but I'd probably go standard C9.25 or even standard C11 (not much difference is mass or length between the two) were I going to do it over again.  Still the C9.25 is a better match for the EM-200 than a C11 would be, and this way if I take the EM-200, I can easily swap between a large refractor and the C9.25 on a camp-out.  The C11 would require more balance and counterweight fiddling.


I'm due for a diagonal refresh I think.  Thanks for the report, Bill.


- Jim

    • Procyon likes this

Before you rush out to get a silvered diagonal, you should read this and the Q&A that follows:


    • StarDust1 and astrophile like this

My apologies if this has been mentioned before but it would be interesting to have a comparison to a straight through view. Also await comparison to the 1.25 T2 prism as that is what is on the Mark V binoviewer?

    • Snippy likes this

Nice review.


I hope the protective coating works well.  I'm always quite concerned about the tarnishing aspect of silver.  

Nice review.


I hope the protective coating works well.  I'm always quite concerned about the tarnishing aspect of silver.  


I am not worried. I've borrowed a Vernonscope Silver that has quite a few years under its belt and no issues.  Also like the way Silver seems to accentuate the views, like on the GRS of Jupiter and heightened colors of stars in clusters.  Makes the observation so much more productive and beautiful.  But even if it only lasts 10-20 years, no big deal as it will be 10-20 years of much better results IMO than can get from any dielectric.  We have high end Silver from Baader and Vernonscope, Aluminum from Tak and probably some others (not sure if TV still makes theirs), and Prisms from Baader and Tak.  Dielectrics I can do without personally.  FWIW no one seems to worry about their Dob mirrors and they never stand the test of time.  :lol:

    • roadi, Procyon, StarDust1 and 1 other like this

Before you rush out to get a silvered diagonal, you should read this and the Q&A that follows:



While this discussion is well and good, it is referring to technologies more than 2 years old.  And in today's world that is a lifetime.  FWIW, current manufacturers show reflectance graphs for their protected silver coating that are not what is given in this forum referenced.  As example, Action Optics and Coatings released last year that their enhanced UV coatings for Silver maintains reflectance between approx. 98-99% from 400-900 - http://www.actonopti... Coated Mirrors.  So this is quite different from the dated discussion talking that from 400 nm to 700 nm - silver varies from 80% to 95%


So today, there are technologies with Silver that have overcome some of the old no longer relevant issues.  And given that each manufacturer has a process that varies from others, we would really need to know exactly the results are for whichever process Baader uses for the BBHS.  The Baader marketing implies that the reflectance is flat from 400 to 2000 nm.  Have not seen any test data to back that up, but have to say that in use on my scopes the whites are accentuated just as much as the colors are so nicely saturated.  So am quite enjoying the greater vibrancy I am now seeing for blues and reds and also brighter appearing whites (sounds like a laundry detergent line doesn't it :lol: ).

    • Procyon, astrophile and mikeDnight like this

Bill, Thanks for the review, very thorough as usual. I've ordered one simply because it's bound to be an improvement over the run of the mill 2" dielectric diagonals I've been using. How significant remains to be seen. Expensive? Yes, but I'm confident that I'll have high quality in the diagonal position of my optical train.


Edit: I use Baader 1.25" click-locks on a couple of T-thread diagonals and wholeheartedly agree that they are by far the most convenient EP holder I've ever used. Fast, easy, good centering  and they completely negate any issues with safety undercuts. I'm looking forward to the 2".

    • swetzel likes this

The greater transmission flatness from 500-700nm should enhance the longer wavelengths.

We'll see if the transmission curves match the UV-enhanced silver in the Acton Optics link.

    • Procyon likes this

Actually I doubt it.  No one provides independently produced transmission graphs that I've seen for diagonals.  I've seen some vendors supply their own from cherry picked equipment, but it carries no weight unless an independent source can select from random production units.  And of course even that is no good unless they are allowed to do the tests on a large enough population drawn randomly.  Tests of single units do not validate anything other than that particular unit.  Besides, I will trust my eyes over a graph produced on some population of one unit.  I'm quite enjoying the view that Silver provides...even more than my prisms now!  Am able to pick up more subtle colors and color variations am unable to using prisms or dielectrics.


Besides, the human eye does not respond to blue well.  Much less sensitive to blue than it is to green and red.  And given the much better response of the red and green cones, means that sensitivity to the mixed colors like yellow, is even higher.  400-625 is really the zone where the sensitivity is above 50%.  And do not think a 1% difference here and there is going to matter all that much as far as changing the appearance of the color. But stranger things have happened.  IMO one should be concerned over this if doing some critical data gathering from sensors.  But for visual?  I don't think it matters.  What is important is which technology is showing me the views the best, and best being subjective.  Having a choice of flatter looking colors from my premium dielectric, or vibrant looking colors from the silver, it is an easy choice.  Of course this is how it appears using my 4" and 6" instruments that utilize the diagonal.  With all the additional light gathering of a 12" Dob, as example, things might change.  But who sells silver primary and secondary mirrors?  Would be an interesting test to compare an all aluminum mirrored Dob to an all silvered one, as well as the dielectric vs silver diagonal on a larger SCT.

Scotopic vision has a peak sensitivity at about 507nm, with a roll off above 550 and below 450

Note that 550 is in the green and 450 is in the violet.



For night use, flat from 450 to 550 is important.

But, as has been pointed out many times, having an extended response at long wavelengths does sometimes matter.

Some nebula filters purposely pass the reds, even though our sensitivity is way down at those wavelengths, and it definitely makes seeing reds in nebulae easier.


Here is a page detailing "protected silver" (simple overcoating) versus "dielectric coated silver" (multi-layer dielectrics added to silver).

It would be interesting to see which curve the Baader comes closest to, but the simple protected silver is pretty nice on its own.


Similar curves for protected aluminum and "enhanced" aluminum show much more pronounced humps in reflectance.

    • jrbarnett likes this

Need comparison of BBHS diagonal with the Zeiss 34mm diagonal using 1 1/4 inch eyepieces . Especially for Planetary and lunar high power viewing .



Thank you 

Similar curves for protected aluminum and "enhanced" aluminum show much more pronounced humps in reflectance.


These "humps" in the last link are 1% or less.  As everyone here likes to say, human eyes are just not that sensitive to small % changes.  So visually, I would say nothing at all to be concerned about as it is effectively flat.  But the real bottom line is never the graph, and always the performance in the field, in which for me Silver far outshines Dielectrics on several fronts based on my direct observations.  So think I will keep the Silver as a mainstay as it just plain does better  :grin:

    • jrbarnett likes this

Don, thank you for the very thorough reply!

    • jrbarnett likes this

Looks like these are starting to hit the market in greater numbers... Agena Astro and High Point Scientific now selling them in stock.

Mar 23 2016 04:55 AM

Indeed, got mine yesterday  :waytogo:

Indeed, got mine yesterday  :waytogo:


Outstanding!  Let me know your thoughts once you've had some time with it.

Mar 23 2016 02:12 PM

Sure, if the clouds dare leaving the area... Weather forecast is not optimistic for the coming days...

I got mine a few weeks ago.  Have to say that the difference the BBHS made for me on Jupiter during a 30 min session was quite astonishing.  Compared to the ES and WO dialectric, colors were improved and scatter reduced.  I switched back and forth several times.  It was similar to dialing the saturation and contrast up and down in a photo editor.


I didn't compare to the Baader T2 yet because it doesn't reach focus without an extender (which I didn't have handy at the time).


Highly recommended if you're into getting the most out of your refractor on planetary observations.

    • Kunama likes this

I've purchased the Lunt 152 after a year thinking about it based ultimately on Bill's excellent review. Now after reading another outstanding contribution by Bill to us here on CN about the BBHS, I purchased it, after selling some items. It sounds like yet another exciting game changer for us like the Lunt was. 


I am not as optimistic about the durability of the silver and believe it will fade in 3-4 years or less, but I promise to make the best of this time! Maybe a more durable one by then.


I am also wondering about its use for White Light observing and would love to hear about any IR affecting this new mirror.  The baader solar film should block the UV I would hope. 


So now I've got a grab and go 6" Apo that can be used visually on an AVX, a Sitall Silver mirror, coupled with a Binotron 27 with the LOAs, 


Yep, the next star party could get a little busy around my place.

Silver is flat well into the infrared, so if it is to be used on the sun, whatever filter is used should cut the IR as much as possible.

If an H-alpha chromosphere filter is used, like the Daystar Quark, that isn't an issue.  But if a white-light photosphere filter is used,

you should definitely check into the amount of IR filtration is there.

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