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THE BAADER BBHS-SITALL SILVER DIAGONAL


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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.

 


Diagonal

Size

Type

Reflectivity Claim

Wave Front Claim

Body Build

Baader BBHS

2"

Silver Mirror

Not specified

Not specified

Diecast and CNC Machined Magnesium

Astro-Physics MaxBright

2"

Dielectric

>99%

 

Inconsistent*

CNC Machined

Baader Zeiss Prism

2"

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.

 

Diagonal

Measured Light Path (mm)

Baader Zeiss 2" Prism

100

Astro-Physics 2" MaxBright Dielectric

103

Baader 2" BBHS

112

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:

 

Diagonal

Time to Acclimate

(minutes)

Baader 2" BBHS

7.0

Baader 2" Zeiss Prism

9.5

Astro-Physics 2" MaxBright Dielectric

11.5

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


224 Comments

Thanks Bill, I'd be interested to hear the results if you ever a critical planetary comparison. Is there a reason why you favour the 1.25" Zeiss ( is this a Baader Zeiss ? ) prism for planetary over the 2" Baader Zeiss prism?

Less is almost always better.  So smaller glass path of the smaller prism means just a slightly less amount of scatter being induced...but that is only for the most critical of observing.  And if I want to do some general wide field binoviewing, then the shorter glass path of the smaller prism does not need a lot of backfocus when not using the OCA.

One of the most informative threads I've ever read, thanks all. Learned a lot on wavelengths, silver, aluminum, coatings here.

 

Before I re-read it, which 2" diagonal would you recommed for DSO's with a CPC 1100? Especially Galaxies, arms and nucleus, open and globular clusters with and without red giants, and all Nebulae.

 

A 2" BBHS Mirror, 2" BBHS Prism,  2" Baader Zeiss prism (Discontinued model), or 2" Baader  Dielectric?

 

Do most users still enjoy their BBHS? 

 

Only thing concerning me now is this quote in one of Don's links:

 

"The reason for going with silver rather than aluminium is a slightly improved reflectivity in the near- and mid-infrared (99.1 per cent at 10 microns), but also that the emissivity of the silver coating is around 38% that of aluminium, which reduces background in infrared observations.

 

The paper reports on durable coatings that reduces the tarnishing that favours an aluminium coating (as well as aluminium's superior performance shortward of 400nm). I guess that these are rather expensive, so aluminium is still the norm unless you want to be re-silvering the mirror very frequently."

 

What did he mean by "reduces background in infrared observations and re-silvering the mirror frequently (Will it work for 10 years at least with no polishing required or any discoloration from tarnishing)"?

 

Have the wavelengths been proven flat from 400nm to 2000nm? 

 

Thx

 

PS> Does this help us visual astronomers at all:

 

"Nobody has yet mentioned the one aspect of silver that the graph depicts. Silver absorbs strongly near 315 nm. If you were interested in UV light from the stars, you would have a hole in your data (between 310 and 320 nm) if you used silver. Not only that, any light gathered with a wavelength less than 310 nm would require longer acquisition times."

Worse, pure silver starts rolling off at short wavelengths around 500nm, and we see well down toward 400nm.

Fortunately, UV-enhanced coatings are commonly applied (and probably are in the BBHS mirror diagonals).

The real question is what is the spectrum of passage through the glass in the prism?

Worse, pure silver starts rolling off at short wavelengths around 500nm, and we see well down toward 400nm.
Fortunately, UV-enhanced coatings are commonly applied (and probably are in the BBHS mirror diagonals).
The real question is what is the spectrum of passage through the glass in the prism?

The spectrum of passage through the glass in the prism is not measurable?

Yeah, some of those graphs were intimidating lol. Sharper looking fall off from 500nm compared to the dielectric graph which started falling much eariler in the 400's, or much later.

But perhaps the Sitall coatings negate this and make the silver coated one flat starting from 400nm?

What does this mean though?

"but also that the emissivity of the silver coating is around 38% that of aluminium, which reduces background in infrared observations."

I bought new a Baader/zeiss 2" prism and truthfully it is not as good as my TeleVue Everbrite. First it has more scatter, a little less contrast, and off perpendicular quite a bit. I have viewed through a T2 Baader/Zeiss and it is considerably better than my 2". If they vary at over $500 each shame on Baader.

Bruce

I question the need to spend $300-$500 on a diagonal when you can buy a quartz 99% diagonal today for around $120.00.

    • daslolo likes this

The spectrum of passage through the glass in the prism is not measurable?

Yeah, some of those graphs were intimidating lol. Sharper looking fall off from 500nm compared to the dielectric graph which started falling much eariler in the 400's, or much later.

But perhaps the Sitall coatings negate this and make the silver coated one flat starting from 400nm?

What does this mean though?

"but also that the emissivity of the silver coating is around 38% that of aluminium, which reduces background in infrared observations."

Sitall is a zero-expansion glass ceramic material, not a coating.

UV enhancements to silver are in the form of a couple dielectric coatings applied over the silver, like SiO on a telescope main mirror.

If you are using the coating for IR studies, if the coating emitted energy in the IR, it wouldn't be much good for the studies.

Silver is WAY better for IR work than aluminum, and both materials are inferior to gold, which is the most common coating for IR work.

Aluminum is a known IR emitter--the material is world-renowned for losing and gaining heat faster than other materials.

    • Jsquared likes this
I would pay 500 for one if it showed me the exact same view as a good dielectric, including the same dark black background, exact same white & blue in stars and other objects, plus the added benefit of seeing more red giants which I always look for.

But if it hinders the white, blues and black background in any way, than I'd think about buying it at 200. Until that's figured out, I think I'll stay with the dielectric clicklock.

I'm curious as to how the white color on a Galaxy with a very visible white nucleus would show versus a good dielectric.

Not all dielectric coatings are created equal, but a good broadband enhanced dielectric coating can have high transmission from 400nm to past 750nm,

something no metal coating gives without enhancing dielectric layers.

If both are done well, then the visual performance is dependent on the substrate.

    • daslolo likes this

This might have been brought up a few pages back, but isn't this a moot point in a scope with mirrors. The diagonal Bill originally wrote about was used in a refractor, right?  In my new to me 11" HD would this diagonal be of any benifit to me?

 

David

Good question.

 

So long as the diagonal has high reflectivity, an accurate surface, and is collimated, then it should be fine.

    • Jon Isaacs likes this

lol.gif   I gotta say...the color of the GRS on Jupiter was astoundingly different between the BBHS and the MaxBright Dielectric.  It really did shock me when I saw it and kept exchanging the diagonals as I just could not believe it when I first saw it.

Does the AP Maxbright have a better mirror, than the Baader of same name? 

 

Bill, from your review, the Sitall silver, for its strength showing reds seems what I want hunting for K, M, R, N, C and other cooler stars. But using a FC100DL F14, and SW 120 Equinox F9 initially.

Once again, If I am thinking correctly, this mainly applies to a refractor style telescope (no mirrors).  If you have a reflector or one of the variants (eg, SCT, Mak, etc...) unless the mirrors in the scope are something special spectral wise, how can you really benefit from one of these aformentioned diagonals?  

Once again, If I am thinking correctly, this mainly applies to a refractor style telescope (no mirrors).  If you have a reflector or one of the variants (eg, SCT, Mak, etc...) unless the mirrors in the scope are something special spectral wise, how can you really benefit from one of these aformentioned diagonals?  

 

It will not restore anything "lost" by aluminum-coated mirrors of a mirrored scope but it will potentially prevent further loss, vs using a dielectric or aluminum coated diagonal. In theory, since errors/losses are cumulative in an optical system, it could still benefit a a mirrored system. In practice, it's not clear whether that is something that would be detectable to the human eye (a point that's been made several times in this thread). 

I think thinking about it terms of restoring loss will not get to the heart of the matter.  I feel it is better to think about how every component in the optical chain, refractive glass or mirror, it providing some level of "filtration" of what it coming through it or bouncing off of it.  Even mirrors do this since they do not evenly transmit the light across the entire spectrum.  When you compare an aluminum vs a silver mirror, with a 45 degree bounce, you can see that the transmission across the visible spectrum varies slightly.  And it is also different depending on whether the mirror has standard coatings vs enhanced ones.  So everything makes a difference.  So in that variation you are in effect, filtering some spectra to transmit less and others more.  These variations will of course impart differently to the eye, depending on what visible spectra are coming from the target one is observing.  Now how much will it matter and will it be at a threshold to be visible?  Without specific testing in a lab it is anyone's guess...and guess only!  However, in the field, I and others have very well and often noted that compared to other diagonal technologies, the reds look accentuated off of the silver diagonals.  And as I recollect, even more so off of gold diagonals.  If I were using a mirrored scope, like an SCT, and wanted to accentuate the red end of the spectrum to more easily pick out the stars that output in this spectrum more, then the BBHS Silver might prove an advantage.  But CNer 25585 listed a wide range of specific star types, saying for K, M, R, N, C.  While I saw the red stars more prominently in the BBHS vs. the other diagonal technologies I was testing, I did not specifically identify those stars so could not say it would do this across all those star types.  Would make an interesting field test to specifically pick stars of those types and see how each fares!  But rather depending on a diagonal to do this, would be cool if a custom filter could be made that would do this!

    • 7Soeurs and Jsquared like this
A silver coated diagonal will filter light from O, A, B, and F stars unless it has additional UV enhancing overcoats. If those coatings are applied, then silver has no disadvantage over aluminum and has a distinct advantage over aluminum for K, M, R, and N stars (i.e. C stars).
Now, in smaller scopes, it is more effective to enhance the violets and blues since red stars are generally of lower magnitude.

Generally, though, a higher transmission will aid the visibility of stars in any aperture of 12" and smaller, and for that a UV enhanced silver coating is better. The real issues are cost and longevity, which might not be as advantageous as the ultimate reflectivity. There, the more cost-effective solution is likely to be the dielectric coating found on many diagonals.
    • daslolo likes this

That is one solid review, Bill!

I had a similar experience when upgrading from a 1.25" to a 2" di WO (the one with the denk s1), suddenly I could see galaxies but to see such a drastic difference among two 2" diagonals is a big surprise.

If you have tried out other Baader, what is the difference between this BBHS and the vanilla 2" baader, the 2956100? they are 200$ apart so I wondered if there was a noticeable differece.

Generally, though, a higher transmission will aid the visibility of stars in any aperture of 12" and smaller, and for that a UV enhanced silver coating is better. The real issues are cost and longevity, which might not be as advantageous as the ultimate reflectivity. There, the more cost-effective solution is likely to be the dielectric coating found on many diagonals.

I would not consider the longevity question (not issue) for two reasons:

 

1. No one really knows what the longevity will be of the new coating process Baader is using.  So one cannot use historical data to predict.  Baader insists they have used this process on silver for quite some time now so longevity will not be an issue.  Everyone really will just have to wait and see how it fares. 

 

2. Let's say that longevity is some sort of an issue and reflectivity decreases after 10 years.  Who would care?  If it is performing better than dielectric technologies, which it clearly does, who would want to have lesser performance for a decade?  I personally doubt that there will be any longevity consequence in less than 20 years.  Makes no sense to me to choose the high scatter of dielectrics and muting of colors they produce relative to silver or conventional aluminized mirror diagonals or prisms.  As I have said before, the advantage of a dielectric is contrived and is marketing as no one before dielectrics were crying about how their prism and mirror diagonals were getting all scratched up or could not be safely cleaned.  If one cannot keep a prism diagonal clean safely then they can also not keep a refractive or reflective main objective safely cleaned either.  So the concept is a double edged sword and when you realize that then the dielectric-advantage claims become even more ridiculous.

 

If you have tried out other Baader, what is the difference between this BBHS and the vanilla 2" baader, the 2956100? they are 200$ apart so I wondered if there was a noticeable differece.

 

The Baader 2" Dielectric #2956100 is what was used in my Mirror vs. Dielectric vs. Prism review here - While I did not directly compare it to the Baader BBHS Silver mirror, in that review I did have a VERNONscope Enhanced Silver Diagonal so think it would be safe to extrapolate that that Enhanced Silver diagonal would perform on-par with the Baader BBHS.  So take a look at the summary at the end of that review and you will see that even there the Silver diagonal attained top performance on planetary and on-par performance with the best non-prism diagonals relative to scatter
 

The Baader 2" Dielectric #2956100 is what was used in my Mirror vs. Dielectric vs. Prism review here - While I did not directly compare it to the Baader BBHS Silver mirror, in that review I did have a VERNONscope Enhanced Silver Diagonal so think it would be safe to extrapolate that that Enhanced Silver diagonal would perform on-par with the Baader BBHS.  So take a look at the summary at the end of that review and you will see that even there the Silver diagonal attained top performance on planetary and on-par performance with the best non-prism diagonals relative to scatter

 

Just read it. The BBHS seems clearly superior than the base clicklock if you like colors and details. I guess for solar you switch to el cheapo dielectric to avoid melting.

For the first time I saw the colors of binary stars and it was vivid. I had done 2 hours of viewing under a poncho. Big difference.

Now I look at things through a pair of binos, so the light goes through a prism and one mirror each eye so this would be the weak link, I'm wondering if a BBHS would make a noticeable difference.

I thought prism diagonal darkened the image?

 

Re. Van Gogh, Messier could see all these with a telescope from that era, these people had much better eyesight than we do. I wonder if a study of the effect of screens on our eyes have been done, and not burried...

  I bought the 1.25" BBHS prism a few days ago, but rather than the click lock I decided to go for the Baader helical micro focuser and a 2" nose to link directly to the 2" back on my FC100DZ. 

  After unboxing and assembling, I wondered what I could look at to compare the new BBHS with my faithful Tak 1.25" prism. I aimed the scope through the double glazing and focussed on a random stone wall about two miles away. The vertical stones on the top of the wall were sharply defined with the morning Sun lighting up each one individually. I then removed the BBHS prism and replaced it with the Tak prism. What a difference! Through the Tak, the individual stones on the top of the wall merged into an undulating Illdefined edge that had a mild chromatic blur. So I 're fit the BBHS, and each stone was again razor sharp, and even has hints of texture on the individual vertical stones as they were lit by the Sun.

  Since then I've had a great time observing Venus and splitting double stars. And sweeping the sky last night using my Baader 35mm Eudiascopic in the DZ, the milky starlight that makes up the backdrop to the milkyway was nolonger milky, it was a dusting of individual stars at the limit of discernability.  I don't think I'll ever look through my Tak prism again!

I thought prism diagonal darkened the image?

Not in any of my testing and actually just the opposite bringing in faintest stars more authoritatively.  Would not see how it would darken anyway as only 2 air-glass interfaces so light loss from just those two is next to nothing...same as a singlet lens.  There is transmittance fall off with length of glass path though so that would add some, but again negligible as sure something like an Ethos with all its many lenses inside probably has similar glass path thru elements as a prism.  Basically a well made prism is a thing of beauty, function, and proven longevity!

    • mikeDnight and daslolo like this

  I bought the 1.25" BBHS prism a few days ago, but rather than the click lock I decided to go for the Baader helical micro focuser and a 2" nose to link directly to the 2" back on my FC100DZ. 

  After unboxing and assembling, I wondered what I could look at to compare the new BBHS with my faithful Tak 1.25" prism. I aimed the scope through the double glazing and focussed on a random stone wall about two miles away. The vertical stones on the top of the wall were sharply defined with the morning Sun lighting up each one individually. I then removed the BBHS prism and replaced it with the Tak prism. What a difference! Through the Tak, the individual stones on the top of the wall merged into an undulating Illdefined edge that had a mild chromatic blur. So I 're fit the BBHS, and each stone was again razor sharp, and even has hints of texture on the individual vertical stones as they were lit by the Sun.

  Since then I've had a great time observing Venus and splitting double stars. And sweeping the sky last night using my Baader 35mm Eudiascopic in the DZ, the milky starlight that makes up the backdrop to the milkyway was nolonger milky, it was a dusting of individual stars at the limit of discernability.  I don't think I'll ever look through my Tak prism again!

You make it sound like Tak prism is mediocre at best, and I do remember your posts about how your DC worked well at really high magnification. DZ, if anything, has longer focal ratio.

In order to be on the safe side, I opted for BBHS mirror with my DF and it is fantastic. Compared with standard dielectric it really is better on the Moon and Jupiter. A friend of mine uses Tak prism with his DC and was unhappy with what he perceived to be some chromatic aberration. Not sure what to say, I thought Tak would not offer a diagonal not worthy of its refractors.

You make it sound like Tak prism is mediocre at best, and I do remember your posts about how your DC worked well at really high magnification. DZ, if anything, has longer focal ratio.

In order to be on the safe side, I opted for BBHS mirror with my DF and it is fantastic. Compared with standard dielectric it really is better on the Moon and Jupiter. A friend of mine uses Tak prism with his DC and was unhappy with what he perceived to be some chromatic aberration. Not sure what to say, I thought Tak would not offer a diagonal not worthy of its refractors.

I can't say I ever saw CA in my Tak prism on the night sky, or on bright objects like the limb of the Moon for that matter. Over the past five years my Tak prism has served me well and shown some highly detailed views of all kinds of targets, from lunar & planetary to faint deep sky such as IC434 and stunning binary stars. The high powers I regularly used on my FC100DC, well over 400X on many occasions prove to me at least that the Tak prism could deliver a high level of image quality. It wasn't until I compared the Tak with the BBHS that I saw the advantage offered by the silvered prism. I think the Tak prism is superb for the money you pay, but I'm looking to fine tune the optical performance of my FC100DZ and the BBHS has certainly provided a noticeable improvement in real terms, not just theoretical. I now have one of the finest 4" refractors in the world, so I might as well turbo boost it by using one of the finest diagonals. 

    • BGazing likes this


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