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THE BAADER BBHS-SITALL SILVER DIAGONAL

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#201 BillP

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Posted 10 March 2018 - 01:45 PM

Very interesting indeed, just found this wondering how it might compare to a Baader Zeiss 2" Prism diagonal. Personally I would have liked more of a comparison between the Baader Zeiss 2" Prism diagonal and Baader BBHS diagonal, in the section 3e rendition of colours? Particularly the difference in definition and contrast on the planets between the two.

 

Dave

 

The two are very close, yet still distinctive from each other.  I seem to run in phases and for some months will keep the BBHS on my primary scope, then other months use the Zeiss 2" instead.  Colors are rendered with high saturation relative to dielectrics in both, with reds getting a bit more prominence with the BBHS.  So as mentioned, GRS viewing is generally more intense with the BBHS.  I have not done a critical planetary competition between these two as I tend to use my 1.25" Zeiss prism for planetary.  If I do I will post results here.



#202 Dave1066

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Posted 10 March 2018 - 02:02 PM

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?



#203 BillP

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Posted 10 March 2018 - 02:15 PM

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.


Edited by BillP, 10 March 2018 - 02:16 PM.


#204 Procyon

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Posted 13 May 2018 - 10:10 PM

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."


Edited by Procyon, 14 May 2018 - 08:09 PM.


#205 Starman1

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Posted 14 May 2018 - 07:51 PM

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?



#206 Procyon

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Posted 14 May 2018 - 08:18 PM

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."

Edited by Procyon, 14 May 2018 - 09:22 PM.


#207 Lola Bruce

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Posted 14 May 2018 - 08:25 PM

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



#208 RichA

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Posted 15 May 2018 - 12:25 AM

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



#209 Starman1

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Posted 15 May 2018 - 12:45 AM

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.



#210 Procyon

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Posted 15 May 2018 - 12:51 AM

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.

Edited by Procyon, 15 May 2018 - 12:58 AM.


#211 Starman1

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Posted 15 May 2018 - 09:00 AM

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.



#212 Neptune

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Posted 15 May 2018 - 08:15 PM

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



#213 Starman1

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Posted 16 May 2018 - 12:10 AM

Good question.

 

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


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