Baader T-2 BBHS ® Mirror Diagonal

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# 2456103

€ 245.00 Price excl. German VAT tax (19%): € 205.88

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T-2 BBHS star diagonal without T-2 outer threads. Provides greatest reflectance over most spectral range from 390 to 2000nm
Much higher in brilliance than cheap dielectric coatings
BBHS = Broadband Hardsilver coating with dielectric protective overcoating
T-2 BBHS-Sitall zenith mirrors on both sides with T-2 Photo thread

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Product Questions

Are the BBHS coatings easy to clean? Do the coatings have a life comparable to your dielectric coatings? Do the coatings degrade over time and at what rate? Is there a difference in performance between your dielectric diagonal and the BBHS one, what are the differences and are they significant or very slight? I own an early Televue APO 4 inch refractor.

Question by: John on Sep 9, 2016 1:29:00 AM | 1 Answer(s)

BBHS-mirror coatings require the same care during cleaning as you would give to the protected aluminum-coatings of a Newtonian telescope. Only dielectric coatings have the ultimate hardness to withstand any kind of mistreatment during a cleaning procedure - very similar to our Phantom-Group hard antireflection coatings applied onto our lens surfaces.

Any reflecting telescope with classic coatings can attain a lifetime of 20 or 30 years - correct handling provided. The same accounts for our protected silver-coatings, whereas the position of a stardiagonal within the optical train does provide much better protection against environmental influences, compared to the exposed surface of a primary telescope mirror.

We do regard the benefit of the BBHS hardsilver coating to be quite noticeable, compared to the reduced spectral range offered by a dielectric coating. Please check in the Internet for statements that would verify our position. Or look for the very extensive tests on star diagonals, performed by William Paolini (see tab "Downloads".

Please read more on the properties of our star diagonals and our design philosophy here: http://www.baader-planetarium.com/en/blog/baader-bbhs-reflective-properties/

Answer by: Baader Web Team (Admin) on Sep 15, 2016 8:22:00 AM

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For use with 1.25" eyepieces, why would I choose this (1) diagonal over:
2. Baader # 2456130 - T-2 / 90° Baader Roof-Prism with BBHS coating (https://www.baader-planetarium.com/en/accessories/optical-accessories/prism-and-mirror-star-diagonals/baader-t-2--90%C2%B0-baader-roof-prism-with-bbhs-r-coating-(t-2-part-02).html), or
3. Baader # 2456095 - T-2 Stardiagonal (Zeiss) Prism with BBHS coating (https://www.baader-planetarium.com/en/accessories/optical-accessories/prism-and-mirror-star-diagonals/baader-t-2-stardiagonal-(zeiss)-prism-with-bbhs-r-coating-(t-2-part-01b).html)

Question by: Peter Boender on Apr 26, 2019 9:42:00 PM | 1 Answer(s)

1) The mirror diagonal will affect the image the least, as it only reflects the light without changing it. Today, mirrors are the most common star diagonals.
2) The roof prism will give you an erect, upright image suitable for terrestrial observations. It is one of the very few of its kind which also work at high magnifications. But there is alwaysa slight chance for reflections at the "edge" of the roof because of the optical design of these prisms.
3) The prism is similar in quality to the mirror, but there may be some colour aberrations in fast telescopes because the light passes through the prism. On the other hand, some lens telescopes were especially designed to work with prisms and delivered best results with prisms. Another benefit of prisms is that they don't require as much back focus as a mirror, that's why we recommend them e.g. for binoviewers.

For a comparison between mirror and prism, you may also be interested in the comparison at https://www.baader-planetarium.com/de/downloads/dl/file/id/160/product/1244/testreview_mirror_vs_dielectric_vs_prism_diagonal_comparison_w_paolini.pdf

Answer by: Baader Web Team (Admin) on Apr 29, 2019 8:44:00 AM

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In regards to this style of diagonal, please clarify T-2 fitting?..
Are the threads (standard) for say a 2inch telescope eyepiece that could directly attach to this unit from the bottom barrel of it? Yes or no? .if not what is the diameter/threading of a T-2 fitting?
Thanks Dennis

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Question by: Dennis Young on Dec 6, 2018 6:40:00 PM | 1 Answer(s)

Related Articles

Baader BBHS ® reflective properties

Exclusively available on Baader Sitall Ceramic Mirrors and on selected Baader prism Star Diagonals: BBHS® reflection coatings predominantly are being utilised on our highest quality grade 2" BBHS® Sitall Stardiagonals (#2456115 – incl. black housing and 2" ClickLock clamp) as well as on the BBHS® T-2 Sitall Stardiagonal (#2456103) - where the housing features a male and female T-2 thread - for shortening the optical path with bino use, and to offer the utmost in adaptation variability as well as much more light throughput than with any conventional 1 1/4" star diagonal. BBHS® stands for Broad Band Hard Silver. When applied onto our Sitall (zero expansion glass-ceramics) substrates, these multiple deposited layers of hard silver are being sealed by a set of dielectric layers to achieve long term durability. With this advance in coating technology our BBHS® coating lifetime equals that of a high quality AlSiO2 coating, matching the durability of standard aluminium coated diagonals (and telescope mirrors) which have been in wide use for many years. The BBHS® spectral bandpass is much wider though, when comparing with our 50 layer all dielectric coatings utilized on the 2" ClickLock Star Diagonals. The all dielectric coating system on the 2" ClickLocks...
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Specifications

Additional Information

Manufacturer	Baader Planetarium
SKU (#)	2456103
Optical Design	Mirror Diagonal
Outer Connection (lens sided)	Thread, T-2 (M42 x 0,75)
Inner Connection (eyepiece/-camera-sided)	Thread, T-2 (M42 x 0,75)
Reflection surface	BBHS coated, Dielectrically protected
Image Orientation	Erect image, Mirror inverted
Optical length (mm)	43
Clamping System	no clamp
Deflection angle	90°
Inner Diameter / Clear Aperture (mm)	33

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