- the backfocus length of your telescope
- a 2" or 1.25" nosepiece, if you can't use the T-2-thread of binoviewer to connect it to your equipment
- maybe a star diagonal - we recommend our T-2-prisms because they allow for a very short adaptation and save valuable backfocus
- probably a glasspat corrector to reach focus - we recommend the 1.25x, as it also removes colour fringes at faster telescopes.
You need to determine the backfocus of your telescope either from the back of the 1.25" or 2" eyepiece clamp or a T-2-thread, if available. You can do this e.g. by pointing the telescope with fully retracted focuser at the moon. Hold a piece of paper behind it and measure the distance at which you can see a sharp image of the moon - that's the available backfocus. Attach all necessary accessories to the telescope when determining the back focus.
If you intend to use it with a star diagonal, you have to include this, too. The available backfocus must be longer than that of the binoviewer with all accessories.
For example, the shortes combination would be
- 2"/T-2-adapter/nosepiece #2408150, optical length 2,5mm
- T-2/90° star diagonal #2456005 with 32mm-prism, optical length 35mm
- MaxBright II Bino in T-2-configuration, optical length ca. 110mm (give or take a little bit for diopter compensation and focal plane of the eyepieces)
then you need a backfocus of at least 147,5mm.
Then you can choose a matching glasspath corrector to reach focus, and/or replace the star diagonal. The glasspath correctors save you back focus, but the also increase the magnification by the given factor:
Glasspathcorrector 1:1,25 for Baader-Binoviewer with T-2 thread (MaxBright II and MaxBright) # 2456314: Backfocus gain 30mm
Glasspathcorrector 1:1,70 for Baader-Binoviewer with T-2 thread (MaxBright II and MaxBright) # 2456316: Backfocus gain 65mm
Glasspathcorrector 1:2,60 for Baader-Binoviewer with Zeiss ring dovetail (MaxBright II and Mark V) # 2456317: Backfocus gain 120mm
So, if you choose the 2.6x corrector, you only need about 28mm of backfocus, but the magnification increases by factor 2.6. We always recommend at least the glasspath corrector 1.25x, because they also remove the colour fringes which are introduced by the prisms inside of the binoviewer at fast telescopes (faster than ca. f/10).
The glasspath corrector is mounted inside of the star diagonal, our T-2-diagonals are prepared for it. If you use your own star diagonal, you can mount 2"/T-2-adapter #2408150, optical length 2,5mm or Baader Nose piece 1¼" / T-2 (T-2 part #14) # 2458105 in front of the binoviewer and insert the glasspath corrector there.
Answer by: Baader Web Team (Admin) on Oct 28, 2019 10:38:00 AM
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