Instruction Manual
Baader CCS Herschel-Prism
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15
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Copyright Baader Planetarium GmbH, all rights reserved
Attaching the Mark V binocular viewer
To use the Mark V binoviewer together with the Herschel prism you need a very big backfocus of ca. 210mm. Most
modern telescopes have no more backfocus than 150-180mm. Usually you can
’
t use this combination because you
won
’
t reach focus. You will need a glasspath corrector which increases the focal length of your telescope.
You can use the following table to see how much backfocus you need with which glasspath corrector.
Herschelprism with
part # 27 and
Giant Binocular Viewer
+ 1.25
Glaspathcorrector
+ 1.7
Glaspathcorrector
+ 2,6
Glaspathcorrector
210mm Backfocus
190mm Backfocus
175mm Backfocus
125mm Backfocus
Very few manufacturers provide the back-focus specifications for their scopes. Thus, the best way to determine
your telescope's back-focus is to measure it yourself. To reduce the possibility of errors, it is best to measure the
back-focus yourself.
The easiest way to measure back focus is to point your scope at the Moon (without eyepiece) and project its image
onto a white card. The focuser should be fully retracted. Hold the card behind the empty focuser and find the posi-
tion where the image of the Moon comes to sharp focus. This position is your telescope's focal plane. Measure the
distance from the card to the end of the focuser. This is the amount of available back-focus for additional accesso-
ries - for example, a binoviewer plus eyepieces. Armed with this information, look at the table above. First, subtract
the recommended 5-10mm to your back-focus value to allow for differences in eyepiece design and vision. Then,
find the first column with a value less then your adjusted back-focus. The heading of this column indicates the ap-
propriate Glasspath Compensator.
For example, let's say your telescope is measured to have 188mm of back-focus. After subtracting 10mm, your
adjusted back-focus value is 178mm. The first column less than 178mm is 175mm, the column for the 1.7x
Glasspath Compensator. The 2.6x compensator would also work, as it requires just 125mm of back-focus. You
would decide between the two by considering the eyepieces you are planning to use, the focal length of your tele-
scope and the desired magnification for your observations. Or, you could purchase both compensators and have
two magnifications available with a single pair of eyepieces.
Image 10:
Attach any standard T-
ring (avaiable for all standard DSLR
cameras) to the T2-adapter #27
Image 11:
Cool Ceramic Safety
Herschel prism with DSLR directly
mounted onto the housing.
