Baader Planetarium MAXBRIGHT Instruction Manual - page 3
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written consent is prohibited. (Worldwide @ www.baader-planetarium.de),(Italy @ www.unitronitalia.it),(USA @ www.alpineastro.com)
provide. Further, few manufacturers even provide the back-focus specification for their scopes. As a result, it is left up
to the user to find out for themselves.
Newtonians typically have the least amount of back-focus. In order to extend the focal point well past the focuser
surface, a larger secondary mirror is required. This increases the central obstruction (loss of contrast) and increases cost.
As a result, many Newtonians have only a small amount of back-focus. For this reason, we offer a very special 1.7X
glasspath compensator that is designed for Newtonians. This compensator also corrects the off-axis coma that affects
fast Newtonians.
Schmidt-Cassegrain and Maksutov telescopes can typically provide large amounts of back-focus, owing to their
movable primary mirrors. This allows many of them to accommodate binoviewers even without any glasspath
compensator (also, depending on the size of star diagonal used). SCT users will find the 1.25X compensator is likely to
be the best match to their scopes, providing all of the glasspath compensating benefits at moderate magnifications.
Refractors vary considerably in the amount of back-focus they provide, sometimes within the same model.
How do I determine how much back-focus my telescope has?
The best way to determine your telescope's back-focus is to measure it yourself. If you are intending to use a binoviewer
with your scope, you will want to measure the back-focus using any adapters or star diagonals that will be present when
using the binoviewer.
The easiest way to measure back focus is to point your scope at the Moon (with accessories, but No Eyepiece) and
project its image onto a flat sheet of paper. The focuser should be fully retracted. Hold a white sheet of paper behind the
empty focuser or above the star diagonal and find the position where the image of the moon comes to sharp focus. This
position is your telescope's focal plane. Using a scale, measure the distance from the paper to the end of the focuser or
star diagonal. This is the amount of available back-focus for additional accessories (ie, Binoviewer plus eyepieces). It is
possible to make a more accurate measurement with the actual eyepieces to be used with the binoviewer, but for most
purposes this white paper projection method should be adequate to help select the necessary glasspath compensator.
In some cases, you may find that your scope does not have sufficient back-focus to work with any of the glasspath
compensators we provide. If you are using a 2" star diagonal in your system, you may want to consider using a shorter
1.25" star diagonal. The Maxbright Binocular Viewer has been especially designed to directly close-couple to our T-2
Diagonals, in order to provide the minimum path length possible. Newtonian users may want to consider shifting their
primary mirror forward (or shortening their truss tube poles) in order to increase their telescope's amount of back-focus.
Configurations
The Baader Maxbright Binocular Viewer is able to be configured many different ways. The front rotating ring of the
Maxbright has an internal T-thread (M42 x 0.75mm), which allows it to be directly coupled to any externally T-
threaded accessory. The rotating feature allows the binoviewer to be oriented as desired, and securely locked in place.
The accessories shown below are just some of the more popular combinations. Of course, you are free to invent your
own, using any of our Astro T-2 System components. For instance, a T2 #6,7 Quick Changer may be added to enable
quick attachment and removal of any T-threaded accessory (such as the Maxbright binoviewer).
How to select the most suitable diagonal prism
When the MaxBright binocular viewer is used with refractors and Cassegrain telescopes, it is much more comfortable to
use a diagonal between the telescope and the binoviewer. But it's not advisable to use a normal, commercially available
1.25" (31.8mm) diagonal prism, since these accessories often (almost always) have a plastic body, and so they are not
able to adequately support the weight of the binoviewer, especially when it is paired with two heavy widefield
eyepieces like the Baader Hyperions. This is compounded by the extra distance needed to support the binoviewer on top
of the diagonal’s existing eyepiece clamp (which also consumes a large amount of additional precious back-focus).
Furthermore these normal diagonal prisms typically use small screws to lock the eyepieces in place, which may be
sufficient to support lightweight eyepieces, but are totally inadequate to safely hold heavy accessories like a binoviewer.
In fact it's quite common, in the astronomical community, to hear about heavy and expensive eyepieces being dropped
to ground (and broken) because of the poor locking system of these cheap diagonals.
The perfect solution for this problem consists of using the Baader T2 diagonals, equipped with male-female T2 threads
and perfectly able to be attached directly and closely to the MaxBright binocular viewer (requiring the minimum
amount of back-focus possible). These diagonals feature Right Angle or Amici prisms (and mirror, in the T2 Maxbright
mirror version) of the absolute best optical quality, incorporating a solid one-piece precision machined metal body
which is perfectly suited to hold the heaviest accessories.
Also offered is a 45degree terrestrial version (using an Amici Prism) which offers correctly oriented images, and is the
ideal choice for observers fond of terrestrial and nature viewing.