22
Manual: MaxBright
®
II Binoviewer
It also compensates the colour aberrations which would otherwise occur beause
of the huge amounts of glass inside of the binoviewer. A GC is more than a simple Bar-
low element! The optical design is from Carl Zeiss and Astro Physics – we have tested
many lens systems from other sources which only extend the focal point, but which do
not remove the colour aberrations.
Another benefit of the GC is to provide additional magnification ahead of the bi-
noviewer. For high magnifications (for example, planetary observation), it is preferable
to magnify the image before the binoviewer, rather than to use shorter focal length
eyepieces. By magnifying prior to the binoviewer, the effects of any optical tolerances
and misalignments in the centering of the eyepieces are reduced. Additionally, longer
focal length eyepieces tend to have longer eye relief and are more comfortable to use.
In general, for binoviewing use we recommend eyepieces with focal lengths of 5 mm or
longer. It is also less expensive to purchase an additional corrector to provide additional
magnifications rather than to purchase additional pairs of eyepieces.
We recommend first choosing the lowest-power corrector that will allow your scope
to reach focus. This will permit the widest possible field of view. In addition, one or
more higher powered compensators can be added to give a greater range of magnifi-
cations.
For selecting the matching Glasspath Correctors, you need to measure the back-fo-
cus of your telescope first, as described in the previous chapter. Table 1 on the previ-
ous page then tells you, which compensators will work.
Please Note: The distances in the table are approximate and are measured from the
front mounting flange of the binocular viewer or nosepiece to the top surface of the
eyepiece holders. Many eyepieces have their focal points located ahead of or behind
their shoulder. The effects of an eyepiece's focal point location are not taken into
consideration here and thus the distance required to reach focus will usually vary from
these values. Additionally, those who are near or far-sighted will also find that more
or less back-focus is needed.
For these reasons, we recommend at least 5 – 10 mm
additional back-focus .
Let's look at an example. The Takahashi Sky90 SV Teleskop is found to have 160mm
of back-focus as measured from the rear surface of its stock 2" eyepiece clamp to its
focal point. Referring to Table 1, this scope can reach focus without a Glasspath Cor-
rector, even when using the Baader Deluxe Amici erecting prism. Anyway, we would
recommend either the 1.7x or 2.6x corrector. This would provide the ability to use the
binoviewer with no compensator for low-power wide field viewing or with the higher
powered corrector for optimum image quality at higher magnification for planetary
observations. Otherwise, the colour abberation would harm the image quality at high
magnifications. Only for wide-field observations e.g. of the Milky Way at low power,
you can work without the Glasspath Corrector.
