Orion 7220 Instruction Manual
Orion 70mm Multi-Use
Finder Scope
#7220
INSTRUCTION MANUAL
Providing Exceptional Consumer Optical Products Since 1975
IN 497 Rev. C 06/14
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Congratulations on your purchase
of the Orion 70mm Multi-Use Finder
Scope (MF70).
The fi nder scope is an invaluable tool
for fi nding objects in the night sky. It is
a miniature telescope that mounts onto
a larger telescope. Because of its low
magnifi cation and wide fi eld of view,
it is much easier to fi rst locate and
center an object in the fi nder scope
before subsequent viewing through the
main telescope. To properly install and
use your fi nder scope, please read this
instruction manual.
70mm Multi-Use Finder Scope (MF70)
The MF70 is a large aperture fi nder scope. Its large 70mm aperture captures
twice the amount of light than a conventional 50mm fi nder scope.
The light gathering power can be calculated as follows:
Divide the telescope aperture (in mm) by 7mm (dilated pupil diameter of a
young person) and squaring the result.
50mm Finder Scope = (50/7)² = 51x
70mm Multi Finder = (70/7)² = 100x
Hence the MF70 captures twice the amount of light than a conventional 50mm
fi nder scope
Figure 1. The Orion 70mm Multi-Finder (MF70).
Figure 2. Field of view (FOV) using
the MF70 with a 15mm Eyepiece
(approximately 4 degrees FOV).
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With its fast focal ratio (f/4) the MF70
can be used as a wide fi eld of view
(FOV) telescope or as a very bright
fi nder scope or guide scope.
Field of View (FOV)
It is important to understand that a
wide fi eld of view is what makes a
fi nder scope a special tool. It allows
viewing a vast portion of the skies with
low magnifi cation.
Use a low power eyepiece to get the
best FOV with the Multi-Finder. We
recommend an eyepiece focal length
of 15mm. This will give about 18x
power which is good for resolving faint
stars and even to observe some deep
sky objects.
Reaching Focus With the 70m Multi-Finder
The MF70 has a very limited focus range of approximately 0->15mm. Some eyepiece and diagonal combinations may not come to focus.
The light path distance of the MF70 is approximately 80mm therefore you will
need to select an accessory and diagonal combination that is within this required
spacing distance in order to achieve focus.
Generally the rule is: if focus cannot be reached with a particular combination of
eyepiece and diagonal then it is recommended to change the diagonal for a 90
degree prism diagonal which requires much less focus travel than other diagonals (Figure 3 & 4). The eyepiece may also be exchanged for one with a smaller
focus travel requirement (Figure 5).
When used as a fi nder scope we recommend using a 90 degree prism diagonal
with eyepieces. When used as a guide scope we recommend using a 90 degree
Figure 3. If more in-focus travel is required a 90 degree Prism Diagonal may be required.
A 45 degree Prism Diagonal requires more in-focus than any other diagonal.
Figure 4. Example diagonal types and
their associated focus travel distance.
Diagonal Focus Distance Chart
Brand/Type
Focus
Distance
(mm)
Orion 90 degree prism 74
Orion 90 degree mirror 94
Orion 45 degree prism 102
Vixen 1.25” Prism 63
Takahashi 1.25” Prism 64
Baader T2 Prism (Zeis) 67
Celestron 1.25” Prism 67
Vernonscope 1.25” Silver mirror 73
Teleview 1.25” Everbrite Dielectric 78
Astro-Tech 1.25” Dielectric 94
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