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Congratulations on your purchase of a quality Orion 2"
Crayford focuser. This focuser is intended for use with New-
tonian reflectors. If you do not have a Newtonian reflector, the
focuser may not be appropriate for your telescope.
Crayford focusers generally perform better than rack-and-
pinion models because the design reduces “focus shift”.
Focus shift is when an image moves position in the eyepiece
when it is being focused. This is very hard to eliminate in
rack-and-pinion focusers due to slight gear and tolerance
imperfections which cause the drawtube to move slightly left
or right when focusing. For the Crayford design, the drawtube
is constantly tensioned (by the focusing shaft and four “roller
bearings”) so the drawtube cannot move perpendicular to the
desired motion.
Installation
This focuser was designed to be a “drop-in” replacement for
the 2" rack-and-pinion focuser that comes standard on Orion
reflectors greater than 6" in aperture, including IntelliScope
and Classic Dobsonians. If you have one of these tele-
scopes, installing the 2" Crayford will be extremely easy. You
will need a Phillips head screwdriver and an adjustable cres-
cent wrench or pliers. Use the procedure outlined below:
Note: The SkyQuest XT8 Classic, or any size Classic
style XT Dobsonian manufactured before June 2002, are
not compatible with this focuser as a “drop-in” replace-
ment. If you have one of these telescopes please skip to
the paragraph following step 7.
1. Position your Newtonian reflector optical tube so it is hori-
zontal. This will prevent any screws or nuts from falling
onto the primary mirror.
2. From the inside of the tube, secure one of the four focuser
securing nuts with the wrench or pliers.
3. Use the screwdriver to completely unthread the focuser
attachment screw from the securing nut currently being
held by the wrench or pliers.
4. Repeat this for the other three nut and screw pairs.
5. Remove the 2" rack-and-pinion focuser from the tube.
6. Place the 2" Crayford focuser where the rack-and-pinion
focuser was previously. Orient the focuser the same as
the removed one was. The through holes in the base of
the focuser should line up with the holes in the telescope
tube.
7. Reinstall the four screw and nut pairs using the wrench or
pliers and screwdriver. Tighten the screws firmly.
If the focuser does not match the mounting holes on your
optical tube you will need to modify your tube so the focuser
will fit. This will require drilling four holes into the tube for
IN 300 Rev G 11/09
Orion
®
2" Crayford Focuser for
Newtonian Reflectors
#13039
Figure 1. The Orion 2" Crayford focuser for Newtonian reflectors.
1.25" adapter
Focusing tension
adjustment set screw
Collimation screws
Focus wheel
Focus lock thumbscrew
Drawtube
Focusing shaft
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