Orion HELICAL FINE-FOCUSING ADAPTER 13025 User Manual
Orion, Helical fine-focusing adapter
Most modern telescopes come
equipped with rack-and-pinion
focusers. These are adequate
for focusing at low powers.
However, when high powers are used, the limitations of the
focuser come into play and make finding the precise focus point
difficult. Worse, the act of adjusting most telescope focusers
applies force to the telescope, resulting in unwanted vibrations
and possibly moving the telescope off its target.
The Helical Fine-Focusing Adapter solves these problems. With
just a twist of the fingers, the observer has precise control over
the eyepiece position. The helical adapter has no backlash and
allows much smaller focusing increments than can be achieved
with standard focusers. When used in conjunction with your tele-
scope’s standard focuser, the helical adapter will greatly enhance
your focusing precision. The gentle twisting action of the adapter
means no extra force is applied to the tube during focusing, so
images remain steadier.
The helical adapter will fit into any 2" focuser and accepts eye-
pieces with a barrel diameter of 1.25" (only).
To install the helical adapter, first remove any existing 1.25"
adapter from the focuser if you have not already done so. Then
insert the adapter into the focuser and secure it with the
thumbscrew(s), just like you would a 2" eyepiece. Then insert the
1.25" eyepiece you wish to use into the adapter and secure it with
The helical adapter requires that the telescope have at least 9mm
of inward focus travel to focus. It requires 17mm of inward focus
to utilize the full focus range of the helical adapter. Most tele-
scopes will have this amount of inward focus travel.
Initial coarse focusing should be done by adjusting the tele-
scopes’s main focuser. Once you are close to being in focus,
rotate the helical adapter with your fingers until the object comes
into focus. Go a little bit beyond sharp focus until the image just
starts to blur again. Then reverse the rotation of the adapter, just
to make sure you’ve hit the exact focus point. You will find the
helical adapter easy to use when making small focusing adjust-
Do not turn the helical adapter past its natural limit of travel. If you
find that you cannot reach focus within the focus range of the
helical adapter, then make further coarse adjustments with the
main focuser before using the adapter to fine-focus.
Care and Maintenance
With proper care, your helical adapter will last a lifetime. Store it
in a protective box or eyepiece case when not in use. Keep the
adapter as clean as possible to ensure that the adapter threads
have the smoothest motion possible. Over time, you may wish to
add a small amount of light oil to the adapter’s threads to aid in
Size: Fits 2" focusers
Eyepieces: Holds 1.25" eyepieces
Focusing design: Helical
Material: Machined aluminum
Extension rate: .16" per revolution
IN 228 Rev B 02/09
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