ORION 7358 Quick-Collimation Cap Instruction Manual
- June 9, 2024
- Orion
Table of Contents
ORION 7358 Quick-Collimation Cap
This Quick-Collimation Cap is a useful but inexpensive tool to aid in the
precise collimation of telescope optics, most often those of Newtonian
Reflector telescopes. The small hole in the center of the Quick-Collimation
Cap ensures that your eye is centered when looking into the focuser during the
collimation process to check the optical alignment.
Insert the collimation cap into the 1.25” collar of the telescope’s focuser,
then follow the instructions outlined below.
Collimation of Newtonian Reflector Optics
Collimation is the process of adjusting the optics of a telescope so they are
precisely aligned with one another and with the telescope tube. For a
Newtonian reflector telescope, the primary and secondary mirrors must be in
precise alignment. Accurate mirror alignment is important to ensure the
sharpest possible images viewed through your telescope, so it should be
checked occasionally. With practice, collimating is relatively easy to do and
can be done in daylight.
It helps to perform the collimation procedure in a brightly lit room with the
telescope pointed toward a bright surface, such as a light-colored wall. The
telescope tube should be oriented horizontally (parallel to the ground).
Placing a piece of white paper in the telescope tube opposite the focuser
(i.e., on the other side of the secondary mirror from the focuser) will also
be helpful (see Figure 2). Check what tool(s), if any, will be needed to turn
the collimation screws for both the primary and secondary mirrors. For the
secondary mirror
Figure 2. Before collimating the telescope, place a piece of white paper inside the tube opposite the focuser, and position the optical tube in the horizontal position as shown.
Capcollimation screws, you will typically need to use either a Phillips
screwdriver or an Allen wrench (and often a metric Allen wrench).
First you will want to check you telescope’s collimation to see if any
adjustment is even needed. Remove the eyepiece if one is installed in the
focuser, and look into the focuser. You should see the secondary mirror
centered in the focuser, as well as the reflection of the primary mirror
centered in the secondary mirror, and the reflection of the secondary mirror
(and your eye) centered in the reflection of the primary mirror, as in Figure
3A. Got all that? Review it again carefully, and compare what you see to
Figure 3A. If anything is off-center, proceed with the following collimation
procedure.
NOTE : Precise collimation is best achieved by using a collimating tool, such as the Quick-Collimation Cap. Figures 3B through 3D assume that you have the collimation cap installed in the focuser.
Figure 3. Collimating the optics. (A) When the mirrors are properly aligned, the view down the focuser drawtube should look like this. (B) Here, only part of the primary mirror is visible in the secondary mirror, so the secondary mirror needs to be adjusted (tilted). (C) Here the secondary mirror is correctly aligned because the entire primary mirror is visible in it. But the reflection of the secondary mirror is off-center. So the primary mirror still needs adjustment. (D) Now the primary mirror is correctly aligned, so the secondary mirror is centered.
Primary Mirror Center Mark
You may have noticed that the primary mirror on your Newtonian reflector
telescope has a small adhesive ring or dot in the center. This “center mark”
allows you to achieve a very precise collimation of the primary mirror; you
don’t have to guess where the center of the mirror is, which is important in
the collimation process. This center mark is especially useful when using a
collimating tool such as the Quick-Collimation Cap.
Note: The adhesive ring/dot should not be removed from the primary mirror.
Because it lies directly in the shadow of the secondary mirror, its presence
in no way adversely affects the optical performance of the telescope, or the
image quality. That might seem counter-intuitive, but it’s true! Leave it in
place.
Aligning the Secondary Mirror
Align the secondary mirror first, as follows.
With the collimation cap installed, look into the tiny hole in the center of
the cap. You will see the telescope’s secondary mirror. If the entire primary
mirror reflection is not visible in the secondary mirror, as in Figure 3B, you
will need to adjust the tilt of the secondary mirror. This is done by
alternately loosening one of the three secondary mirror alignment screws then
lightly tightening
Figure 4. Secondary mirror collimation is performed using the three screws (usually Philips or Allen screws) circled here on the secondary mirror holder.
the other two (Figure 4). The goal is to center the primary mirror reflection in the secondary mirror, as in Figure 3C. Don’t worry that the reflection of the secondary mirror is off-center. You will fix that in the next step. It will take some trial and error to determine which screws to loosen and tighten to move the reflection of the primary mirror to the center of the secondary mirror. But be patient and you’ll get it.
Aligning the Primary Mirror
The final adjustment is made to the primary mirror. It will need adjustment
if, as in Figure 3C, the reflection of the primary mirror is centered in the
secondary mirror, but the small reflection of the secondary mirror is off-
center. The tilt of the primary mirror is adjusted using (usually) three
spring-loaded collimation knobs and three smaller locking thumbscrews on the
back end of the optical tube (Figure 5).
First loosen the three locking thumbscrews a turn or so. Then tighten one of
the collimation knobs about a quarter turn and see if the secondary mirror
reflection has moved closer to the center of the primary (where the center
ring/dot is). If it moved farther away then try loosening the same collimation
knob a bit. Repeat this process on the other two sets of collimation screws,
if necessary, adjusting them one way or the other and seeing if the secondary
mirror reflection moves closer to the center of the primary mirror. It will
take a little trial and error to get a feel for how to tilt the mirror in this
way. When the center hole in your collimating tool is centered as much as
possible in the ring/dot on the primary mirror, your primary mirror is
collimated. The view through the collimation cap should resemble Figure 3D.
Finally, very lightly tighten the three locking thumbscrews so that the
primary mirror stays in that adjusted position. A simple star test will tell
you whether the optics are accurately collimated.
Star-Testing the Telescope
When it is dark, point the telescope at a bright star and accurately center it in the eyepiece’s field of view. Slowly de-focus the image with the focusing knob. You should see a series of diffraction rings surrounding a dark center spot, which is the shadow of the secondary mirror. If the diffraction rings are perfectly circular around the dark spot, telescope is correctly collimated (Figure 6). If the image is unsymmetrical, with rings that are not perfectly circular and the dark spot is not centered within them, the scope is out of collimation.
Figure 5. The optical tube’s rear cell has three pairs of collimation screws. The larger knobs are the (often spring-loaded) collimation knobs while the smaller thumbscrews are the locking screws.
Note, however, that if the bright star you have selected is not centered in the eyepiece, the optics will always appear out of collimation, even though they may be perfectly aligned. It is critical to keep the star centered, so over time you may need to make slight corrections to the telescope’s position in order to account for the sky’s apparent motion.
Figure 6. A star test will determine if the telescope’s optics are properly collimated.
One-Year Limited Warranty
This Orion product is warranted against defects in materials or workmanship
for a period of one year from the date of purchase. This warranty is for the
benefit of the original retail purchaser only. During this warranty period
Orion Telescopes & Binoculars will repair or replace, at Orion’s option, any
warranted instrument that proves to be defective, provided it is returned
postage paid. Proof of purchase (such as a copy of the original receipt) is
required. This warranty is only valid in the country of purchase.
This warranty does not apply if, in Orion’s judgment, the instrument has been
abused, mishandled, or modified, nor does it apply to normal wear and tear.
This warranty gives you specific legal rights. It is not intended to remove or
restrict your other legal rights under applicable local consumer law; your
state or national statutory consumer rights governing the sale of consumer
goods remain fully applicable.
For further warranty information, please visit
www.OrionTelescopes.com/warranty.
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Toll Free USA & Canada:
800-447-1001
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Customer Support: support@telescope.com
Copyright © 2022 Orion Telescopes & Binoculars. All Rights Reserved. No part of this product instruction or any of its contents may be reproduced, copied, modified or adapted, without the prior written consent of Orion Telescopes & Binoculars.
References
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