Celestron STAR HOPPER Instruction Manual page 14

Prior to re-collimating the primary mirror, locate the collimation screws on the end plate at the base of the telescope
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tube. These three screws are to be adjusted one at a time. Normally, motions on the order of an / turn will make a
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difference, with approximately a / to / turn being the maximum required.
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With Polaris or a bright star centered within the field of view, focus with either the standard ocular or your highest
power ocular, i.e. the shortest focal length in mm, such as a 6mm or 4mm. Another option is to use a longer focal
length ocular with a Barlow lens. When a star is in focus it should look like a sharp pinpoint of light. If, when
focusing on the star, it is irregular in shape or appears to have a flare of light at its edge, this means your mirrors
aren't in alignment. If you notice the appearance of a flare of light from the star that remains stable in location, just
as you go in and out of exact focus, then re-collimation will help sharpen the image.
Take note of the direction the light appears to flare. For example, if it appears to flare toward the three o'clock
position in the field of view, then you must move whichever screw or combination of collimation screws necessary to
move the star's image toward the direction of the flaring. In this example, you would want to move the image of the
star in your eyepiece, by adjusting the collimation screws, toward the three o'clock position in the field of view. It
may only be necessary to adjust a screw enough to move the star's image from the center of the field of view to about
halfway, or less, toward the field's edge (when using a high power ocular).
Collimation adjustments are best made while viewing the star's position in the field of view and turning the
adjustment screws simultaneously. This way, you can see exactly which way the movement occurs. It may be helpful
to have two people working together: one viewing and instructing which screws to turn and by how much, and the
other performing the adjustments.
IMPORTANT: After making the first, or each adjustment, it is necessary to re-aim the telescope tube to re-center the
star again in the center of the field of view. The star image can then be judged for symmetry by going just inside and
outside of exact focus and noting the star's pattern. Improvement should be seen if the proper adjustments are made.
Since three screws are present, it may be necessary to move at least two of them to achieve the necessary mirror
movement.
ANSWERS TO FREQUENTLY ASKED QUESTIONS
Q. If I re-collimate the primary mirror, will alignment remain as I set it?
A. Yes, unless or until the telescope is severely jarred or bumped.
Q. Is exact collimation necessary?
A. For the majority of users, the collimation of the telescope, as delivered, will be satisfactory. Probably only those
requiring extremely sharp imagery will want or need to perform collimation, and then only once.
Q. Why is it necessary to re-center the star after each mirror adjustment?
A. All Newtonian telescopes have what is called off-axis coma (see glossary). Due to this, the best images are always
obtained in the center of an eyepiece view. Therefore, that is where you should judge star symmetry.
Q. On some nights the star's image fluctuates in size, position and symmetry without my doing anything. What is
the cause of this?
A. This represents turbulent "seeing," which is caused by several factors (please see pages 18 and 19 for a full
description). Some steps you can take to minimize visual disturbances are to let the telescope tube remain outside for
30 minutes before judging symmetry, allowing time for the temperature within the telescope tube to balance with that
of the outer environment. It will also help to wait for a still night or a still time of night. Further, be aware that
using your telescope near a heat source such as a rooftop, car hood or any surface retaining daytime heat on a cool
night will cause local thermal turbulence and must be avoided.
Q. What if the daytime adjustment appears off after star collimating the primary mirror at night?
A. If star images look great, that is the bottom line. No further adjustment is necessary.
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