Manual Celestron NexStar EVOLUTION (page 11 of 15) (English)

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Telescope Maintenance

Your NexStar Evolution telescope requires little maintenance.

There are a few things to remember that will ensure your

telescope performs at its best.

Dew Prevention

Schmidt-Cassegrain telescopes are especially susceptible

to condensation forming on the front corrector lens because

the glass is immediately exposed to the outside air, just like

the windshield on your car. If the temperature outside drops

below the dew point, dew may form on the corrector within

minutes.

The easiest way to prevent dew is to add an optional dew

shield, available from Celestron, which shrouds the corrector

and keeps the air immediately surrounding the corrector

slightly warmer than the ambient temperature. If conditions

are more severe, a dew heater, commonly available from

other manufacturers, can be added to apply slight heat to the

corrector lens to keep it dry all night.

If dew has already formed on the corrector, point the tele-

scope downward and allow the telescope to dry. You can

also use a hairdryer to heat the corrector and evaporate the

moisture to dry the telescope.

Dew does not harm the telescope, but can lead to faster

dust build up. You should only cap the telescope when it’s

dry. Do not store the telescope if covered in dew. Allow the

telescope to dry ﬁrst.

Care and Cleaning of the Optics

Occasionally, dust and/or moisture may build up on the

corrector plate of your telescope. Special care should be

taken when cleaning any instrument so as not to damage the

optics.

If dust has built up on the corrector plate, remove it with

a brush (made of camel’s hair) or a can of pressurized air.

Spray at an angle to the lens for approximately two to four

seconds. Then, use an optical cleaning solution and white

tissue paper to remove any remaining debris. Apply the

solution to the tissue and then apply the tissue paper to the

lens. Low pressure strokes should go from the center of the

corrector to the outer portion. Do NOT rub in circles!

You can use a commercially made lens cleaner or mix your

own. A good cleaning solution is isopropyl alcohol mixed

with distilled water. The solution should be 60% isopropyl

alcohol and 40% distilled water. Or, liquid dish soap diluted

with water (a couple of drops per one quart of water) can be

used.

If moisture condenses on the inside of the corrector, remove

the accessories from the rear cell of the telescope. Place the

telescope in a dust-free environment and point it down. This

will remove the moisture from the telescope tube.

To minimize the need to clean your telescope, replace all lens

covers once you have ﬁnished using it. Since the rear cell is

NOT sealed, the cover should be placed over the opening

when not in use. This will prevent contaminants from entering

the optical tube.

Internal adjustments and cleaning should be done only by the

Celestron repair department. If your telescope is in need of

internal cleaning, please call the factory for a return authoriza-

tion number and price quote.

Collimation

The optical performance of your telescope is directly related

to its collimation. Collimation is the alignment of the optical

system. Your Schmidt-Cassegrain telescope was collimated

at the factory after it was completely assembled. However,

the telescope may have to be collimated after it’s transport-

ed. The only optical element that may need to be adjusted, or

is possible, is the tilt of the secondary mirror.

To check the collimation of your telescope you will need a

light source. A bright star near the zenith is ideal since there

is a minimal amount of atmospheric distortion. Make sure

that tracking is on so that you won’t have to manually track

the star. Or, if you do not want to power up your telescope,

you can use Polaris. Its position relative to the celestial pole

means that it moves very little thus eliminating the need to

manually track it.

Before you begin the collimation process, be sure that your

telescope is in thermal equilibrium with the surroundings.

Allow 45 minutes for the telescope to reach equilibrium if you

move it between large temperature extremes.

To verify collimation, view a star near the zenith. Use a

medium to high power eyepiece. It is important to center

a star in the center of the ﬁeld to judge collimation. Slowly

move in and out of focus and judge the symmetry of the star.

If you see a systematic skewing of the star to one side, then

re-collimation is needed.

To accomplish this, you need to adjust the secondary colli-

mation screw(s) that move the star across the ﬁeld toward

the direction of the skewed light. These screws are located

on the secondary mirror holder.

Secondary Mirror Collimation Adjustment Screws

Make only small 1/6 to 1/8 adjustments to the collimation

screws and re-center the star by moving the scope before

making any improvements or before making further adjust-

ments.

1. While looking through a medium to high power eyepiece,

de-focus a bright star until a ring pattern with a dark

shadow appears. Center the de-focused star and notice in

which direction the central shadow is skewed.

2. Place your ﬁnger along the edge of the front cell of the

telescope (be careful not to touch the corrector plate),

pointing towards the collimation screws. The shadow

of your ﬁnger should be visible when looking into the

eyepiece. Rotate your ﬁnger around the tube edge until

its shadow is seen closest to the narrowest portion of the

rings (i.e., the same direction in which the central shadow

is skewed)

3. Locate the collimation screw closest to where your ﬁnger

is positioned. This will be the collimation screw you will

need to adjust ﬁrst. (If your ﬁnger is positioned exactly

between two of the collimation screws, then you will need

to adjust the screw opposite where your ﬁnger is located).

4. Use the hand control buttons to move the de-focused star

image to the edge of the ﬁeld of view in the same direction

that the central obstruction of the star image is skewed.

5. While looking through the eyepiece, use an Phillips head

screw driver to turn the collimation screw you located in

step 2 and 3. Usually a tenth of a turn is enough to notice

a change in collimation. If the star image moves out of

the ﬁeld of view in the direction that the central shadow

is skewed, than you are turning the collimation screw the

wrong way. Turn the screw in the opposite direction, so

that the star image is moving towards the center of the

ﬁeld of view.

6. If while turning you notice that the screws get very loose,

then simply tighten the other two screws by the same

amount. Conversely, if the collimation screw gets too tight,

then loosen the other two screws by the same amount.

7. Once the star image is in the center of the ﬁeld of view,

check to see if the rings are concentric. If the central

obstruction is still skewed in the same direction, then

continue turning the screw(s) in the same direction. If you

ﬁnd that the ring pattern is skewed in a different direction,

than simply repeat steps 2 through 6 as described above

for the new direction.

A collimated telescope should appear symmetrical

with the central obstruction centered in the star’s

diffraction pattern.

Perfect collimation will yield a star image very symmetrical

just inside and outside of focus. In addition, perfect collima-

tion delivers the optimal optical performance speciﬁcations

that your telescope is built to achieve.

If seeing (i.e., air steadiness) is turbulent, collimation is difﬁ-

cult to judge. Wait until a better night if it is turbulent or aim

to a steadier part of the sky. Stars in a steady part of the sky

will be still, not twinkling.

Even though the star pattern appears the same on both sides of focus, they are asymmetric. The dark obstruc-

tion is skewed off to the left side of the diffraction pattern indicating poor collimation.

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Celestron NexStar EVOLUTION Manual

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