This article was contributed by Dr. Clay Sherrod of the Arkansas Sky Observatory ( A few notes were added by OPT if it was felt that clarification was needed, etc. OPT wishes to thank Dr. Clay for his continued support of the amateur astronomical community. Visit the ASO website for other informative articles pertaining to the hobby and science of astronomy.




Telescopes are made to be used outdoors, obviously. But even made that way, the worst thing that can happen to them (unless you are careless) is the effect of outdoor conditions.

MOISTURE is the biggest natural enemy of a telescope. TEMPERATURE is the second. HUMAN USE is a close third to numbers One and Two.

Outdoor Moisture: Every time we take our scope outdoors we are subjecting it to moisture; I correspond with one nice fellow from Scotland who actually observed the moon (for a project) while it was raining on his balcony. Not a particularly good idea for most of us....Don't do that.

Normal moisture, collecting somewhere on the telescope, will happen nearly every time you take the it out. You will have either DEW or FROST; they are both the same and form when the AIR TEMPERATURE drops to, or below, the "dew point" that the weather man always mentions on your local forecast. Expect dew or frost; it's one of those necessary evils of the hobby. Note that dew nor frost rarely form when a brisk breeze is blowing at night.

Below are some common-sense care tips for dealing with outdoor condensation:

1) NEVER wipe off your optics no matter how much dew or frost gets on them; bring your scope in or cover it up (with a pillow case or sheet) if it gets that bad.

2) Always monitor your objective lens to see if dew is forming; never let it get so bad as in 1), above. The best way to monitor is with a flashlight aimed ACROSS, not directly in front of, the glass. If you see a cloudy film, then you may as well quit unless it is a special event such as an eclipse.

3) If the OUTSIDE parts (the fork arms, tube, tripod, etc. - NON OPTICAL) get moist, don't worry about it until you bring it'll drive yourself crazy wiping it off.

4) Keep eyepieces covered in their little cases until ready to use, and once done replace them back into the cases.

5) All of your charts and sky maps should be covered for protection from dew as well; they will form dew quicker than your telescope.

6) Keep moisture AWAY from all electronic components, such as your hand controller and DC or AC inverter if you are using one. Even the electrical plug connection should be raised above ground level if the grass is beginning to get wet.

7) When you wish to come in from a night of observing and dew or frost HAS FORMED on your lens, DON'T COVER UP THE FRONT LENS! However, ALWAYS plug up the eyepiece holder so that moisture cannot condense INSIDE the telescope! Editor's Note: A 35mm film canister works beautifully for this purpose.

8) In winter months, if moisture HAS NOT formed on your lens, cap it up securely (do not overtighten the lens cap) and bring indoors with all optics covered. Condensation will immediately form on the outside of the telescope and mount; don't worry about this right now.

Editor's Note: Let your telescope sit indoors, with all caps on, until the telescope dries. This can take a few hours. Do not peek at the corrector plate! Go take a nap, play with your kids, or watch a movie and leave it alone. Once the telescope has warmed up and reached the temperature of everything else indoors, you can take off the lens caps, check out your telescope, and then begin the process of putting it away.

9) During other (non-winter) months, if moisture DOES form on the lens, bring it in uncovered and let it evaporate NATURALLY and slowly indoors. If you can see any significant - and I mean significant - spotting from the moisture after the optics have had time to dry completely, clean the lens carefully using the cleaning method described elsewhere on this web site.

10) No matter whether the moisture forms outdoors or indoors, after bringing in the telescope, use a soft cloth (I prefer Terrycloth) towel and gently wipe down all metal and plastic parts (NOT OPTICS) until free of water.

11) Electronic components outdoors - Your electronic components are temperature-sensitive and must be protected from extreme heat and cold. In very cold weather, electronic hand controls can do strange things and they should be kept warm whenever possible. Many people keep them (yes they do) in small can coolers when not in use, and carry them in their pockets if going inside for an extended time.

12) "Parking the Telescope" - if you are at a star party, camping, or even at home and know the weather is going to be nice again tomorrow night and do not want to bring the telescope indoors, follow these rules to protect the telescope:

a) if it is not going to be raining, or if the winds are not excessive, it is perfectly okay to leave the scope out, provided you have run all the burglars away first.

b) Make sure your power connections are undone and your off-on switch is "off".

c) Cover the telescope with a soft, clean pillow case or cotton sheet.

d) Cover the sheet or pillow case with a small plastic tarp with elastic "tie downs". Attach those to something firm on the ground. DO NOT tie the plastic tightly around the telescope or moisture will condense during daylight hours!

e) Uncover telescope about 1-2 hours prior to use to equalize for the evening.

13) Optics on a hot day - if you are going camping or getting ready for a night-long star party and want to set up early there is a very important rule: NEVER LEAVE YOUR TELESCOPE in direct sunlight for a long period of time. Just like in a closed car, the inside of your optical tube assembly is capped off from ventilation and will become VERY hot! The baffle on the secondary uses adhesives to hold it in place and there are cements used in various places throughout your telescope. Always protect it from HEAT outdoors. When transporting in an automobile USE THE CHILD-CARE RULE: "Would I leave an infant in conditions like this?"



To me, the worst treatment that a telescope gets is NO treatment at all....not ever using it. This allows dust to accumulate, and - yes - dust does settle inside of the fork arms and the drive base, causing problems in motion over long periods of time.

In addition, a stored telescope tends to redistribute its lubricants (the drive gear, the bearings, the fork arm drives in the ETX EC, and even the focus mechanism) when it sits in one position for a while. Gravity - a very strong force over time - will take the lubricant and put it where IT wants it. You are left with a very dry driving system, except in one spot.

Even if you do not use your telescope to observe with for an extended period of time, go in where you have it stored and move it around occasionally....turn on the motors and slew around. Focus on nothing in particular. Let the telescope know it is still loved.


Dust needs to be kept off of your telescope; you bought a beautiful instrument, keep it that way! Remove dust gently and ALWAYS with a soft damp cloth. Do not use "Pledge" or any other dusting compound! Use water, and only a little bit of that. NEVER use window cleaner on ANY part of your telescope! Use only the optical solution described on the web site for your optics and only use water for the rest of the telescope. Water will restore the brilliant shine and color to your tube assembly. Once the dust has been removed from the telescope, gently buff it with a soft towel to make it shine like new (I use an old diaper).

REMEMBER.....the more you take care of your telescope, the more it will take care of YOU in the future. You have made a great investment, so always treat the telescope with my "baby rule:"


One last editor's note: Make sure that the foam inside of your telescope case is TOTALLY DRY before putting your telescope in and closing her up! The fungus and rust that could result will make you wish for the days when all you had to worry about was a little dew!