Telescope Use and Care

Everything presented in this guide should be regarded as general best practices. Always refer to the owner’s manual for your equipment for specific guidelines, recommendations, and procedures.

On This Page
Telescope Usage
Telescope Storage
Cleaning Optics
Additional Resources

Telescope usage

Sun safety

Never look directly at the sun with the naked eye or any kind of optic, such as a telescope or binoculars. Immediate and permanent eye damage may result. The only exception is if a proper solar filter is used. Do not point an unfiltered optic at the sun, as internal heat buildup can damage the optic or cause it to shatter or explode. Do not leave an optic unattended during the day where someone, especially a child, could move the optic and point it at the sun. See Solar Viewing and Eclipse Safety for more information.

Moisture

In The Field

Moisture can collect on telescope surfaces during usage as temperatures frequently fall to near the dew point at night. Do not wipe moisture or condensation from optical surfaces or scratching can result. To prevent dew formation on optical surfaces, use a dew shield or a special dew-prevention heater. If you are out at an observing site and moisture forms on the optics, use a hair dryer on its low setting at a safe distance, or point the telescope down until the moisture evaporates. When you are finished observing, replace all caps and covers to ensure safe transport.

At Home

Once at home, to remove dew and moisture from optical surfaces, use a hair dryer on its low setting at a safe distance, or place the telescope indoors in a location away from dust, smoke, pet hair, cleaning and cooking activities, with all caps, covers, eyepieces, and accessories removed for 12 to 24 hours, or until all moisture has evaporated. Dry eyepieces and accessories in the same manner. Once everything is dry, store as usual.

Care

Never touch the surface of a lens or mirror, because the acids in skin oil can degrade optical coatings over time. If you get fingerprints on an optic, clean it off using the methods described below.

Collimation

From time to time, reflectors need to be collimated. This is not necessarily a complicated process. In all cases, you should follow the instructions that come with your telescope or those that are provided online by your telescope supplier. For more information, see Collimation.

Telescope storage

Before storing the telescope, ensure the telescope, eyepieces, and accessories are dry. Replace all caps and covers on the telescope, eyepieces, and accessories after use. Obtain replacements for missing caps or make your own by using shower caps or bowl covers. A plastic bag or lint-free cloth held by a rubber band also works. The plastic canisters for 35mm film fit 1-1/4-inch focusers. Remove all batteries to prevent leakage and corrosion.

  • For all telescopes, cover the end of the telescope where light enters.
  • For refractor telescopes, plug or cap the eyepiece holder.
  • For reflector telescopes, plug or cap the eyepiece holder, and cap or cover the bottom end of the tube.
  • For truss-tube Dobsonians, both mirror sections should be covered or placed in bags.
  • For catadioptric telescopes, plug or cap the rear cell where the diagonal or eyepiece attaches.

The idea is to keep dust, insects, and moisture out of the telescope by covering or plugging any opening on the telescope. Small components like eyepieces and accessories should be kept in a protective box or storage case; if yours are missing, obtain replacements from a telescope accessory dealer. Do not leave telescopes inside a sealed car on warm days because excessive temperatures can damage the telescope’s internal lubrication and electronic circuitry, if equipped.

Cleaning optics

Proper use and storage will prevent dust and dirt accumulation, which will allow you to avoid the need to clean.

Cleaning should be done as rarely as possible because of the risk of scratching or damaging the optics. A slight amount of dust is not detrimental to the operation or performance of a telescope. Shining a flashlight onto the mirror at night to decide if it needs cleaning is not recommended because this test will make a clean mirror appear dirty. Touching causes scratches, and scratches are permanent. Leave the optics alone unless they are so dirty the need to clean is obvious.

When cleaning is necessary, start with the gentlest cleaning method, verify the result, and progress to the next more powerful method only if necessary.

  1. Clean loose particles with an air-blower puffer (available from telescope or optical accessory dealers) or an ear syringe (available from drugstores). Electric dusters may be used as long as they are clean and do not ingest particles that could be thrown against and scratch delicate surfaces.
    • Canned air dusters are not recommended because they are prone to discharge liquid, which could leave a residue.
    • Blowing with your mouth and breath is not recommended for the same reason.
    • Leaf blowers, air compressors, and vacuum cleaners in reverse are not recommended because their airflow is too powerful and could affect optical alignment, and they could throw particles against delicate surfaces, causing scratches.
  2. If particles remain after using air, use a lens cleaning brush (usually made of camel hair and available from telescope or optical accessory dealers). Use light strokes. Keep the brush capped when not in use to avoid contamination.
  3. The air and lens brush should remove almost all particles. Do not worry about a few remaining particles.
  4. For more severe build-up, or organic material such as fingerprints or eyelash oil, use a liquid cleaner only after using an air puffer and a lens brush.

Supplies for liquid cleaning

Wipes

Use lint-free lens wipes (such as Kimwipes) or untreated lens tissue.

Do not use paper towels, facial tissue, bathroom tissue, and nothing with scent or lotion.

Liquid

Use a liquid that is safe for multi-coated optics (such as Purosol), or distilled water and 99% isopropyl alcohol. Do not use household glass cleaner, eyeglass cleaner, or photographic lens cleaner.

Start with a 75/25 mix of distilled water to isopropyl alcohol (3 parts distilled water to 1 part isopropyl alcohol). If contamination remains after several cleanings, step up to a 60/40 mix of isopropyl alcohol to distilled water (3 parts isopropyl alcohol to 2 parts distilled water).

Procedure for liquid cleaning

Do not spray or drop the cleaning liquid directly onto optics, because it could seep into the edges and carry contaminants onto the optic. With an eyepiece, the liquid could seep inside the eyepiece and leave a residue where it is inaccessible.

Wear gloves to prevent skin oil from contaminating the cleaning process. Apply the cleaning solution to a wipe and then wipe the lens. On large telescopes and lenses, use low pressure strokes from the center of the optic straight to the outer edge and change wipes often. For small lenses and eyepieces, wipe in a circle and change wipes often. When finished cleaning, use a dry lens wipe to remove all liquid from the surface of the optic.

Special cleaning considerations

Eyepieces

Do not disassemble eyepieces. There is a risk of damaging coatings, chipping the glass, or not reassembling everything in correct alignment and orientation. Internal adjustments and cleaning should be done only by the manufacturer.

Refractor telescopes

Do not disassemble the telescope, and do not remove the front lens, due to the risk of chipping the glass and not reassembling everything in its original orientation and alignment.

Clean the front lens in place by using the cleaning methods described above. Internal adjustments and cleaning should be done only by the manufacturer.

Catadioptric (Schmidt-Cassegrain and Maksutov-Cassegrain) telescopes

Do not attempt to clean the inside of the telescope, and do not disassemble the telescope.

Clean the exterior surface of the front corrector plate by using the cleaning methods described above. Internal adjustments and cleaning should be done only by the manufacturer.

Reflector telescopes

To clean the mirrors in a reflector telescope, you will need to be confident about taking the telescope apart and putting it back together, and be confident in collimating (aligning) the telescope once it is reassembled. If there is any doubt about performing this process, leave the cleaning to trained individuals. With that disclaimer out of the way, here is how to clean the mirrors.

  1. Point the tube level (parallel to the ground) so nothing will fall out when the fasteners are removed. Remove the tube from its mount if possible and lay it on a workbench or table, because removing the mirror will change the balance of the tube and may cause it to move suddenly when the balance changes.
  2. Remove the screws that attach the primary mirror cell to the back of the tube. Carefully pull the cell out of the tube without touching the mirror.
  3. Wearing powder-free gloves, release the clips that hold the mirror to the cell, and carefully remove the mirror from the cell without touching the mirrored (shiny) surface. Place the mirror shiny side up on a clean soft towel.
  4. Remove the holder for the small secondary mirror inside the front of the tube, then remove the secondary mirror from the holder. Place the mirror shiny side up on a clean soft towel.
  5. Remove loose dust and grit from the mirrors by using a puffer bulb and lens brush.
  6. Fill a clean pan or bucket with enough room-temperature water to cover the mirror, a few drops of liquid dishwashing detergent, and an ounce of rubbing alcohol.
  7. Submerge the mirror shiny side up in the water and let it soak for a few minutes. Extremely dirty mirrors may need to soak for several hours.
  8. Wipe the mirror under water with lint-free lens tissues, using extremely light pressure, and proceeding in a straight line from the center to the edge. Change tissues after each stroke.
  9. Rinse the mirror under a stream of room-temperature water.
  10. Place the mirror on a clean soft towel, and dry it with a puffer bulb or hair dryer on low.
  11. Cover the mirror surface with a lens tissue, and leave it until it has dried completely.
  12. Reinstall the mirrors into their holders, install the holders in the telescope, and collimate the telescope.

A few additional References