Cleaning Telescope Optics - Mirrors Lenses

A telescope's greatest nightmare is the possibility of having an over passionate owner who constantly attempts to keep their telescope optics as speck clean as possible. These guys should never use their telescope in the first place and a telescope would rather they leave it stored in a secure vacuum chamber. Cleaning telescope optics should only be done when necessary (after you use your tube as a human cannon launcher or a trip down to a coal mine), and so for the rest of us, here's some advice.

**Warning** If you own an air spaced refractor, please contact your manufacturer for specific advice on cleaning. Do NOT remove refractive lenses from the lens holder as there are very few individuals who have the experience and equipment to properly handle these complex lenses. This advice also applies towards most complex eyepieces. If you doubt your abilities in any way, then you're probably right. Cleaning that is done properly will not degrade the optical performance of your telescope.

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Since most refractors and Cassegrain telescopes are closed systems, it is not necessary to clean the inner lens surfaces. Cleaning the field (R1 or outer) lens may be done with the lens in the cell attached to the optical tube. If you need to, remove the lens cell from the tube. It is better to leave the lens retaining ring in its place, and progess with the lens in the cell. Try not to make any adjustments to the retaining ring. It is normal to hear a slight rattling sound if you shake a refractor objective in its cell since the factory set spacing accommodates expansion of the lens due to typical environmental temperature changes.

Most Newtonian telescope mirrors are held within a Mirror Cell which can be removed in one piece from the telescope. Pay careful attention to the orientation of the lens/mirror cell within the tube. You may also wish to mark the tube and lens cell where they meet with a dab of liquid paper/whiteout. Just be careful that your cleaning procedure doesn't remove the index marks. Set up the optics onto a clean well-padded platform, with the surface of a mirror or lens to be cleaned upright. After that, loosen the retainers on the lip of mirror and remove them, while taking extra precaution not to tilt or rotate the mirror.

STEP 1: Purchase or build a hood to protect the telescope when its not being used.
STEP 2: Always keep the lens cap on when not using the telescope. Make a lens cap for your eyepiece out of the top of a plastic film canister.
STEP 3: Store your telescope facing downwards to prevent dust from collecting on the lenses.
STEP 4: Extra eyepieces and lenses should be stored in sealed plastic bags or food containers.
STEP 5: Always avoid touching the mirrors or lens. Your skin contains dirts and oils which can damage them. 
STEP 6: If you did touch it, clean the lens immediately.
STEP 7: Unless done properly with great care and gentleness, the process of cleaning lenses or mirrors often causes tiny scratches called sleeks.

**Dirty telescopes can always be cleaned, but scratched optics can only be replaced. Do not attempt to shine a light down the telescope tube and clean it on the basis of what you see there. If you see it this way, it will always look dirty. You normally end up doing more damage then harm cleaning this way.

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