Cleaning Optical Surfaces

Cleaning optical surfaces is a delicate endeavor, potentially dangerous for the equipment.
It must only be done when really necessary (organic dirt o heavy dust).

We might have to clean lenses or mirrors.

Cleaning Fluid Preparation:

For Lens Cleaning:

Thoroughly clean a 1,000 ml (1 quart) spray bottle with distilled water.
Label it "Lens Cleaning"
Mix 850 ml of distilled water with 150 ml of ethyl alcohol, or isopropyl, if unavailable (a 15% solution).
Both should be of the highest purity (alcohol 99%-97%), from a pharmaceutical supplier.
Add 2 drops of a mild liquid dishwashing soap, without color or fragrance.

An excess of soap could leave a visible residue.

For Mirror Cleaning:

Thoroughly clean a 1,000 ml (1 quart) spray bottle with distilled water.
Label it "Mirror Cleaning"
Fill it with distilled water of the highest purity, from a pharmaceutical supplier.
Add 2 drops of a mild liquid dishwashing soap, without color or fragrance.

Note we do not use alcohol for cleaning mirrors, it could damage the aluminum coating.
An excess of soap could leave a visible residue.

Surface Preparation:

Clean the surface with an air jet and a very soft brush to eliminate all dust.
Make sure both the air and the brush are completely clean.
Spray it with the cleaning fluid, letting it run to a cotton ball or a piece of absorbent paper.
Make sure you do not wet the optic's mount.

Surface Cleaning:

Spray on a cotton ball and apply it with minimal pressure on the surface, then absorb the fluid by contact with a clean cotton ball.
Repeat until you get the whole surface clean. Do not wipe it, you might scratch it!

Notes:

Do not disassemble a refractor telescope or SCT to clean internal surfaces, send it to the manufacturer.

Clean the objective of a refractor or the corrector plate of an SCT spraying up from below, so no water can get into the tube.

Reference:

Cleaning Optics (www.astro-tom.com)

This page was updated in September 25 '03, June 18 '14

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