15
Maintaining the NGT-12.5
The following maintenance routines will preserve the accuracy and reliability of your telescope and help prolong its
life.
Cleaning Front-Surface Mirrors
Never wipe a dry mirror with a lens tissue or other material, as this will scratch the surface coating.
Follow these steps to properly clean the NGT mirror and preserve its life. Do not clean the mirror too frequently. If
properly handled and protected from dirt, the mirror should require cleaning only once or twice a year. The mirror can
be cleaned without removing it from the cell, however the cell should dry completely before it is returned to the
telescope.
First, gather the following materials:
A large box (50 count) of soft, absorbent cotton balls.
Be sure the cotton is 100% pure (such as Red Cross). Other cottons may contain wood pulp or other foreign matter
that will scratch the mirror surface.
Mild detergent (such as Dawn)
Distilled water
Acetone, ethanol or compressed air in a can.
Observe all cautions and warnings on the labels.
Acetone and its vapors are harmful.
Rubber gloves are
recommended to prevent absorption of acetone through the skin. Acetone is available at most paint or hardware
stores. (If acetone is used, remove the central dot prior to cleaning, as the acetone will dissolve the adhesive
causing it to run and stain the mirror surface.
The dot is required for collimation.
Replace it after cleaning.)
Ethanol—also known as ethyl alcohol, 200 -proof alcohol or drinking alcohol—may be substituted for acetone.
Do
not use rubbing alcohol on your mirror surface
, as it adversely reacts to the aluminized surface and can ruin the
mirror coating over time. Compressed air can also be used as long as you are careful to keep any propellant from
being discharged onto the mirror.
A tub large enough to allow the mirror to be fully immerse.
Fill the tub with a solution of lukewarm distilled water and mild soap. Rinse the mirror by pouring distilled water,
flooding the surface to remove loose dirt and dust—if large particles are not removed they will scratch the mirror
during the cleaning process. Next, immerse the mirror in the tub and allow it to soak for 1.5 to 2 hours. Let the liquid
do the work as much as possible to minimize contact with the mirror surface. Soaking overnight with pure distilled
water will loosen almost any particles and will not hurt the glass or mirror surface.
After the mirror soaks, raise it to within 1cm (1/2-inch) of the water's surface and use the cotton balls to remove any
remaining particles. It is best to roll the cotton ball over the mirror's surface—with the leading edge rolling upward—
allowing the particles to be lifted away. Replace the cotton ball after one rotation, thus preventing the dirtied cotton
from contacting the mirror surface. Do not apply pressure to the cotton—simply allow the weight of the wet cotton to
do the work. Clean the entire surface of the mirror in this fashion. You may find it easiest to work from the mirror's
center, spiraling outward.
Lift the mirror out of the tub and place it at an angle to drain as you rinse. Rinse with distilled water to remove all soap
solution from the mirror surface.
Finally, before the mirror can dry, rinse again with acetone or ethanol or use compressed air to chas e the water beads
from the surface.
Acetone and ethanol will evaporate to leave a pristine surface.
(If necessary, remove any
remaining water spots by dabbing them lightly with clean, dry Red Cross cotton. Dab, but do not wipe.)
Summary of Contents for NGT-12.5
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