Cleaning procedures for SDSS 2.5-m telescope
optics
Sloan Digital Sky Survey Telescope Technical Note
19980908
Patrick Waddell, Mark Klaene
Contents
Introduction
The Sloan Digital Sky Survey 2.5-m telescope has a diverse set of
optics ranging from the large primary to a selection of c-mount
lenses used to assess the performance of the stray light baffles.
This document summarizes the cleaning guidelines to be followed
during the maintenance of these optics.
Cleaning guidelines for the 2.5m telescope
transmissive optics (the common, camera and spectrograph
correctors)
WARNINGS AND CAUTIONARY NOTES:
ALWAYS WORK WITH CLEANING FLUIDS IN WELL
VENTILATED AREAS
ELIMINATE ANY SOURCES OF IGNITION. KNOW THE LOCATION OF
THE NEAREST FIRE EXTINGUISHER AND CHECK ITS PRESSURE GAUGE IF
ANY.
DO NOT CLEAN OPTICS IN THE FIELD - OPTICS MUST BE
REMOVED FROM THE TELESCOPE AND CLEANED IN A CLEAN INDOOR WORK
ENVIRONMENT.
CLEANING MUST BE DONE WITH LIGHTING CONDITIONS SUCH
THAT SURFACE DUST AND PARTICLES CAN BE BRIGHTLY ILLUMINATED AND
CLEARLY SEEN.
AIR SOURCES FOR BLOWING SURFACE DUST MUST BE DRY AND
OIL-FREE AND HAVE AN IN-LINE FILTER FOR PARTICULATE
MATTER.
Materials:
All of these optics have hard AR coatings which can stand
up to strong cleaning agents. Reagent grade acetone or methanol or
isopropyl alcohol are highly recommended. Never return unused
cleaning fluid to the bottle and cap the bottle when not in use.
Distilled water
Large and small tissues such as Kimwipes
Preliminary steps for the common and spectrograph corrector:
The common corrector and the spectrograph corrector must
be cleaned while supported such that the optical axis is normal to
the floor.
To clean the correctors, the plastic emergency retainer must be
removed from the side to be cleaned. Before removal, mark the
orientation of the retainer relative to the corrector mount so
that it can be reassembled in the same orientation.
The retainer may be removed only from the side which is facing
upward. Do not invert the corrector with a retainer removed.
Only one retainer is to be removed at a time. After cleaning
each surface, the retainer is to be reinstalled immediately.
Instructions
1. Blow off surface dust using an air source meeting the
criteria discussed above.
2. Inspect for large dust particles. If present, moisten a
small tissue with the distilled water and coax the particles off
onto the tissue. Discard tissues after single use.
3. Inspect surface for water drop stains. If present, depending
on size, moisten a large or small tissue with the distilled water
and lightly wipe the area to remove the dried-on material. The
wiping should not be rubbing; the sum of gravity and adherence due
to water tension should be the dominant force between the tissue
and the glass. Allow to dry.
4. Moisten a large tissue and gently wipe the lens, starting at
the center and going out. There should be sufficient liquid that
the tissue and liquid can "glide together" across the surface, and
not so much that the fluid can flow away from the tissue on its
own. Discard tissues after single use and be sure that oils from
fingers does not contaminate the tissue which will contact the
glass.
5. Continue out until the area cleaned is within about 10 to 15
mm from the elastomer bond between the glass and the steel
mounting ring. Go no further; avoid getting the liquid in contact
with the elastomer bond.
6. Inspect the surface for streaks and remnant contamination.
If the lens was excessively dirty it may be necessary to repeat
steps 4 and 5.
Cleaning guidelines for the spectrographic fiber
harnesses
WARNINGS AND CAUTIONARY NOTES:
ALWAYS WORK WITH CLEANING FLUIDS IN WELL VENTILATED AREAS
ELIMINATE ANY SOURCES OF IGNITION. KNOW THE LOCATION OF THE
NEAREST FIRE EXTINGUISHER AND CHECK ITS PRESSURE GAUGE IF ANY.
AIR SOURCES FOR BLOWING SURFACE DUST MUST BE DRY AND OIL-FREE
AND HAVE AN IN-LINE FILTER FOR PARTICULATE MATTER.
Materials
The fiber harness optical surfaces have no coatings and can stand
up to strong cleaning agents such as alcohol and acetone. Reagent
grade methanol or isopropyl alcohol are highly recommended. Also, one
must be careful to preserve the cleanliness of the alcohol. Never
return unused alcohol to the bottle and cap the bottle when not in
use.
Cotton swabs
Instructions
1. Harness cleaning should be done with good lighting
conditions and while viewed under magnification.
2. The selected cleaning fluid should be applied with clean
cotton swabs. Although a single swab can probably be used for
several ferrules, be careful to always clean with a fresh part of
the swab.
3. During cleaning, strokes should all be made in the same
direction across the face of v-groove blocks and the polished ends
of the ferrules. This pushes the dirt to one side rather than
moving it back and forth across the optical surface.
4. Let fibers air dry.
5. Check for remnant cotton swab fibers and blow off using an
air source meeting the criteria discussed above.
Cleaning guidelines for miscellaneous small
optics (c-mount lenses, etc.)
WARNINGS AND CAUTIONARY NOTES:
ALWAYS WORK WITH CLEANING FLUIDS IN WELL VENTILATED AREAS
ELIMINATE ANY SOURCES OF IGNITION. KNOW THE LOCATION OF THE
NEAREST FIRE EXTINGUISHER AND CHECK ITS PRESSURE GAUGE IF ANY.
NEVER USE ACETONE ON COMMERCIAL OPTICS - IT COULD REACT WITH
PAINTS OR PLASTIC ITEMS.
DO NOT CLEAN OPTICS IN THE FIELD - OPTICS MUST BE REMOVED FROM
THE TELESCOPE AND CLEANED IN A CLEAN INDOOR WORK ENVIRONMENT.
CLEANING MUST BE DONE WITH LIGHTING CONDITIONS SUCH THAT THE
SURFACE DUST AND PARTICLES CAN BE BRIGHTLY ILLUMINATED AND CLEARLY
SEEN.
AIR SOURCES FOR BLOWING SURFACE DUST MUST BE DRY AND OIL-FREE
AND HAVE AN IN-LINE FILTER FOR PARTICULATE MATTER.
Materials:
All of these optics have hard AR coatings which can stand
up to strong cleaning agents. Reagent grade methanol or isopropyl
alcohol are highly recommended. Never return unused cleaning fluid
to the bottle and cap the bottle when not in use.
Distilled water
Small tissues such as Kimwipes
Instructions
1. Blow off surface dust using an air source meeting the
criteria discussed above.
2. Inspect for large dust particles. If present, moisten a
small tissue with distilled water and coax the particles off onto
the tissue. Discard tissues after single use.
3. Inspect surface for water drop stains. If present, moisten a
tissue with the distilled water and lightly wipe the area to
remove the dried-on material. The wiping should not be rubbing;
the sum of the spring tension of the tissue and adherence due to
water tension should be the dominant force between the tissue and
the glass. Allow to dry.
4. Moisten a tissue and gently wipe the lens, starting at the
center and going out. There should be sufficient liquid that the
tissue and liquid can "glide together" across the surface, and not
so much that the fluid can flow away from the tissue on its own.
Discard tissues after single use and be sure that oils from
fingers does not contaminate the tissue which will contact the
glass.
5. Continue out until the area cleaned is within about 10 to 15
mm from the elastomer bond between the glass and the steel
mounting ring. Go no further; avoid getting the liquid in contact
with the elastomer bond.
6. Inspect the surface for streaks and remnant contamination.
If the lens was excessively dirty it may be necessary to repeat
steps 4 and 5.
Cleaning guidelines for the 2.5m telescope
reflective optics
WARNINGS AND CAUTIONARY NOTES:
ALWAYS WEAR EYE PROTECTION.
NEVER LOOK INTO THE APPARATUS
NEVER POINT APPARATUS AT YOUR EAR OR ANY OTHER PART OF YOUR
BODY.
NEVER POINT APPARATUS AT ANOTHER PERSON.
NEVER STORE OR TRANSPORT CO2 TANKS IN DIRECT SUNLIGHT OR A WARM
CONFINED SPACE SUCH AS THE TRUNK OF A CAR. SUCH HANDLING CAN
RESULT IN EXPLOSION, ASPHYXIATION, AND DEATH.
ALWAYS TIE DOWN GAS TANKS.
ALWAYS WORK IN A WELL VENTILATED AREA. REMEMBER, CO2 IS A
RELATIVELY HEAVY GAS AND WILL DISPLACE BREATHABLE AIR. FAILURE TO
PROVIDE ADEQUATE VENTILATION CAN RESULT IN ASPHYXIATION AND
DEATH.
THE APPARATUS IS INTENDED FOR USE ONLY WITH CO2 AT 750 PSI.
NEVER USE APPARATUS NEAR MATERIALS WHICH CAN BE IGNITED BY A
SPARK. THE APPARATUS CAN BUILD UP STATIC ELECTRIC CHARGE ON ITSELF
AND THE PIECE TO BE CLEANED.
DO NOT CONTACT COLD METAL PARTS WITH BARE SKIN WHEN USING THE
APPARATUS. FROSTBITE CAN RESULT. USE HANDGRIP, PLASTIC VALVE KNOB,
AND WEAR INSULATED GLOVES.
READ THIS BEFORE ATTEMPTING TO USE APPARATUS!
OBSERVE ALL CAUTIONS! RETAIN THIS INFORMATION FOR FUTURE
REFERENCE
Instructions
1) Use at least 99.99% pure medical grade carbon dioxide
(CO2) at a nominal tank pressure of 750 psi. Some critical
cleaning operations will require even better grades of gas, and
purities of 99.9999% are available. Test all cleaning procedures
first on a small expendable sample.
2) Make sure CO2 tank has a siphon or else tip tank on its side
so that liquid carbon dioxide can enter apparatus. ALWAYS TIE GAS
TANKS DOWN! Also, it is best to select a larger tank over a
smaller one. Some contaminants come off the inner wall of a tank
and a large tank has a smaller surface to volume ration than a
smaller one. A 40 to 50 lb. tank is best.
3) Remove aluminum foil covers on each end of apparatus and
make sure plastic or cardboard washer is in CO2 nut (tank end of
line; see p. 5) before connecting apparatus to tank. Tighten
carbon dioxide nut to about 10 ft.-lbs.
4) Make sure all valves are closed before use. Then crack tank
valve open slowly. Next, slowly open point-of-use valve (hand held
valve) by not more than 1/16th of a turn. At first only CO2 gas
will vent from the apparatus. Wait at least 3 seconds for the snow
stream to begin. Longer delivery lines may require a longer wait.
Adjust flow at the point-of-use valve for your application.
5) Before first use of the apparatus, let CO2 flow through the
apparatus for at least 20 seconds. This will purge the line of any
slight residual dirt or oils.
6) Occasionally CO2 tanks are badly contaminated with oils, so
test the system on a test object (such as a clean microscope
slide) first before each new gas tank is used.
7) Never dwell on one small part of an area to be cleaned. All
industrial and medical grade CO2 is contaminated with small
amounts of oil, which can leave a spot over a prolonged period of
time. Only "spectral grade" gases have non-detectable hydrocarbon
levels. Typically, the jet of CO2 snow and gas emerging from the
apparatus should be about 12-18 inches long and should make an
angle of 45 (to the surface to be cleaned. The distance from the
exit end of the apparatus (see p. 5) to the surface should be
about half the jet length. The jet should be swept across the
surface at a rate of at least 1 square foot in 20 seconds. Further
bombardment of the surface with carbon dioxide snow will not
appreciably improve surface cleanliness.
8) After use, shut tank valve. Then open point-of-use (hand
held) valve to bleed high-pressure CO2 from the apparatus. When
hissing stops, shut point-of-use valve for storage. This latter
precaution will prevent dirt from entering the system, and the
unexpected discharge of high-pressure gas the next time the system
is started up.
9) If apparatus should plug for any reason during operating,
shut all valves, bleed the apparatus (as in step 8 above), let
apparatus return to room temperature, then try to use apparatus
again. If the apparatus will not bleed let the apparatus reach
room temperature with all valves shut; then bleed the system. If
none of these procedures is successful in bleeding the system, you
will have to loosen the CO2 nut VERY SLOWLY AND CAREFULLY to
relieve the pressure. If damage is permanent, label apparatus for
repair and inform personnel responsible for equipment.
10) Never run the carbon dioxide snow cleaning apparatus for
more than 5 minutes continuously. After such a time period, stop
work, bleed the system (as in step 8 above), and allow apparatus
to return to room temperature. You may then resume work. If ice
builds up on the apparatus during use in a humid environment, stop
work, bleed the system (as in step 8 above), and allow apparatus
to return to room temperature. You may then resume work.
11) When the pressure gauge reading drops below 750 psi, the
liquid CO2 is depleted and it is time to get more CO2.
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