Cleaning Eyepieces
Paul Gustafson, Williamsburg, VA
I'm one of the obsessive eyepiece cleaners, both in the field and after each observing session. I find the smallest amount of eyelash oil or dirt has a dramatic deleterious effect on the image contrast. I've been carefully following this procedure for many years and the coatings on my eyepieces are pristine, no scratches or signs of wear. I always use the following:
1) Blow off any particulates with a large ear bulb syringe.
2) Lightly brush off any stubborn particles with a sable artist's brush.
3) Blow off again to remove anything released by the brush.
My cleaning solution is Kodak lens cleaning solution. It's a known entity with a long track record of safety on very expensive coated camera lenses. I've used the Zeiss clean-ing solution, also, but the Kodak usually works better for me. You may find that one solution may be more effective than the other on certain contaminants.
4) Use surgical roll cotton, extremely soft with no particulates. Very inexpensive, available from drug stores or medical supply stores.
5) Avoid using too much cleaning solution. You want to prevent any solution wicking around the edge of the eye lens into the innards of the eyepiece. An old photog taught me a trick -- shake the Kodak cleaning solution so it has a head of suds, then hold the bottle upright and dispense a dab of foam onto the cotton. It is the perfect amount of fluid.
6) Roll the cotton against the direction of movement across the glass, so the leading edge lifts any particles off the glass and doesn't rub them across the glass surface. Replace the cotton after one complete rotation. Use zero pressure, only the weight of the cotton.
7) I make my own q-tips by twirling a wooden applicator stick (can be purchased at medical supply stores, same place as surgical roll cotton) while dipping the tip lightly into the surgical roll cotton. Once you have picked up a dab of cotton with the tip, roll it between your fingers to shape it. With a little practice you can make them look like they came out of a factory and can customize the size to whatever is appropriate for that particular eyepiece. You can make one the size of a fist for corrector plates or objective lenses if you wish. For those tiny eye lenses in short focal length orthos, you can snap an applicator stick in half and use the fine point to twirl up a dab of cotton to make a q-tip as small as 1 mm.
8) Final puff of air to remove any lint left by the surgical cotton.
Roland Christen had the following to say about dirt on eyepieces in the Yahoo Astro Physics users group: "Eyepieces are mega-mucho far more affected by tiny sleeks and surface contaminations than telescope mirrors or objective lens surfaces. The images are highly con-centrated and pass through only the tiniest fraction of the eyepiece lens element. A tiny defect on that surface will be very large compared to the image. A dust grain will be a mountain on Mars. Anyone who has seen the effect of a mote of dust on a CCD chip cover plate will know instantly what I'm talking about. That same dust mote or sleek will have zero effect at the front objective."
I can't bring myself to use one of those lens pens, just can't see rubbing anything across the coatings. All it would take is just one tiny particle...
Paul Gustafson is a member of the Back Bay Amateur Astronomers and the Skywatchers Astronomy Club at NASA/Langley Research Center (He doesn't work at NASA, but is just a member of their club.)
