I have just learned an amazing method for cleaning optics that I want to pass on.
I attended a class on some laboratory analyzers that measure particle sizes (all the way down to particles that you cannot see) using three lasers, lenses, and front-surfaced mirrors, in addition to the sensors in the optical path. As you may imagine, the optics in these machines are extremely sensitive to dust, scratches, and anything deposited on them.
The surfaces of the front-surfaced mirrors (the mirror surfaces are actually deposited on the outside of prisms) are probably the most delicate of the optical surfaces when it comes to cleaning. If they are dirty, most folks using lens tissues and lens cleaning fluid would tend to create a haze of tiny scratches on the very delicate mirror coatings. Thus, the lab supervisor experimented quite extensively and came up with the following procedure that is astoundingly simple and works perfectly every time for him. He uses it for every lens in the system.
Before I progress, I must say that the lenses are not like camera lenses. Several are single elements which are mounted to adjustable stands. The stand can be removed and reinstalled on reference pins, and the lens can be removed still attached to the stand without affecting the adjustments themselves.
The cleaning procedure requires removal of the lenses or mirrors from the analyzer. Thus, you are not going to be able to use this procedure for an SLR’s mirror.
Here are the steps:
1. You will be working at a sink with either de-ionized water or highly filtered water available through a faucet.
2. The key product is Dawn dish detergent. Do not substitute other brands. The contents of Dawn were determined to be ideal for this work, and other detergents are not the same.
3. After getting all the cleaning materials and the lenses/mirrors to be cleaned together near the sink, wash your hands thoroughly using the Dawn dish detergent.
4. Rinse the optical device a gentle stream of water – use no significant pressure to the stream.
5. Apply a small blob of Dawn detergent to the surface.
6. While holding the optical device under the running water, use your (cleaned) finger to swirl the Dawn around and clean the entire surface.
7. While holding the optical device under the running water, keep running your finger over the whole surface until you finally feel a “squeaky clean” surface under your finger. The feeling is very much like that when you run your damp finger around a fine crystal glass and make it “sing”.
8. The optical surface is now clean, and the trick is to be able to get it dry without touching it.
9. Holding the optical surface at an angle, you let the water stream trickle over the highest edge and start pulling the optical surface up and away from the water stream. The water will sheet over towards the lower edge. This is a tricky step, but a little practice will make it work for you. At the very end of this process, you will have a totally dry surface except for the lowest edge. Remove the optical surface totally from the water stream.
10. Using the corner of a lens tissue, just touch the remaining water at the edge of the optical surface and let it “suck” the remaining water off without touching the optical surface itself.
I would not suggest using this procedure for many camera lenses, as you may get water inside the lens. However, it is an absolutely perfect procedure for photographic filters (glass ones, that is), front-surface mirrors, and lenses that you can get to the sink and not risk damage from the water.
What damages so many optical surfaces is bad cleaning procedures. Particles that may be too small to see often get ground into the surfaces of lenses, filters, and front-surface mirrors, and cause tiny – but significant – scratches in the surfaces. This procedure, when done properly, totally eliminates this. In addition, the haze (often colored – usually tending to be purple) that you often see on a freshly “cleaned” lens is never seen with this procedure.
