Sunday, May 8, 2011

Cleaning Lenses and Optics Part I: Best Practices

Here's my first ever guest post, from Spencer Luster at LightWorks. Enjoy ...

Dust happens. As does debris, fingerprints, and occasionally the nasty products of a sneeze. When it does, it might be time to clean your system optics such as lenses, mirrors and windows.

The FIRST STEP, writ large, is to blow off as much stuff as you can using clean, dry air from an empty squeeze bottle.  Then do it again -- seriously. The idea is to remove as much abrasive material as possible before you start in with lens tissue and solvent, otherwise you risk scratching something you shouldn't.

When it comes to cleaning there are several rules to follow. I'll call these "Best Practice" rules while wearing an optical engineer's hat. Later, we'll talk about field expediency advice.

1)       Use clean, soft, lint free tissue. I highly recommend a product called Pec*Pads from Photographic Solutions. [] In twenty-five years I've found no better product.
2)       Wear powder free latex, nitrile or PVC gloves. (Use ONLY latex for acetone.)
3)       Use the purest solvent possible. For alcohols or acetone use reagent grade or better. Don't use pharmacy or paint store solvents!
4)       Use the mildest solvent that still does the job.
5)       Use a solvent that dries very quickly. (Otherwise, it picks up contaminants from the air and leaves a residue when it finally does dry.)

Those last items are contradictory. Distilled or de-ionized water is as mild as it gets, but is poor for oil and grease and takes a long time to dry. Acetone dries quickly, is effective on many contaminants, but can attack certain older coatings and more importantly adjacent paint or plastic. Even the vapor can cause damage. Isopropanol and methanol are good mid-range candidates. Light Works prefers Eclipse brand of ultra pure methanol which is also available from Photographic Solutions. It's pricey, but worth it!

Never squirt or spray the solvent; it's too difficult to control where it goes. Place a few drops on the tissue to moisten it – don't soak. At this point you can follow one of the two classic cleaning methods.

Spiral: Start at the center of the optic and gently wipe in a single, continuous spiral to the outer edge.

Drag: Start at one end and gently drag the moist tissue across the surface. This is preferred, but can be difficult for mounted lenses.

For either case, only make one pass per tissue. Otherwise, you'll just redistribute the dirt. Repeat until clean.

copyright © 2011  Spencer Luster, LIGHT WORKS LLC

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