Cleaning Optical Filters

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IPA and Acetone each have benefits and drawbacks. Generally, more active solvents (like acetone) attack a broader range of contaminants more quickly, but also evaporate more quickly than gentler solvents.  Acetone has excellent cleaning action but it dries very quickly and is thus much more susceptible to leaving behind residue on the surface of the optic. Furthermore, care should be taken when using Acetone around certain plastics and most adhesives, as these can also be dissolved by acetone.  IPA may require the user to wipe multiple times to remove all contaminants but dries slowly, reducing the risk of leaving a solvent residue on the optic.

Maintain continuous motion at a constant speed, but do not apply pressure to the swab or wipe. Some people prefer to clean using a "figure 8" pattern (shown below, left) while others choose to start in the center of the part and wipe outward in a spiral pattern (shown below, right). Each time the wiping motion comes to a stop, it is likely that residue will remain on the surface at that point, so maintain constant speed until the swab has moved off of the surface of the optic.

Note: The optimal wiping speed is determined by the solvent and environmental conditions – the faster the solvent evaporates, the faster you should wipe (hence Acetone requires a faster wiping speed than IPA, for example). When wiping at just the right speed, you should see signs of the solvent evaporating on the surface only a few millimeters behind the moving wipe tip.

3) Inspect filter. Use a room light or any bright light source to inspect the optic to ensure that it is clean. Tip, tilt, and rotate the optic while viewing it as close to your eye as you can focus. If contamination remains, start with a brand new wipe or swab and repeat step 2 above. For every new cleaning attempt, ALWAYS use a new wipe!

4) Repeat steps 1 – 3 for the other side of the filter if contamination exists. 

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