Advisory on Cleaning Filters

[JessePinkmanYo]

This is an advisory on cleaning and upkeep of filters and by extension lenses wherever applicable. Much of this was written in response to queries from buyers of my filters but others may find it useful too.

Many of us frequently purchase filters second hand wherein the filter comes brushed in all sorts of packaging material and loaded with dust, lint and/or debris that lends itself to fungal growth. It becomes necessary to clean these filters before using, not only to remove matter that may lead to fungal growth but also to get the best resolution out of the filter. This becomes especially important when :-

(1) There are traces of fungal infestation that need to be arrested immediately

(2) There is visible debris lodged at the edges which could lead to fungal growth

(3) The filter is bought second hand and has come in direct contact with plastic, bubble wrap, high density foam or packing cardboard leaving smudges and "organic" fungus friendly debris

(4) The filter is of "unknown origin" and could have been used under "unfriendly" circumstances like exposure to seawater/spray or having been used on lenses already having fungus.

I will not count air blowers as cleaners since they are just the first step and quite insufficient by themselves for cleaning filters. But once the large particles have been blown off, there are two alternatives :-

(1) The Ezee/soft soap bath - Warm water with light soaps like Ezee mixed in is the less aggressive yet effective method of cleaning filters. A 30-60 second treatment will usually do the trick followed by gentle drying. There are however, a couple of things you have to be very careful about. One, the water should be as pure as possible, distilled preferably. Otherwise it can leave residue upon drying. And two, drying is a tricky task given the fungus friendly nature of water. It has to be quick and thorough.

(2) The Isopropyl Alcohol bath - Inspite of reservations regarding use to alcohol for cleaning, it remains the easiest, most widely used and the most effective method for cleaning filters and lenses long as you know what you are doing. Again a couple of things to note - use clinical grade alcohol (I recommend something like Merck) and whatever you do, dont rub too much. Thankfully, most modern filter/lens coatings are able to stand this much better than their earlier counterparts.

Neither of the above treatments will damage coatings on most filters as long as they are not done too often/overdone or wiping is not too aggressive.

PS - The oft overlooked part in upkeep of filters (and lenses) is the upkeep of lens caps. Since these are in closest contact with the filters/lenses and also most susceptible to trapping dust/pollen or fungus prone material from pockets, bags, etc, they need to be cleaned just as regularly and thoroughly. Thankfully, thats much easier to do !

[Bharat Varma]

CPL and Variable ND filters need special care to prevent anything getting into the junction between the two elements.

Question: Why do filters kept under controlled humidity still develop a slightly oily coating on the exposed surface over a period of time (if attached to a lens)?

[JessePinkmanYo]

Almost forgot about such "special" filters. Any filter which is made by sandwiching layers of optics (variable ND/CPL) or dyes (color/bandpass filters) or of absorptive nature (some IR-Cut filters) will be always be trickier to clean. Those oily coatings/smudges acquired over time can be of various origins like lubricants used betwixt the rings or low viscosity cleaning agents or decay of chemicals used for pasting the layers or most commonly from use of cleaning fluids that leach at the edges of the glass. This can happen both inside or outside of dehumidifiers.

Bathing such filters in entirety is NOT a good idea. One approach (assuming the elements can be separated as in variable ND or CPL) is by 'opening up' the filters and treating each element separately. This ensures thorough cleaning. Only thing to keep in mind is marking the position of the elements relative to each other and to that of the rings so that there is no need for recalibrating the markings.

If the filter cannot be pried open or for dye based filters, there's not much you can do except localised wet dab cleaning but otherwise mostly dry cleaning. Making sure all the time, to steer clear of the edges to avoid risk of delamination. Never try to bath the entire filter as it will only worsen the situation.