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Don't Forget about Filter Maintenance ! [updated]

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#1 Andrea B.

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Posted 29 June 2019 - 16:21

Schedule Routine Filter Maintenance Every 6 Months

I got caught up in a whirlwind of life events and did not use my filter sets for about a year. When I opened up my filter case a couple of days ago, I was horrified to see that some of my beautiful blue and blue-green filters (all uncoated and unstacked) had begun to oxidize!! One of them even had a kind of greasy substance in the center. Ugh!

Well, horrified I was, but not particularly surprised. I know perfectly well that this can happen with uncoated filters of any color. Typically I have a mid-winter inspection and clean-up so that all filters are examined about every 6 months for signs of oxidation or other problems. Oxidation can advance to the point where it deteriorates the surface of the glass and the filter becomes unusable. Please do be sure to schedule some routine filter maintence for your own filter kit to prolong the life of all those little pieces of colorful glass on which you have spent scads of $€£.

Two good oxidation removal methods for UNCOATED filters:
  • Hydrogen peroxide: an overnight bath followed by a rinse and good drying.
  • Cerium oxide paste: polishing with a tiny dab followed by a rinse and good drying.
    Or, you can avoid the rinse and simply wipe the paste off carefully with a microfiber cloth.
If you have a glue-stacked, uncoated filter which is showing signs of oxidation, then using cerium oxide is probably the best way to remove oxidation. I'm always hesitant about completely immersing a glue-stacked filter in the H2O2.

If you keep up with the oxidation removal, you can extend the life your uncoated filter glass for years. My Baader Blue and Blue-greens are probably the very worst in my filter kit for oxidation, but they are now about 11 years old and still sparkling give-or-take a few minor scratches from field use.

I note for the record that using a graphite-based cleaner like a Lens Pen does not remove oxidation. The Lens Pen just makes a weird squeaky sound on the oxidized area. And the greasy type of oxidation could ruin the Lens Pen.

Periodically we do discuss filter cleaning here, but a fresh topic serves as a good reminder. Please feel free to contribute any filter cleaning methods or suggestions that have worked for you.

ADDED:
  • added the adjective uncoated where appropriate to clarify above
  • added remarks about cleaning other types of filters below
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Cleaning Coated or Dichroic Filters

Sometimes simply brushing away any dust and polishing with a clean microfiber cloth is all that is needed for any filter. If a wet cleaning is needed, then you want use a well-known filter cleaning solution recommended for cleaning coated filters and lenses. Some dichroic filters have a coating over the electronic sputtered, hard, dichroic layer, some do not. And I don't think it is very easy to determine this by looking. So it is probably best to treat dichroic filters as though they were coated.

When I do need to wet clean a filter, then for years I have used Formula MC multi-coated filter and lens cleaner on any filter (or lens). Formula MC will remove fingerprints, smudges, sticky nectar, tiny pollen grains and dirt. The cleaning process has two steps: after brushing away anything granular, use a drop of the solution and clean the filter with lens paper or microfiber cloth in the usual gentle, circular manner from center to edge. Then with a fresh lens paper or dry microfiber cloth, gently dry and polish the filter surface. For the record, Formula MC will not remove oxidation.

There are other such filter/lens cleaning solutions that are equally good. So add your suggestions below if there is one you would particularly like to see mentioned.

These days I no longer use lens papers much. They seem to leave some little fibers behind. Microfiber cloths are my personal preference when cleaning filters or lenses. How about you?

[The usual disclaimer: UVP is non-monetized and has no financial association with any manufacturer of photo gear or accessories.]




In personal practice, I've used the following on dichroic filters: Eclipse, Windex, isopropyl alcohol, soap and water, H2O2 and whichever lens/filter cleaning solution is in-house at the time. But you might want to be more careful with your dichroics than I have been <sheepish grin>. Also note that dichroic filters can get scratched although I'm again not sure whether it's a coating over the dichroic layer or the dichroic layer which has gotten scratched.

.
Andrea G. Blum
Often found hanging out with flowers & bees.

#2 dabateman

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Posted 30 June 2019 - 10:43

Andrea,
You need to start this post outlining the difference between a dichroic (interference) filter and an absorbing filter, typically with out any coatings.

Do not clean your Baader venus U filter with Cerium oxide paste. I don't know what a bath of hydrogen peroxide would do to it either.

But your U1, UG5 and even S8612 filters may need this cleaning.

Most of the cheap bandpass filters I have are dichroic and will need some special cleaning. My Zeiss microscope lens cleaner has worked and not pulled off color yet from some I have cleaned. But even with that I think you need to be careful as some Astrophotographers have pulled off coatings with it. It seems to be a detergent with some type of unknown alcohol or butane. I was lucky to get my small bottle directly from Zeiss at a product show. There are counterfeit Zeiss cleaners for sale on Amazon.

#3 Andrea B.

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Posted 30 June 2019 - 18:40

Thanks David for reminding me.
I added the word uncoated where needed. :lol:

Now I'll add a remark or two in the first post about cleaning dichroic or coated filters.
Andrea G. Blum
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#4 Andrea B.

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Posted 30 June 2019 - 19:23

My uncoated UG or U filters have held up quite well so far. They do not seem to oxidize quickly like the Blue or Blue-green glass.

Same remark for my uncoated RG and IR filters.

Brand name filters are not necessarily immune from oxidation. My Kolari UV-pass had a ring of oxidation just in from the edge on one side (but not in the center) and went into the H202 bath last night. This afternoon it has been dried, polished and restored to its usual shiny self. I think the Kolari is coated? But I don't know any other way to remove oxidation than what was mentioned above. Suggestions always welcomed. :D
Andrea G. Blum
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#5 dabateman

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Posted 30 June 2019 - 20:23

Andrea,
You may find this cleaning protocol amusing after your recommend frequency.

http://arksky.org/asoclean.htm

#6 Andy Perrin

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Posted 30 June 2019 - 22:25

Can someone here show me a photo of what oxidation on a filter looks like? I have not noticed any, but I don't know what I'm looking for, really!

#7 Andrea B.

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Posted 01 July 2019 - 01:52

You may find this cleaning protocol amusing after your recommend frequency.

Oh my! That is quite interesting.
And methinks cleaning telescope mirrors is a whole nother thing entirely from cleaning the filters we use for photography. I would *not* want that job, for sure. That is quite an interesting solution they mix up. Might be interesting to try that for our photo filter use also.

I take a very practical approach to photo filter cleaning - especially since my filters get so much actual field use - like out in a field, literally. Or the woods. Or the rocky shore. Or the desert. No matter how careful you are and how hard you try, field-used filters come home dusty, sticky and/or smudged. I've more than once had a pollen-laden bee bump into a filter and leave a sticky pollen mess. (Was the bee warning me away from its flower with that bump? Was it attracted by shiny? Who knows??) And I've had filters fall off or get dropped into dirt, water, mud, gravel, etc. Only a couple of times, though, have I had to replace a filter due to a serious scratch or ding. That statement does not include the stepped-upon BaaderU which met its dreadful end when I tried to get up from a crouch on some desert gravel and lost my balance. Saved the camera/lens/tripod though. And missed the cactus. Can't complain. Could have been worse.



Andy, oxidation on a filter looks like a splotchy, filmy layer, like something wet has dried on the surface of the glass. It blocks light and is very difficult to simply rub off with just a microfiber cloth. There is also an oxidation or deterioration phenomenon which looks like a greasy smear which literally will take fingerprints as though a thin film of butter were smeared on the glass. Sorry I can't make any photos for you right now of oxidized filters as I just cleaned them all up these last two days.

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Andrea G. Blum
Often found hanging out with flowers & bees.