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Recently I was using an old Pentax 50mm f/2 that had a quite big green spot, and later I was informed that it was a fungus.

A couple of questions raised from this:

  1. Why does fungus form inside the lenses? What kind of "food" does it find in a glass element?
  2. How does it form? Due to condensation? Due to bad storage?
  3. Does it have any impact in the final image? Some scratches in a lens will probably not appear in the image because to they will be very out of focus. Is this also true for fungus?
  4. Finally, when a lens is "fungused": How do you get rid of it?

What to do about mold/fungus in a camera lens?

by Yuttadhammo

I am living in a tropical country where humidity is pretty high. I never thought it would be possible that something could grow inside a lens, so I haven't been so careful with my canon camcorder. Now I see there is a white spore growing on the inside of the camera lens (see photo below). Is there any way, short of finding a camera shop (doubtful there are any in the country that can handle this), to remove this?

The spore is the white dot in the centre (it's opaque), and the dusty patch on the right of the lens is also on the inside, must be the same stuff.

fungus spore on lens

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7 Answers 7

up vote 17 down vote accepted

For all the following: YMMV*, caveat emptor, no responsibility taken for advice given, you decide whether to try this at home. It may even work :-). Be aware that damage may already be fatal and/or that fatal (to the lens) damage may occur along the way. Best attitude is to regard the lens as a writeoff now, with anything you can gain from it by the methods below being a bonus.

Fungus in a lens will always degrade the image but the amount of degradation may be invisible to mere mortals or may make the lens completely unusable by any standards. Often even a very visually significant lens defect - such as a chip or scratch, will not be instantly obvious in final images to a casual observer. Experts will usually be able to detect almost any defect (or say they can - mere mortals will not be able to tell if they are correct :-) ). Also, lens settings will affect how much a given defect affects a given image.

In some cases the advice given in 1a and 1b below will transform results from generally unacceptable to generally acceptable. In other cases they won't. Only trying it will tell you how good a method will be.

The best advice (but too late :-( ) is to never let it happen. Fungus only grows in moist conditions. Keep your lenses in a well ventilated dry location with dessicant sachets. However -

If it's inside the lens there are two options (apart from disposal). Unfortunately, while either may work, neither is certain to work well.

  • 1(a) Shining UV (ultraviolet) light into the lens for an extended period will "discourage" the fungus, how well and how long is uncertain. Simply leaving a lens with iris fully open on a sun facing window ledge in a dry location for weeks to months may produce good results. Cap lens at rear, and tilt so that sun shines into lens during sunnier parts of each day. (Be ware that sun shining directly along the axis of the lens or close to it may focus light onto end cap and melt it - unlikely but check point and degree of focus.) I tried this procedure with an extremely old Minolta 50mm f1:1.4? manual lens and achieved tolerable results. I simply left the lens as above for many months and when I next looked found that mold presence had been very substantially reduced.

    1(b) Light from a germicidal (short wavelength) UV lamp may be used in place of sunlight. This sort of light can blind you or damage your eyes permanently if looked at for substantial periods and can cause "arc eye" - painful but usually temporary inflammation of the eye. This does not mean you should not use such lights at all - simply that they need to be used with due respect. These lights are available from many sources for many purposes and can be very low cost.

    Note that "black light" UV light is not suitable for this purpose. It is longer wavelength and not very biologically active.

    Note also that the short wavelength high energy UV (which is why you are using it) from germicidal UV lamps will also degrade other materials such as some plastics and miscellaneous other material - including, possibly, parts of a plastic lens housing. This depends on material, distance, light energy and exposure time. YMMV but caveat emptor - ie know that you are using a tool with sharp unguarded blades (even though you can't see them) and use with due caution.

    All the above may put some people off UV germicidal lamps. If so, that's good. They are a great and useful tool but not suitable for use by careless or unthinking people.

  • 2 . Dismantle and clean. If the lens is so degraded that it is unusable and if the method above does not work well enough then the lens must be dismantled. If the lens is otherwise a 'writeoff" and you are competent mechanically you may wish to try this yourself. Reassembly of a lens capsule is considered to be an expert task and realignment on reassembly may require arcane knowledge. This is why qualified lens servicing people are still in business and cost money to use.

    Fungus often attacks lens surface coatings and may etch the glass itself so the lens may be noticeably or fatally degraded regardless. How much the may/may/may applied in your case is tbd. Some lens cleaning works very well indeed. An aficionado and a good MTR test will probably tell you that something has happened but the results may be very tolerable in practice.

    You will find articles on the internet on lens cleaning methods. I read a paper by either Zeiss or Leitz that suggested that cigarette ash makes an excellent fine cleaning compound (!!!).

  • YMMV - Your mileage may vary.

  • Caveat emptor - let the buyer beware = you are on your own.

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The only course of action here is to get the lens professionally serviced. Once mould spores have got into your lens and started to grow like this there is no other way to get rid of them. In order to prevent this in the future always store your camera in a sealed bag with a couple of sachets of silica granules to absorb any moisture that may have got into the camera during use. This is especially important if you're in very humid environments or if the camera has got at all wet.

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I hate to say it, but the best thing that can be done is to get rid of it. Especially a lens like a 50mm f/2, it shouldn't cost very much at all to replace it. There isn't a good way to clean the middle elements of a lens.

You've already mentioned the green spot, it'll cause enough problems.

You can minimize fungal growth by protecting from the elements (Especially water), making sure to use it periodically, etc.

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I've heard a lot of 'meh' things about the old 50mm f/2. They're practically giving them away on ebay. I've even had people just straight up offer to give me one. Better to replace than mess with that lens. –  rfusca Aug 10 '11 at 20:54
Or you could get the smc Pentax-FA 50mm f/1.4 I think you can get a used one for around $300. Money well spent. –  Jakub Aug 10 '11 at 23:23
I would replace it, then try and clean the one you have. Since you already have a replacement, it doesn't matter if you mess up, and either way, you'll learn a lot about how lenses are constructed. –  Evan Krall Aug 11 '11 at 6:06

I recently saw on YouTube - BTW an interesting place for instructions and answers - that you should never store cameras or lenses in camera bags. The fabric in the bag is a great place for mold spores to get imbedded. So dark, moist places surrounded by lower grade of fabric invites disaster. It was suggested when cameras and lenses not in use to put them in an air-tight, transparent, plastic or acrylic case with silica gel. To recap what invites disaster: fungus needs heat, damp and darkness to thrive.

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I can tell you with absolute certainty that the Leitz recommendation is not a sealed container with desiccant but an area with constant air circulation. I used to be with Leitz Germany. –  user19602 Apr 27 '13 at 6:24

Addendum: Do not store a lens with mold together with other lenses! Also don't attach a lens with mold to your camera, it might contaminate all of your gear.

To protect against contamination, Zeiss only allows lenses without mold into its service centres. [p.85, c't Digitale Fotografie 04/2013]

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Fungus is just a biological, er, thing, which will grow when the conditions are right. Sorry for the poor information, I just wanted to say: untreated fungus can etch the coating on your lens and therefore damage it permanently. Better do something about it.

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Ad 1a : What kind of "food" does it find in a glass element?

Dust. There is dust inside your lenses. It's almost never visible on the photos, sometimes you can see some of it by shining flashlight from the other side, but the dust is there. Some of it is biological (including fungi spores) and this is what fungus eats. This is why it's so important to control humidity; both food and spores should be considered as already in place so water supply is the only thing owner can control.

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