It occurred to me recently that, given that fungus growth is a dreaded malady of photo gear, it would make sense for front/rear lens caps and body caps to be made transparent.

Making precision parts from transparent resins might be more difficult than making them from ABS, but I've seen some cases for lens filters that fit together pretty nicely... am I over-estimating how much this would help? Is it because manufacturers don't think they would be esthetically viable? Some other reason that I'm overlooking? Just curious...

6 Answers 6


No! You want opaque lens caps because:

  1. Keep light out of the camera when not using it. In film cameras, the sensor is effectively always on. The shutter should in theory block all light, but stuff happens.

    With digital sensors, light hitting the sensor when not exposing doesn't corrupt the next picture, but you still want light not entering the lens when it doesn't need to. With the lens cap off or transparent, you always have to think about accidentally pointing the camera at the sun. Highly concentrated sunlight for multiple seconds can cause damage to a camera.

  2. Various things degrade with exposure to UV. It's best to block this as early on and as much as possible, like when the camera is not in use.

  3. Most cheap plastics that would be used for such a lens cap would themselves be susceptible to UV. That would cause them to yellow, crack, become weak, etc.

  4. It doesn't solve anything. You never explained why you think light entering the camera helps reduce fungus growth. Perhaps you are thinking UV from sunlight will inhbit it. That is probably true for the fungus, but this "transparent" lens cap will probably absorb significant UV. If not, the lens coatings and the glass in the lens will absorb it. There is little UV left deep in a lens.

    Even if the fungus were killed by UV, other organisms will benefit from the extra light.

  • 1
    Nice summary of the points. Note that it wasn't a yes/no question, though. ;) Jun 22, 2016 at 17:43
  • Regarding #1, the only way you would get highly concentrated sunlight would be if the lens is on the camera. So this is only really an argument against the front cap being clear, not the back cap or body cap. That said, the other points make that detail largely moot. :-)
    – dgatwood
    Aug 4, 2017 at 20:02

Lens caps are opaque to keep light out of the camera. This is something you really want when there's light-sensitive film in it rather than a digital sensor. Most shutters work well, but a tiny leak will result in fogging if light's allowed in over the long term.

I'm not sure the fungus angle is valid or not since there are other things that would grow with light.

  • Not to mention that direct solar illumination passing thru a transparent cap could damage a solid-state sensor. Jun 22, 2016 at 11:53
  • Funny, I think about film so seldom these days that I hadn't even considered that historical angle. Jun 22, 2016 at 16:51
  • ...but it seems like you would have to go out of your way to get something like algae growing in your lens... does that actually happen? Jun 22, 2016 at 16:59
  • @junkyardsparkle: I suppose it could happen. Plenty of other things besides fungi start their lives as spores. Algae is one of them.
    – Blrfl
    Jun 22, 2016 at 17:44
  • @CarlWitthoft I am actively looking for hard evidence of sun damage to solid state sensors. Do you have any references?
    – Wirewrap
    Aug 5, 2017 at 16:18

Interestingly enough, optics made for hunting rifles often come with transparent lens caps for both the front and rear lenses. This allows the scope to be used, albeit with less optical precision, without taking the time necessary to flip up or remove the covers if game unexpectedly presents itself.

The main reason lens and body caps are still black plastic is probably because they have always been black plastic. When cameras held light sensitive film, there was a good reason for keeping light out of the camera even when it was not being used.

Beyond that:

  • Perhaps the plastics needed to make a transparent lens cap would be less resistant to wear from removal and replacement.
  • In the case of camera bodies, there are perhaps some components that would be prematurely aged by constant exposure to UV light.
  • It might also be possible that the materials needed to make cheap transparent plastics block the majority of UV light, which is what is needed to kill or prevent fungus growth.
  • 1
    I guess the question (for a different SE) this leaves me with is whether UVC is actually needed to discourage fungal growth, or only for killing it once it's established... but yeah, you're probably right about The Main Reason. Jun 22, 2016 at 1:36

Lens caps aren't transparent because it would look terrible.

  • Well, those caps with big white areas for white balancing exist... and one with transparent instead of white would look closer to plain old black. :P Jun 22, 2016 at 1:37
  • 1
    Those caps that you mention aren't included by OEM manufacturers. As an aftermarket purchase, sure get a rainbow colored cap. To have a chance at a DSLR being selected by a consumer on a store shelf; manufacturers don't want their products to look ridiculous in general.
    – dpollitt
    Jun 22, 2016 at 1:41
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    THis is a joke, right? //runs off to 3-D print some lens caps using glow-in-the-dark filament (yes, there is such a thing) Jun 22, 2016 at 11:54
  • @CarlWitthoft: I'll take a couple... I actually had strips of GITD spike tape on mine at one point, since replaced with strips of hi-vis yellow... Jun 22, 2016 at 17:03

it would make sense for front/rear lens caps and body caps to be made transparent.

I think the main reason is probably that clear plastics like ABS tend to crack and turn yellow with exposure to UV light, whereas black versions are UV resistant. Experience seems to bear this out: I have some lenses from the early 70's that have original caps, and they're still in fine condition. But I've seen other items made of clear or smoky acrylic or polycarbonate that aren't nearly as old and which definitely show signs of aging.

Other likely reasons include price (black plastics may be cheaper than clear) and aesthetics (black matches most cameras and lenses).

Still, it's an interesting idea that's worth exploring. A lens cap would be an easy 3D printing project. It's easy to find existing models (here, here, here, etc.) that you can download and print, and clear ABS filament is available.

Unless you have a number of lenses that already have a fungus problem, it might be hard to know if clear caps really make much difference. You'd have to take extra steps (leave your lenses exposed to light, remove any UV filters), and the absence of fungus might just mean that you do a good job keeping your lenses dry.

  • 1
    I have eye glasses with polycarbonate lenses that are well over 20 years old and have been exposed to sunlight for thousands upon thousands of hours while being worn. Other than a couple of scratches, they're still just as clear as when they were new. That type of polycarbonate isn't cheap, though, at least not when cut for use as optical lenses in eye glasses.
    – Michael C
    Aug 5, 2017 at 8:20

At the time when I got fungus on my lenses and camera sensor, I was actively using all of them in bright sunny environments. The humidity in the region was heavy, and so was the fungus growth. The suggestion that you need sunlight into the lens is just a hearsay. It just something people heard somewhere and they repeat it. Scientifically, fungus is susceptible to certain wavelengths of light, UV/Sunlight. Realistically and practically that information is nearly useless to us as photographers.

One thing that could work is, making a box with a light specifically designed to kill fungus. Then taking apart the lens, cleaning it thoroughly to the extend you're able. Placing all the parts inside this box for some hours. Rotating parts from time to time. But even that seems not very practical for most people. I have no space/time for it presently, but it's something I could try later.

  • If you go to the extent of taking the lens apart, you might as well just use ozone... probably easier to insure contact with all surfaces (and probably just as destructive to any non-glass/metal parts). ;) Aug 4, 2017 at 19:51
  • I bought this anti-fungal lotion today. But this stuff is made for humans. It contains Luliconazole 1% looks oily and transparent. The medics probably had to think about not damaging the human (at least not too much) So a higher percentage of this stuff will probably be more effective for machines.
    – Emil
    Aug 4, 2017 at 20:02

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