Why aren't lens/body caps transparent?

Question

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...

Answer 1

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.

Answer 2

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.

Answer 3

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.

Answer 4

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

Answer 5

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.

Answer 6

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.