why lens cap must be black and opaque

[EinstStein]

A white half-translucent chip can cap is better.

[rdonson]

please explain...

[NancyP]

This probably has to do with white balance, and some lens cap-like WB gadgets are out there already.

[TonyVentourisPhotography]

Yeah I've seen that before too.  Like keeping an expodisc on each lens in a sense.

[stever]

Cost and aesthetics.  Black hides the details of the locking mechanism which are not necessarily pretty or free of cosmetic irregularities (and molding irregularities in general).  Black plastic is generally cheaper, particularly with UV inhibitors added. Easy to meet color uniformity requirements and no requirement for uniform translucense.

[Otto Phocus]

Often I think there is too much black in photography.  Gosh that sounded bad.   

Too many accessories in photography are unnecessarily black.

Looking in a black lined equipment bag for a black cap that may have slipped under some black cords, while in a dimly lit environment is not exactly fun. 

I am sure I am not the only person that has one of those tiny LED flashlights clipped to their bag for the sole purpose of illuminating the black hole of equipment bags.

We need more whiteness in photography!  No, that sounded worse! 

I guess black is more "serious" and more "Pro".

[Dave Rosser]

Often I think there is too much black in photography.  Gosh that sounded bad.   

Too many accessories in photography are unnecessarily black.

Looking in a black lined equipment bag for a black cap that may have slipped under some black cords, while in a dimly lit environment is not exactly fun. 

I am sure I am not the only person that has one of those tiny LED flashlights clipped to their bag for the sole purpose of illuminating the black hole of equipment bags.

We need more whiteness in photography!  No, that sounded worse! 

I guess black is more "serious" and more "Pro".

I think it all goes back to the days of film when a light leak could fog the film and ruin everything without you knowing.  I can't think of a real compelling reason to have things black except, of course, in the interior of camera and lenses.

Dave.

[sbay]

I have a bunch of multi-colored silicone caps that fit over my lee adapter rings.

[Randy Carone]

Black also allows the manufacturer to use regrind back into the molding system, with no loss of physical properties. And, as mentioned before, carbon black pigment holds up well to UV rays and doesn't become brittle from exposure.

[Rob C]

Just as I was growing bored... thank goodness for something new about which to worry and obsess!

;-)

Rob