Recently I needed to find a better lens cap for my 500/4 IS. The Canon cover is bulky and cannot be used with the hood in the shooting position.
Several folks have posted reports of using the Tupperware lids. I purchased these but found that they had several shortcomings. They were very difficult to use with the hood in shooting position, nearly impossible to use with gloves in cold weather and, in my opinion, were too flimsy to really offer much protection for the front element when packed and traveling.
Then I found the lens caps made by Don Zeck.
These are machined pieces of very tough polypropylene, about 1/2” thick. Unlike with the Tupperware, with this lens cap on your front element is truly protected. It is solid.
Because of this I feel comfortable traveling with my 500/4 with the hood reversed and the Zeck lens cap in a Kinesis long lens case. This is important to me, as many of the planes I end up on are the smaller commuters. I with the Zeck cap and the hood reversed I can get my 500/4 and a pro body (and some clothes, battery chargers, etc) in a Kinesis 511 long lens case. This will fit in the overhead of any commercial flight. And because of its toughness, putting the cap at the base of a Kinesis case causes no worries, whereas the Tupperware left me concerned. Between this and some pockets in a coat I know that none of my camera gear will be checked, no matter what kind of plane I end up on.
With the hood in the shooting position and the optional “loop”, putting the lens cap on/off with the lens in shooting position is very easy. On a recent trip in cold weather many others with the same lens thought it overkill that I was putting the lens cap on when we were walking between locations, thinking that the hood was enough to protect the lens. However, with blowing snow, all of them ended up with melted snowflakes on their front elements. I imagine the same would be true in any windy environment, be it with sand, dust or whatever. Having a cap that goes on/off easily, with the hood in shooting position, with gloved or bare hands for me is a real necessity.
The final thing that sold me on the caps was their construction. These are thick pieces of plastic with rubber o-rings to fit them into the opening of the lens. The Tupperware covers work, but these work perfectly – a tight fit with solid protection.