Channelling Fred Spira - The Clear Lens Cap
The rest of you will have to buy your own, but the cost won't be onerous. We have a whole rack of extremely useful clear lens caps in our Frugal Foto Fun section. They range from 62 mm to 77 mm. and have good solid mounting rings. They are uncoated optical glass that will protect your valuable lens.
If you have ever missed a snap shot in the confusion of trying to take off a conventional cap and screw on a lens hood...well, just keep one of the Emolux clear lens caps on and shoot as fast as you can. UFO's and costume malfunctions wait for no-one!
And they're only $ 10 each.