Originally posted by amaurosis I recently bought... an original Pentax cap in replacement but found out that it wouldn't fit properly on the lens.
It is definitely the correct lens cap but just a millimeter too wide for it not to fall of the lens. Does anyone have an idea what the problem could be?
Perhaps the original equipment cap was meant to slip on a built-in lens hood, not on a filter or the lens itself. That's like the slip-on cap for the DA 35 Ltd., and it certainly does not fit very securely. It's much more secure and convenient, to use a snap-in pinch-style lens cap that grips the inside of filter threads -- unless you're using a 'thin' filter without front threads to avoid vignetting on your wide-angle.
Robin Kanta Photographic sells both the pinch-style and the slip-style caps. Also, screw-in types. Note that if you are ordering a slip-style cap, you need to measure the actual outside diameter of the lens/filter, NOT the nominal diameter of the filter threads!
Incidentally, if anyone wants a genuine Pentax slip-on style lens cap for the 35 Ltd, I have one I'd be happy to send to anyone for free. Its inside diameter is 55mm. Just send me a PM.