If it was not for fungus there would be no Barn!!! Only thing holding the beer in!!!!

Apparently it's related to the size of the mount. The Canon mount is larger than the Nikon one so there's room for a Nikon lens plus the adapter.

Elbert - is this ANOTHER lens that has fungus? You had that in a lens a couple of years back, didn't you?

But you're right - my Canon lenses are at least four years old and there's no trace of fungus in any of them. But I do keep them in a padded & porous bag whenever not in use.

I think the best long zoom lens now is the Sigma 50-500 OS, the "Bigma II". I don't know for certain, but I believe it's pretty well sealed. And the performance is superb. Comes in mounts for pretty well all bodies. You can see picture samples at http://photography-on-the.net/forum/showthread.php?t=841795

pelican case's RULE!

But in our climate only when used with a powerful dessicant. I was talking to a visitor yesterday who's only been here three days, and keeps all his expensive camera gear inside a large Pelican case. He of course keeps that inside his A/C hotel room at night (the alternative being to leave it out on the veranda with a "please steal" sticker on it). He opened it to use a camera and found every lens fogged up internally. He was distraught that there might be permanent damage to every lens he owns, as well there might. And to the electronics of the bodies as well.

mine are loaded with pelican's own dessicant things,, at least 3 in each. cook them in the oven when they need recharged.
i don't live with AC so i have none of those fog issues. of course going from hot and humid straight into AC with no adjustment period is not a good thing. like when i get out of the AC in the truck and my glasses fog up.
years ago, before digital, i packed up the gear in the camera bag and put it on the shelf. when i made the switch to digital, all my lens needed to be sent in for refurbishment.
since then everything lives in the pelicans.
seems to be the answer for me.

I have always kept my Minolta circa 1970 model in and old army ammo case with desicant. No problems yet. Always fun going thru the airports till I repainted it.

Yes its a second lens with the fungus.
I have a sort of philosophy with my camera care, called 'healthy disrespect' I cant allow myself to care more for the equipment than the shot. If its in a case it isn't ready when the shot opportunity presents.
I get the fungus because the camera is always with me and I'm in the weather... its just a price i pay for having my camera with me.
my teacher called lens caps 'Never-ready caps'.
a scratch on the lens is the price of a shot of a lifetime.

For those interested, the lens advertised in this post is still available.

Elbert -
I find that exposed glass soon acquires a patina of greasy salt that fogs any image, and cleaning it takes far longer than removing & replacing the lens cap. But if I'm using a long lens I always use a lens hood, and if (as is usual) I'm keeping the camera/lens in an ever-ready case which covers and protects the lens I usually leave the cap off.

When you're carrying an extra lens to switch to as needed, do you leave the body-end lens cap on or off?