Originally posted by LeDave Reading all of these fungus stuff scares me, is it easy to get fungus infection on your lens?
Don't be scared. No seriously, don't.
The spores are everywhere, and most likely there were some in the Pentax factory where your lenses were made. The problem is not fungus spores but
moisture. The fungus needs moisture to grow. If you keep your lenses dry, and store them so that there is free flow of air, then you'll be OK.
The only lens I have that has fungus is 45 years old and in mint condition. It looks like it was used once, then put in the Asahi Takumar leather case and left there for 45 years before I bought it. Consequently it got a little bit of fungus:
Fungus needs some nutrients, which it typically gets from the cement joining groups of lenses. In my case, this was not the case, so a good clean with methanol removed the stuff. However, I did have to remove the front element to get at the fungus (which took me a while), but it turned out to be quite easy once I had found out how.
So the message is: keep your lenses dry. But don't be scared of fungus, the people who freak out about a lens with fungus are being silly.
To the OP: the A50/1.7 is a great lens. If the fungus does not affect the images (and I doubt if it could) then the lens will still be great. So keep it and use it. If you want to sell it make sure that you describe carefully that it has fungus, and take some photos (use it as a macro project and a learning experience). I wouldn't be surprised if you'll get more than half the money of a lens withiout fungus, if the lens is in otherwise good condition. If the fungus is accessible, then why not try cleaning the lens?
Richard