[SME]

Hello,
the seller of a high quality used lens writes in the description of the condition of the item: there is a tiny bit of fog inside the lens which does not affect the image quality. What does this mean, and in case it is a handicap, can it be repaired (easily) ?
Gratefull for your coments.
Stefan

[jatrax]

Hard to say without knowing the lens make and model and seeing pictures. A small bit off to the side might make no difference, a bit dead center might. It also might matter which element it is on, front or back.
On some lenses it is easy to take off the front element and clean, on others I would never attempt, especially if it is a rare or expensive lens. Which means sending it off for repair.

"Fog" can be many things particularly if the seller is not familiar with lenses. it might be condensation, oil, fungus, separating elements or a coating failing. Some of those are easy, some very hard or impossible to fix.

Sorry, no simple answer.

[Action Jackson]

It may be a number of things. Fungus comes to mind. In my case the only way to really tell is to shine a light right through the lens and you'll see it. My Vivitar 105 2.5 had a bit of haze in it, which I suspect was the blade oils evaporating in a warm environment. I had the lens professionally cleaned b/c I do not have the expertise to open it up.

For me it did affect image quality as I thought that I had a sudden case of glaucoma and couldn't focus properly.

[Na Horuk]

"Fog" can be many things particularly if the seller is not familiar with lenses.

Yep. Who knows what the seller thought.
Jatrax listed the concerns well. Many of those things cannot be repaired at a reasonable cost, but some might be a cheap fix. Though, as an amateur, I wouldnt try "fixing" a lens myself.
Maybe if you post a photo here. And tell us which lens it is, maybe we can estimate a repair cost. But unless you get this lens super cheap (as in, practically free), it might be best to look for one in better condition. If the "fog" is a fungus, its better not to touch it, unless you know what you are doing.

[TomB_tx]

bit of fog inside the lens which does not affect the image quality...

Every time I've had a lens cleaned of "slight" fog the image quality has improved. Haze lowers contrast, but not sharpness, so it is often not noticed. You also tend to see a "glow" around highlights as if shooting through slight fog.
It is usually worth getting it fixed.

[jatrax]

which does not affect the image quality

And just FYI, they all say that. Whether the seller is qualified to judge that or not. I love it when they say that and then say they did not test it because they don't have a camera that the lens fits.

[dms]

For myself--if it is a expensive lens and I am getting it cheap--and I have no problem returning it--I figure it's worth the risk. But I only do it with KEH/would do it w/ B&H. I tried it twice (on lenses that were about $200 vs $600 if OK) and each time the haze was severe enough to destroy resolution, so I was out $20 in each case. Personally, except for getting a lens "I have a need for" and would not choose to spend the money on, I would think there are enough lenses w/o a problem. BTW if it's really only a little haze would the seller have even mentioned it?