Quote Originally Posted by wblynch View Post
On judging lenses...

Considering the age of these lenses, you can get a lot of sample variation depending on its storage and usage.

Many have internal haze that needs to be cleaned. You might not even notice it right away but it can affect the IQ.

People are hesitant to admit that the lens was kept in a smoky house or one that cooked with a lot of grease.

And it's natural for photographers to unfairly declare a lens "bad" when what it needed was cleaning.

Half of the lenses I got over the past 5 years need a good professional cleaning. I need to get that done one of these days....
The other thing to beware of is fungus. Most of the time it'll clean off without doing noticeable harm, but it seems fond of the adhesive used to stick lens elements together and will get between them. It would be very difficult and expensive to have the elements separated, cleaned and re-glued.

You can clean most smaller lenses yourself, you just need the right tools (especially a cheap pair of vernier callipers to use as a lens wrench), a pair of surgical gloves (to stop the natural oils on your fingers from ending up on the elements) and a "Rocket Blower" or similar. Work in the least dusty room, you will inevitably get some dust but it doesn't seem to do much harm to image quality. I've cleaned three 50mm primes, a 28-50mm zoom and an 80-200mm zoom this way, all work perfectly.