Scratched Lenses Many people don't know this, but many of the pictures you see in Magazines that are taken by Pro's are taken with scratched lenses. I have met many Pro photographers that use scratched lenses.  I have seen the pictures.  I have tested scratched lenses against unscratched lenses.  The bottom line?  They perform great. Small scratches on lenses yield fine photos that are indistinguishable from photos taken with unscratched lenses.  There are exceptions. The biggest problem with scratched lenses is flare.  Flare reduces image quality.  The fix is to touch up the scratch with flat black paint or marker.  This is only necessary if the scratches are Heavy and on the front element.  Small scratches, especially those on the back element of the lens, won't make much difference.  Scratches on the sides of the elements are also less likely to create a problem, especially when you stop down.  The part of the glass with the scratch on it will not even be in the light path! Next time you see a lens with small scratches on it selling for peanuts compared to an unscratched one, buy it!  Try it and you will see that these lenses can still be great users. Fogging/Haze The best way to check for fogging or haze in a lens is to shine a bright flashlight through one end of the lens and look through the other end of the lens.  The fogging/haze will show as a white colored cloudiness on the lens elements. Will this reduce the performance of the lens?  Well, that depends how you look at it.  Sharpness and contrast may suffer from this because of an increased tendency for the lens to flare.  On the other hand, if this lens is being used for portraits, this may prove to be an ideal situation and will actually enhance your photos. Can it be cleaned?  I most cases, yes.  Some cases are severe are include deterioration of the lens coatings.  If this is the case, then the lens cannot be cleaned properly without removing the lens coating. This will alter the lens.  However, the nice warm glow associated with these differences may be to your advantage. Sometimes its good to have a couple lenses available in your kit that are fogged.  They will lend a nice 'glow' to the photo.  Especially people pictures.  Lets face it, lenses are a photographers tools, and its good to have the right tools for the job.  Just try taking a needle sharp picture of your loveley wife or girlfriend with a summicron, and you will soon find out why Leica invented the soft focus Thambar lenses.  The concussion you receive from that expensive lens being smashed over your head by your wife or girlfreind is proof enough. Fungus Personally, I don't like fungus.  I don't like it in my lenses either.  Happens alot on the East coast and other humid climates.  Sometimes it can be cleaned if you catch it early enough.  Other times the fungus can actually etch the glass.  Is the lens ruined?  No, just altered.  Shoot with it, see what the differences are in the photos and then try to take advantage of the differences.  If you don't want it, send it to me, I'll use it. Coating Marks Coating marks are often the same as cleaning marks.  The soft flourite coatings of Leica lenses are easily scratched by improper cleaning.  A small amount of lens cleaning marks or coating marks will make no perceptual difference in the performance of the lens. A large amount of cleaning marks or coating marks will make a very small almost imperceptual difference by possibly introducing a little flare.  Not a big deal, but usually hurts the re-sale value quite a bit.  Once again, good users. Pinholes in the Shutter Curtain This is a joke right?  Even I would not recommend this, but I am wrong!  An exquisite photograph was taken by Mr. Gerald Widen using a Leica IIIc, with pinholes in the sutter curtain, that is included in the photo section entitled 'Starry Window'.  You will see how he took this flaw and created an amazing photograph with it.  Just goes to show you that what you may consider a flaw in your equipment can be turned around and used to your advantage.