Whenever you hear opinions on old lenses, take them 'cum mare salis'. Those lenses are not likely to be as they were when new. They may have haze (has no effect), fungus (also has no effect), cleaning marks (no effect), decentration (no effect, even though the front of the barrel is folded flat), or all of the preceding. And it's interesting how many fail to see these problems. I use old lenses from before the war - before the War to End All Wars, not the one after. A few light cleaning marks will have no discernible effect, but a fine network will spoil the definition beyond the ability of a hood to prevent. Haze is common, and can be surprisingly hard to see. Fungus affects the lens like a combination of haze and scratches, if it is ignored long enough it can actually remove the coating and etch the glass. Decentering is the result of dropping the lens, or taking it apart without knowing what you are doing. I will not buy a lens which shows signs of impact damage or careless/unskilled dis - and re - assembly.
Originally Posted by Ken.Cartouche
Also, don't expect old lenses to perform like modern lenses, they aren't and they won't. I used to have a prewar Contax with an uncoated f:2 Sonnar. Comparing that lens to my beloved f:2 Nikkor Hs, it wasn't that great. But looking at 8x10 prints of negatives I made under existing light in a machine shop, using Tri-X at 800, the old Sonnar was lovely and I wish I'd kept it.