I often see older lens with the description including 'oil on the aperture blades'. Where does the oil come from, how does this effect performance, do/will new lenses also exibit this characteristic as they age? Thanks

-- Doug Ford (dford@san.rr.com), January 11, 2002

Answers

I dunno where it comes from, Doug, but I had a 35mm Summaron with Oil on the aperture blades. It happened under warm/hot desert conditions. Apparently it thinned and flowed from where it was supposed to be, to where it wasn't.

-- Bob Fleischman (RFXMAIL@prodigy.net), January 11, 2002.

Aperture blades pivot near their base to swing across the lens and block light. The pivot is lubricated ('oiled') to make keep this movement smooth, esp. since the blades are thin metal and would fold and/or crinkle if the mechanism jammed.

The oil can over time (or if overenthusiatically reapplied during service) start to spread and form a shiny film on the visible parts of the blades.

But not all shiny spots on aperture blades actually ARE oil - sometimes the blades polish each other as they slide past and create a shiny finish WITHOUT any oil - over time.

If there IS oil on the blades, it can (just like auto oil) get sludgy, start acting more like a glue than a lubricant, bind the blades, and cause the same kind of damage it was originally (45 years ago) supposed to prevent.

I believe at least some modern lenses/cameras use graphite powder lubes, which don't do this.

-- Andy Piper (apidens@denver.infi.net), January 11, 2002.

Some lenses are more prone to getting oily blades--like many of the East German Zeiss lenses for the old Contax. It's more cosmetic in a rangefinder lens unless the oil is so bad its getting on the inner element. In an SLR lens with auto diaphram, it can be a bigger problem. The automatic close down/open up sequence will start to get sticky, which will interfere with the functioning of the lens and need to be serviced.

-- Andrew Schank (aschank@flash.net), January 11, 2002.

Thanks for the education.

-- Doug Ford (dford@san.rr.com), January 11, 2002.