Post by doubs43 on May 22, 2007 12:34:15 GMT -5
..... or how to get rid of the yellow without Pepsodent.
For those familiar with Pentax lenses, it's well known that certain older formulas included the use of elements with radioactive properties caused by the use of thorium in the glass. While not dangerous in the quantities used, the thorium will cause the element to take on a yellow hue over time that can create problems when using color film. It's far less of a problem when using B&W film and may actually improve some photographs by acting as a filter. The Takumar lenses prone to yellowing include the early 50mm f/1.4 and some of the 35mm lenses.
Another lens that is commonly effected is the East German Carl Zeiss 50mm Pancolar. I'm "cooking" one at this very moment. When well done, the yellow lens element should be crystal clear once again.
The technique is really quite simple. Use a piece of aluminum foil and place it shiney-side toward the glass over the front of the lens. Then wrap the whole lens with the foil shiney side out and leave only the rear element uncovered. Place the wrapped lens in the sun for a couple of weeks or so and the yellow should disappear. To check for progress, before wrapping look at a bright-white sheet of paper through the lens to see how yellow it looks. Check the lens after treatment for a couple of weeks and it should be clear or nearly so depending upon the time in the sun and the strength of the UV rays which neutralize the yellowiing. The foil reflects the UV rays back through the lens so they pass both ways for quicker clearing.
Do not confuse the amber coating used on some lenses for the thorium elements having yellowed. While there may be others out there, only the Pentax Takumar and ZCJ Pancolar are subject to this yellowing as far as I'm aware.
So, if you have one of these yellow lenses, cook it well and "cure" what ails it.
Walker
For those familiar with Pentax lenses, it's well known that certain older formulas included the use of elements with radioactive properties caused by the use of thorium in the glass. While not dangerous in the quantities used, the thorium will cause the element to take on a yellow hue over time that can create problems when using color film. It's far less of a problem when using B&W film and may actually improve some photographs by acting as a filter. The Takumar lenses prone to yellowing include the early 50mm f/1.4 and some of the 35mm lenses.
Another lens that is commonly effected is the East German Carl Zeiss 50mm Pancolar. I'm "cooking" one at this very moment. When well done, the yellow lens element should be crystal clear once again.
The technique is really quite simple. Use a piece of aluminum foil and place it shiney-side toward the glass over the front of the lens. Then wrap the whole lens with the foil shiney side out and leave only the rear element uncovered. Place the wrapped lens in the sun for a couple of weeks or so and the yellow should disappear. To check for progress, before wrapping look at a bright-white sheet of paper through the lens to see how yellow it looks. Check the lens after treatment for a couple of weeks and it should be clear or nearly so depending upon the time in the sun and the strength of the UV rays which neutralize the yellowiing. The foil reflects the UV rays back through the lens so they pass both ways for quicker clearing.
Do not confuse the amber coating used on some lenses for the thorium elements having yellowed. While there may be others out there, only the Pentax Takumar and ZCJ Pancolar are subject to this yellowing as far as I'm aware.
So, if you have one of these yellow lenses, cook it well and "cure" what ails it.
Walker
