> This question relates to the effect that dust or dirt particles on the > interior lense elements may have on the quality of the photograghic image. > I had read comments on another site about dust problems in some of the new > Pentax lenses. In the process of doing a thorough cleaning of my equipment > last week I though that I would see how my lenses faired in this regard. I > held a lense (Pentax A 35-105 mm) up to bright window light and looked > through the back (mount end). As I turned the zoom and focusing rings I > noticed small particles come into focus. They were not dust or lint and > were on one of the interior elements. After looking at all my lenses in > this manner I found that particles of dirt were more prevalent in zoom > lenses vs primes and appeared to a greater degree in size and number in > older lenses vs new. In fact my three newest lenses all primes were clean. > > Has anyone one read any material on this matter or done any testing to see > if this is a real problem. Again I was not seeing dust but what appeared to > be small flects of paint.
Mike, First, check to see that the dust or dirt isn't actually on the front and back elements. Even lenses that look perfectly clean when you look AT them prove to be not quite clean when you look THROUGH them. Almost all lenses have at least a slight bit of dust or dirt that is visible when the lens is backlighted. It generally does not have any detectible effect on picture quality; the most it could do is increase veiling glare somewhat and decrease contrast. This effect would be slight unless there was quite a lot of dust (if you've ever shot with a lens with a very dirty front element--especially one with fingerprints on it--you'll know what I'm talking about). The real problem is that early fungus growth often looks like dust. What you will see in a backlit lens are small particles that look like dust, but that resemble tiny eyelashes. They often appear to be randomly scattered and not just between one set of elements. If you catch fungus at this stage, it will not have done damage to the lens yet, and you can still have the lens dismantled and cleaned--although the fungus may still come back. Lots of times when you see eBay auctions for lenses that say "some dust inside the lens, does not affect picture quality," it may well actually be fungus. However, I don't think I've ever seen a single lens that is perfectly clean inside. --Mike J "The 37th Frame," an independent newsletter for photographers www.37thframe.com - This message is from the Pentax-Discuss Mail List. To unsubscribe, go to http://www.pdml.net and follow the directions. Don't forget to visit the Pentax Users' Gallery at http://pug.komkon.org .
