Dust in Lens: When does it matter?

Discussion in 'Leica and Rangefinders' started by kevin m., Mar 23, 2003.

  1. Couldn't a find focal length lens be sealed? Focussing the lens would only draw dust into the camera body behind the lens, not into the lens itself,
     
  2. Reminds me, I have a Panasonic camcorder with the usual wide zoom range.

    I once had it zoomed out, and then wondered about the strange view on the LCD display.

    I finally figured out that the AF had managed to almost focus on dust on the UV filter.
    With enough depth of field, it can do that.
     
  3. For years we were told that specs and bubbles were common in optical glass, which was often produced in small, platinum pots for casting. These defects largely disappeared in the 70's due to improved processing. Dust in assembly has largely been eliminated by filtration and laminar flow hoods, developed for semiconductor and pharmaceutical operations. What happens in the real world is another matter.

    Dust in the lens is visible because the intervening elements act like a magnifying glass, and you see the particles illuminated against a dark background. The closer they are to one of the nodes, the less their effect on the image. Dust on the outer objective or filter may be seen if the lens focuses close enough (common with big zooms on sub-inch video cameras). At worst, dust inside the lens might contribute to flare, but it would need to be pretty gross.

    Lenses what focus and zoom internally are unlikely to suck in dust. That can't be said for lenses which shrink or expand significantly in these operations.

    For what it's worth, lenses, semiconductors and digital sensors are produced in the same type of lab gear used to make space modules, for the same reasons.
     
  4. And for usual depth of field reasons, dust or bubbles will be more visible when stopped down.

    Other effects are visible with a bright light source, like the sun, within the field of view.
     

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