Double vs Single Condenser Lens

Discussion in 'Darkroom Developing and Printing' started by A R, Apr 13, 2008.

  1. A R

    A R Guest

    I've started taking 6x6 photos. Instead of buying a new enlarger, I'm
    adapting my trustworthy MPP condenser to take 6x6 negs. This has
    involved fabricating a new lens board, fabricating a new neg holder,
    purchasing a new enlarging lens and replacing the condenser.

    Now, I have a pair of spherical condenser lenses but unfortunately I
    have no cell to mount them in. A single lens on its own fits snuggly in
    the enlarger head and seems (by eyeball) to give a uniform illumination
    across the easel.

    I know some enlargers use single apsherical lenses but what
    advantage/disadvantage do I have using a single spherical lens?

    Come to think of it, I'm not to sure why condenser lenses come in pairs!
     
    A R, Apr 13, 2008
    #1
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  2. A R

    Peter Guest

    Broadly, I think the objective of a condenser system is to (i) as you
    said evenly illuminate the negative, (ii) pass as much of the light
    through the negative as is practical and (iii) pass it through as
    nearly colimated as possible.

    With one lens, if the convex side is toward the negative, objective
    (i) would likely be fulfilled. I have doubts about (ii) and (iii).
     
    Peter, Apr 13, 2008
    #2
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  3. A R

    A R Guest


    But what if the lens was turned flat side towards the negative?
     
    A R, Apr 13, 2008
    #3
  4. A R

    Peter Guest

    It should be evident if you try it.

    The extent of the effect depends on the lens and the distance from the
    light source and the film. For a distant light source it should the
    lens should cause the light to converge. As you bring the light
    closer to the lens it willl converge to a lesser degree. Measuring
    the focal length and doing a bit of ray tracing with paper and pencil
    should clarify the behaviour.

    Since you have the lens, you can just try it (small light, dark room
    and white piece of paper as a target).
     
    Peter, Apr 13, 2008
    #4
  5. message
    Symmetry corrects coma, lateral color, and geometric
    distortion. The improved coma and distortion probably
    results in better uniformity of illumimation and lateral
    color will reduce color fringing from the condenser system.
    The symmetry does not correct spherical aberration but the
    plano-convex shape of the condenser reduces it. Actually,
    the spherical of the two halves of a symmetrical lens add.
    Some enlargers use only a single condenser but, since
    most condenser enlargers also use light sourses of
    relatively large area and diffuse surface the aberrations of
    the condenser have less effect.
    Ideally the condenser should focus the source on the
    entrance pupil of the enlarging lens but the focus is not
    too critical where a large lamp with a diffuse surface is
    used.
     
    Richard Knoppow, Apr 13, 2008
    #5
  6. A R

    gr Guest

    The double condenser;
    -shortens the focal length of the condenser a lot
    -the symmetry cancels our most spherical aberration (make the light
    more efficient and even)
     
    gr, Apr 14, 2008
    #6
  7. A R

    gr Guest

    Wooops..... my reply was based on dimly remembered things (like symmetry
    canceling stuff, but not spherical I guess. Please disregard the wrong
    info in my previous post!
    gr
     
    gr, Apr 14, 2008
    #7
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