condenser/difusion enlarger question

Discussion in 'Darkroom Developing and Printing' started by 10x, Nov 3, 2003.

  1. 10x

    jjs Guest

    Yadda, yadda! So, someone can make his/her mark and reputation here: why
    does a diffusion enlarger make prints just as sharp as a consumer
    'condenser' enlarger (like the Leitz Focomat iia, iib, etc) and NOT print
    the DUST! Yes, I see the potential arguments, but make my day and OUT with
    it. Post it. Make your reputation: How does an enlarger that does not
    render detail as fine as dust still manage to print the full detail and
    contrast of a negative printed on a condenser enlarger?

    Yea, this is all Usenet so you can lie and impress yourselves to hell, but
    tell me "HOW" (then please do the Missourit thing and SHOW ME!)
     
    jjs, Nov 4, 2003
    #21
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  2. I am going to guess: As I am not an Optical Physics Major.

    Because the condensors Colliminate the light to the upper
    surface of the negative. Where as the diffuser basically spreads the
    light out evenly across that surface. Dust can be focused with a condensor from
    any of 5 seperate surfaces versus, a diffusion enlarger where you would
    have only one surface to truely consider,...that is the top side of the negative. (assuming your
    enlarging lens is clean). The image sharpness is determined
    by the enlarger lens solely and by the focal length of the bellows
    in relative relation to that focal length. There; how did I do for a guess?
     
    Gregory W. Blank, Nov 4, 2003
    #22
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  3. Hmm; bring that paragraph into my shop next week. I think I can do a CLA on it.

    But seriously, even though the muddle of your words I pick up that you're
    basically saying that since the condenser collimates the light, that dust
    particles will cast a sharper shadow than with a diffuser, where the light is
    coming from many directions.

    Is that kinda what you meant? And the next question is, is this really why
    condenser enlargers show dust more than diffusers?
     
    David Nebenzahl, Nov 4, 2003
    #23
  4. Yup; to my knowledge its because any above the negative dust is clearly
    focused onto the negative's topside. The light passes through the negative only
    to be refocused by the enlarger lens. The small amount of scatter from light passing through the
    film is not enough to hide the focused dust. As a matter of experience I found its magnified
    if its on one of the condensors,....you end up with a small fleck of dust that looks
    huge on your print. Thats why I use diffusion enlargers only.
     
    Gregory W. Blank, Nov 4, 2003
    #24
  5. 10x

    jjs Guest

    Now that would indicate that the light is, indeed, somewhat columnated,
    right? So, it is not columnated _enough_? Is that it? Sharp dust, sharp
    negative? Why not?

    More, people. From experience. Fess up, now.
     
    jjs, Nov 4, 2003
    #25
  6. Not sure what your driving at. A condensor system "IS" colliminated
    the light passes through the tube at one end and the rays remain parrallel
    passing through the otherside at the bottom of the second condensor.
    If the negative ain't sharp but the dust is, something is misaligned relative
    to the negative.

    Its because the rays are sharp without much internal
    scatter above the negative that the dust appears sharp on the negative topside
    and sharp in your print. Its plain and simple.

    A simple illustration would be to use direct flash versus a soft box. Get the "picture".
     
    Gregory W. Blank, Nov 4, 2003
    #26
  7. The article was older than I thought. It was a two-part article
    entitled "A Tale of Three Enlarger Heads" written by Ctein for the
    Jan-Feb and Mar-Apr 1999 issues of Photo Techniques. Slight
    differences in contrast were measured. "The diffusion head produces
    prints with higher contrast in the shadows but lower contrast in the
    highlights. " None the less, the typical curves for the two heads are
    very close from start to finish. He adds, "Hence, it is not generally
    possible to exactly match a condenser print with a dichroic diffusion
    print by changing paper grade or changing film processing (though one
    might get lucky)." And finally, he says, "Chromogenic negatives print
    the same with all heads, indicating that any differences in the printing
    qualities of the heads are a result of the silver grain image, not an
    inherent property of the light source."

    So, while the difference is measurable, it is indeed slight.


    Francis A. Miniter
     
    Francis A. Miniter, Nov 4, 2003
    #27
  8. 10x

    Mark A Guest

    I don't get the same conclusion as you from the quotes you excerpted. I
    don't think you understand the article.

    I am not sure why you accept Ctein carte blanche anyway, since Dr.Henry
    disagreed with many of Ctein's claims, especially the one you
    quoted..."Hence, it is not generally possible to exactly match a condenser
    print with a dichroic diffusion print by changing paper grade or changing
    film processing ."

    As previously mentioned in this thread, no two condenser enlargers are
    exactly the same in terms of commingled light, nor are diffusion enlargers
    the same in terms of diffused light.
     
    Mark A, Nov 4, 2003
    #28
  9. I use a Durst G139 with a glass carrier and a CLS1000 color head. Durst claims
    that the CLS1000 makes very diffuse light because they use two mixing boxes
    in series. Before that, I had the standard condensor head with the standard large
    opal bulb (110mm diameter).

    I have several prints from older negatives (developed softer than now) with
    both heads. Usually, I have not much of a problem with dust, but occasionally
    I have a print with a large dust fluff on it. I use Apo-Rodagons (in 50mm and 90mm)
    and a Apo-Componon HM (150mm) for all my printing, all are used with f8.

    Dust between the negative and the lower glass is identical in sharpness on my
    actual prints and the old ones. Between the negative and the upper (AN-) glass
    the diffusion head prints the fluff much less prominent, and dust on the top
    of the upper glass is nearly invisible, an very unsharp, light grey shadow.
    With condensor light this shadow is much darker, but not sharper. Obviously
    the shadow is much less disperged with condensor light and much more visible.

    The overall sharpness is the same, I have made enlargements up to 1x1.50m from
    6x7 Delta100 negatives that show details like a 3mm sized tractor on a field in
    the distance. Yes, you can see who made the tractor (a MBTrack), and the cables
    of a power line about 1km away are visible, too.

    Martin
     
    Martin Jangowski, Nov 4, 2003
    #29
  10. 10x

    Alexis Neel Guest

    Not really. If you know how to print, you can achieve the same
    results using either. The important thing is to have a good negative
    to begin with.

    Alexis
    www.alexisneel.com
     
    Alexis Neel, Nov 4, 2003
    #30
  11. 10x

    Dan Quinn Guest

    RE: (Dan Quinn) wrote
    That should read: It will only affect VC papers.


    FWIW, enlarger condensers do NOT collimate the light. Mr. Knoppow
    has described a method for measureing the focal length of the
    condensers. Using a slight variation of the method I found that the
    focal length of the condenser assembly of my Omega B8 to be a
    fraction of an inch beyond the longest focal length lens
    reccomended for the B8.
    In other words condenser assemblies have very short focal lengths
    and are not at all collimated. Dan
     
    Dan Quinn, Nov 4, 2003
    #31

  12. It isn't so much the density as the contrast. Condenser enlargers
    will print the same negative with higher contrast than a diffuse
    source.
    For the usual condenser head where the source is a large, diffuse,
    lamp, the difference is about one paper grade. True specular sources
    can have much higher contrast but they are used only for special
    purposes such as printing from microfilm
    If either the paper contrast or the negative contrast is adjusted
    to compensate for the type of illumination the resulting tonal
    rendition will be the same.
    Different film manufactuers list development times for different
    contrasts so you must read the data that comes with the charts.
    Kodak usually gives times for diffusion enlarging or contact
    printing. Ilford for a compromise value between diffusion and
    condenser values. Agfa doesn't seem to be consistent but does list a
    contrast index of 0.65 for some of its charts, about the right value
    for diffusion enlarging.
    The amount of adjustment of developing time depends on the film and
    to some extent on the developer. For most conventional films, that is,
    non-tabular grain films, one paper grade change in contrast
    corresponds to about a 30% change in development time, either up or
    down. For Kodak times adjust the time downward by 30% and increase
    exposure by about 3/4 stop.
    T-grain films, like Kodak T-Max, Ilford Delta, and Fuji Acros,
    change contrast more rapidly with change in development. About 15% to
    20% change in time is enough to change contrast by about a paper grade
    with these films. Again, if you adjust the time downward you must
    increase exposure by about 3/4 stop. To be clear I mean the film
    exposure, not the paper exposure.
    Diffusion sources tend to suppress blemishes on the film somewhat,
    especially those on the support side. However, if the same negative is
    printed on a condenser enlarger the necessary reduction of paper
    contrast will also tend to reduce the visiblilty of blemishes, so the
    difference is not as much as might be supposed.
    The difference in contrast is due to the scattering of light by the
    individual silver grains. This change in apparent density is called
    the "Callier effect" after its discoverer. In general, the coarser the
    grains, and the thicker the emulsion, the greater the Callier effect
    will be. For most B&W silver pictorial films it is about one paper
    grade for the type of lamphouses described above. Light from the
    condenser source hits the silver grains essentially from only one
    direction. Those which are scattered in directions other than where
    the lens is are lost. The diffusion source supplies light from
    (ideally) a 180 degree range. So, some of the light scattered from the
    silver is reflected _toward_ the lens, lowering the apparent density.
    I said above that the difference was due to contrast rather than
    density, but that isn't quite true because, of course, the two are
    connected. Because of the Callier effect the same silver deposit will
    seem to have greater density for a condenser source than for a
    diffusion source, to the RANGE of densities will be greater with it,
    hense the greater contrast.
    The image on color film is composed of dye particals, which are
    both very small and transparent. As a result color film has virtually
    no Callier effect so the densities and contrast is about the same
    regardless of the type of illumination. For color film a diffusion
    source has more of an advantage in suppressing blemishes than for
    silver B&W. I say silver B&W to distinuish it from the new dye image
    B&W films which are essentially monochrome "color" film.
    Condenser sources in general have an advantage in producing greater
    illumination. For instance, when printing from a 35mm negative the
    light level is partly contolled by the size of the film. The light
    output of a true diffusion source is constant per unit area. The
    smaller the area in use the lower the illumination. So, a cold light
    head which is capable of printing 4x5 negatives rapidly may be
    inadequate for 35mm negatives. This is also partly due to the greater
    magnification needed for a given size print from the 35mm negative.
    Since the condenser source concentrates more of the lamp output at the
    lens the image brightness will be greater for a given total lamp
    output.
    Each type has its virtues and vices but equally as good prints can
    be made with either.
    I hope this is helpful and not information overload:)
    And, BTW, welcome back :)

    Richard Knoppow

    Los Angeles, CA, USA
     
    Richard Knoppow, Nov 4, 2003
    #32
  13. I disagree, although by definition its maybe not a true "this is a collimator
    kind of thing " Like a survey transit.

    The introduction of two glass lenses inside a "tube" above the negative will
    produce more specular light than a diffused light source.

    Whether the light rays start as parrallel and are bent then straightened
    again or remain parrallel from from the source to the negative topside.
     
    Gregory W. Blank, Nov 4, 2003
    #33
  14. 10x

    jjs Guest

    Indeed. I can't see how light could be collimated in such a short
    condenser lens system (but maybe it can).

    But (but, but, but) how the devil does a diffusion enlarger print images
    just as sharp as a condenser enlarger yet not print dust as sharply (and
    in some cases at all)?
     
    jjs, Nov 4, 2003
    #34
  15. 10x

    jjs Guest

    Yes, not truly.

    Ach, I give up. I'll stick to my Leitz 'condenser' enlargers for up to 6x9.
     
    jjs, Nov 4, 2003
    #35
  16. 10x

    10x Guest

    Thanks to all of you for the information.
    This gives me a starting point on developing the negative for a
    condensor enlarger.

    Best to you all.
     
    10x, Nov 4, 2003
    #36
  17. The 'dust factor' is about the same. Scratches on the base side appear
    more distinct with a condensor.
     
    Michael Scarpitti, Nov 4, 2003
    #37
  18. Francis, Ctein's current edition of of "POST EXPOSURE . . . " has a
    cartoon showing the percentage differences in the refraction/scattering of
    light at the edge of a silver grain depending on whether the impinging
    light rays are more collimated or more diffuse... According to his expert
    sources the non intuitive result is that the more collimated the light rays
    the higher the percentage of rays refracted/bent out of focus right at that
    particle edge, causing a more distinct visual edge effect (not truly Callier
    effect, but we call it that in our collective ignorance) And larger
    particles, i.e. dust being larger than a single silver grain (usually), have
    more of this edge effect compared to the smaller silver grains.. So more
    collimated light enhances the edges of a large (relatively) dust particle to
    a greater extent than it does the smaller silver particles... Less
    collimated light does not result in as much preferential edge enhancement of
    the larger particles..

    Thus, one can understand why laser light being highly collimated extremely
    enhances this edge effect and thus is very useful in forensic science making
    surface markings visible that are invisible under ordinary light sources...
    A laser light source for your enlarger would be the photographers nightmare
    from hell for making clean prints...

    Denny
     
    Dennis O'Connor, Nov 4, 2003
    #38
  19. In most condenser enlargers, the surface of the light source is focused
    by the condensers at the aperture of the projection lens. In movie
    projectors, the light source is projected on the film gate. That is why
    the film instantly goes up in flame if the transport stops while the
    lamp is on.

    There is another difference between most dichroic and condenser heads.
    The quartz-halogen lamp has a higher color temperature than the lamp
    used in most condenser enlargers. This difference tends to make higher
    contrast in the dichroic enlarger than a conventional lamp would in the
    same illumination system, at least when used with VC paper. The
    combination of higher color temperature and diffused source should give
    back some of the contrast of the condenser system while not emphasizing
    dust and scratches.

    If you replace the opal enlarging lamp in the 23c with a dichro head,
    you should only notice the difference due to color temperature. This is
    speculation on my part. I have a 23d and a C760 dichro side by side, but
    no dichro head for the 23c.
     
    Patrick Gainer, Nov 4, 2003
    #39
  20. Collimation is the act of running light through a tube. Boiled down
    both systems collinate light somewhat, the condensors just leave it
    more than less directional.

    The enlarger lens is what focuses the image, the condensors
    meerly gather the light, while at the same time focus the dust.

    Diffusion systems bounce the light within a lined box
    so any dust within the system is not focused, I have seen
    under the correct conditions for it large anonmolous
    specks in some of the dichro head I have used,...as a result
    of dust/dirt on the top side of the diffuser panel.

    If you took two systems and used the same bulb in both
    the diffusion head would print your image with a longer
    exposure time. The output of the condensor based system
    is less only because they use a much much less brillant bulb
    by comparison.
     
    Gregory W. Blank, Nov 4, 2003
    #40
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