The difference in enlarging lenses

Discussion in 'Darkroom Developing and Printing' started by John, Jan 28, 2004.

  1. John

    John Guest

    Hello,

    I recently purchased a Elwood enlarger with a pair of
    Wollensak Graphic Raptar lenses. Specifically the enlarger is a late
    model, all cast aluminum 5X7 Elwood. While quite large it is also
    quite light and I can easily pick up the entire unit and move it
    without any disassembly.

    Regarding the lenses, the better of the two Graphic Raptars is
    7.5 inch/192mm f/4.5 lens which is in very near mint condition. The
    161 mm certainly appears to be in excellent condition as well but
    there are a couple of cleaning marks in the coating.

    Here's where my quandary starts.

    I also purchased a 180/5.6 Componon-S last year. While it was
    used, it's in mint condition and was shipped with all the original
    documentation and packaging. I've mounted this lens into a Durst lens
    cone which was subsequently mounted to the lensboard for the Elwood
    using screws at roughly 120 degree spacing.

    I selected a portrait of my son that I had shot on my 5X7
    Linhoff using Kodak Tri-X which has a fabulous scale and prints
    wonderfully on a G2 Galerie. I made prints from this negative using
    the unusual 5X7 cast metal carrier of the Elwood complete with both
    upper and lower pieces of glass at the same magnification and using
    the same f/11 aperture.

    What I see in looking at both of these prints side by side and
    with a 6X loupe, is only a slight increase in contrast. That's it.
    Shouldn't there be other visible differences between what is
    acknowledged to be one of the best lenses available today and a lens
    that is generally considered to be mediocre and somewhat antiquated
    today ?

    Regards,

    John S. Douglas, Photographer - http://www.darkroompro.com
    Please remove the "_" when replying via email
     
    John, Jan 28, 2004
    #1
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  2. Your findings are identical to my experiences. I compared a new
    Schneider Apo-Componon HM 4/150 with a silver Tessar-type Componar
    from the 60's, enlarging a extremely sharp 4x5" negative.

    When enlarged to 24x30cm (about 2.5x) you could see _no_
    difference, even with a strong loupe. At 40x50cm (rougly
    4.5x enlargement) the Apo was better at the edges, with a Peak
    grain focuser one can see it has a better flatness of field.

    Both lenses were used 2 stops down, the Apo at f8 and the
    Componar at f11. The Apo had visibily more contrast,
    a little more magenta took care of that (I think it is
    a difference of about 10-15 ISO-R or 1/2 grade).

    I think that even old LF-enlarging lenses are good enough.
    The real differences show with smaller formats, but even
    then you have to go pretty low to see big differences.
    A test with a 2.8/50 Apo-Rodagon, a 2.8/50 Componon-S,
    a 4.5/50 Focotar and a 4/60 Rodagon shows that it's only
    possible to identify the Focotar because it hat some
    curvature of field. (24x36 enlarged 10x to 24x36cm, all lenses
    stopped down two stops). It is easily seen with the 10x loupe
    of the Peak, but more difficult to identify on paper. The
    other three show only infinitesimal differences.

    A three lens Trinar was easily identified ;-)

    Martin
     
    Martin Jangowski, Jan 28, 2004
    #2
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  3. John

    Bob Salomon Guest

    Or 50mm 2.8 Apo Rodagon-N?
     
    Bob Salomon, Jan 28, 2004
    #3
  4.  
    Martin Jangowski, Jan 28, 2004
    #4
  5. John

    Bob Salomon Guest

     
    Bob Salomon, Jan 28, 2004
    #5
  6. John

    jjs Guest

    Bob, are you saying that the glass carrier is part of the optical formula?
    Does a glass carrier do more than simply keep the negative flat? Tell me
    it does so that I have some rationalization for the dust I put up with. :)
     
    jjs, Jan 28, 2004
    #6
  7. Oh, absolutely:

    1) Attracts dust: helps keep the rest of your darkroom dust free

    2) Creates Newton's rings: Adds color and pattern to your pictures

    3) Decreases contrast: Keeps those pesky highlights under control

    4) Alters light path: Helps achieve that sought-after 'soft focus' look

    5) Shatters when dropped: Maintains full employment in the glass industry
     
    Nicholas O. Lindan, Jan 28, 2004
    #7
  8. John

    Bob Salomon Guest

    The glass carrier does 2 things that are critical for optimal results
    when enlarging.
    1: It holds the film flat over the entire area of the film that is being
    printed.
    2: It prevents the film from moving during exposure.

    As to dust I don't find it to be a problem with glass as if there is
    dust on the glass there would be dust on the film. And I would prefer to
    clean glass rather then film.

    So I have painted my darkroom with a washable enamel where it isn't
    tiled, have tile on the floor and plastic sheeting under the ceiling
    tiles between the joists of the ceiling. There are also no open shelves
    or spaces where dusting would be difficult to do. Lastly the room is
    slighly higher pressure than the hall way leading to it and the air
    vents are filtered. So there is minimal dust to beging with.
     
    Bob Salomon, Jan 28, 2004
    #8
  9. John

    Bob Salomon Guest

    Film also attracts the dust in your darkroom.
    Not when AN glass is used
    Says who?
    Nope. It is above the lens not below it
    Butterfingers?
     
    Bob Salomon, Jan 28, 2004
    #9
  10. John

    jjs Guest

    Okay, I knew that. I was wondering if there were some magic I had overlooked. :)
    My darkroom is pretty much stone-age, almost literally. The house is quite
    old for this part of the country (1886); stone basement and the house is
    small. Dust is problem. It does not help to have a woodworking shop next
    to the darkroom door. I'm really 'into' dust management, but that's an
    ariticle in itself.
     
    jjs, Jan 28, 2004
    #10
  11. John

    jjs Guest

    Nope. A large, charged ABS plastic sink attracts the dust. Just wipe it
    clean once a day. It's like magic.
    Never had Newton's rings with the Leitz Focomat IIa enlarger.
    Nice try, but not true.
    Now you are frightening me. No more coffee before printing!
     
    jjs, Jan 28, 2004
    #11
  12. John

    HypoBob Guest

    John,

    Search this ng's archives for articles by Michael Gudzinowicz about
    enlarging lenses. He gives the optical formulas for depth of field at
    the negative stage. Doing the computations for your situation will most
    likely convince you that a glass carrier and a "perfectly" aligned
    enlarger are necessary for the best results your system can deliver.

    Bob
     
    HypoBob, Jan 28, 2004
    #12
  13. Glass between the negative and the lens affects the focus slightly,
    depending on the thickness of the glass. It does that by refraction, of
    course, which means that the effect varies with thickness of the glass
    as well as color of the light. Some lenses are designed to be used with
    a glass carrier of certain thickness. Whether any of us mortals could
    tell the difference is another matter. In any case, you can see how
    glass might affect chromatic aberration and curvature of the field for
    better or worse, depending on how the lens is designed.
     
    Patrick Gainer, Jan 28, 2004
    #13
  14. John

    Bob Salomon Guest

    Any shift in focus would be compensated for when the enlarger is
    focused. It is a non-issue.
     
    Bob Salomon, Jan 28, 2004
    #14
  15. John

    jjs Guest

    That reads like impressionistic keyboard engineering. I've never seen it
    IRL.
     
    jjs, Jan 28, 2004
    #15
  16. put up with. :)

    The glass is not part of the formula and has insignificant
    effect on the light in the optical path. What Bob is getting
    at is that high quality enlarging lenses are designed to
    image a flat object onto a flat surface. If the negative
    bows, as it will in a glassless holder, the corner
    performance of the lens is compromised. Despite the extra
    bother of the glass sandwich holder it does increase
    sharpness, particularly at the corners, and eliminates
    motion of the negative during exposure. This last can be the
    explanation for the occasional complaint of getting not
    quite sharp prints from sharp negatives even though the
    lenses are of excellent quality.
    The choice is whether these advantages are worth the
    considerable extra effort of keeping four glass surfaces
    absolutely clean and free of blemishes. For some printing,
    particularly where a great amount of magnification is
    involved, I think the glass carriers are a must.
    There are lenses designed to work from curved surfaces.
    Some slide projector lenses, for instance, the Kodak Ektanar
    series, are so designed, intended to work with cardboard
    mounted slides. The problem is that many times these slides
    are much closer to being flat than was assumed in the lens
    design so a flat field lens will give better pictures.
    Slides are another case where glass, in this case glass
    sandwich slide mounts, has advantages in consistent
    sharpness despite extra effort being needed to keep
    everything clean.
     
    Richard Knoppow, Jan 28, 2004
    #16
  17.  
    Richard Knoppow, Jan 28, 2004
    #17
  18. A plane parallel glass sheet will have an effect on image
    forming light passing through it. The amount of effect
    depends on the "vergence" of the light and the properties of
    the glass or other material. If the light is collimated,
    that is, if the light waves are parallel, as they are when
    coming from a great distance, there is no effect. If the
    light is convergent or divergent the sheet will introduce
    spherical aberration and chromatic aberration. The former is
    because light will be bent depending on its original angle
    of incidence. The second is really due to the same thing
    except that the index of refraction of glass is not constant
    with wavelength. Glass bends, or deviates to use a more
    correct term, light more for blue than for red. The amount
    of this difference is called dispersion. In lenses this is
    compensated by using combinations of positive and negative
    lenses of different kinds of glass.
    The above is the reason that filters can have a degrading
    effect on a lens. When a filter is used between a lens and a
    distant object the effect is insignificant. When used where
    the light is angled (vergent), as on the back of a lens in
    normal photography, or on either side for macro/micro
    photography, the effect can be significant. That's why thin
    gelatin filters are used where the best quality imaging is
    done. Gelatin has a low index of refraction, so its effect
    is small, plus gelatin filters are very thin compared to
    glass.
    In an enlarger, where the glass is close to the negative
    or transparcency, it has little effect on the light or on
    the quality of the reproduction. If it were next to the
    lens, it would have such an effect because the relative
    angles of the light passing through it would be much
    greater.
     
    Richard Knoppow, Jan 28, 2004
    #18
  19. John

    HypoBob Guest

    jjs,

    Please be more careful with your snipping. You have made it look like I
    made the statement below, which I did not.

    Thanks,
    The real HypoBob

    ----------------------------------
     
    HypoBob, Jan 29, 2004
    #19
  20. Not true. The focus can only be compensated for one wavelength. The
    prism in binoculars affects the chromatic aberration of the system and
    is accounted for in the design.
     
    Patrick Gainer, Jan 29, 2004
    #20
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