Unsharp image: Lens or negative carrier?

Discussion in 'Darkroom Equipment' started by srs5694, Jan 17, 2008.

  1. srs5694

    srs5694 Member

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    Hi,

    Until recently, I've done mostly 35mm photography, but I've been doing more medium format (6x6) recently. I mostly do 8x10-inch and smaller enlargements, but I've done a few 11x14-inch enlargements in the past, all from 35mm negatives. Using a Philips PCS130 enlarger and a Nikon f/2.8 50mm lens, this has produced fine results. Last night, though, I made an 11x14 print from a 6x6 negative, using the PCS130 and an "EL-OMEGAR" 75mm f/3.5 lens. I found that at f/5.6, my enlargement was sharp in the center but very unsharp near the edges. (8x10 and 8x8 enlargements using this lens, mostly at f/8 or f/11, are OK.) I stopped down to f/11, with substantial improvement, although the edges still aren't quite satisfying.

    The negative carriers I've got are all glassless, so this leaves me with the question: Is the problem the lens (which I bought used on eBay) or the glassless nature of the negative carrier? I don't expect a definitive answer given the information I've provided, but if there are any simple tests or things I could look for to help answer the question, I'd appreciate hearing about them.

    Also, if my problem is more likely to be the glassless negative carrier, does anybody have any suggestions on how to obtain a suitable insert for my PCS130 negative carrier? My initial thought would be to buy some anti-Newton glass from B&H for another enlarger, ensuring that it's bigger than I need, and have a local glass shop cut it down to size. If there's a better or less expensive approach, though, I'd love to hear it.

    I've got my eye on a few Schneider Componon, Rodenstock Rodagon, and Fujinon EP 75-80mm lenses on eBay, so getting a (hopefully superior) replacement lens shouldn't be a problem, if the lens is the most likely culprit. Are there any good "sleeper" lenses in this range? Which are the best Nikon models in this range? (I don't know offhand which is their 4- vs. 6-element design in this size.)

    Of course, I realize that getting both a better lens and glass for flatter negatives is the best approach. I just want to be able to prioritize my purchases.

    Thanks for any input.
     
  2. Jon Shiu

    Jon Shiu Subscriber

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    Hi, to test you could place a piece of glass over your negative to flatten it, such as a glass from a medium format slide mount.

    Nikon's 75mm lens is 4 elements and 80mm is a 6 element lens.

    Jon
     
  3. photographs42

    photographs42 Member

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    You certainly don’t need a glass carrier for the print sizes you are doing. Get a good lens and your problems will most likely be solved.
    Jerome
     
  4. bdial

    bdial Subscriber

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    Your carrier should hold the film reasonably flat. What you're describing sounds more like it's due to the lens. If it's softer than the 50 at a similar magnification, then it's certainly the lens.
    Spend your money on a better lens, you'll be able to enlarge a washboard.
     
  5. David A. Goldfarb

    David A. Goldfarb Moderator Staff Member Moderator

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    The universal glass carrier with built-in masking blades was standard for that enlarger, so you may be able to find one, but Philips enlarger parts are hard to find in general. I'd keep an eye out for one and snap it up when you see it. The Philips enlarger uses a mirror to redirect the light, so it doesn't have a big problem with negs popping due to heat, but a glass neg carrier usually improves things at any size enlargement.

    A better lens will probably improve things as well. Enlarger lenses are cheap these days, so a 6-element Componon-S or Rodagon should be fairly affordable, and even used Apo lenses have come down drastically.

    If stopping down to f:16 improves your edge sharpness and doesn't result in excessive exposure times, go for it. The improvement in edge sharpness is likely to be greater than the diffraction associated with stopping down.