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Enlarging lens comparisons

Discussion in 'Everything Film' started by huwevans, May 16, 2006.

  1. dyncoed

    dyncoed Well-Known Member

    ive got a couple of schneider lenses i might be able to loan out if their of any value, both componon lenses.

    one's a 50 f/4, the others an 80 f/5.6.

    will be interesting to see the results.

    mark
     
  2. Fair enough ! As a matter of interest, how would I go about testing the quality of my own lens ? I never make prints bigger than 8x10 inches, so am I ever likely to see much difference in quality of results by using different lenses ? I suppose I do sometimes do selective enlargements, but these would usually go on a 7x5 inch print. I know that the negative is a major factor, so there's no point testing an enlarging lens using a negative that's been made using a poor camera lens, but I have recently broken my personal record for "most expensive lens purchased" when I got a Minolta 100mm/2.8 macro lens which seems to have excellent reviews - so I think I should be capable of producing a good negative on slow film.
    Regards,
    Andy
     
  3. huwevans

    huwevans Not Really Here

    Small prints are fine - no sense in wasting large expensive sheets of paper. But you will want to test the lens at various different enlargement factors, and for a couple of reasons.

    In all probability at 10x8 the lens should be giving something like its best performance. But do try it at different apertures, from wide open to two or three stops down. There's not much point going beyond that.

    Make sure you're using a film with grain large enough to focus on. It might be counter-intuitive, because we're always wanting fine-grained films for best image quality, but if you want to test the enlarging lens it's really the grain that matters - the image made by the camera lens is neither here nor there. So choose a negative that has plenty of well exposed tones in the middle of the range. But you'll also want some deep shadows to get an idea of how well the lens copes with low contrast, so maybe another neg that's a stop or two under-exposed would be good to try as well.

    Make sure your enlarger is as well aligned as possible - the testing procedure itself may show up misalgnment, so it could be an iterative process. After that of course you will need to observe all the usual best practices, like making sure you focus carefully on the grain, and process the print properly, in fresh chemistry. Then it will be a case of careful examination of the print under a good lupe and a bright light.

    But try also a large magnification. Small crops will be fine. Print from the centre, and also from each corner of the neg. Make sure you make a note of which way round the neg was in the gate, if it's not obvious, because this is where you will get clues about any alignment problems. Don't stop down too far for a test like this, because the lens will be heavily diffraction limited - good enlarging lenses almost always are at high magnifications, and this is the worst case scenario. So try wide open and one stop down, but don't go much further than that. You'll want to see if field curvature of the lens and/or alignment of the enlarger is losing definition in the corners. Compare the grain in these test shots directly with that of the smaller print, where it should be at its best, you're only using the centre 'sweet spot' of the lens, and where you should in any case be able to get enough DoF at a couple of stops down to iron out any problems without also letting diffraction take its toll.

    That should do for basic testing of any lenses you want to work with. A lot of the things I'll be looking at will only be relevant in the context of comparing different lenses with the same negative, so they won't really apply. All of the above is in the context of monochrome enlarging - I may also look at testing the lenses with colour paper and filtering in order to look at things like chromatic aberrations, but that will get a bit involved.
     
  4. RonM

    RonM Alpha Napper

    Sorry for 'phiggying this thread Huw, but, just in case you're still going ahead with this test, I may be about to get my hands on a Meogon S 50mm f/2.8 another enlarger lens the late Barry Thornton reckoned was as good as the likes of Schneider, I'll keep you posted as to availability.
     
  5. huwevans

    huwevans Not Really Here

    No problem, Ron. Yes, it's still going ahead, though you might rightly deduce from my silence on the matter for the last few months that I haven't actually got started yet! :) One for the long winter evenings ahead, I guess.

    If Barry Thornton rated the Meogon that's good enough for me - definitely one to include, if you'll be able to spare it for a few days.
     
  6. RonM

    RonM Alpha Napper

    Well if I get my hands on the Meogon then that will be 3 for you to try out from me as soon as I know more about the Meogon I'll let you know.
     

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