Confused about focal lengths and bellows draw

Discussion in 'Enlarging' started by BetterSense, Sep 29, 2009.

  1. BetterSense

    BetterSense Member

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    I have an Omega D2 for printing 4x5 negatives. I have a 135mm lens. I can just barely print an 8x10, if I loosen my lens several turns for more extension. Any smaller, and my bellows racks all the way out before I obtain focus. So if I want to print a 5x7 from 4x5 right now I can't.

    My first instinct is "Oh, I need a longer lens, then the baseboard image will be smaller". But wouldn't a longerr lens need MORE bellows draw? Or would a longer lens force me to put the enlarger higher, paradoxically resulting in less bellows draw (real focal length)? This is confusing my brain.

    Also, has anyone ever printed medium format and/or 35mm with the 4x5 condensers in place? I understand that they make special condensers for smaller formats but I'm having a hard time understanding why, considering that if it works for 4x5 it shouldn't work the same for 35mm, considering 35mm is basically a crop out of a 4x5 negative.
     
  2. David A. Goldfarb

    David A. Goldfarb Moderator Staff Member Moderator

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    A 135mm lens on an Omega D2 should be on the medium sized cone (around 2 inches) if I remember correctly. It sounds like you probably have it on a flat lensboard. That would be your problem.

    The original D-II, which I have, only came with the option of 4x5" condensers, and smaller format and variable condensers came into place later.

    The main purpose of the condensers is to produce even illumination across the negative, and in this regard, you should have no trouble using condensers for a larger format when enlarging a smaller format negative. Having condensers matched to the format would give you more efficiency (brighter illumination) with smaller formats, but in my experience the difference isn't enormous. (Of course you can't use a condenser designed for a smaller format with a larger format neg, or you won't illuminate the whole neg evenly).

    Another issue that some people think is important is the role the condensers play in the collimation of light in the system, and if this is significant, then condensers that are well matched to the format and focal length of the enlarging lens could produce sharper prints, more like a point source enlarger, so Durst, for example, offers a wide range of condenser sets for different enlarging lenses and formats. I could see this being important, if you were making a lot of enlargements to the same size, and the condensers, format, and enlarging lens were matched for that specific reproduction ratio, but change the magnification ratio without adjusting the condensers accordingly, and as I see it, the system is no longer matched, so I'm a bit dubious about matching condenser lenses closely to format in general for the purpose of improving sharpness.

    And in any case, I prefer cold light.
     
  3. BetterSense

    BetterSense Member

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    May I ask, why do you think cold light better? Is it just because cold light heads tend to be diffusion heads? I don't even know if that's true I'm just wondering about cold light heads. All I know about them is they use fluorescent tubes, which would keep heat down in the darkroom.
     
  4. David A. Goldfarb

    David A. Goldfarb Moderator Staff Member Moderator

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    Less spotting and a smoother look with diffuse light sources. Ansel Adams also explains in The Print that diffuse light sources reduce the Callier effect, which can cause high values to become blocked, which I haven't attempted to sort out for myself, but I like the look.

    Condensers produce sharper grain than diffuse light sources, if you like that.
     
  5. jeffreyg

    jeffreyg Subscriber

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    Check into the Aristo VCL4500. I've used one for many years and have found it to be very worth-while. They are not cheap but you don't need different paper grades and can easily vary the contrast within an image ( multigrade paper ).
     
  6. BetterSense

    BetterSense Member

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    Do you mean that with a cold-light head, you can vary the contrast of graded paper?

    I don't quite understand this.
     
  7. DLawson

    DLawson Member

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    With SOME cold light heads, you can vary the color mix of the light. This does the same thing as the variable contrast filters. So you can vary contrast of VC papers.
     
  8. jeffreyg

    jeffreyg Subscriber

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    The Aristo has 2 bulbs, one blue and one green. There are three different modes and you can dial in the contrast grade when using multigrade paper. A "plain" cold light would require using variable contrast filters. www.aristgrid.com
     
  9. RalphLambrecht

    RalphLambrecht Subscriber

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    That's possibly the only misinformation AA ever distributed. There is no difference in tonality or gradation between both types of enlarger if the negative was developed accordingly. Yes, a condenser will block the hightlights in a negative developed for a diffuser, but not if the negative was developed for the condenser.
     
  10. jeffreyg

    jeffreyg Subscriber

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  11. David A. Goldfarb

    David A. Goldfarb Moderator Staff Member Moderator

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    I'm inclined to agree with that in general, and I believe that Adams acknowledged that you could just develop to lower contrast for condensers as opposed to cold light, but I do wonder about how the Callier effect causes detail to be rendered differently in dense portions of the negative as opposed to light areas. I've never tried to test this definitively, but to answer the question I think it would be necessary, say, photograph a series of resolution charts on a Zone board or something like that, so some of them are in Zone I and some at Zone X and at all steps in between, and then process one neg for a condenser enlarger and one neg for a diffusion enlarger, make prints at the same contrast, and then compare resolution in light and dense areas of the neg on both prints, and compare the prints to each other. Of course the difference in the way diffusion renders grain compared with a condenser enlarger probably makes more of a difference in resolution than the Callier effect.
     
  12. RalphLambrecht

    RalphLambrecht Subscriber

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    David

    Dr. Richard Henry did that for his book 'Controls in Black and White Photography', and I repeated it with more modern materials. I got the same results as he did; no difference between diffuser and condenser enlarger as long as the negative is developed accordingly.
     

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  13. David A. Goldfarb

    David A. Goldfarb Moderator Staff Member Moderator

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    Actually, that shows something different from what I'm thinking about. Your graph shows that you can match print densities by developing the negative accordingly, and I don't dispute that, but I'm asking whether the sharpness of highlights is different due to the light scatter in areas of higher density of the neg and the way they are rendered using a condenser enlarger as opposed to a diffusion enlarger. Of course if the contrast is matched, the highlights need to be even more dense for a diffusion light source, and beyond that diffusion light sources are all about light scatter, but maybe a more precise question would be: is the difference in sharpness between highlights and shadows for prints made with a condenser enlarger different from the difference in sharpness between highlights and shadows for prints made with a diffusion enlarger.

    It's kind of an academic question, because I don't think this is a thing that anyone tries to control in practice, but an answer might add to what we generally understand about the difference in the way prints made using a condenser light source look when compared with prints made with a cold light head.
     
  14. RalphLambrecht

    RalphLambrecht Subscriber

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    Condenser enlarger do indeed produce more micro-contrast (apparent sharpness) than diffuser enlargers. Hence, more spotting with condensers. Other than that, no difference. Did I still miss your question?
     
  15. dancqu

    dancqu Member

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    You're instincts are correct. The 4x5 set will cover any
    smaller format and may be expected to do it very well.
    Auxiliary sets for smaller formates are not available
    or an extra with many enlargers.

    Smaller formates need greater enlargement. To keep
    exposure times reasonable the light source is brought
    to a shorter focus. Coverage is reduced while light
    intensity is increased.

    My 'test strips' are full negative very small prints
    printed 2 up on 5x7 paper. On my junior D2, an
    Omega B8, I use a 105mm lens for 6xX. Dan
     
  16. David A. Goldfarb

    David A. Goldfarb Moderator Staff Member Moderator

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    I'm thinking of something more specific than that, though as I say, it's something of an academic question. Let me try posing it another way. If there is more light scatter in dense areas of the negative than in thin areas of the negative when projected, we might expect highlights on the print to be less sharp than shadows. I'm fairly sure this much is true, because a thinner negative is generally a sharper negative than a denser negative. So my academic question is whether the difference in sharpness between highlights and shadows is more apparent on prints made with a condenser enlarger than with a diffusion enlarger. In other words, is the effect of light scatter in the highlights on sharpness, not print density, greater when the light source is relatively collimated than when it is diffuse.
     
  17. RalphLambrecht

    RalphLambrecht Subscriber

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    David

    I understand your question, but I need to dig into this a bit deeper. There definitely is a difference between highlight and shadows as far as Callier effect goes, but I have not seen a tonal difference between diffusion and condenser enlargers because of it.
     
  18. bdial

    bdial Subscriber

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    Ctein has a good evaluation of the differences between condenser, diffusion enlargers in Post Exposure.
    His conclusion was that the differences are more subtle than just contrast, but now I don't remember the details, and I don't know where my copy is hiding.
    Maybe someone who has a copy at hand could elaborate.
     
  19. David A. Goldfarb

    David A. Goldfarb Moderator Staff Member Moderator

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    I'd forgotten about that chapter in Post Exposure, but yes, he does have some conclusions along these lines.

    One interesting point that he makes is that while a condenser enlarger resolves grain better than a diffusion enlarger, it does not seem to resolve image detail better than a condenser enlarger, image details being larger than individual film grains.

    Ctein observes--

     
  20. RalphLambrecht

    RalphLambrecht Subscriber

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    That's a conclusion many support.
     
  21. BetterSense

    BetterSense Member

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    I think that's the theory behind drums scans...you control the aperture of the photomultiplier tube so that it's larger than individual grains, and this somehow lets you average out the grain while not losing image detail.