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  1. #1
    NDP_2010's Avatar
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    Some enlarging questions

    I am new to the world of film printing and have done some black and whites.

    I am curious with a few questions.

    What is the advanatage of stopping down an enlarging lens? Is there any advanatage in having a fast enlarging lens?

    I also have a few questions about exposure time.

    I noticed that i left a few pictures enlarging for too long and the contrast was quite low and the picture was very dark. I tried a shorter time and the picture had much more contrast.

    If i enlarge for a short period of time, does this mean highlight details will not be captured? If i have a picture where the forground is quite dark, can i ever effectively recapture these details while keeping the picture relatively contrasty or is it impossible as the picture was not taken correctly.

    Thanks.

  2. #2
    Marek Warunkiewicz's Avatar
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    Hi, here are some answers...

    ***What is the advantage of stopping down an enlarging lens?***

    Better sharpness from edge to edge. Most lenses have a sweet spot of sharpness/acutance etc around 2 or 3 stops down from the most wide aperture.

    ***Is there any advantage in having a fast enlarging lens?***

    Yes there is. basically it concerns the point above and printing speed. When you have a 2.8 lens and stop down two stops you get 5.6. Assume your time to get a good print is 12 seconds at 5.6. If you had a 5.6 lens and you stopped it down to 11, your time would be 48 seconds. It's all about the exposure time.

    The ***dark contrast print*** question has more to do with your negative and contrast filter. To really answer that question we would need to know the paper used, time(s) of exposure of the different prints, developer and time in developer, the contrast filter used (if any) and ideally a scan of the negative prints.

    You can capture a wide range of tones in a negative, it's all about the exposure and development (Zone system).

    Marek
    Marek Warunkiewicz

  3. #3
    RalphLambrecht's Avatar
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    Quote Originally Posted by Marek Warunkiewicz View Post
    ... ***Is there any advantage in having a fast enlarging lens?***

    Yes there is. basically it concerns the point above and printing speed. When you have a 2.8 lens and stop down two stops you get 5.6. Assume your time to get a good print is 12 seconds at 5.6. If you had a 5.6 lens and you stopped it down to 11, your time would be 48 seconds. It's all about the exposure time. ...
    I see another advantage in using a 'fast' enlarging lens. Even if you enlarge at the 2-3 stops down from wide open, a wide-open lens will make it easier to accurately focus the image on the base board before you stop it down and enlarge to get the most out of the lens.
    Regards

    Ralph W. Lambrecht
    www.darkroomagic.comrorrlambrec@ymail.com[/URL]
    www.waybeyondmonochrome.com

  4. #4
    RalphLambrecht's Avatar
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    Quote Originally Posted by NDP_2010 View Post
    ... I also have a few questions about exposure time.

    I noticed that i left a few pictures enlarging for too long and the contrast was quite low and the picture was very dark. I tried a shorter time and the picture had much more contrast.

    If i enlarge for a short period of time, does this mean highlight details will not be captured? If i have a picture where the forground is quite dark, can i ever effectively recapture these details while keeping the picture relatively contrasty or is it impossible as the picture was not taken correctly.

    Thanks.
    It's hard to answer this one without knowing what your printing method exactly is, but I can offer two articles, which may help you:

    http://www.waybeyondmonochrome.com/W...xposureEd2.pdf

    http://www.waybeyondmonochrome.com/W...rintingEd2.pdf
    Regards

    Ralph W. Lambrecht
    www.darkroomagic.comrorrlambrec@ymail.com[/URL]
    www.waybeyondmonochrome.com

  5. #5

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    In answer to your first question, there are several reasons to use a smaller aperture on an enlarging lens.

    1. Lenses can be slightly sharper closed 1 or 2 stops. Thus an f/2.8 lens might be slightly sharper closed down to f/4 or f/5.6 (any difference is likely to be small).

    2. If you want to give some parts of the print more or less than the basic overall exposure—called printing in and dodging—it’s useful to use a smaller aperture to give you sufficient time to perform these operations.

    3. Composition and gross focusing of the projection is most easily done with the aperture fully open for the brightest, most easily seen image. But when you fine tune the focus with a grain focuser the image may be uncomfortably bright for your darkroom-adjusted vision. By closing down to the working aperture you’ll find grain focusing the dimmer image more comfortable to your eye and the grain is more easily resolved with the lens stopped down 1 or more stops.

    4. In some cases, if you have no glass negative carrier and the negative isn’t as flat as you’d like, closing the lens may increase depth of focus at the negative sufficiently to give a slightly sharper print.

    5. Though not a problem with modern lenses, older lenses sometimes had a defect called spherical aberration. Such a lens might be focused wide open, but would change focus as the aperture was closed down to make the exposure. That’s why darkroom workers were often cautioned to refine the focus after stopping down to the working aperture to compensate for focus shift due to possible spherical aberration in the lens.

    The advantages of a fast lens are:

    1. Brighter, more easily seen image for faster composition and gross focusing.

    2. Potentially faster printing time. For example, an f/2.8 lens closed 2 stops at f/5.6 will print in half the time of an f/4 lens closed 2 stops at f/8.

    For the second question, longer exposures don’t generally result in reduced contrast. I suggest checking carefully for light leaks prior to the lens. Some enlargers spill light from around the negative carrier or elsewhere striking the wall near the enlarger and bouncing back to the paper. This is exacerbated by the greater reflectance of a white or light colored wall close to the enlarger.

    It’s likely not much of a problem with a large aperture as the total exposure time is so short that the spill light has little effect. But with a small aperture the printing time is much longer. It’s possible that such a long printing time will allow the spill light to “flash” the paper. If so, then the contrast will be reduced. That might explain your observation.

  6. #6
    Bob Carnie's Avatar
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    I think a lot of expectations of improved sharpness by closing down is highly overrated.

    An APO enlarging lens is designed be sharp at open apetures.
    We in fact focus on the grain , with a grain focuser, do we not.

    Can anyone here say that the grain gets sharper as you close down an Apo lens.
    I for one have never seen this effect when using glass carriers in my darkroom. The grain is sharp, my print is sharp.

    I am only stating what I see every time I focus, if anyone here can explain to me the theory of closing down improving grain sharpness, I am open to here it.

  7. #7
    Bob Carnie's Avatar
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    I should add , the theory should also be backed up with actual prints showing better sharpness when one is using an aligned enlarger, good optics, image centered to the neg, condensor and bulb. Also I would expect a glass carrier.

  8. #8
    fotch's Avatar
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    I think what it means that if something is not perfectly aligned, or parallel, the slight increase in depth of field will help in edge to edge sharpness. Not everyone has top of the line equipment nor the skills and patience to get the enlarger, lens board, easel, etc., into perfect alignment.
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  9. #9
    Bob Carnie's Avatar
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    To my knowledge we are not talking depth of field , rather depth of focus , which with an Apo enlarging lens there is extremely little or none.

    Quote Originally Posted by fotch View Post
    I think what it means that if something is not perfectly aligned, or parallel, the slight increase in depth of field will help in edge to edge sharpness. Not everyone has top of the line equipment nor the skills and patience to get the enlarger, lens board, easel, etc., into perfect alignment.

  10. #10
    fotch's Avatar
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    Quote Originally Posted by Bob Carnie View Post
    To my knowledge we are not talking depth of field , rather depth of focus , which with an Apo enlarging lens there is extremely little or none.
    Bob, I will admit this is way over my pay grade, however, in what the OP asked "advantage of stopping down an enlarging lens?", so,how is either different? Both depth of field and depth of focus are strongly dependent on changes in aperture, are they not?

    The APO lens is not the average enlarger lens so I am not sure how that fits in to the answer for the original question.
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