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  1. #31
    Ole
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    At the same magnification, the exposure should be the same regardless of distance. So the inverse square law doesn't enter into it from that point of view.

    But inside the enlarger it's a different matter: The longer lens will be a longer distance from the negative. Now if all the light were perfectly focussed through the negative the exposure would still be exactlu the same. But since you either have (1) diffused illumination, where the inverse square law works inside the bellows or (2) condensers focusing the light through the negative onto the lens, you end up with a greater light loss than the inverse square law (as applied to the distance from lens to paper) would predict. The loss in condenser systems is actually the most difficult to predict.
    -- Ole Tjugen, Luddite Elitist
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  2. #32
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    Quote Originally Posted by TheFlyingCamera View Post
    Ole- ok, perhaps not twice, but I know that my 50mm for my Contax cameras supposedly resolves 120+lp/mm, whereas the 80mm for my Hasselblad resolves around 96. Not a huge difference, but still statistically significant.
    http://www.hevanet.com/cperez/results.html

    I too used to believe that 35mm lenses were twice as sharp, until I compared slides shot with the same film type in a Bronica ETRS with 35mm back and one of Nikon's finest prime lenses. Under a good microscope the Zenzanon won hands down.
    -- Ole Tjugen, Luddite Elitist
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  3. #33

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    Quote Originally Posted by TheFlyingCamera View Post
    Yes, but at the same time, using the longer lens will put the image area projected on the baseboard firmly in the lens' sweet spot. This will mean that the smaller neg is evenly illuminated across the entire negative area, and that corner-to-corner resolution will be consistent as well.
    True, but:

    • What I've written is also true; they're just two factors that are at work in determining the final results.
    • In practice, both sides of this coin are theoretical and meaningless unless and until you measure the actual characteristics of specific lenses. If somebody asks me whether it's better to use a Brand X 50mm lens or a Brand Y 80mm lens to enlarge 35mm negatives, my reply is to test them both. The theory is useful for understanding what's going on and for making predictions, but in this case, there are theoretical factors that are in conflict, and the only way to resolve that conflict is to perform tests. The results will be specific to the particular lenses tested.

  4. #34
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    Quote Originally Posted by srs5694 View Post
    ...imagine you've photographed a resolution chart with a magical camera lens and film that produce infinite resolution, and you're enlarging onto paper with infinite resolution; thus, any limitations you see in the print are due to the enlarging lens. You photograph the chart twice, once to fill the frame of your 6x6 camera and once to fill only a 24x36mm part of the negative. Your enlarging lens is a non-magical variety, so your enlargement will reveal limitations. You now make life-size prints of the original chart, which means you'll be enlarging more when you make the enlargement from the 24x36mm crop, which means the resulting print won't be as sharp.
    Of course. I was commenting on a different notion. A 24mm X 36mm transparency area (regardless of film format) enlarged to 8" X 10" with lenses of two different focal length.

    Quote Originally Posted by srs5694 View Post
    In other words, and stepping back to something more closely resembling the real world, using a longer focal length than necessary when making an enlargement means that you're not getting the lens's optimum sharpness. Whether that's better or worse than using a shorter lens, though, depends on the specific lens-to-lens comparison.
    The emphasized portion may be true but I'm still lost as to how A follows B here, in my example of the same neg and two lenses.

  5. #35
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    Thanks for all the replies-------looks like some interesting debates were generated from my post. I think from what I've been able to ascertain, I would like to get a more powerful enlarging lens for my 6x7 neg, about 100 to 105mm.

    Thanks all,

    Chuck

  6. #36

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    Quote Originally Posted by jstraw View Post
    Of course. I was commenting on a different notion. A 24mm X 36mm transparency area (regardless of film format) enlarged to 8" X 10" with lenses of two different focal length.
    ...
    The emphasized portion may be true but I'm still lost as to how A follows B here, in my example of the same neg and two lenses.
    First, note that from my very first post in this thread, I've said that the only way to be sure which of two lenses is better is to test them! Any other claim is purely theoretical -- you cannot make an honest and absolute statement that an 80mm lens is better than a 50mm lens for enlarging a 35mm negative, or vice-versa, except perhaps in terms of specific attributes such as head height.

    As to the rest of my point, let's try it again from another perspective. Using the center resolution figures for the 50mm Vega-11U lens (70 lpmm) and 75mm Industar-90U lens (50 lpmm) (just because I happened to have the URLs handy), consider what happens when you enlarge various negatives. Optimistically ignoring center vs. edge resolution effects, the 50mm lens resolves 2520 lines across the horizontal distance (36mm) of a 35mm full-frame negative and the 75mm lens resolves 2750 lines across the horizontal (or vertical) distance of a 6x6 negative (55mm per side). The 75mm lens therefore produces better resolution from the 6x6 negative than the 50mm lens does from the 35mm negative, ignoring effects of the taking lens and the film's resolution. Use the 75mm lens on a 35mm negative, though, and it can resolve just 1800 lines across the horizontal length of the negative. Of course, as was pointed out in another post, you won't really get the full 2520 lines from the 50mm lens because its edge resolution isn't as good as its center resolution, but this effect will be much smaller with the 75mm lens when enlarging a 35mm negative. If we assume that 50% of the negative's area gets the specified edge resolution (40 lpmm) when using the 50mm lens, that gives 1980 lines, which still beats out the 75mm lens's 1800 lines, although with a different pattern of where the sharpness lies.

    Thus, there's a theoretical reason to think that using a longer-than-necessary lens may produce worse results than using a lens of the standard focal length. Getting back to my first, and emphasized point, though: This depends on many factors of the specific questions, such as the lenses' individual factory-spec resolutions, manufacturing flaws, any dust or scratches they've acquired over time, etc. I'm sure you can find lens pairs whose specifications would produce different results than the ones I've just presented. A meaningful practical comparison requires comparing two specific real-world lenses, including all their idiosyncratic flaws (not just what's in their specification sheets).

    FWIW, the only reason I brought up this point was that I was getting the impression that people were singing the praises of using longer-than-normal lenses to make enlargements, ignoring the downside of the equation.

  7. #37
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    Thanks, I get it now.

  8. #38
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    Quote Originally Posted by srs5694 View Post
    A meaningful practical comparison requires comparing two specific real-world lenses, including all their idiosyncratic flaws (not just what's in their specification sheets).

    FWIW, the only reason I brought up this point was that I was getting the impression that people were singing the praises of using longer-than-normal lenses to make enlargements, ignoring the downside of the equation.
    Just a query here, becaue I don't know how the resolution numbers for lenses are determined..

    As an example, say I had a 24x36mm (135) negative, and an associated 50mm enlarging lens. In addition, say I had a 105mm enlarging lens (normally used with a 56x87mm (6x9) negative). Say as well I was given resolution data in lpmm for both lenses.

    Theoretically, you could print full frame 4"x6" prints from the 135 negative using either lens - you would just need to change the height and focus adjustments on the enlarger.

    My question is, are the resolution tests that yield lpmm resolution data dependent on negative size? Does using a lens on an enlarger set up for higher magnification result in a change in the lpmm resolution numbers? Is that change an increase?

    Matt

  9. #39

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    Quote Originally Posted by MattKing View Post
    My question is, are the resolution tests that yield lpmm resolution data dependent on negative size? Does using a lens on an enlarger set up for higher magnification result in a change in the lpmm resolution numbers? Is that change an increase?
    Ordinarily I wouldn't post just to say "I don't know," but as you quoted me to begin your query, I feel compelled to respond.

    I don't know. Sorry.

  10. #40
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    I have used a 210mm lens for 8x10 and I can say that the edges are not as sharp as with a 300mm or maybe larger.
    Second
    I save my losers till I drymount the good one and then throw it away. It isn't going to get any better stored anyway, unless you want someone to see your losers and I you don't have any pride I guess you would give them to someone or even let them see them. Even if my print isn't to someone's standard but is the best I can do, that is the only print I will keep. I have even thrown out the best one after drymounting if I still have any question about the quality of the print. Like bad stock, I'm not married to bad prints either.

    Michael Andersen
    "Capturing an image is only one step of the long chain of events to create a beautiful Photograph” See my updated website: mandersenphotography.com

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