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  1. #21
    jstraw's Avatar
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    Quote Originally Posted by srs5694 View Post
    Another issue about lens focal length is that you won't get as great a resolution in the final print when using a given lens to enlarge a small negative to a specific size than when you use the same lens to enlarge a larger negative to the same size. For instance, when using an 80mm lens to make an 8x10 enlargement of a 35mm negative vs. a 6x6 negative, the 35mm negative can be thought of as a crop of the 6x6 negative, and you'll get resolution in the enlargement similar to what you'd get from a larger enlargement of the 6x6 negative -- roughly 15x18, if I've done the math right.
    I'm totally lost in that paragraph.

    I'm pretty sure that an 8x10 of a 35mm neg will have the same resolution no matter what focal length lens you use but I have no idea if you're saying that it will or will not.

  2. #22
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    Quote Originally Posted by srs5694 View Post
    Another issue about lens focal length is that you won't get as great a resolution in the final print when using a given lens to enlarge a small negative to a specific size than when you use the same lens to enlarge a larger negative to the same size. For instance, when using an 80mm lens to make an 8x10 enlargement of a 35mm negative vs. a 6x6 negative, the 35mm negative can be thought of as a crop of the 6x6 negative, and you'll get resolution in the enlargement similar to what you'd get from a larger enlargement of the 6x6 negative -- roughly 15x18, if I've done the math right.

    Of course, the question was about using one lens vs. another, and that throws in the monkey wrench that the two lenses may have different resolution characteristics. If a given 80mm lens is sharper than a given 50mm lens, that fact may more than compensate for any loss of resolution from using the 80mm lens with a "too-small" format. Also, for some of the purposes that have already been mentioned, such as getting desirable additional head height when making small prints, the loss of resolution may not matter much.
    I'm not quite sure where you're coming from with this - of course the resolution of a smaller neg enlarged to a given size will be less on the final print than that of a larger negative. But this will happen regardless of the focal length of the enlarging lens being used. A 35mm neg enlarged to 8x10 with a 50mm lens will have the same resolution as a 35mm neg enlarged to 8x10 with an 80mm lens, but the resolution of the 8x10 print from a 2 1/4 neg using an 80mm lens will be sharper because the enlargement factor is less.

    To give you a situation, lets say that all film is capable of recording 500 lines of resolution per inch. A 35mm negative therefore has 500 horizontal lines (1 inch long on the short dimension). A 2 1/4 square negative has 1125 lines.

    Enlarge the 35mm neg to 8x10 - that's an 8x enlargement, so you end up with 62.5 lines per inch on the 8x10 print (500 divided by 8). By using the same lens to enlarge the 2 1/4 neg (to eliminate variation caused by different amounts of distortion, resolution loss, etc caused by the lens), we end up with a 4x enlargement, which means that the 2 1/4" neg puts 281.25 lines per inch on the 8x10 print. This is of course assuming that the taking lens on the 35mm camera was exactly the same as the taking lens on the 2 1/4" camera. 35mm taking lenses are known to have higher resolving power than 2 1/4" lenses - a 35mm lens is capable of resolving about 2x the resolution of a medium-format lens. So even if we adjust the curve to compensate for this, the 35mm is still producing 62 lines per inch, whereas the 2 1/4" is producing 141 lines per inch. This magnifies even further with large format film. Even when you control for the "normal" lens per each format, assuming the same is true with enlarging lenses as with taking lenses for a given format (not necessarily true in this case, but for the sake of argument we'll say it is), you're getting 62 lines for the 35mm neg, and 71 for the 2 1/4. The size wins, but it has nothing to do with the lens.

  3. #23

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    Quote Originally Posted by jstraw View Post
    I'm totally lost in that paragraph.

    I'm pretty sure that an 8x10 of a 35mm neg will have the same resolution no matter what focal length lens you use but I have no idea if you're saying that it will or will not.
    Enlarging lenses have resolution characteristics, so the claim that "an 8x10 of a 35mm neg will have the same resolution no matter what focal length lens you use" is wrong -- the print's resolution will necessarily change when you change lenses. That was the point of my second paragraph, which you didn't quote.

    To rephrase my original point, 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. 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.

  4. #24
    Ole
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    Quote Originally Posted by TheFlyingCamera View Post
    ... 35mm taking lenses are known to have higher resolving power than 2 1/4" lenses - a 35mm lens is capable of resolving about 2x the resolution of a medium-format lens. ...
    This is just not correct, I'm afraid. You could say that a lens for a 35mm camera needs twice the resolution, but it doesn't happen in the real world.
    -- Ole Tjugen, Luddite Elitist
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  5. #25

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    Quote Originally Posted by Mattg View Post
    I haven't tested this recently but you shouldn't be increasing the exposure time as long as you are comparing prints the same size. The reason light falls off with the square of distance is it's spread over a greater area. In this case the same light is spread over the same area, isn't it?
    This makes logical sense to me; however, I just tested it experimentally and found that you do need to increase exposure time when using a larger lens -- or at least, that's what my color analyzer told me. (I didn't make any actual prints.) I got a recommended time of 4.5s with a 50mm lens at f/8 and a column height of 40cm. Replacing that lens with a 75mm lens at f/8 and a column neight of 55cm to match the print size (4x6 inches from a 35mm negative), the analyzer told me I'd need a 10s exposure. That's even a bit longer than what the inverse square law says would be needed, but I'm willing to chalk that up to measurement error, inaccuracies in one or both lenses' apertures, and differences in the light transmission through the two lenses' elements.

  6. #26

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    Quote Originally Posted by TheFlyingCamera View Post
    I'm not quite sure where you're coming from with this - of course the resolution of a smaller neg enlarged to a given size will be less on the final print than that of a larger negative. But this will happen regardless of the focal length of the enlarging lens being used.
    You're looking at it backwards from the way I was (or I'm looking at it backwards from your perspective). You are, of course, correct that different formats' films and camera lenses have an impact on the final print resolution. My point is different: When you use an enlarging lens meant for a larger film format with a smaller film format, you're not getting the benefit of the enlarging lens's full resolution potential, measured in terms of lines of resolution per full enlargement -- some of those lines fall outside of the negative's frame. That said, you could still be better off doing this than when using a "proper-sized" enlarging lens, depending on the performance of both lenses. In practice, it'd take some test prints with specific lenses to know for sure.

  7. #27
    Ole
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    You would expect the exposure times to be identical if the illumination system were optimised for each lens. But not even exchangable condensers can provide that - the condenser system for a longer lens will also spread the light over a larger area at the negative stage.

    So in theory, it should be the same. In practice, it won't be.
    -- Ole Tjugen, Luddite Elitist
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  8. #28
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    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.

  9. #29
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    Quote Originally Posted by srs5694 View Post
    You're looking at it backwards from the way I was (or I'm looking at it backwards from your perspective). You are, of course, correct that different formats' films and camera lenses have an impact on the final print resolution. My point is different: When you use an enlarging lens meant for a larger film format with a smaller film format, you're not getting the benefit of the enlarging lens's full resolution potential, measured in terms of lines of resolution per full enlargement -- some of those lines fall outside of the negative's frame. That said, you could still be better off doing this than when using a "proper-sized" enlarging lens, depending on the performance of both lenses. In practice, it'd take some test prints with specific lenses to know for sure.
    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. I look at it from this point of view - when using high-quality enlarger optics (Nikon, Schneider, Rodenstock), the lens is a non-factor in the final image quality relative to resolution on the final print. And at the point I'm worrying about which lens I'm using to enlarge because it offers 6 lp/mm less resolution, I'm not making photos anymore, I'm reproducing USAF resolution charts.

  10. #30
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    Quote Originally Posted by Ole View Post
    You would expect the exposure times to be identical if the illumination system were optimised for each lens. But not even exchangable condensers can provide that - the condenser system for a longer lens will also spread the light over a larger area at the negative stage.

    So in theory, it should be the same. In practice, it won't be.
    In other words, the Inverse Square Law has nothing to do with the drop-off in illumination for prints of the same area using different lenses? If that's what you're saying, it makes sense to me now.
    If I had been present at the creation, I would have given some useful hints for the better arrangement of the Universe.
    Alfonso the Wise, 1221-1284

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