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  1. #11

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    If your film is exposed properly, Diafine will not cause excessive contrast. The effect on speed of using Diafine is different with each film. In general Diafine produces less contrasty negatives. That's why it's preferred for contrasty lighting. When the Olympus OM system came out, several camera magazines described the Zuiko lenses as having unremarkabe resolution but very high contrast. Even the famous 50/2 Dual Range Summicron, which has very high resolution, is considered to be low in contrast by today's standards.

  2. #12
    phenix's Avatar
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    Quote Originally Posted by dynachrome View Post
    ...When the Olympus OM system came out, several camera magazines described the Zuiko lenses as having unremarkabe resolution but very high contrast. Even the famous 50/2 Dual Range Summicron, which has very high resolution, is considered to be low in contrast by today's standards.
    When contrast (or acutance) increases, resolution falls. The reverse is not always valid.

    The explanation is simple: increase in contrast means fewer grays. Or, at higher resolutions, even the blackest black and the whitest white show up as very close gray tones, that a high contrast glass or film will not be able to see and record. Contrast (or acutance) means constant-high visibility at lower and middle resolution values, after which this visibility drops abruptly.

    Now the reverse: having a low contrast glass doesn’t necessarily mean that it allows high resolution. It simply can be a bad piece of glass. But if it’s a good one, it should do high resolution.
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  3. #13

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    Quote Originally Posted by phenix View Post
    When contrast (or acutance) increases, resolution falls. The reverse is not always valid.

    The explanation is simple: increase in contrast means fewer grays. Or, at higher resolutions, even the blackest black and the whitest white show up as very close gray tones, that a high contrast glass or film will not be able to see and record. Contrast (or acutance) means constant-high visibility at lower and middle resolution values, after which this visibility drops abruptly.

    Now the reverse: having a low contrast glass doesn’t necessarily mean that it allows high resolution. It simply can be a bad piece of glass. But if it’s a good one, it should do high resolution.
    I don't agree.

    Increase in contrast means that light is spread less over areas it shouldn't be in.
    At higher resolutions, even the blackest black and the whitest white will still be the blackest black and the whitest white.
    That increases resolution.

    Increase in contrast does not mean fewer grays. Only fewer false greys. Less, or no, veil over areas that should be black.

    Such a veil (that is producing the low contrast in low contrast lenses) is produced by light that should be in highlight areas, so they are reduced in intensity - become more grey - too.

    Grey tones are still rendered as grey tones. No light is added nor taken away.


    Low contrast lenses do spread light over areas it should not be in.
    The veil drowns fine detail, fills troughs between highlight detail, and fills dark detail.
    That does not necessarily make them disappear, but will make them less apparent (which is why MTF, a function of contrast against detail size/frequency is used as a measure for lens performance, not resolution or contrast alone).

    While high contrast does not mean fewer greys, low contrast does mean fewer blacks (and whites).

    So "When contrast (or acutance) increases, resolution" increases as well.
    Last edited by Q.G.; 08-01-2009 at 04:40 AM. Click to view previous post history.

  4. #14
    David A. Goldfarb's Avatar
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    Keithwms is probably right.

    The XA2 has a tessar type lens--not "strange" at all, but the most popular lens design in the history of photography--which should be fairly contrasty. I haven't owned an XA series camera myself, but hunting around for comments there is some sentiment that the XA2 tessar-type seems sharper than the fancier 6-element XA lens, which isn't surprising. With the same coatings, a tessar will often look contrastier than a plasmat or planar type, but it won't be as sharp in the corners. For some kinds of photography (standard types of portraiture, for example), sharp in the center and soft in the corners is just fine.

    Also, you can't really compare EI 800 on an XA2 to EI1250 on your SLR, unless you know that the shutters are both accurate--and even then, it's hard to say what that means when the XA2 has a leaf shutter and the SLR has a focal plane shutter--and the meters would have to work in the same way, which they don't. Beyond being within a stop of each other, I wouldn't really expect to be able to make the kind of critical comparison you're making here.

    You don't mention what film you're using, but it is likely that by giving more exposure on the XA2, you're pushing the image to a steeper part of the curve, and that is giving you more contrast. Put another way, maybe at 1250, more of the shadows are resting on the toe of the film's characteristic curve, so the highlights aren't very high up on the curve, and if you exposed at 800, you would get more tonal separation throughout the tonal range.
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  5. #15
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    You don't mention what film you're using, but it is likely that by giving more exposure on the XA2, you're pushing the image to a steeper part of the curve, and that is giving you more contrast. Put another way, maybe at 1250, more of the shadows are resting on the toe of the film's characteristic curve, so the highlights aren't very high up on the curve, and if you exposed at 800, you would get more tonal separation throughout the tonal range.
    This makes sense.

    I'm using Tri-X, which pushes pretty well with Diafine. The last couple half-rolls I've tried pushing with D-23 hoping to get finer grain with a developer that I can control contrast with. But there's seems to be less shadow speed with the conventional developer and the grain isn't much different. I always wondered if Diafine actually increased 'real' speed or just seemed like it because it was such a low-contrast compensating developer that protects the highlights and thus doesn't 'look pushed'. I haven't done any formal tests but I think it actually does give a little bit more speed.
    f/22 and be there.

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