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  1. #1

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    Resolution of color media

    I admit that I am fairly obsessive about resolution and purchased a medium format system with this in mind. I recently tested my 80 mm lens using a USAF resolution test chart and obtained the expected ~70 line pair per mm. I used Tmax 100 film to make the exposure and bracketed the focus and, of course, used a good tripod.

    I recently did the same test using Velvia 50 and found that the resolution was one half that of the Tmax film. I also noticed that my 8x8 RA-4 prints (Fuji CA) seemed slightly fuzzy and used the B&W negative of the USAF chart to test the resolution of the paper. I bracketed the enlarger focus to convince myself that the problem was not a mis-calibrated grain focuser (also I had two of the latter and they both agreed with each other).

    Looking through the grain focuser, I was able to see all of the patterns that I could see by examining the negative with a microscope. Thus, the enlarger lens (an el-Nikkor 80 mm f/4) and enlarger light source (dichroic, i.e. diffusion) were not at fault.

    The results were that the paper seemed to have a resolution which was about 5 times worse than the tmax film for 8x8 prints (this would be less of a problem with larger prints). Are these resolution degradations the usual case with color media? If so, I wonder why I go to the trouble of using MF for color, since I would imagine that a 35 mm system would do as well.

    Any suggestions would be welcome. Thanks.

    Warren Nagourney

  2. #2
    AgX
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    Negatives and slides are typically enlarged today. So they should yield a resolution that makes that possible.

    Papers are typically not enlarged. The most critical case would be looking at them with blank eyes at minimm viewing distance.
    If they yield enough resolution to match those of the eays (or twice that...) it's okay.

    Though there are theories that even higher resolutions are beneficial to the perception.

  3. #3

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    Hi Warren,

    from my own tests and experiences:

    Resolution of T-Max with my best 35mm prime lenses at lower to medium contrast (2 - 3 stops): 140 - 155 Lp/mm.
    Resolution of Velvia 100 with the same lenses: 130 - 150 Lp/mm.
    Resolution of Velvia 50 with the same lenses: 120 - 130 Lp/mm.
    Velvia 50 has a bit lower resolution than 100 because of significantly coarser grain.
    Resolution of Ektar 100: 90 - 100 Lp/mm. Fuji Reala gets 110 Lp/mm.

    With my best MF primes I got 90 - 110 Lp/mm with TMX and 85 - 100 Lp/mm with Velvia 100.
    A friend of mine got with TMX 130 Lp/mm with his 80/f4 mm Mamiya Sekor at his Mamiya 7. Marvellous glas.

    I have never seen a difference in resolution between Ilfochrome with my slides and Ilford Multigrade with my BW prints. I am using APO enlarging lenses.
    But I have not tested RA-4 paper, because I don't use RA-4 in my own darkroom.

  4. #4

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    Thanks for your replies.

    From my tests of a 2.25x2.25 negative blown up to 8x8 (magnification of ~3.5), it would seem that there will be loss of resolution for small enlargements (less than or equal to 8x8) and one should therefore use at least an 11x11 print to avoid this. I received a PM which concurred about the much lower resolution of papers (and incidentally suggested that an APO enlarger lens is a waste of money).

    I am wondering why my Velvia slides didn't do better -- their measured resolution was about 35 lpm, which is much lower that Film-Niko's 125 lpm. I confess that I was using film that was about 2 years out of date and that I developed it myself (my first attempt at E6), but the colors seemed perfect, so I wouldn't necessarily expect processing errors. I also wouldn't expect that out of date film would have lower resolution, but I might be wrong.

    Cheers,

    Warren N

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    Since Velvia is a reversal slide film, and RA4 is intended to make prints from negative C41 films, how did you do the print process? Did you make an internegative? Did you cross process the paper?

    This would help and perhaps explain the problem.

    PE

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    The prints were made from a B&W negative (tmax 100) which was taken of a USAF resolution chart -- the colors would be wrong of course, but the resolution test should still be meaningful (the chart had 100% contrast). I was prompted to test the paper resolution since some of my prints seemed a little fuzzy.

    The slides were of course a reversal film. My question was about possible resolution degradations in color media, hence I talked about both RA-4 and E6 with no intention to connect them in any other way.

    Warren N

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    Ok, then here is a possible explanation for you.

    Color paper has the cyan layer on top and the yellow layer on the bottom. Due to multiple internal reflections, the cyan layer is like an object on top of a mirror with some plastic between. These reflections cause degradation of the cyan layer and the human eye is most sensitive to cyan and magenta images as far as sharpness is concerned.

    To alleviate that, Kodak puts a cyan and magenta dye into the paper to absorb back reflection and to improve sharpness. These dyes are called acutance dyes. That gives the Endura papers their blue purple color. IDK what Fuji does.

    In any event, expect color prints to be less sharp than B&W prints. The acutance dyes are not perfect and the thicker layers and spread of dye image clouds contribute to degradation of sharpness.

    OTOH, the papers are adjusted to give roughly equal apparent image sharpness at normal viewing distance, such that as you enlarge a print, you view it from a greater viewing distance.

    PE

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    Thanks, I should make 11x11 prints to prevent the paper resolution from being the limiting step.

    Do you have any idea why an E6 transparency would have much lower than expected resolution?

    Warren N

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    Look on the Fuji and Kodak web sites. They show resolution I believe as part of the product specifications. Maybe that would help. Just remember thought that the same limitations of 3 layers and turbidity apply to all color products.

    PE

  10. #10
    AgX
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    Quote Originally Posted by Photo Engineer View Post
    Look on the Fuji and Kodak web sites. They show resolution I believe as part of the product specifications.
    No, they don't.The only datashests that typically gave that information were those for the Polacolor materials. But of course due the technique behind them they were out of the game anyway.

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