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Thread: detail expectation

  1. #1

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    detail expectation

    Hi

    I am beginning with LF and trying to work out whether I am expecting too much from my LF camera/films, or if there is a failure in my process, with regards to focus and detail.
    I am thinking when shooting test shots that I am not getting the level of detail and sharpness with my negs and scans.

    in a scenario like shooting in an average sized back yard, with trees & grass with a 90mm rodenstock lens. Let say the the trees are between 15 and 20 feet away.

    In a correctly exposed image on 4x5 Ilford delta 100 b&w negative, how much details in trees & grass should I be seeing in the neg? When I scan in at 2400, and I look at 100% crop - what is that likely to be equivalent to when printed out (i.e. is that my nose up against a 10 foot high print?)

    I am wondering if I have too high expectations from my equipment or if I need to revise my methods

  2. #2
    8x10, 5x7, 4x5, et al Leigh's Avatar
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    Re: detail expectation

    Achievable resolution depends on a whole bunch of factors, including but not limited to:
    - subject contrast
    - quality of the lens
    - shooting aperture
    - camera movement (shutter shock, wind, etc)
    - film being used
    - how the film is developed

    The best you can hope to achieve with common materials is about 100 lp/mm for high-contrast subjects.
    The resolution drops dramatically as subject contrast goes down.

    100 line pairs/mm = 200 pixels/mm. 4" = 100mm, so 20,000 pixels along the short dimension of 4x5.
    The 5" dimension would be 25,000 pixels, so the full image is 20,000 * 25,000 = 500 megapixels

    Remember, this is absolute max theoretical resolution. I doubt you could achieve it in the general case.

    However, scanning at 2400dpi reduces the resolution by a factor of 4.
    2400 * 4 = 9600 dots; 2400 * 5 = 12000 dots. 9600 * 12000 = 115 megadots.

    To accurately reproduce any analog subject (photograph, drawing, song, etc) you need at least two samples of each original data point*. So for the 200 pixel/mm negative you need 400 samples/mm. The resulting data file would be 500 * 4 = 2,000 Megapixels.

    So your 2400dpi scan is actually reducing the resolution by a factor of 8 rather than 4.
    Sorry if this is a bit technical, but the subject is technical.

    - Leigh

    *NB: This is from classical sampling theory and the Nyquist limit.
    If you believe you can, or you believe you can't... you're right.

  3. #3
    Randy Moe's Avatar
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    Re: detail expectation

    Go to a museum and look at LF prints.

    Download a known good LF scan.

    Maybe your eyes are bad, mine are, with lots of floaters.

    Then examine everything Leigh has posted.

  4. #4

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    Re: detail expectation

    Achieving proper focus is essential. Are you using a loupe to verify focus on the groundglass?

  5. #5

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    Re: detail expectation

    At 15-20 feet @ f/16 your 90 mm lens should cleanly separate blades of grass on film. Forget about what you can see on the GG, resolution will improve somewhat when stopping down a little from wide open and anyway the GG has less resolution than your film can deliver.

    Leigh is right. Poor technique kills image quality. Shoot from tripod. Use a cable release. If y'r focus is off a little, no matter because somewhere in the frame the grass will be in focus. And you can't judge what's in a negative from a scan. If you want to know what's in a negative, look at it. You'll quickly find that at 12x everything is mushy. And this is why we use LF. A larger negative allows a larger print before the mush shows.

  6. #6
    Corran's Avatar
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    Re: detail expectation

    Quote Originally Posted by LotusEsp View Post
    When I scan in at 2400, and I look at 100% crop - what is that likely to be equivalent to when printed out (i.e. is that my nose up against a 10 foot high print?)
    Typical monitor @96 DPI will show at 100% from a 2400 DPI scan a rough approximation of a print 10 feet wide from a 4x5 inch negative (check your settings, if your monitor is at 144 DPI it would be closer to 7 feet). That's a 24x enlargement, which may be a bit much to expect. Plus assuming your scanner is a typical Epson you are pushing the limits of its resolution. Back out to 50%, add a reasonable amount of unsharp masking, and it should look pretty sharp on screen. If not you may have issues at capture, but a lot of people think they are going to get super-sharp scans at 100% from an Epson but that is a tall order. If you want try scanning at 3200 or 4800, adding the unsharp masking to taste at 50% or even 25% view and then resize the file down to 2400, and see if you get a bit more from the scanner.

    100lp/mm is high quality small format lens stuff. The best lenses tested HERE show at most ~70 stopped to typical apertures (diffraction limited @ f/22). 75mm Rodenstock (they didn't test the 90) shows 54 in the center/middle, even less on the edge. 50lp/mm x 4x5 dimensions (120mm x 96mm) = 11700x9600 or about 2400 DPI so your scan has to be perfect to get every last drop of resolution, which is going to be hard. For the highest rez scan I do 6000 DPI on a high-end flatbed and resize down to 3000 DPI or appropriate resolution for printing after some slight sharpening.
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  7. #7
    Drew Wiley
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    Re: detail expectation

    With the right film and lens, you should be able to clearly see an aphid on a blade of grass fifteen feet away. But just by the nature of subject matter in the real world, it's pretty rare that everything in the scene can be in focus at the same time, even with the use of judicious view camera movements, which is one of the first things you need to learn. And how detail is itself used in an aspect of composition, involving aesthetic choices and priorities. Perception of detail is also related to contrast. Then you hit all kinds of secondary logistical problems. How flat is your film plane to begin with, including how flat the film lies in the holder? How rigid is your complete camera/tripod system? How much visual information are you potentially losing in the scan and printing protocol afterwards? All this stuff adds up, and you need to isolate each variable in succession to know what is really going on. This starts with a good groundglass loupe, not with a bunch of hypothetical math. Get to first base first.

  8. #8

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    Re: detail expectation

    Mathematical analysis aside, if you already have the equipment, test it out and see if it meets your actual subjective requirements.

    You don't have to print an entire 8x10 foot print to see how parts of it will appear at full size: print sample sections instead.

    Sharpening can't add visual information, but it can change the impression of visual information. With appropriate sharpening I've been able to make sharp prints at sizes surprisingly larger than I would have expected based solely on theory.

  9. #9

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    Re: detail expectation

    Quote Originally Posted by Randy Moe View Post
    Download a known good LF scan..
    thanks
    do you have any suggestions?

  10. #10

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    Re: detail expectation

    Thanks all
    I'm going to take another shot and print that out at the max I can at home (a3+) and see what it looks like and go from there

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