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  1. #1
    gma
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    Obviously there is great concern for the resolution of lenses, both camera and enlarger. Does anyone have any data on the resolution of print papers (in lines/mm)? I can't imagine that any FB or RC paper can resolve even 5 lines/mm and if it can you will need a magnifier to appreciate the result. I think I read somewhere that large format quality lenses resolve about 30 l/mm. Lenses for 35 mm cameras often are in the 100 - 150 l/mm range. Current conventional film emulsions are limited to a range of 70 - 125 l/mm.

    I am curious about how many l/mm the naked eye can perceive in a print. Can you tell that I am bored on a rainy Saturday morning?


    gma

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    While I have no information as to the LPM resolution of papers, I have always heard that the enlarging paper is not the weak link in the chain. I imagine that this is due to the enlarged image degrading through enlargement far more then the limitations of the paper resolution.

    This subject of paper resolution comes up from time to time.

    If it were me and I was wanting to extract the greatest resolution from my materials and equipment, I would work on the following:

    1. Limiting the effects of possible camera movement

    2. Achieving accurate focus

    3. Limit the possible effects of lens defraction at both the taking and enlarging lens stage. This means not stopping the lens down beyond a certain point if possible. For me on 4X5 that amounts to no more then F32... preferably F11 - F22. In 8X10 that amounts to F45. In 12X20 that amounts to F64 on the taking lens. If enlarging I try to work 2 stops down from wide open.(F11-F16)

    5. Choice of film, film developer, and processing procedures.

    These will all make a noticeable difference in resolution. This process is truely a chain and it is no stronger then the weakest link.

  3. #3
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    Just from experience - here - I have ruined so many LF negatives by being concerned about over stopping. I wind up with DOF problems when I am reluctant to stop down. Since I started stopping down without fear - the negative quality has gone up. I have yet to see it in my own work where lens diffraction was in any way apperant. Of course in cute little film it might really be a consideration but for MF up to 8x10 - Stop it down - Get the dof - I don't have scientific charts or data for all this - Just a drawer full of expensive experience. I believe it was the"f64 club" not the .... f - can you get that down to f22 'cause I might get difraction club.


    Ok - it drove me insane and now I am recovering from that. sorry for the rant -
    My photos are always without all that distracting color ...

  4. #4

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    Quote Originally Posted by fhovie
    Just from experience - here - I have ruined so many LF negatives by being concerned about over stopping. I wind up with DOF problems when I am reluctant to stop down. Since I started stopping down without fear - the negative quality has gone up. I have yet to see it in my own work where lens diffraction was in any way apperant. Of course in cute little film it might really be a consideration but for MF up to 8x10 - Stop it down - Get the dof - I don't have scientific charts or data for all this - Just a drawer full of expensive experience. I believe it was the"f64 club" not the .... f - can you get that down to f22 'cause I might get difraction club.


    Ok - it drove me insane and now I am recovering from that. sorry for the rant -
    I certainly can't argue with Franks experience. However, I know that in my epxerience any format that is enlarged to any degree that defraction is noticeable...at least to me. Howard Bond,among others indicates that he does not go below F32 if possible on 4X5, F 45 on 5X7, and whatever it takes on 8X10 and larger. I don't have a problem with anything that I contact print. I do however have a problem with anything larger then a 11X14 print from 4X5 for instance...that is where defraction starts being noticeable. It shows up as visibly progressive softening of sharpness.

    Too often, it seems, stopping down excessively is an attempt to circumvent taking the time to adjust the view camera properly before stopping down. I have heard other photographers indicate a lack of concern with defraction effects...however they seem to be in the minority.

    If anything it is in smaller formats that defraction effects are less a problem then in large formats. It is a condition of aperture dimension compared to lens focal length. As focal length increases and film format size increases the effects of bending light also become more apparent.

    I have no argument with what others choose to be acceptable. I know what is acceptable to me.

    I just came back from making three 8X10 exposures this morning...lens focal lengths of 375 and 450 mm. My smallest Fstop was F22. The negatives will be sharp.

  5. #5

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    I don't think gma's question is relevant to ULF photography, only to enlargements from 4x5 or smaller. I say that because I have never encountered diffraction problems with contact prints in 8x10 or 11x14. In ULF, lenses are usually longer than 14 in. and exposures are often longer than 2 sec. DOF and movement are the boogie men, not grain, diffraction, or lens resolution (No offense Sally Mann!)
    While in Zion NP last week I intentionally tried to bring diffraction into the equation with three identical images at f45, 64, and 90. With identical development I can't distinguish them with the 10x loupe. I gave up trying to label them by f-stop.
    That said, I agree that for MF and 4x5, from film choice to enlarger f-stop there is a chain of image degrading steps that must be minimized at every step, not just one.

  6. #6

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    gma,
    to answer your question, conventional wisdom was always that the eye couldn't perceive more than 15 - 20 lines per millimeter in a print.

    Ctein of "Camera and Darkroom" fame claimed a 30 LPM number was more accurate. He also a number of B&W papers and came up with a resolution for the paper of about 45 LPM. Paper is not the limiting factor.
    Take care,
    Tom



 

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