Page 2 of 4 FirstFirst 1234 LastLast
Results 11 to 20 of 38

Thread: Paper Resolution

  1. #11
    Mark Sawyer's Avatar
    Join Date
    Jul 2004
    Location
    Stuck inside of Tucson with the Neverland Blues again...
    Posts
    6,268

    Paper Resolution

    Oren-

    Right you are on the "line pairs." Can't believe I never knew that...
    "I love my Verito lens, but I always have to sharpen everything in Photoshop..."

  2. #12
    Moderator
    Join Date
    Jan 2001
    Posts
    8,640

    Paper Resolution

    Mark -

    No problem. We all know things that seem obvious in hindsight but that we didn't grasp until someone else helped show the way...

  3. #13

    Paper Resolution

    First, I want to thank you all for your comments.
    I went to my enlarger today and using my grain magnifier found that the negative-enlarging lens combination was resolving 18 - 20 lp/mm at the paper plane for a negative (Tmax 100) made by my 150mm Schneider Super Symmar HM @ f16 that measured 75 lp/mm view by microscope of a RIT resolution target (high contrast).
    The print, on Ilford multigrade V FB using grade 3 filtration, measured 12 lp/mm.
    After viewing the Greenspun bboard, I'm going to buy a box of Bergger VC paper to see if I can have better resolution on my prints.
    Granted, you can't see the difference with the eye, yet I want my prints to come closer to what my lenses and film can resolve than I'm getting now. Why waste all that effort and expense only to have it compromised by a paper.

  4. #14

    Join Date
    Nov 1999
    Location
    San Clemente, California
    Posts
    3,804

    Paper Resolution

    Patrick, I'm glad you're going to sample Bergger VC. Since that posting three years ago, I've switched to Bergger Graded NB. Sharpness wasn't the reason; tonal rendition of graded papers just seems more pleasing. Please give both papers a try!

  5. #15
    Abuser of God's Sunlight
    Join Date
    Aug 2004
    Location
    brooklyn, nyc
    Posts
    5,796

    Paper Resolution

    "Why waste all that effort and expense only to have it compromised by a paper."

    well, if you intend your prints to be viewed with a loupe, then more resolution makes sense. But if you intend them to be viewed normally, or even squinted at up close, then anything beyond 12lp/mm will be invisible. This has to do with the density of rods and cones on the human retina. It's based on current enough research that it's what Schneider engineers uses as a guideline when adjusting a lens's MTF response.

    I would be more concerned with the VISIBLE factors that make a print appear sharp. More resolved detail beyond 11 lp/mm has no affect on this. But slight incrases in edge contrast in the neighborhood of 5lp/mm has a huge affect on it. There is zero corellation (in modern optical systems) between ability to resolve microscopic frequencies and ability to produce strong contrast at visible frequencies.

    Beyond that, when you consider all the tonal qualities that actually make a print worth looking at, I wonder if microscopic resolution is really a worthwhile factor to consider when choosing a paper.

  6. #16

    Join Date
    Nov 1999
    Location
    San Clemente, California
    Posts
    3,804

    Paper Resolution

    "...then anything beyond 12lp/mm will be invisible."

    Per Ctein, 30 lp/mm is required in a print for "perfect sharpness" as a result of our eyes' sensitivity to image acutance (edge sharpness).

  7. #17
    Abuser of God's Sunlight
    Join Date
    Aug 2004
    Location
    brooklyn, nyc
    Posts
    5,796

    Paper Resolution

    I like a lot of Ctein's articles, but I have to say, he tends to conduct some pretty simple, homegrown experiments and then present his findings as fact. The kind of perceptual science involved in determining the limits of human resolution are very, very complex--way beyond anything Ctein has demonstrated in the articles I've seen, and certainly way beyond what anyone gets from a BS in physics in the 1970s. The perceptual science that Schneider uses is based on controlled experiments that take into account many more variables than anyone can in a darkroom.

    The real issue is that microdetail has very little impact on our sense of sharpness. It's the relatively coarser detail at 4-7lp/mm that provides our brains with a sense of sharpness. What guys like Ctein frequently don't realize is that the things they're doing to increase resolution (maximum frequency rendered above a minimum modulation threshold) may well be increasing the modulation in the critical 4-7lp/mm range, and through that seperate process, increase your sense of sharpness.

    This is important to lens designers, because they often need to compromise between resolving the finest detail and resolving less fine detail at higher contrasts. This is actually part of optimizing a lens for a particular magnification. An enlarger lens designed for lower magnifcations can relinquish some microdetail in order to provide higher contrast in the critical range, and therefore appear sharper.

    I've seen a a print that resolves 20 lp/mm held side by side with a print of the same negative that resolves 5 lp/mm. The lower resolution print was tack sharp, and the higher resolution print was blurry! These were prints produced by Schneider to illustrate a point. They were both ugly. but it was interesting none the less.

  8. #18
    Abuser of God's Sunlight
    Join Date
    Aug 2004
    Location
    brooklyn, nyc
    Posts
    5,796

    Paper Resolution

    I've just double checked some human optical research online.

    Most subjective tests I've found (using printed samples illuminated with reflected light, using a viewing distance that corresponds to the average near-limit of human vision, 10 inches) find an actual maximum resolvable resolution of 6 to 7.5 line pairs per millimeter. At this point subjects were unable to distinguish between a bar pattern and a field of flat gray.

    Actual retinal resolution limits are higher. The spacing of rods and cones on the human retina is about 2 microns, or 29 seconds of arc. This corresponds to an absolute maximum resolution of about 60 cycles (line pairs) per degree. If we accept that the near limit (closest focus distance) of the eye is 10 inches, that translates to 13.5 lp/mm maximum resolution. If you have unusually good eyes and can focus at 8 inches, you'd be able to resolve a maximum of 16.9 lp/mm.

    These theoretical maximum values, while about half of what Ctein claims, are still much higher than what anyone can actually see on a print. They do not account for diffraction, optical aberations of the lens, and what is likely a reolution limiting function of our brain's optical processing, which exists to prevent aliasing and other interference patterns from becoming visible.

    They also do not take into account the eye's extreme sensitivity to contrast. We can come closer to our retinal resolution limit when trying to resolve point sources of light. In these tests, the smallest separation at which we can define two point sources is used to calculate maximum resolveable frequency. The contrast of a bar chart or sinusoidal bar pattern is much lower, so our maximum resolveable frequency is much lower when looking at them. And the contrast of fine details in a photographic print is much lower still, no matter how much you paid for those lenses!

    After looking at this research, it seems like Schneider's figure of 11-12 lp/mm is actually optimistic.

  9. #19

    Join Date
    Jan 2002
    Location
    Besançon, France
    Posts
    1,617

    Paper Resolution

    Details for Oren Grad
    I used a glass/chromium photomask of size 3" as my test target. Not a film. The contrast of such an object is huge, the optical densiy of a chromium photomask is something like 3-4 depending on which wavelength is used ; I simply used an enlarger as my light source and projected an empty frame of the contact printing stuff. The photomask was simply pressed against the paper on another flat glass surface underneath to ensure a good overall flatness. Most probably I pressed by hand. When you simply contact print a microscope plate coated with photoresist even without pressing you easily get a resolution of 4-5 microns per cycle i.e. you easily get 100 cycles per mm. without a complex equipment.

    For my silver halide contact prints, the results were examined with a metallographic microscope fitted with 10x and 20x lenses and 10x eyepieces. Resolving 50 lp/mm is an easy job for a 20x microscope lens. But on a few mm field. The criterion was rough and analogous to all sharpness criteria with a USAF test target, groups of 3 bars were clearly separated at a period of 20 microns. At the time I had access to an excellent micro-densitometer but my goal was not a very precise evaluation ; I was just curious to check what I could see and that was amazingy sharp.

    Abous this experiment by contact printing being realistic or not, I simply want to comment quietly that the overall resolution of a print combines different factors. My point is that a traditional silver halide glossy paper itself is not the limiting factor, period. Now we can start discussing about other causes of lack of sharpness, but this is another story. If the projected image has already a low contrast, the optical transfer process plus de-focusing is to be blamed, not silver halide on paper. I'm not speaking of other papers with a well-marked texture, I'm just speaking about traditional glossy paper on a thin paper support.

    If ILford can achieve more than 60 lp/mm with Ilfochrome (and Ilford know their product and would not state anything unrealistic), I cannot imagine that the resolution in the final colour print is better than the original resolution of the silver halide image which I asume present in the early stage of the Ilfochrome photochemical process (I assume that there is at least one layer of silver halides in Ilfochrome, I may be wrong).

  10. #20
    Abuser of God's Sunlight
    Join Date
    Aug 2004
    Location
    brooklyn, nyc
    Posts
    5,796

    Paper Resolution

    My original observation about there being a practical resolution limit on an enlarged print actually had nothing to do with lack of sharpness. It was about a phenomenon that I noticed, and one that would only matter if you were in the habbit of looking at prints with a loupe, or if you were trying to scan a print in order to make a larger print from it.

    Just a couple of general comments: when you're investigating sharpness, or lack of it, it's important to make a distinction between sharpness and resolution. sharpness is a subjective quality related to the edge contrast of details, and which corresponds pretty well with MTF at certain frequencies. Resolution is a pseudo-objective quality based on the highest frequency of detail visible, usually under some arbitrarily chosen set of conditions. It's possible to have very high resolution and very poor sharpness at the same time. And vice versa. So it's helpful not to confuse the issues.

    It's also worthwhile to note that sharpness (and resolution) are not typically lost through bottlenecks or "limiting factors." They are lost progressively through every link of the image chain. Even the sharpest film degrades the image. A paper surface that can theoretically resolve a million line pairs per millimeter degrades the image. The air that the light passes through degrades the image. And the degradation is cumulative. If you take the MTF graphs of every link--the taking lens, the film/developer combination, the enlarging lens, the paper--and multiply them, you will get the MTF of the entire system. MTF values are less than 100%, with a handful of odd exceptions, so multiplying will always give you a smaller number. Unless there's a part of the signal chain that is hopelessly worse than the others (like, your enlarger is out of focus, or you're using a holga lens on your 8x10 camera, and wondering why things are a little fuzzy) you'll be able to get improved quality by making a significant improvement anywhere along the line.

Similar Threads

  1. lens resolution
    By kreig in forum Lenses & Lens Accessories
    Replies: 12
    Last Post: 8-May-2005, 13:04
  2. It's the experience, not the resolution
    By Jack Davis in forum Digital Hardware
    Replies: 35
    Last Post: 10-Mar-2005, 14:53
  3. Resolution of photopaper
    By Michael S. Briggs in forum Darkroom: Film, Processing & Printing
    Replies: 5
    Last Post: 14-Oct-2003, 04:43
  4. resolution of LF lens
    By Simon ZENG in forum Lenses & Lens Accessories
    Replies: 13
    Last Post: 10-Oct-2000, 18:41
  5. Is paper truly the resolution bottleneck it appears to be?
    By Bill Glickman in forum Darkroom: Film, Processing & Printing
    Replies: 12
    Last Post: 25-Feb-2000, 18:34

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •