Switch to English Language Passer en langue française Omschakelen naar Nederlandse Taal Wechseln Sie zu deutschen Sprache Passa alla lingua italiana
Members: 70,539   Posts: 1,544,287   Online: 818
      
Page 3 of 3 FirstFirst 123
Results 21 to 29 of 29
  1. #21
    Bill Burk's Avatar
    Join Date
    Feb 2010
    Shooter
    4x5 Format
    Posts
    3,280
    Images
    46
    You did. It's brilliant. When shooting extremely long-range subjects it is a great idea to match the points chosen so they are more relevant to the part of the scale that you use.

    Michael only hinted at applications where the shape makes a difference. There are some unresolved threads about the application of staining developers and multigrade papers. It's possible that it might take more than an average gradient to deal with the contrast in that application.

  2. #22

    Join Date
    Feb 2010
    Location
    Montreal, Canada
    Shooter
    Multi Format
    Posts
    4,731
    I resolved the staining developer/multigrade issue in other threads but people kept arguing so I stopped writing

  3. #23
    Stephen Benskin's Avatar
    Join Date
    Jan 2005
    Location
    Los Angeles
    Shooter
    4x5 Format
    Posts
    1,218
    There's an often repeated mantra, "open up 1/2 stop, and reduce development by 20%." I've attached a CI / Time Curve showing seven curve families. Four of the curves are from two films developed in two different developers. Good rule of thumb?
    Attached Thumbnails Attached Thumbnails Six Films, CI Time Curve.jpg  

  4. #24

    Join Date
    Feb 2010
    Location
    Montreal, Canada
    Shooter
    Multi Format
    Posts
    4,731
    I think I'm just not understanding CI very well (sorry about this, more reading to do I guess). Perhaps it is just a different way of saying the same thing as a H&D curve, but I'm not getting it. Don't you have to plot curves and determine densities in the first place in order to derive CI? I can see going in that direction, but not the other way. In my mind, CI and other gradient methods are just a number, a slope. So how does it describe a curve?

    Perhaps an example will illustrate my misunderstanding. Stephen, recall a while back I posted some H&D curves for three films, exposed the same way (in camera) and developed to essentially the same macro contrast. Apologies in advance for zone system parlance and the fact the chart has zone intervals on the x-axis as this is an old attachment. Contrast in this case defined in the typical zone system terms as the difference between zone I and VIII. My purpose in the original test was to compare the relative characteristic curves, and show that in the particular developer, the films' curves were nearly identical up to zone IX, beyond which the Fuji film behaves quite differently. How would this be described by say CI? Further, different developers can have pronounced effects on the shape.
    Attached Thumbnails Attached Thumbnails Flat grain curves.JPG  

  5. #25
    Bill Burk's Avatar
    Join Date
    Feb 2010
    Shooter
    4x5 Format
    Posts
    3,280
    Images
    46
    I can use CI to fit subject brightness ranges to negative density range. I want my negatives to have a range approximately 1.0

    Michael, your extended-range chart tells me right away that CI would be OK to model Acros, but if you need to use the part of the curve above XI you need to be aware of the shoulder.

    To the open 1/2 stop and develop 20% less, I don't know what that would accomplish. It would produce a shorter-range negative with better shadows. If the negative would otherwise be too "contrasty", the action would kick the contrast down "about a grade" but it's not very accurate.

  6. #26
    Stephen Benskin's Avatar
    Join Date
    Jan 2005
    Location
    Los Angeles
    Shooter
    4x5 Format
    Posts
    1,218
    I've already explained how no method encompasses all situations nor should they. The basic CI method accurately covers 95% of conditions faced.

    Curve shape is a good question. This is the argument made in the Contrast Index paper. Gamma only uses the straight-line portion of the curve, which is not only difficult to determine in some cases, but also doesn't entirely represent the portion of the curve in usage. The paper doesn't cover shoulders though. The Theory of the Photographic Process does note that "the gradient of the characteristic curve is of such importance, especially in connection with the problems of tone reproduction, that it is often desirable to use a derivative curve...This graphic form is useful when it is desired to determine precisely the exposure value corresponding to some particular slope of the D-log E curve...for many purposes it presents the data in more convenient form and gives a more vivid mental picture of the relation between gradient and exposure."

    Should variations in the upper end affect the overall average? According to tone reproduction theory, the perception of a quality print allows for compression of the shadows and highlights, but requires the midtones to be over a gradient of ~1.11 of that of the original subject. Tone reproduction theory also states that there isn't a perfect correlation between the negative density range and paper LER. According to Loyd Jones, "for the soft papers, the density scales of the negative (NDR) should in most cases exceed the sensitometric exposure scale of the paper (LER) (see Tone Reproduction Curve attachment). According to Theory of the Photographic Process, "For scenes having unusually long log luminance ranges (2.5 to 3.0), the tone reproduction curves for the first-choice prints were slightly to the left of the curve shown (in the example)...The gradient in the middletone region was always greater than 1.00 (usually 1.10 - 1.20) for the preferred prints of all scenes studied." So, there are no absolutes. A perfect match isn't necessary. Average gradient is a tool to describe how the subject is generally translated into density.

    If you measure the entire range from the example, you get (top to bottom) 0.51, 0.41, 0.39. Which in a fixed flare developmental model is from -1 to -3. However, if you measure only up to where the two bottom curves begin to shoulder off at Zone X, you get 0.48, 0.47, 0.45, or -1 1/2 to -2. Then there is the question of flare. Flare for an average scene is around 1 to 1 1/3 stops. Flare's rule of thumb is that flare increases by 1/3 stop per stop increase in the luminance range. A fourteen stop luminance range could have around 3 stops of flare. This would mean measuring the density range of the curves at Zone XI instead of Zone XIV. Which one would best translate into a quality print? Good question. I don't test for such extremes. I don't even know if there is a paper that has a LER of 2.14 from the Acros curve. If there is, what would happen to the all important midtone contrast? I've attached a four quadrant reproduction curve with a ten stop luminance range and two stops flare. The film has a CI 0.43 and the NDR closely matches the paper's LER. Also, there's an example with a slightly higher paper grade. With the higher contrast, the midtone reproduction gradient has just reached 1.00.

    These are all interesting questions. In extreme situations, does measuring the entire effective log-H range produce more desirable prints or does limiting the range of measurement in some way work best?

    Whatever the answer, it doesn't negate the effectiveness of any of the average gradient methods in most situations generally encountered.
    Attached Thumbnails Attached Thumbnails Quad 4 - Tone Reproduction Curve.jpg   10 stop luminance range.jpg   10 stop luminance range higher paper grade.jpg  

  7. #27

    Join Date
    Feb 2010
    Location
    Montreal, Canada
    Shooter
    Multi Format
    Posts
    4,731
    Quote Originally Posted by Bill Burk View Post
    I can use CI to fit subject brightness ranges to negative density range. I want my negatives to have a range approximately 1.0
    .
    I guess that's part of my point - what is the range? From darkest to lightest scene lumincance? Or from darkest to lightest to fit the paper (assuming no print manipulation)? And what about the effects on local contrast throughout the density range when fitting SBR to NDR?

    For me all these things are variable depending on the particular image. And very often I need to make use of the range into zones XII or XII. How and when shouldering occurs with a given film/developer combo and different development methods makes a big difference to me. Sometimes it might be better to have alot of highlight contrast and work to print those values down. Lots of different possibilities depending on the subject and the visualization.

    Anyhow, interesting discussion as usual. And thanks to Stephen for sharing his material and knowledge on these topics.

  8. #28
    Bill Burk's Avatar
    Join Date
    Feb 2010
    Shooter
    4x5 Format
    Posts
    3,280
    Images
    46
    Quote Originally Posted by Michael R 1974 View Post
    what is the range? From darkest to lightest scene lumincance? Or from darkest to lightest to fit the paper (assuming no print manipulation)?
    I'm starting to enjoy the "fact" that when you have anywhere from enough to too much range in a negative, it can make a nice print on Grade 2. And when you have almost no range and a very thin negative, Grade 3 will re-create the mood that led to that situation in the first place.

  9. #29
    Stephen Benskin's Avatar
    Join Date
    Jan 2005
    Location
    Los Angeles
    Shooter
    4x5 Format
    Posts
    1,218
    Bill, you might find this interesting. Below are a number of four quads. The example #1 is considered normal. The reproduction curve, quad 4, should be to the left of the reference line which represents the original scene. If the print tones equal the original scene's, the print will appear dark and would require twice the viewing illumination as what was in the original scene. For a print to be considered of high quality, the midtones should have a gradient at least 1.0, but best over 1.10.

    Example #2 has the same shooting conditions as the first. The negative was under developed and printed on a higher grade of paper to compensate. Notice how the higher tones in the reproduction curve are lighter and at a slightly lower gradient. The midtones and lower tones are at a higher gradient than in the first example.

    Example #3 has a short luminance range. The negative CI has been increase to compensate and it is matched to a grade 2 paper. The fourth example also has a short luminance range, but the negative as processed normal and printed on a higher grade of paper. Interestingly, there is little difference in the reproduction curve.
    Attached Thumbnails Attached Thumbnails Under Dev.jpg   Short Luminance range - NDR match 2.jpg   Short Luminance range - LER match 2.jpg   Normal Dev.jpg  

Page 3 of 3 FirstFirst 123


 

APUG PARTNERS EQUALLY FUNDING OUR COMMUNITY:



Contact Us  |  Support Us!  |  Advertise  |  Site Terms  |  Archive  —   Search  |  Mobile Device Access  |  RSS  |  Facebook  |  Linkedin