Switch to English Language Passer en langue franÁaise Omschakelen naar Nederlandse Taal Wechseln Sie zu deutschen Sprache Passa alla lingua italiana
Members: 70,557   Posts: 1,545,160   Online: 989
      
Page 13 of 18 FirstFirst ... 3789101112131415161718 LastLast
Results 121 to 130 of 174
  1. #121
    Bill Burk's Avatar
    Join Date
    Feb 2010
    Shooter
    4x5 Format
    Posts
    3,304
    Images
    46
    I was going to draw a curve family to include flare.

    Then I froze in my tracks when I saw how the spotmeter seems to include flare.

    Steve,

    I think you have some references that break down what I am seeing, maybe it is distance effect.


    To get moving again, I am going to act like I don't care about what the spotmeter sees.

    I will plan to factor that back in later, I think this may cancel out.

    ---

    For this exercise, I assume flare is related to subject brightness range.

    I admit if there was a direct or predictable relationship we'd have the numbers, but for now I will assume it is a tendency.

    A starting point might be to make a table like this:

    8 stops SBR? (somewhere above 0.4)
    7 stops SBR = 0.4 flare.
    6 stops SBR? (somewhere between 0.0 and 0.4)
    ...
    1 stop SBR = 0.0 flare.
    ---
    Are there "flare for subject range" numbers out there to fill in the blanks? Otherwise I will make a few assumptions and draw the curves...
    ---

  2. #122
    Stephen Benskin's Avatar
    Join Date
    Jan 2005
    Location
    Los Angeles
    Shooter
    4x5 Format
    Posts
    1,218
    For those who are still here and still interested, I found a previous film curve example of Chuckís. The top curve is what was originally uploaded. In the bottom curve the parts that I've worked are in red.

    Click image for larger version. 

Name:	Gradient and Chucks Curve.jpg 
Views:	12 
Size:	245.8 KB 
ID:	46597

    It should be obvious to anyone who is taking the discussion seriously that gradient is an integral part of contrast determination even if the value isn't determined. But if you determine it, you'd know that if you measured the curve at a different point, say at 1.80, youíd still produce the same gradient value which means the same contrast. Gradient is also useful in predicting density ranges for different situations.

    Letís say Chuck wants to use a condenser enlarger. According to The Negative, the density range for a condenser enlarger is 1.15. At what contrast would Chuck produce a negative density range of 1.15 for his conditions? 1.15 / 2.1 = 0.55.

    Gradient also reduces the need to testing. You do a family of curves, determined the gradient for each, and youíve determined you processing for silver printing on a diffusion enlarger, but then you want to shoot some negatives for platinum printing, you donít have to test the film again. If you know the LER of the platinum paper, you just recalculate. My program has a gradient calculator. Just enter the set of conditions, and it gives the gradients for -3 to +3 as well as the processing times. To find the processing times, I use a CI / Time curve. Phil Davis lays this out pretty well in Beyond the Zone System.

    Do you need to know the gradient in order to shoot. Of course not. With the shear preponderance of subjects near the statistical average combined with the varying personal preferences of the viewer, you really donít need to know much of anything to produce a workable negative at least 60-70 percent of the time.

    But who doesnít prefer to have more information? Who doesnít prefer additional insight? If the tool is available, why not use it when it can be useful? Understanding gradient made it possible to analyze two seemingly disparate methodologies and determine they are not dissimilar at all. They just measure the film curve in different places. The apparent difference between the negative density range of the Zone Systemís 1.25 and the ISO paper grade 2 LER value of 1.05 is explained simply by using gradient.

  3. #123
    Stephen Benskin's Avatar
    Join Date
    Jan 2005
    Location
    Los Angeles
    Shooter
    4x5 Format
    Posts
    1,218
    Quote Originally Posted by Bill Burk View Post
    Are there "flare for subject range" numbers out there to fill in the blanks? Otherwise I will make a few assumptions and draw the curves...
    ---
    The rule of thumb is 1/3 stop change per stop luminance range. I believe it is only intended to be applicable for a limited +_ range of say 2 to 3 stops.

    I've posted this before. It's a CI / LSLR graph of a number of different flare models.

    Click image for larger version. 

Name:	Fix, no, variable flare graph copy.jpg 
Views:	10 
Size:	111.5 KB 
ID:	46598

    I believe the reason Kodak used a fixed flare model for their chart was due to the unpredictable nature of flare. Next time you are in the testing mood, take two targets, one with a small black square in the center surround by white, and the other with a small white center surrounded by black. Meter a gray card and make exposures of both targets. Check the density range. They have the same luminance range, but will they have the same density range?

    Another way of looking at Kodak's decision is that there are a lot of different areas of photography where errors tend to cancel each other out. Allen Stimson in Measuring and Judging Photographic Exposure of Color Film for Automatic Exposure Controlled Cameras writes about exposure, "The many tolerances and uncertainties in exposure control systems add up to an alarming possible error. However, many of the errors are usually opposite in direction and, therefore, are mutually compensating."

    It could also be a question of the need for precision because there's the whole psychological aspect.
    Last edited by Stephen Benskin; 02-19-2012 at 02:59 PM. Click to view previous post history.

  4. #124
    Bill Burk's Avatar
    Join Date
    Feb 2010
    Shooter
    4x5 Format
    Posts
    3,304
    Images
    46
    Quote Originally Posted by Stephen Benskin View Post
    The rule of thumb is 1/3 stop change per stop luminance range. I believe it is only intended to be applicable for a limited +_ range of say 2 to 3 stops.

    I've posted this before. It's a CI / LSLR graph of a number of different flare models.
    Great! Let me see if I can work backwards from "practical" flare and my family of curves. I'll label them as N+ / N / N- for ease of visualization.

  5. #125
    Stephen Benskin's Avatar
    Join Date
    Jan 2005
    Location
    Los Angeles
    Shooter
    4x5 Format
    Posts
    1,218
    Quote Originally Posted by Bill Burk View Post
    Great! Let me see if I can work backwards from "practical" flare and my family of curves. I'll label them as N+ / N / N- for ease of visualization.
    The variable flare model reflects the 1/3 stop factor. The practical flare model uses the average between the fixed and the variable flare model. It's designed to include one of the exceptions to the LER / NDR relationship. From Jones, "For the soft papers, the density scales of the negatives should in most cases exceed the sensitometric exposure range of the paper, whereas, for the hard papers, the density range of the negatives should in most cases be less than the sensitometrically determined log exposure range of the paper."

    The variable flare model agrees best with reality. I believe the practical will work best with use.

  6. #126
    Bill Burk's Avatar
    Join Date
    Feb 2010
    Shooter
    4x5 Format
    Posts
    3,304
    Images
    46
    Quote Originally Posted by Stephen Benskin View Post
    The variable flare model agrees best with reality. I believe the practical will work best with use.
    I guess it's one thing to know what flare does, and another thing to know what you really need in the darkroom. I'll go with what you need in the darkroom.

  7. #127
    CPorter's Avatar
    Join Date
    Feb 2004
    Location
    West KY
    Shooter
    4x5 Format
    Posts
    1,662
    Images
    24
    Quote Originally Posted by Stephen Benskin View Post
    For those who are still here and still interested, I found a previous film curve example of Chuckís.
    Here is the curve family that I ultimately arrived at for d-76 1:1 and TMX, absent any flare factor of course. What I found interesting with the test for EI is that it actually turned out to be 100 for me as the curve reached the Zone VIII target , just about right on the money. When +2 dev is planned, I reduce the exposure by 1/3 stop due to increased fog density and when -2 dev is planned, I increase the exposure by 1/3 stop due to reduced fog density. The curves don't show enough deviation in fog density at +1 and -1 to make a similar exposure adjustment. To date, these times have worked beautifully for me, of course, all I have to offer is my own anecdotal evidence of my own analysis and I'm not able to offer any more than that.

    The "N" development comparison curves just represent, for me anyway, marked behavioral differences between d-76 and hc-110 with TMX in each of the three divisions of the curve (toe, straightline, shoulder). Knowing the CI values of each curve would be informative, I guess, but no decision would hinge on it. I evaluate differences in CI, figuratively speaking, in each major division of the curve when compared to another, in this way, the entirety of the curve is given full attention. Perhaps this explains my somewhat simplified point of view better, IDK.

    I'm obviously not a technical minded as you and Bill because my road to the end result, seems just my own, within the confines of this thread that is, but I do take it seriously and find it interesting. If you are dieing to know the development times for the curves you posted last night, I arrived at:

    At neg density 1.3, based off of development times from between 4 and 8 minutes and using Zone VIII as my target high value:

    +2 dev, Zone VI (at log exp 1.5) = time interpolated at 7:30
    +1 dev, Zone VII (at log exp 1.8) = time interpolated at 6:45


    Normal dev, Zone VIII (at log exp 2.1) = ~6:00, the curve is within the range of 1.25 to 1.35


    -1 dev, Zone IX (at log exp 2.4) = ~5:00, the curve is within the range of 1.25 to 1.35
    -2 dev, Zone X (at log exp 2.7) = ~4:00, the curve is withing the range of 1.25 to 1.35

    If I knew the ISO, I would break down my evaluation of the EI's for those four curves.
    Attached Thumbnails Attached Thumbnails comparison-curves001-W.jpg   tmx&d-76-1-1001-1.jpg  
    Last edited by CPorter; 02-19-2012 at 07:34 PM. Click to view previous post history.

  8. #128
    Bill Burk's Avatar
    Join Date
    Feb 2010
    Shooter
    4x5 Format
    Posts
    3,304
    Images
    46
    Chuck,

    Those curves are beautiful and I think I see where flare is hiding.

    As I get ready to draw my TMY-2 curves with flare included, I imagined your curve of N+1 with Zone I a little bit denser. To visualize only, what if Zone I really came out on film at 0.3 instead of 0.1.

    You wind up with a camera negative that you developed with an aim of 1.2 NDR, but because of flare it comes out closer to 1.0 NDR.

    And how do you deal with that? You don't need to. Your model anticipates flare by telling you to choose an artificially high NDR target. Higher than you really want. On your enlarger you want 1.0 NDR just like me.

    Now since I picked a real negative that was really 1.0 NDR - I have to make sure to estimate flare before I decide development time because my charts don't have flare included and my aim NDR doesn't include adjustment for flare.

    There may be more to it than that, but that's what I think I see right now.

  9. #129
    Stephen Benskin's Avatar
    Join Date
    Jan 2005
    Location
    Los Angeles
    Shooter
    4x5 Format
    Posts
    1,218
    Quote Originally Posted by Bill Burk View Post
    You wind up with a camera negative that you developed with an aim of 1.2 NDR, but because of flare it comes out closer to 1.0 NDR.

    And how do you deal with that? You don't need to. Your model anticipates flare by telling you to choose an artificially high NDR target. Higher than you really want. On your enlarger you want 1.0 NDR just like me.
    This is what I've been saying for years! It's about the way the film curve is interpreted. The film curve is created under no flare test conditions, but there's flare in actual shooting conditions. In order to have agreement between the two, a flare value needs to be applied to the no flare film curve during the interpretation process (speed and contrast determination). The other way is to create a false aim value, such as a higher NDR to compensate for flare which is to be used only for the determination of contrast. Both approaches work, but one way reflects use and the other is a "fix" that can cause confusion if the concept of the "fix" isn't readily known. This is the difference that is observed between the Zone System NDR of 1.25 and the Grade 2 LER aim of 1.05. The difference is an illusion created by two different approaches but resulting in the same NDR even if they aren't aware of it. This is one reason why I like to say people aren't getting what they think they're getting.

    The use of some form of average gradient in determining film contrast eliminates this potential confusion, in much the same way it was used to explain it.

  10. #130
    markbarendt's Avatar
    Join Date
    May 2008
    Location
    Ignacio, CO, USA
    Shooter
    Multi Format
    Posts
    5,734
    Blog Entries
    3
    Images
    19
    Chuck are you carrying through specific subjects/zones measured in the scene or are your zones defined at the negative?

    What I'm getting at is that if measured at the negative then camera/scene based flare wouldn't be represented, right?
    Mark Barendt, Ignacio, CO

    "We do not see things the way they are. We see things the way we are." AnaÔs Nin



 

APUG PARTNERS EQUALLY FUNDING OUR COMMUNITY:



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