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  1. #141

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    I'm sort of in Adams camp on this, in that I test and plot the full curve. I suppose then one can calculate the various indices based on the curve. My issue is that since I'm dealing with long SBRs outside the "norm", I really need to see a full curve rather than a "line of best fit", whether it be CI, gamma etc. However if one is generally working with more typical luminance scenarios, the curve for most current films is more or less a straight line anyway, once you're past the toe. What I still don't understand, though, is why one would not always plot curves? Don't the curves derive CI and other indices anyway?

  2. #142
    Stephen Benskin's Avatar
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    Quote Originally Posted by Michael R 1974 View Post
    (again in Adams, but in other books too) that a film with a relatively "long toe" is generally more useful under low flare conditions such as those encoutered in studio work. Why would this be? To me it seems the opposite.
    As you know, flare reduces contrast in the lower parts of the film curve. The higher flare in exterior scenes with a shorter toed film will create the same basic curve shape in the toe as a long toed film shot under controlled studio lighting. Long toed films also generally have an up sweep in the higher densities which is desirable for skin tones in portraiture.

    From your descriptions, it sounds like your observations are supported by theory. Have you found the safety factor that higher flare gives you in those extreme conditions a help or hindrance?

  3. #143

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    Quote Originally Posted by Stephen Benskin View Post
    From your descriptions, it sounds like your observations are supported by theory. Have you found the safety factor that higher flare gives you in those extreme conditions a help or hindrance?
    Interesting question. I can't really say whether it helps or not, because I am basically adjusting for it in printing, whether or not I realized it in the past. Thinking about it, I don't see how flare can really help in any of my work. While flare can raise the effective EI, it lowers local contrast in shadow areas. For me EI is nothing in and of itself. It is simply a way for me to make sure my shadow densities are on the straight line, so that the local separations are good. If flare flattens that part of the curve, what do I care if it raises my EI? I'm still a net loser from a tonal perspective. In fact, if films had longer scales extending up to say zone XX, I might even argue given a high flare scene it would be better to lower your EI by several stops so that the shadow values are past the most flare-impacted portion of the curve.

  4. #144
    Stephen Benskin's Avatar
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    Quote Originally Posted by Michael R 1974 View Post
    Interesting question. I can't really say whether it helps or not, because I am basically adjusting for it in printing, whether or not I realized it in the past. Thinking about it, I don't see how flare can really help in any of my work. While flare can raise the effective EI, it lowers local contrast in shadow areas. For me EI is nothing in and of itself. It is simply a way for me to make sure my shadow densities are on the straight line, so that the local separations are good. If flare flattens that part of the curve, what do I care if it raises my EI? I'm still a net loser from a tonal perspective. In fact, if films had longer scales extending up to say zone XX, I might even argue given a high flare scene it would be better to lower your EI by several stops so that the shadow values are past the most flare-impacted portion of the curve.
    Here are a few more things to consider. You don't have to reduce the processing as far with flare as without, so the average gradient is higher than it would be without flare. Flare doesn't actually flatten out the toe. It compresses the exposure in the shadow area and moves it to the right on the curve. The shifting of the exposure off the toe actually reduces the compression to a degree. To begin to understand the way it’s all perceived, you have to turn to the topic of subjective tone reproduction. That will make your head spin.

    I found something in Jones’ Brightness Scale paper that speaks to your question about flare in various situations. There were a predominance of front lit scenes used in the testing. That means the data set contains a more limited luminance range and range of flare than can potentially be encountered. He divided scenes into four subdivisions: 1) distant, 2) remote, 3) near-by and 4) close-up.

    1). Distance – Landscape
    2). Remote – They use a street scene as an example
    3). Near-by - They use a single house
    4). Close-up - The example shows a full shot of a boy sitting down.

    Jones writes, “It is interesting to note that the average Bmin (min luminance) value decreases progressively and in an orderly manner from groups 1 to 4, inclusive. The average brightness scale (range) increases progressively in these groups.

    The flare factor increases systematically from group 1 through 2 and 3 and 4. The value of delta B (luminance) however, decreases progressively from group to group. These two facts taken together mean that while, in general, a distant open landscape results in a higher absolute value of flare light on the focal plane, its effect in reducing the illumination scale (range) of the image is less than in the case of a group 4 scene. This follows from the fact that the shadow brightness (luminance) of a group 4 light results in a greater proportionate reduction of the illumination scale (range) of the image corresponding to an increase in the flare factor.”


    And later, “It will be seen that the flare factors vary enormously from scene to scene. This variation is due largely to the variable brightness (luminance) distribution found in these scenes and in their environments. From the summary of the entire group at the bottom of Table II, it will be seen that the flare factors vary from 1.15 to 9.50.”


    If you want to know what that is in log-H, simply convert it to logs: log(9.5) = 0.98 or 3 ¼ stops.

    I like the idea of the degree flare effects the image depends on the minimum luminance value. Darker tones from distant scenes will arrive at the camera lighter because of atmospheric haze and something called the blending distance. The effects of flare have little effect that high on the film curve.

    “The average flare brightness scale (luminance range) also increases progressively through these four groups and, as a matter of fact, there is a good correlation between the average flare factors and the average brightness scales (luminance ranges).”

    Some of the Summary

    “1. The maximum and minimum brightness (luminance) of 126 exterior scenes of a wide variety of types has been measured. Form these data it is found that the average brightness scale (luminance range) is 160.

    3. For the average type of small portable hand camera used predominantly in the amateur field, the average value of the flare factor is approximately 4.0. This value is based on a large mass of statistical evidence not published as a part of this communication. For the equipment used predominantly in the amateur field, therefore, the average value of image illumination scale (illuminance / exposure range) is 40.”



    A 160 luminance range is 7 1/3 stops or 2.20 logs. A flare factor of 4.0 is two stops. Coated lenses cut the value in half.

    Below is Table II.
    B min and B max – minimum and maximum luminance value in footlamberts.
    BS – Luminance range
    IS – Illuminance or exposure range - if no flare is present IS will equal BS
    FF – Flare factor

    Click image for larger version. 

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  5. #145
    Bill Burk's Avatar
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    I have created an unusual graph that on the surface looks like any other curve family.

    This curve family includes 0.4 fixed flare (dashed lines are flare-influenced), and shows my target 1.00 Negative Density Range (solid line that slopes about 20-degrees downward).

    The low densities Zone I and Zone II are not precisely predicted in this graph so they are horizontal dotted lines. For this first iteration I picked Zone II as the anchor for the influence of flare.

    Click image for larger version. 

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  6. #146
    Bill Burk's Avatar
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    To see where it came from, this is the curve family without flare.

    http://beefalobill.com/imgs/Sept9TMY2.pdf

    To get the flare "curve" you turn the Log numbers to mathmatical values.

    At the speed point for ASA 400, the Log value is -2.7 (as used on a calculator with log functions) which translates to mathematical 0.002 mcs (meter-candle seconds). The amount of light that hit the film in non-flare conditions.

    Stepping over to the right 0.4 log units is the speed point for ASA 160, Log is -2.3 translates to mathematical 0.005 mcs. The amount of light estimated to hit the film when flare becomes involved.

    Amount of light estimated to hit the film minus amount of light that would have hit the film without flare, 0.005 mcs - 0.002 mcs = 0.003 mcs added to the entire sheet of film due to flare.

    To graph flare, then becomes a simple graphing task.

    For every data column, get the mathematical mcs number, add 0.003 mcs to it. Convert it to Log to find the actual mcs that would have arrived at that column. Then using the actual curve family for each dot of the plot, take the dot from the graph underneath the new column.

    So I started with the nearest data column to the ASA 400 speed point, the speed point for ASA 250, -2.5 Log mcs, 0.003 mcs.

    0.003 mcs non-flare exposure for that column + 0.003 mcs flare over the whole sheet of film = 0.006 mcs exposure really hit the film under the speed point for ASA 250. This is -2.22 Log.

    Thus on the graph for the column under the ASA 250 speed point, instead of plotting the test results, I use the plots from under the effective exposure that I find on the non-flare curve family graph under -2.22 log.

    The boring process is repeated: For each data column mcs, add 0.003 mcs for flare, find the Log and then look at the non-flare curve family and take the points from that column. Basically the non-flare curve family graph tells you exactly what density you get when you hit the film with a certain amount of light.

    For the flare study you try to estimate how much light would hit the film in a camera when flare is involved. So where you expected Zone II you get Zone II + 0.003 mcs which is pretty significant on the toe. It starts to get down to no effect as you go higher, for example there is less than 0.1 Log flare at Zone IV (0.015 mcs) + 0.003 mcs = 0.018 mcs.

    I hope to be able to take this flare study curve family to the field and use it for planning exposure and development, and have a reasonable expectation that the negative densities will fall where I placed the metered exposures. This wasn't happening for me when I used non-flare curve family. I was getting greater densities in the Zone II than I predicted.

    This chart is how I plan to deal with flare. I expect process variation, errors and other realities to cause +/- 0.10 density of what I aim for.

    Other ways of dealing with flare can get you just as close. For example, Chuck, I bet your N-times for TMY-2 are very close to mine even though I aim for 1.00 NDR and you aim for 1.20 - the difference is very close to the effect of flare.

  7. #147
    CPorter's Avatar
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    Quote Originally Posted by Bill Burk View Post
    I hope to be able to take this flare study curve family to the field and use it for planning exposure and development, and have a reasonable expectation that the negative densities will fall where I placed the metered exposures. This wasn't happening for me when I used non-flare curve family. I was getting greater densities in the Zone II than I predicted.

    This chart is how I plan to deal with flare. I expect process variation, errors and other realities to cause +/- 0.10 density of what I aim for.

    Other ways of dealing with flare can get you just as close. For example, Chuck, I bet your N-times for TMY-2 are very close to mine even though I aim for 1.00 NDR and you aim for 1.20 - the difference is very close to the effect of flare.
    Bill, I can identify somewhat----

    I've had times when checking post-processing negative densities relative to the shadow placement that they were so close to what was expected and at times they have not been. I admit early on in my understanding that I was not sure why this was so----why some densities were very satisfactory for one negative and while some seem too far off for another, although not really to the detriment of the the integrity of the actual shadow density. Meaning, most always the added low value density could be 'printed through', yes, a phrase I gleaned from AA. I came to realize that because it was not a consistent thing and that it was subject related, that lens flare was the cause. So, doing my own simplified approach to it i.e. a little web searching and referencing my own materials, I came to view it as just like pre-exposure in it's affect as discussed in The Negative. I make attempts to compensate for potential higher flare situations when I can, that is to reduce exposure to the negative to some degree to protect the toe of the curve as much as possible.

    Regarding the TMY-2, I haven't used it, but want to eventually test with it, but if you had some results for TMX in d-76 1:1, perhaps a comparison could be made.

  8. #148
    Bill Burk's Avatar
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    Quote Originally Posted by Michael R 1974 View Post
    What I still don't understand, though, is why one would not always plot curves? Don't the curves derive CI and other indices anyway?
    You are right. The curves give you the indices.

    I always plot them out.

  9. #149
    Bill Burk's Avatar
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    Quote Originally Posted by CPorter View Post
    ...I came to view it as just like pre-exposure in it's affect as discussed in The Negative. I make attempts to compensate for potential higher flare situations when I can, that is to reduce exposure to the negative to some degree to protect the toe of the curve as much as possible.
    That is a good way to visualize it.

    Quote Originally Posted by CPorter View Post
    Regarding the TMY-2, I haven't used it, but want to eventually test with it, but if you had some results for TMX in d-76 1:1, perhaps a comparison could be made.
    I haven't done a whole curve family, but I hit a little above N in 11:15 minutes in D-76 1:1

    Our times are different but the curve characteristics are similar. So I believe there is a process difference. I use open trays and shuffle several sheets, my times tend to run longer than others'
    Last edited by Bill Burk; 02-22-2012 at 10:09 PM. Click to view previous post history.

  10. #150
    Bill Burk's Avatar
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    Quote Originally Posted by Michael R 1974 View Post
    In fact, if films had longer scales extending up to say zone XX, I might even argue given a high flare scene it would be better to lower your EI by several stops so that the shadow values are past the most flare-impacted portion of the curve.
    I don't think it works that way...

    In a really long-scale scene that includes Zone XX, flare is probably up around Zone IX.



 

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