Dynamic Range of a Film?

[david_henderson]

<p>I do hope the OP understands that he can get by well enough in photography without knowing or even understanding this stuff.</p>

[Ed_Ingold]

<p>I posted a correction (edited, if you prefer) moments after the previous post, and half an hour before you replied :-)</p>

<p>You keep introducing information about printing, the function of the human eye and other things irrelevant to the response of film to light. You have added information regarding the prediction of the film's behavior, based on experimentation with the developer and development time. While interesting, it does not contradict the basic fact that you can measure these effects and produce a new characteristic curve that reflects the changes. The link you provided expands on the predictive process, but is largely irrelevant to the issue of interpreting characteristic curves.</p>

<p>ISO is relevant, but I thought I had covered that. ISO may be calculated from the characteristic curve. If the curve changes, so does the ISO rating.</p>

<p>It is discourteous to readers at large when you throw out boutique three-letter acronymns without explanation. Perhaps it's an ego thing, or a symptom of excessive texting :-)</p>

[Dave Luttmann]

<p>Ed, this has already been covered. The area of the curve where you claim the DR resides is not complete. Where you've indicated the DR is just your opinion of the complete range. As I've been able to pull more from the film than your brackets include.....one of us must be wrong. As I've achieved ranges beyond what you place in brackets after measuring with a wedge and densitometer, I know that the actual DR extends beyond this. I've mentioned it before.....odd that you ignored that and contine to post the limited range that resides in your opinion. Worse yet, the range you bracket this time is even less than what you claimed before.</p>

<p>Now let me see....Mark ran a pro lab....I have done photography professionally for 20 years....offering both printing and scanning services as well. What have you done exactly.....other than misread charts from Kodak and quote figures lower than even they do with basic processing and standard developers?</p>

 

[photo_smith]

<p><em>"The link you provided expands on the predictive process, but is largely irrelevant to the issue of interpreting characteristic curves".</em><br>

<em></em><br /> But not increasing dynamic range of a known material!<br /> Edward<br /> Characteristic curves on their own while interesting, are not the central issue. I have tried to explain the different factors in obtaining the maximum for each film. The curves you post have very limited information, and are only relevant to ISO standards and the range that is used to generate them. They give you enough information to calculate gamma, contrast index etc and give a rough idea of how the film works in a standard developer with a fixed brightness range for a given developer/time/agitation. <br /> What they are not is an absolute written in stone, have you ever wondered how lens flare factors into the equation? have you noted how old un-coated lenses seem to compress shadows and give separation in those areas?<br /> What you seem to be suggesting is that films DR (sorry for the acronym) is somehow fixed and that gamma, exposure and developer choice don't matter- you may like to think that over.<br /> My take on this is as a photographer, it is the scene brightness range that is key, leaning how to compress that onto a film using development and exposure techniques and then make those tone appear in the print is vital to my art.<br /> <br /><em>It is discourteous to readers at large when you throw out boutique three-letter acronymns without explanation. Perhaps it's an ego thing, or a symptom of excessive texting :-)</em><br>

<em></em><br /> Wouldn't know about texting only sent a couple in my life.<br /> But-where have I done that? I have taken great pains to explain acronymns as I've gone along but in case you have missed any:<br /> SBR= scene brightness range normally expressed in a number i.e -7 (which is equal to 64:1 log 1.8) <br /> B&W = black and white, for this I mean conventional monochrome film rather than chromagenics.<br /> log= logarithms i.e log of 87 is 1.9 (I have this in my head) :(<br /> DR= Dynamic range either from the scene (in SBR) or optically measured from the film or paper or a product of the gamma and density as expressed in stops.<br /> D-Max= density maximum (a product of exposure and development)<br /> D-min= density minimum sometimes known as stain or base<br /> EFS= effective film speed often expressed as EI (exposure index) rather than ISO<br /> ISO = International Standards Organisation. A body based in Switzerland which publish standards, the film ones are constantly under review but are similar to ASA (American Standards Ass)<br /> BTZS= Beyond the zone system. A system developed by the late Phil Davis to enable photographers to work our how to fit SBR onto tested film materials. If it helps it is kind of an extension to the zone system put forward by Ansel Adams.<br /> WRT= with respect to.<br /> N.B latin short for nota bene meaning please note or note well.<br /> Hope I haven't missed any ;-)<br /> Look Edward, I'm going away for a few days and really can't be bothered to explain this any further, but if you believe that the films DR and its capability of recording tonal range is 'fixed' by the manufacturers published curve that's fine by me as I'm done here.</p>

[ned1]

<p>Ilford claims that FP4 does 14 stops. That's probably true, but you would have to do some very painstaking development and printing to get it. Color negative is less than B&W, although the new Ektar seems to come close. Chrome is about the same as digital, slightly wider for Astia and E200.<br>

I've accidentaly overexposed Tri-X by 3 stops and was still able to get a good image out of it. Try doing that with digital.</p>

[c._sharon]

<p>DR of 9.3 stops as shown by Edward Ingold from the datasheet is correct. One can get usable results from more than 9.3 stops by simply using the overexposure latitude of the film but that does not mean the actual DR is higher.<br /> Ilford claims that FP4 can give usable results even with 6 stops of overexposure. I believe the 14 stops mentioned above includes these 6 stops of overexposure.</p>

[Dave Luttmann]

<p>I disagree C. Sharon. Edward has not gone far enough down the toe in his DR bracket on the graph supplied. </p>

<p>That said, try overexposing any DSLR by 6 stops and see what you get ;-)</p>

[c._sharon]

<p>Dave, the proper technique is to get the point on the curve where density is 0.1 above base+fog. This is around where Edward has drawn the vertical line on the left. Going all the way to left won't be correct.<br /> Of course a dSLR cannot be overexposed by 6 stops and yet give usable results. But this is not a film v digital comparison. This is just to help the OP get the right answer to his question from the characteristic curve.</p>

[Ed_Ingold]

<p><em>Look Edward, I'm going away for a few days and really can't be bothered to explain this any further, but if you believe that the films DR and its capability of recording tonal range is 'fixed' by the manufacturers published curve that's fine by me as I'm done here.</em></p>

<p>I have consistently maintained that there are many curves, depending on the development process. My diagram clearly shows three distinct curves based on development time in D-76. What needs an explanation?</p>

[Ed_Ingold]

<p><em>As I've achieved ranges beyond what you place in brackets after measuring with a wedge and densitometer, I know that the actual DR extends beyond this. </em></p>

<p>Dave, if you have this data, please graph it for all to see, describe what film you used and how you developed it. That graph, incidently, would constitute a characteristic curve.</p>

[Ed_Ingold]

<p>Presumably you could increase the exposure beyond that shown in the Kodak data sheets (Fuji, Ilford, etc). I would expect the density would flatten out, ultimately reaching a value dependent on the amount of silver in the emulsion. There could also be a shelving effect, with lower DMax from underdevelopment. Without data, we don't know how film behaves outside the published charts.</p>

<p>I'm surprised that Kodak stops the chart where they do, but I have charts going back to the 40's, and they're all the same - little or no shoulder is present in the curves. If we had more data, we could use the same tools to estimate the dynamic range as shown in my chart. My purpose in this discussion was to show how curves can be analyzed, which is a valid way to compare various types of film and processing. The problem is coming up with the right curves. Numbers trump opinions any day.</p>

[photo_smith]

<p>"Presumably you could increase the exposure beyond that shown in the Kodak data sheets (Fuji, Ilford, etc). I would expect the density would flatten out, ultimately reaching a value dependent on the amount of silver in the emulsion".<br>

<br /> Actually what I have been suggesting all along and why I think you are wrong when you stated.<br /> Exposure does not change the curve, merely which part of the curve you are using.<br /> The curve pretty much rises then flattens, drops slightly and strangely rises again.<br>

<br />"Without data, we don't know how film behaves outside the published charts".<br>

<br /> Yes we do because we unlike you test the actual film and plot our own curves, rather than looking at manufactures published curves as the 'be all'- you need to have your own figures.<br>

<br />"I'm surprised that Kodak stops the chart where they do, but I have charts going back to the 40's, and they're all the same"<br>

<br /> Why is that a surprise? when the charts use standard step wedges and a limit light input to generate the curve? why should the data go further?<br /> Obviously curves tell you only a small part of the story, a king of rough idea of ballpark results expected for a SBR dictated by ISO standards.<br>

<br />"If we had more data, we could use the same tools to estimate the dynamic range as shown in my chart".<br>

<br /> Eureka! the penny has dropped, either that or you have been reading the links I provided.<br /> The problem is coming up with the right curves. Numbers trump opinions any day.<br /> Yep I have those numbers, taken from many years of testing, I also have the curves plotted for each film I use, in each developer. I can tell you the film from the curve you posted has a limit of around 17 stops when developed to a CI of 0.55<br /> Get BTZS from you library, you'll see how having all the info in front of you helps you understand how gamma, exposure, development and EFS all all linked to recording the ratio of tones (SBR) in your scene<br /> Back tomorrow (hopefully! as I'm posting this from a fiends PC I can't post any data)<br /> <br /><br /></p>

[Dave Luttmann]

<blockquote>

<p ><a href="../photodb/user?user_id=419409">Edward Ingold</a> <a href="../member-status-icons"><img title="Subscriber" src="http://static.photo.net/v3graphics/member-status-icons/sub8.gif" alt="" title="Subscriber" /> <img title="Frequent poster" src="http://static.photo.net/v3graphics/member-status-icons/3rolls.gif" alt="" title="Frequent poster" /> </a> , Mar 29, 2009; 03:45 a.m.</p>

 

<p><em>As I've achieved ranges beyond what you place in brackets after measuring with a wedge and densitometer, I know that the actual DR extends beyond this. </em></p>

 

<p>Dave, if you have this data, please graph it for all to see, describe what film you used and how you developed it. That graph, incidently, would constitute a characteristic curve.</p>

 

</blockquote>

<p>Tests are long gone Ed. I did them for myself and haven't looked back. I did the tests as a part of establishing EI for sheet films I was using.</p>

<p>If you think think your estimates of the graphs are correct....then you should be happy.</p>