Velvia 50 - 14 stops

Discussion in 'Film and Processing' started by mauro_franic, May 16, 2009.

  1. While on a trip I took two pictures at the beach. One with Velvia 50 (when the reflections where subdued) and one with Ektar (when the reflections were too harsh to even look at them). The shots were taken reasonably close to each other.
    The shot taken with Ektar (though challenging even for Ektar) would have been impossible with Velvia.
    Now with both shots, a simple color match in PS using Velvia as the source and Ektar as the Target, does a SPOT-ON COLOR CONVERSION. (This would not work unless the target and the source are similar pictures).
    Et Voila.
     
  2. I don't see 14 stops.
     
  3. Mauro, do you have a densitometer? I have found that most people that claim incredible dynamic range from transparency film go only by appearance. IF you have a 21 step step wedge and a densitotmeter, you can accurately determine how many stops your velvia can record. Likely you'll find it's 6 or 7 stops max, if exposure and processing is spot on.
    Modern C41 film is really amazing, I measure 10-12 stops easily with 160NC and 160S, the two films I use most often.
     
  4. Erie, let me clarify:
    The stops come from the picture taken with Ektar, the colors from the Velvia shot.
     
  5. I still don't see 14 stops.. I see Photoshop contrast on the high and low ends no middle tones.
     
  6. Larry,
    You cannot "see" stops on a picture on a screen unless you have the real scene next to it.
    A picture on the screen could only go from gray to dark gray (a e.g.) and still reprent a 20 stop scene captured.
     
  7. For example, cutting the DR of the ektar shot in half (going from 14-12 stops to 7-6 stops) can give you a rough idea of what the shot may have looked with Velvia:
    00TNGC-135005684.jpg
     
  8. Seeing and putting #'s to them are different.. I like the picture... if that helps but My screen goes pretty high and low and the#'s mean nothing... I am glad you are happy with your creation and keep shooting film.
    Larry
     
  9. Just another tool to use since both films are available on 120 and I can simply swap the loaded backs.
     
  10. tools are good.. thank you. I also use 120 with different backs...
    larry
     
  11. The shots are nice and the range of color negative film in general is astounding, but I can't see 14 stops in pictures that can be displayed on the www.
    I do dimly remember that one of the photo magazines last year or so had a test of how far CN film could go, but it was nothing like 14 stops, more like 7 or 8, I think.
     
  12. JDM, you are confused; you can display a 14 stop scene capture (or any number) on the www. Same as you can display a 50 stop HDR on the www. Any number of stops on a scene can be represented (compressed) into any output (not considering the step loss).
    Regarding the 14 stops of Ektar, I have tested it myself.
     
  13. Here is the Ektar DR test:
    http://www.photo.net/film-and-processing-forum/00Rb8S
     
  14. I'm not sure what can be concluded from this. But what I see is that by colormatching in PS, you have adjusted the contrast of the Ektar image to look like Velvia. Shadows are now blocked. The color balance looks like it has also changed, but the biggest change looks like the contrast. I think the first Ektar picture could have it contrast manipulated to give a better image w/o a colormatch with Velvia. By the way, I recently got a pro pack of 120 Ektar and look forward to using it. It's a great film. But then, so is the Portra line.
     
  15. Yes, color matching also increased the contrast on the Ektar show (S curve) but the stops are still there.
    You can manipulate the Ektar shot to produce different and better results. The example is only if you are looking to get the Velvia colors while capturing additional stops in the scene.
     
  16. Interesting technique- it wouldn't have occured to me to try this.
     
  17. The original scene might have had 14 stops from the deepest shadow to the sun's disk, but once on Velvia 50, the top 9 stops are burned through the emulsion by the sun. What Mauro fails to realize is that stops don't count unless one step can be distinguished from the next. All white (clear) is all white - no detail beyond that junction. I'm not sure what kind of light meter you would need to even measure a span of 14 stops - not my Sekonic 508 anyway. Then there's the claim of 50 stops for HDR (2^50 or a ratio of over a quadrillion to one), LOL.
    According to Fuji's technical data sheet for Velvia, there are about 5 stops of dynamic range (of capture) - 6 stops if you are extra generous. Anything more is pure fantasy. It's time to end this madness. I see that Stouffer step wedges are not outrageously expensive. That would provide a visual representation for those unable to digest objective data published by the manufacturer.
     
  18. One part in a quadrillion is like measuring the distance to the moon to within 0.3 millimicrons (3 angstroms, in the hard X-ray band). We should task Mauro with this job.
     
  19. JDM, you are confused​
    Don't feel bad, you're not the first person to tell me this. ;)
     
  20. "According to Fuji's technical data sheet for Velvia, there are about 5 stops of dynamic range (of capture) - 6 stops if you are extra generous. Anything more is pure fantasy."
    What does this have to do with the dynamic range of color negative film (specifically the Ektar 100 used above)? Nobody is saying Velvia can record 14 stops.
     
  21. the top 9 stops are burned through the emulsion
    point is that not through the emulsion of ektar 100 ... which has colors of velvia, but dynamic range of ektar ;-)
     
  22. My Sekonic L-508 supposedly has a dynamic range of 21 stops (EV-2 to +19 at ISO 100). I'm a little skeptical, but that's what the specifications say.
     
  23. How do you get 14 stops from a film, Ektar 100, capable of only 10 stops dynamic range?
    In the attached photo, I start with the characteristic curve for Ektar 100, published by Kodak. I have drawn the exposure range (horizontal axis) over which you get a useable variation in density (vertical axis), which constitutes the dynamic range the film can capture. The scale is logarithmic (base 10), so to find the range in f/stops divide the span (3.2) by log 2 (0.301).
    The small boxes on either side are intended to be histograms of a subject, like a box of crayons or a small figurine (per our notable "scientists" on this forum). The subject spans a dynamic range of 3 or 4 stops. Let us vary the exposure of this subject over a range of 14 stops. We see from the diagram that part of the range of the subject still falls inside the usable range of the film, consequently some degree of detail can be discerned. As long as any detail can be seen, the frame is "counted" in these "scientific studies".
    The fallacy is that the extra 4 stops or so actually fall outside the true dynamic range, as demonstrated on this diagram, due to the complexity subject under test.
    One valid method is to use a step wedge in which the boundary between adjacent steps is either visible or not. Each step has a single density value, with a known ratio to the adjacent steps. The results from a single exposure would approximate the range calculated from the manufacturer's curve.
    00TNUh-135097584.jpg
     
  24. To my eye, the original Velvia shot is the best because it looks well saturated and natural. Why muck ariound with it in PS, only to arrive at a similar result? Mauro has been hyjacked by the PS soldiers. Get off the computer and back behind you camera? Maybe the art of exposure bracketing to get the best result has now been lost?
     
  25. To my eye, the original Velvia shot is the best because it looks well saturated and natural. Why muck ariound with it in PS, only to arrive at a similar result? Mauro has been hyjacked by the PS soldiers. Get off the computer and back behind you camera? Maybe the art of exposure bracketing to get the best result has now been lost?
    Thank you for your insight, Stephen. But when someone makes a preposterous claim, as in the title, which subsequently proves to be misleading (the colors of Velvia transferred to Ektar), there are consequences. Besides, I though Ektar was God's gift to photography - scanned true to life without any effort.
    Well, it ain't so. Ektar is solid, with fine grain, but nothing can be scanned without effort. Why don't we accept things the way they are, instead of how we fantasize them to be, and just get on with the job?
     
  26. What I find interesting about the exercise is not how many stops can be recorded but how much useful work can be done when scanning a high quality color negative. From what I understand you can't shoot Elite Chrome 100 and then make it look exactly like Velvia in pp in every lighting situation but you can make many changes. I have also started shooting Ektar 100 in 120 (6X7). It has an interesting look. If I knew I would need a very large print I would use it. If I needed a print no larger than 11X14 from a medium format negative I might prefer one of the Portra films.
     
  27. Edward, the exersise is simple:
    Shoot a scene with Ektar to record a wide dynamic range, and shoot a similar scene with Velvia to run a color match if you wish to.
    Not sure why this upsets you that much ot what part you don't agree with.
    Please explain your quotes so I can understand them better and try to answer them:
    1- "What Mauro fails to realize is that stops don't count unless one step can be distinguished from the next".
    Edward, I'm not sure how you deduct that.
    2- "According to Fuji's technical data sheet for Velvia, there are about 5 stops of dynamic range (of capture) - 6 stops if you are extra generous. Anything more is pure fantasy. It's time to end this madness."
    Edward, as explained, the stops are captured with Ektar.
    3- You must have posted the need to use a step wedge to satisfy your belief in Ektar's dynamic range, or post a curve that is designed to show the curve of the response not the boundaries. You are welcome to run the exercise.
    4- "But when someone makes a preposterous claim, as in the title, which subsequently proves to be misleading (the colors of Velvia transferred to Ektar), there are consequences."
    Edward, this forum is intended to share experiences. Consequences? If there is a conflict, it is yours. The forum works just fine.
     
  28. The excersise can be summarized as "The colors from Velvia transfer well to Ektar; using similar shots". This allows to use Velvia-similar colors and Ektar's dynamic range, by shooting the same scene with both.
     
  29. Mauro,
    How did you get a 14 stop wide DR scanned? I'm just curious.
     
  30. Coolscan 9000 and Ektar 100.
    Here:
    00TNnK-135285584.jpg
     
  31. Just ignore the 40D results. No need to compare against digital on this topic.
     
  32. Only need to work on these strips:
    00TNnb-135289584.jpg
     
  33. The "consequences" are that misleading and incorrect information will be challenged ;-)
    The test results Mauro posted illustrate what I am talking about. Notice that there is about a 4 stop range of brightness in the figurine. Mauro accepts the results if any part of the figurine can be seen in a particular panel. As I have shown in the diagram, detail is only visible where the range of the panel overlaps with the true range of the film. At the extremes, most of the image is outside that range, giving the illusion that the dynamic range is greater than it really is.
    In conclusion, Kodak data shows that the dynamic range of Ektar is about 10 stops, Mauro says that his test proves that the range is 14 stops. Doesn't that seem too good to be TRUE?
     
  34. Well Edward,
    I'm using my eyes. Mauro's test does indeed show 14 stops or so. From you, we have a published curve using standard exposure and processing.....no example.
    Guess who people should be listening to?
     
  35. This is all so boring. Get your cameras out of the bag and go take some nice photos folks. There a no test charts hanging in galleries and no one counts the stops of the ones that are. Trust me on this.
     
  36. Mauro -
    I appreciate your testing efforts and I will consider the results of your testing efforts as they apply to the photography that I do myself. Frankly, I am interested in the examples you've posted, whether they can stand up to scientific scrutiny under a mathematical microscope or not. Call me deluded, there are just some things that can only be "measured" subjectively. Thank you for your time and efforts!
    Edward -
    It is all very well and good that you [apparently] have a Phd in something. Most of us are just photographers who enjoy taking pretty pictures and, speaking for myself, I'm not using a characteristic curve or a logarithmic scale to determine whether I will try to make an exposure of something that pleases me or not. I can pretty much eyeball a scene and decide how much range I can get out of it anyway, as can most of us. I suppose if I were being paid $30K for a color photo layout of the latest Toyota, I'd give it a little more thought. Why don't you give Mauro a break? He's obviously gone to some good length to share some of his experience with us here, why not choose to appreciate it for what value it does have.
     
  37. I’m curious to know how the 14-stop range is derived.
    Looking at the original pictures, I see the dark areas (but not carbon-black dark), and the sun (a real-file light emitter), but the sun in the print is not a light emitter; neither is the negative.
    A stop change is a factor-of-2 change, so 14 stops is a range of 16384.
    Looking at the test strips from the May 17, 2009; 09:25 a.m post, I read the immediate 3-stop difference (f/8 and f/22), and I count 7 frames, 1 to the left of the blue square, 6 to the right. Recalling Photo-1 test strip procedure (pick an exposure time, say 3 sec., . . . . . ), another 5 stops are shown, for a total of 8. This is a range of 256.
    Will someone point out the 6 that I’ve missed?
     
  38. Ed, it is f22 + ND8 filter.
     
  39. "I read the immediate 3-stop difference (f/8 and f/22)" and "another 5 stops are shown, for a total of 8."
    The ND8 is snother 3 stops. 11 total, for the test strips. 3 more to go.
     
  40. Edward - you've been down this road before. You're arguing with someone who has never shot a step wedge and never used a densitometer, yet still insists he is right and Kodak is wrong. Dave asks if we should believe Mauro's test or Kodak's curve. Hmm...a boy and his toys or the film manufacturer? There's a hard choice! I think we should probably listen to the film manufacturer and the professionals who designed the film and understand it's exposure characteristics having properly tested it throughout its development cycle. But maybe I'm just funny that way.
    As Ed has illustrated for us, we can't even agree on how many stops Mauro's toy test shows because it's wide open to interpretation before one even considers the errors. There's a reason why paid professionals use step wedges and instruments like densitometers.
    But if you really want to continue to argue with Mauro, do yourself a favor and shoot a step wedge. He will still insist his test is right, but at least he will look more foolish doing so when the step wedge scan is staring everyone in the face. Pick the same wedge that dpreview uses and we will then finally have a reasonable point of comparison against current digital bodies. As opposed to faulty tests with glossy toys, moving lights, no reference points for agreement on measurements, and God only knows what settings.
    Better yet, why don't we take a step back and ask why this nonsense is even discussed? Mauro learned to make Ektar look like Velvia. So what? Am I the only one to notice that both Velvia and the Velvia version of the Ektar scan are way too contrastry for this situation? Every day photographers around the world manage coastal sunset scenes using graduated neutral density filters, exposure blending, and HDR, and get far better results than this in terms of dynamic range, contrast control, detail, and color. It's now a cliche so many people are doing it. Here's but one example of a photographer who has mastered this genre on photo.net http://www.photo.net/photodb/member-photos?user_id=1173668
    Velvia didn't render particularly pleasing colors in this case, so why mimic those colors in Ektar? The excessive contrast plus lack of shadow detail in the Velvia and Ektar-Velvia versions pretty much make this shot look like an amateur drugstore print when compared to standard work in this genre. (To say nothing of the uninspiring composition.) So what advantage did Mauro gain by shooting Ektar and Velvia over any Joe with a DSLR and knowledge of exposure blending or HDR? None that I can see. What a waste of time...
     
  41. Daniel, thank you for the contribution.
     
  42. Mauro, I admire your patience.
     
  43. All of ours.
     
  44. Mauro, I think your measurement is valid, but you are not interpreting the results correctly. If you look at the figurines, the dynamic range of the film is actually from the darkest to lightest, but for the exact same spot on the figurine. The point is, your figurines are 3 dimensional objects, and the light on one side isn't the same as the light on the other. This means that for say the figurine with the maximum overexposure, points on the figurine's left side are blown to pure white, whereas points on the left are not. On the frame with the maximum underexposure, the dark side is black but the light side is now underexposed.
    You can't measure dynamic range by measuring the stops from the point where the light side loses detail (on the underexposure side) to the point where the dark side loses detail (on the overexposure side). This will give you a range that is the sum of the DR of the film and the difference of exposure between the light and the dark sides of the figurine.
    Looking at the same side of the figurines, I can't see more than 10-11 stops of DR, quite in line with what Edward derives from the Kodak curve.
    Make sense?
     
  45. Did anyone mention that though it is not 14 stops it is a nice picture.
     
  46. Absolutely, picking the left arm or the belt (one side of them) would be best. Also note that the capture could have continued a couple stops to the bright side though without blowing. In my opinion Ektar is between 12 and 15 stops (give or take). Certainly several stops wider than my DSLR and at least twice as Velvia.
    The post was not intended to argue about Ektar's 14 stops, but to show how well the colors can transfer from Velvia. Still the Ektar discussion is valid.
     
  47. LOL Ektar is 1 great film I hope to see a 400 ISO of it soon.
     
  48. You can't measure dynamic range by measuring the stops from the point where the light side loses detail (on the underexposure side) to the point where the dark side loses detail (on the overexposure side). This will give you a range that is the sum of the DR of the film and the difference of exposure between the light and the dark sides of the figurine.
    Exactly! Well said.
    The point of using a step wedge is that each segment has a single value for reflectance (or transmittance) and a single color (neutral grey). The dynamic range is determined by the number of patches which can be distinguished from at least one adjacent patch. All the patches are photographed in one shot, which avoids the errors introduced in successive shots. It is especially difficult when scanning to eliminate variations introduced by the scanner and its software as it attempts to compensate for differences in color or exposure.
    It is not necessary to know the absolute exposure level if all you care about is the range from low to high, and the step wedge extends beyond those limits.
     
  49. Vijay, either you are a technical writer or you should be one. That was so well put even I understood it. LOL
     
  50. Edward is right about using a step wedge. That is the correct way to test the dynamic range of a film.
     
  51. The point of this post is not whether Ektar can capture 12 or 15 stops. It is about getting Velvia colors with twice the dynamic range.
    No one argues against a step wedge. If someone want to run the test and post it, most people would appreciate it.
     
  52. No one argues against a step wedge. If someone want to run the test and post it, most people would appreciate it.
    There is no scientific reason to repeat work which has already been published and accepted. Kodak has been performing and publishing characteristic curves for at least 60 years (I have bulletins from the 1940's), using the best techniques and equipment. It is not so obvious to laymen how to interpret these curves. I have attempted to put a "photographic" face on these numbers by relating the scales to f/stops, slope to contrast, and span to dynamic range.
    An image of a step wedge would serve little purpose (other than to prove you had one), unless accompanied by a plot of exposure vs density (e.g., a characteristic curve). Web images, or even prints, have too little dynamic range to see the results objectively. The Photoshop "Information" box could be used in lieu of a densitometer, or you could accept the results from DXO software (which I find inadequately documented).
    It would be interesting to publish results which are not easily available, as for variations in processing of B&W film, or various digital sensors. DPReview.com now publishes dynamic range data for DSLRs under test, based on step wedge measurements. Again, why duplicate those tests, which appear to be well designed and objectively presented. The results of Ektar 100 are locked in - C-41 processing is not ordinarily subject to variations (other than Tetanal, which I find produces uniformly low quality results).
    I can't get too excited about testing color film. As noted, objective data is already available. More important, I don't think about dynamic range, characteristic curves, etc., when I use film. It make more sense to shoot enough and scan enough to get comfortable with a particular emulsion. The "science" is useful to solve problems, predict performance, or (most certainly) to satisfy one's intellectual curiosity.
    I am curious about the actual performance of my CFV back. Hasselblad states (as do Phase One and Leaf) that the dynamic range is 12+ stops, but without objective data to substantiate this claim. Stouffer step wedges cost as little as $20. If I do the work, I will share the results. None are small enough to fit against the sensor itself, so it will have to be through a lens, which will degrade the results to some extent.
     
  53. Mauro,
    In such a presentation, wouldn't it help if you had spot metered and recorded the extreme ends that you wanted captured in detail. Then we know for sure the dynamic range you are talking about.
     
  54. "The point of this post is not whether Ektar can capture 12 or 15 stops. It is about getting Velvia colors with twice the dynamic range."
    Mauro - You're the one making the ridiculous claim of 14 stops. Look at the title that you placed on this thread! And Edward is right again - I'm not about to repeat work that was properly performed by the manufacturer.
     
  55. I have attempted to put a "photographic" face on these numbers by relating the scales to f/stops, slope to contrast, and span to dynamic range.

    Edward why attempt to find dynamic range from Kodak curves? Surely you understand they are derived from Stouffer type wedges?
    Those wedges were not designed to find out the limits of the dynamic range but rather to find out the films response over a limited range of density values which with a 21 step transmission wedge is around 11 stops (curious coincidence?).
    Remember our discussion on why the curves stop on the right hand side? How many stops does a step wedge cover? why don't Kodak plot further along the curve?
    Your decision to start counting density at 0.7 (rather than base +0.1) still puzzles me why use slope and contrast build when a set of standards has been in use by Kodak since 1942- just use the Jones point!
    Trying to make absolutes from estimates in order to give figures a "photographic face' is pointless if those figures don't give you all the data you require.
     
  56. DPReview uses a Stouffer 1/3rd stop step wedge with 41 steps, covering a dynamic range of 13 stops (http://www.stouffer.net/TransPage.htm).
    Kodak makes no assignation of dynamic range, nor any standard method for its determination*. I suggest measuring from a point on the curve with a certain slope because the slope is related to contrast, hence the amount of useful information recorded on the film. If the slope were less than about 0.20, it would be difficult to distinguish white from black in the image, let alone any reasonable scene.
    This is more generous than measuring from the extrapolated "corner" value (the preferred method from an engineering and mathematical analysis background). At the other extreme, DXO measures from the point where the density is just barely discernible from the noise level of the measurement. IMO, this exaggerates the useful dynamic range by 2 or 3 stops, trivializes any differences between sensors, and fails to consider whether the toe region can actually register an useful image.
    * q.v., http://motion.kodak.com/motion/uplo...en_motion_education_sensitometry_workbook.pdf
     
  57. Edward Ingold.
    DPReview uses a Stouffer 1/3rd stop step wedge with 41 steps, covering a dynamic range of 13 stops (http://www.stouffer.net/TransPage.htm).

    No Edward that's wrong the 41 step is still 11.5 stops just that the density increments are smaller 0.5 (1/6 stop) vs . 1.5 (1/2 stop) for the 21 step they also do a 31 step wedge with 1/3 stop increments the density range is the same 11.5 stops. I'm starting to think you've never used a step wedge let alone lecturing others on their use!

    I suggest measuring from a point on the curve with a certain slope because the slope is related to contrast

    That's just plain silly, we have a set of standards already in place that use 0.1 plus base fog as a speed point, anywhere after that density is building. Your method smacks of re-inventing the wheel for the sake of your own arguments-just use the method everyone else does the ISO standard.

    As for the Kodak PDF you link to I was the one who made you aware of it! Please read it and use Kodaks modus rather than you own cludge
     
  58. The Stouffer T4110 step wedge has 41 density increments of 0.1, which are equivalent to 1/3rd stops, as clearly stated in Stouffer's specifications (q.v.). Therefore 41 steps encompass 13 stops.
    Kodak does not specify "speed point" as a base line for dynamic range. Kodak and the ISO procedure refers to the determination of sensitivity. In fact, dynamic range is not mentioned in either method. Taking the Kodak paper at face value, the dynamic range would commence at the 0.7 density point - well above the corner value. I have stated my assumptions, which can be reproduced by anyone interested. Furthermore I have stated the justification for these assumptions. If that is "silly" to you, then you have never written nor reviewed a scientific paper.
    Kodak has apparently updated their equipment since the 1940's. The Ektar 100 characteristic curve covers a span of 13 stops. Kodak apparently feels that the maximum exposure in these curves is sufficient to describe the useful range of the film. It is, after all, nearly 7 stops above the point which defines the ISO sensitivity.
     
  59. Our new Dynamic Range measurement system involves shooting a calibrated Stouffer Step Wedge (13 stops total range) which is backlit using a daylight balanced lamp (98 CRI). A single shot of this produces a gray scale wedge from (the cameras) black to clipped white (example below). Each step of the scale is equivalent to 1/3 EV (a third of a stop), we select one step as 'middle gray' and measure outwards to define the dynamic range. Hence there are 'two sides' to our results, the amount of shadow range (below middle gray) and the amount of highlight range (above middle gray).
    This is from DPReview.​
     
  60. Edward the Ektar curve shows data for the 21 step as it only goes to density 3.05 or do you think the curves drop off the face of a cliff?
    The Kodak paper is NOT the ISO paper but you can estimate the dynamic range by looking at the curve, but that curve has been generated by using a 21 step wedge with a maximum density of 3.0 if Ektar is capable of more density then your assertions are incorrect
    Taking the Kodak paper at face value, the dynamic range would commence at the 0.7 density point
    Seriously I think you're just being obtuse now, that would place it above the mid tone zone V
     
  61. Mauro,
    Whether or not there are 14 stops of DR in Ektar (personally dubious, but haven't run tests), for me the bottom line of your interesting experiment is that one can benefit from the large DR of negative and its flexibility to emulate the color rendition of a reversal film. Congratulation. On emight even think of having a special profile such that right at the scanning step, the file would come out as Ektar-like, or Velvia-like, or... Without the need of a simultaneous shoot with the target emulsion.
     
  62. Kodak apparently feels that the maximum exposure in these curves is sufficient to describe the useful range of the film. It is, after all, nearly 7 stops above the point which defines the ISO sensitivity.
    Edward that's not how ISO is defined, did you read the linked PDF?
    Kodak plot curves using a 21 step wedge (page 6 PDF)
    ISO sensitivity is not defined by the 0.1 plus base fog that is just the point we measure as the inertia point from that we measure 1.3 log units to the right of that point then follow up to the curve and measure that density value film speed will then be that number divided by the antilog of the point.
    For instance if you take 0.1 then go along the curve for 1.3 log E and the value is 0.9 the correct way to determine speed is the antilog of 0.9 (8) divided by 800 therefore the film has a speed of 100
    Read the PDF.
    Meanwhile asserting that the Kodak curve shows data for 13 stops is obviously incorrect it clearly shows 11.5 and the maximum density is 3.05 on the blue channel the same as the maximum for the 21 step wedge.
    o prove that Ektar is only capable of 10 stops you will need to plot your own test as the Kodak curve has insufficient data to draw that conclusion.
     
  63. ISO sensitivity is not defined by the 0.1 plus base fog that is just the point we measure as the inertia point from that we measure 1.3 log units to the right of that point then follow up to the curve and measure that density value film speed will then be that number divided by the antilog of the point.

    True, which place the ISO point on the linear portion of the curve, about 7 stops below the maximum exposure value ;-) On a pragmatic scale, Mauro's data confirms a 10-11 stop dynamic range if you look at just one point on the figurine.
     
  64. Not so fast remember this is colour film with 3 curves the data should be averaged. The figurine is not a good test better one would be to photograph a white fluffy towel for 15 steps 7 each site of the metered point (mid grey) then measure with a densitometer base and d-max then count the steps between the two where detail is present.
    I would imagine that about 11 is realistic but you can't make absolutes from estimates, you certainly can't use a curve derived under contact printed 21 step wedge conditions to ascertain what range a film/lens combo will yield.
     
  65. A step wedge in contact with the film/media is the best method in not the most practical. A lens is subject to various aberations, but particularly flare, which can only adversely affect the results.
    All measurements are estimates! If you know the uncertainty of your standards and methods, you can assign an uncertainty to the results. The less the uncertainty, the better the estimate.
    In the case of Ektar, it makes little difference whether you measure dynamic range from the red, green or blue line or some composite of the three. The density is different, but the curves are nearly parallel in the toe area. The absolute value of the density is irrelevant, just the shape of the curve as it affects the start and end points along the horizontal axis.
     
  66. A step wedge in contact with the film/media is the best method in not the most practical. A lens is subject to various aberations, but particularly flare, which can only adversely affect the results.

    Which is why the step wedge is of limited value, I generally use lenses when I photograph what about you? They impart their signature to my images which is why the test is more useful to a photographer than the curves issued by film companies- they are real world.
    Why do you think ISO standards call for D log 1.3 as a brightness range? do you think they try to factor in flare aberrations? What other curves do they use when working out parameters? Have you seen a quadrant diagram?
    What is the flare factor in the latest ISO standard?

    If you know the uncertainty of your standards and methods, you can assign an uncertainty to the results. The less the uncertainty, the better the estimate.

    Sure but in this thread you have berated the OP for not using the Kodak data from the curves, then have formulated your own DR measurements based on poor methodology and limited data.

    In the case of Ektar, it makes little difference whether you measure dynamic range from the red, green or blue line or some composite of the three.

    During this thread you've shown that you don't understand how to read the curves, you are aware the method for reading colour negative is different from mono ones?What difference does the colour masking make?

    The density is different, but the curves are nearly parallel in the toe area. The absolute value of the density is irrelevant

    Sure they are parallel in the toe area, what about the D-Max? do you think there is no info to the right? If we used the D-Max 4 step wedge would there be more data in that part of the curve? Or does the curve drop of a cliff?
    The only way to test a film is to test it in the conditions you use, with the camera/lens combination you use.
    The published curves are of limited use with limited data, please don't berate people for trying to establish their own working tests.
     
  67. Sure but in this thread you have berated the OP for not using the Kodak data from the curves, ...
    Not quite! I showed how his method added the dynamic range of the subject to that of the film, exaggerating the results by 3 or 4 stops. He is not alone in this fallacy.
     
  68. No Edward what you did is use your own method for calculating dynamic range, one where you start at a density of 0.7 because you 'feel' that is a more relevant method than others use.
    If you want to approximate DR with mono you need to use Base fog +0.1, normally this will give a start point of around 0.24 why do you insist on using your contrast method rather than the traditional one? You must have noticed it shaves off almost 2 stops from the DR figures people get with the conventional scientific methods used by people like Phil Davies?

    The fallacy is all yours, if you insist others are wrong in their calculations because they use convention methods to find density ranges recordable by film it makes me wonder why you continue to make these assumptions based on your modus?
    Certainly you should defer from saying other exaggerate when you are using figures derived from your questionable methodology.
    You state that no measurement for DR exists, that's not strictly true, but then someone who starts reading curves at 0.7 and ignores the possibly of the curve data going beyond the right hand side probably has their own agenda and isn't interested in the truth.
     
  69. Sure they are parallel in the toe area, what about the D-Max? do you think there is no info to the right? If we used the D-Max 4 step wedge would there be more data in that part of the curve? Or does the curve drop of a cliff?

    You would not need a special "DMax 4" step wedge. Since we are only interested in relative measurements, not absolute sensitivity, it would suffice to increase the exposure by a stop or two to measure well into the DMax region of the film. Perhaps someone cares to perform this experiment and report the results.
    No Edward what you did is use your own method for calculating dynamic range, one where you start at a density of 0.7 because you 'feel' that is a more relevant method than others use.
    Actually, I based my starting point on the slope, not some arbitrary density value, which is related to contrast, hence the ability to record detail. Methods improve all the time, otherwise scientists would be limited to the teachings of Paracelcius or Aristotle.
     
  70. I am glad I just take pictures that people like and quit argueing about it... just went out and shot a roll in an old Box camera...... Have a great day.
     
  71. Larry,
    I'm reminded of the wind player who gets hopelessly lost in, say, the Beethoven's Sixth Symphony, raises his hand and says, "Can we tune?". Enjoy your box camera :)
     
  72. Actually, I based my starting point on the slope, not some arbitrary density value, which is related to contrast, hence the ability to record detail. Methods improve all the time, otherwise scientists would be limited to the teachings of Paracelcius or Aristotle.

    Yes you based your point (density 0.7) using calculations based on YOUR interpretation of contrast building. The figure 0.7 BTW is very close to mid grey certainly higher than open shadow on a sunny day. Why start so high up the curve? do you think no detail is recorded between the inertia point and 0.7?

    Yes scientific methods improve all the time, but your calculations are not an improvement are they! We have the International Standards Organisation and scientists that work on film speed standards; they have set 0.1+ base fog as the point in which contrast builds- why do you think they are wrong? why should we chop off the lower 2 stops.
    I know! so we can have retarded arguments on the internet about why we feel our own standards are better than those of the ISO.
    I'm done.
     
  73. Bernard Lazareff
    I tried it, but the color match profile changes as the lighting conditions change. It only works acurately with two cloesly timed and composed shots.
     
  74. Edward, the step wedge test on dpreview you mention gives the 40D over 9 stops.
    In your own experience, how much wider is Ektar than the 40D? ( Please answer directly without twisting words if possible "using a number of stops" in the answer; or answer "I don't know").
     
  75. "Mauro - You're the one making the ridiculous claim of 14 stops"
    Robert, can you please clarify how many stops, based on your experience, Ektar has?
     
  76. Yes you based your point (density 0.7) using calculations based on YOUR interpretation of contrast building. The figure 0.7 BTW is very close to mid grey certainly higher than open shadow on a sunny day. Why start so high up the curve? do you think no detail is recorded between the inertia point and 0.7?
    In fact, I did not draw the sketch in this thread to scale. It was intended strictly to illustrate the problem with Mauro's interpretation of his test. I presume you refer to the green curve (to which my witness line extends). It really doesn't matter which color you choose because there is no difference other than the value for DMin - the curves have the same shape in the toe area. The density value of 0.7 is a coincidence, not by design.
    ISO sensitivity measurement starts at 0.10 density units above DMin*. Since the DMin value for the green line is approximately 0.60 density units, it is perfectly reasonable to measure from 0.70 density units for both sensitivity and dynamic range. The slope at that point is approximately 20%, which is also a reasonable figure for the minimum usable contrast. So it appears we agree in fact if not in principle. We also seem to agree that DMin is not a reasonable starting place.
    * ISO sensitivity is calculated from the amount of light it takes to increase the density from 0.10 units above DMin to 0.9 units above DMin.
    00TQoj-136827584.jpg
     
  77. Is anyone considering the orange mask for Ektar? Dmin gets affected by that; unless Kodak did some test with a special emulsion sans the orange mask.
    Given the presence of the orange mask, a corner obtained by making the linear region intersect with a line of zero slope and height of Dmin is acceptable as the starting point for the DR calculation. I can't see any argument with that.
    As for finding out Dmax; Kodak's curve is quite useless. I mean, it is so blatantly useless as to be a waste of time for them to even publish. Who cares about a half of a characteristic curve? This could be because their wedge ran out steps or whatever, but it is sloppy methodology nonetheless.
    Unfortunately, without an accurate Dmax corner, an accurate dynamic range derivation isn't possible; but we have to assume that there isn't much curve left after the max on the curves primarily because if there were appreciable length to the curve beyond what's shown, Kodak would want to shout it out from the proverbial rooftops and would presumably devise a test to measure it.
    So let's say we'll add a stop of DR (that doubles the range, by the way) to what can be derived from the curve. Edward's lower corner derivation is quite generous; a corner derived by the actual zero slope line intersecting the linear line gives you barely -2.1 or so as the lower corner. The curve stops at about 1.15 or thereabouts. So you get 3.25/log2 which is about 10.8 stops. Add a stop, you get 11.8 stops, say 12 stops at most.
    Mauro's test doesn't show 12 stops, it shows somewhere between 10 and 11. Besides, Mauro and I have a difference in what we call a range: for say 0 - 10, my definition of range is 10, Mauro's is 11. Actually, 10 is correct by all conventions, but what is right is immaterial. When Mauro says Ektar has 12-14 stops of DR, it is 11-13 by my definition. A generous derivation from the curve puts it at 12, bang in the middle of Mauro's 11-13.
    Where's the argument?
     
  78. The generally accepted definition of DMin is the density of the base plus fog. The relatively high DMin for each color is consistent with the presence of the orange mask when the curve was drawn, as is the relative position of the three curves to each other.
     
  79. That is exactly my point. The orange mask increases the absolute value of Dmin, so a measurement of 0.7 or even 0.9 is not incongruent with Dmin for a channel. Zero slope (or nearly zero) is therefore good enough to find a corner, without getting into Dmin values. IOW, Edward, my point of view is that your methodology is quite OK for the lower bound and would be for the upper bound as well, were it not for Kodak's publishing a useless chart that doesn't show the shoulder.
     
  80. * ISO sensitivity is calculated from the amount of light it takes to increase the density from 0.10 units above DMin to 0.9 units above DMin.
    No its not, that is incorrect even for B&W part there but inaccurate. Colour neg uses a different calculation. Colour neg has a mask, the calculation for colour neg factors out the masking and averages the 3 plots so your modus is incorrect. Why not just use the ISO standard?
    People have already done the maths for this, there are tests just because you are unaware of them doesn't mean you make your own inaccurate ones valid.
    A generous derivation from the curve puts it at 12, bang in the middle of Mauro's 11-13 Where's the argument?
    The argument Edward is in you berating him for his tests based on inaccurate methodology, you then go on to put forward YOUR inaccurate method -both of you are wrong.
    That is all I'm pointing out. Dynamic Range has no test per se but recordable density range does, I think in practice they are similar- why not use those tests.
    The ISO have a perfectly adequate set of workable standards- no need for your methods
     
  81. As for finding out Dmax; Kodak's curve is quite useless. I mean, it is so blatantly useless as to be a waste of time for them to even publish. Who cares about a half of a characteristic curve? This could be because their wedge ran out steps or whatever, but it is sloppy methodology nonetheless.

    Yep, like most curves they are generated using a 21 (11 stops) test wedge. To be fair to Kodak they are only providing the info needed as defined by standards which use a pre defined exposure range which is deemed to be an 'average scene' somewhere about 7:1 from memory. In some text books they plot B&W curves a lot further, you may be interested to know that density normally builds but then rolls off, the strange thing is it then builds again. There is a name for this effect which escapes me for the moment.
    Its an academic point though because at those levels the highlight is slightly de-saturated an effect Kodak call 'tonal crushing' in their literature.

    As a photographer I could use this effect, by placing my subject in shadow,specular highlights in the background drop slightly in tonal value and also colour value making them less distracting.
    The best film for this was Agfa Portrait which could take an immense amount of overexposure (but no under) and did this quite beautifully specular highlights 'crushed' to a point where they are only just above diffuse ones meant no burning in during printing.


     
  82. Edward, my point of view is that your methodology is quite OK for the lower bound and would be for the upper bound as well, were it not for Kodak's publishing a useless chart that doesn't show the shoulder.
    I agree that data for the upper bound is needed. This should be easy to obtain using a Stouffer T4110 step wedge. I will probably have a go at it once things calm down with end-of-school-year activities (which helps pay the bills). The analysis is the hard part. I think Excel will do Legendre polynomials, otherwise I will have find something that does, or resurrect programs I wrote over 15 years ago.
    Mark - I have attached a chart from the Kodak publication on sensitivity showing the determination of B&W film speed from an H-D chart (characteristic curve). Point A is 0.10 density units above DMin. A point on the curve 0.80 density units above this is located, and the differential exposure required is read from the horizontal axis. (Hint - 0.1 plus 0.8 equals 0.9 above DMin).
     
  83. ... The image (PSD doesn't work)
    00TR8Q-136957584.jpg
     
  84. Almost there...
    What you are missing is the further calculation what you have calculated is point A now we take 1.3 log units to the right (the brightness ratio set by the average scene) the part here is labelled B we then need to do a further calculation to determine the speed.
    BUT
    this is ONLY relevant for MONO films Ektar is a COLOUR film none of the above works its not relevant, there is another standard for reversal films that is again different mixing up the three is plain daft.
     
  85. What you are missing is the further calculation what you have calculated is point A now we take 1.3 log units to the right (the brightness ratio set by the average scene) the part here is labelled B we then need to do a further calculation to determine the speed.
    What YOU are missing is that is the incremental 1.3 log(exposure) is the dependent variable. The independent variable is the 0.8 increment in density, which establishes point B according to the function expressed by the curve. This chart demonstrates how the process works, the calculations are trivial.
    If you have something positive to contribute to this discussion, do so. If all you can do is parse words and misquote posts, give it a rest. Did I miss something?
     
  86. What YOU are missing is that is the incremental 1.3 log(exposure) is the dependent variable.
    Jeeze Edward I'm missing the average brightness 1.3 log exposure is the dependant variable- REALLY ? how many times do I have to explain this to you?
    This chart demonstrates how the process works, the calculations are trivial
    The chart shows you how to find the speed of a MONOCHROME film, and is of no use WRT to this discussion
    It is only of use to those testing their own film/development curves- if you use the manufacturers curves to find film speed why bother?-the speed is on the box
    What though this discussion YOU have tried to do is prove that your modus for finding DR is of more value than practical tests.
    There is no test for DR, certainly yours doesn't fit the bill.
    What we need to find is the range of densities that film is capable of recording information a MUCH better method would be to use the films overall latitude.
    Did I miss something?
    do you really need to ask that?
    What is your agenda here? Why push your erroneous contrast driven method? why?
    I can only think that you have something missing...
    I'm done with you
     
  87. Mark, you say: "There is no test for DR, certainly yours doesn't fit the bill."
    Allow me to point out that if you can define dynamic range, then merely by definition there has to be a test to measure it and quantify it. I postulate that contrary to your assertion, both Mauro's test and Edward's curve based derivation fit the "bill". And there is nothing to limit the number of different tests to measure DR to just these two methods. Many more tests could fit the bill, all one needs to do is be aware of the accuracy and precision of the test.
    The only thing I see is that there was a difference in the interpretation of both Mauro's and Edward's results; so what? Within the margin of error of either (esp. with having to guess at Dmax) they indicate the same rough figure for the DR of Ektar.
    Where did the question of measuring the ISO speed of the film, which has little to nothing to do with dynamic range, btw, come from?
    On an unrelated note, why on earth do you need Legendre polynomials to find out a simple dynamic range, Edward?
     
  88. And here is another way to estimate Ektar's DR:

    If you accept DP review's DR of over 9 stops for the 40D, Ektar has over 13 stops since it has at least 4 stops more than the 40D in my tests.
     
  89. Edward, if you promote dpreview's step wedge test at the same time you promote your theory of 11 stops, it would mean the Ektar has only 1 stop and change DR over the 40D. (Which I hope you know it is far from reality).
     
  90. On an unrelated note, why on earth do you need Legendre polynomials to find out a simple dynamic range, Edward?
    (1) Legendre polynomials are used to interpolate the results and plot them as a smooth curve rather than a polygon. (2) The first derivative of the polynomial expresses the slope as a function of exposure. It is simple and graphic to determine the dynamic range if you plot the slope (as is common practice in radiology), and (3) Because I can ;-)
     
  91. Damn this is still going? What is Next Tmax- and Tri-X combined ?
     
  92. I would have probably done something more like this to the ektar shot
    00TST8-137585584.jpg
     
  93. Stuart, what we like is very subjective. I -personally- like the color match version I produced with Velvia better.
    Edward what do you like?
     

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