 |
 | Home | Contact Us | FAQ | Search & Site Map | Link to Us |
 | Sign In | Join | Other 45 Sites in Network |
| PhotoKB HomeDiscussion Groups Digital Photography Digital PhotoDSLR CamerasZLR CamerasPoint & Shoot CamerasFilm Photography 35 mmLarge FormatMedium formatDarkroomFilm and LabsOther EquipmentPhoto Technique Nature PhotographyPeople PhotographyTechnique GeneralGeneral Photo Topics General TopicsAustralian PhotographyUK PhotographyDirectoryPhoto Clubs |
Photo Forum / Film Photography / Darkroom / August 2005(OT?) Reciprocity
First of all, let me apologize for this off topic post. Could you please direct me to the appropriate newsgroup? I couldn't find one quite right. My question was just this. If a light meter suggests an exposure of 4 minutes for Ilford HP5 Plus (really 1 minute f/4, but I need f/8), what would be a suitable reciprocity adjustment? Ilford's online technical document stops at 30 seconds (where it says to use 200s instead). Unfortunately pushing wasn't much of an option as most of the images on this roll will not be taken in such unfavorable circumstances, although for future reference I would also like to ask whether, if you have time to wait for an exposure, pushing and using a shorter one is still superior? Many thanks, Stephen McKeown >My question was just this. If a light meter suggests an exposure of 4 >minutes for Ilford HP5 Plus (really 1 minute f/4, but I need f/8), what >would be a suitable reciprocity adjustment? Ilford's online technical >document stops at 30 seconds (where it says to use 200s instead). wow. that is going to be an oscenely long exposure. try using tmax100 instead,as its reciprocity failure isnt so bad. >Unfortunately pushing wasn't much of an option as most of the images on >this roll will not be taken in such unfavorable circumstances, although >for future reference I would also like to ask whether, if you have time >to wait for an exposure, pushing and using a shorter one is still >superior? for future reference, use faster film (like tmax 100 with long exposures, or TMZ3200 pushed to 6400 for short ones) if you underexpose, you simply will not have the density you need in the dark sections to be anything but black. night shots are not tremendously pushable unless you want VERY high contrast. > First of all, let me apologize for this off topic post. Could you > please direct me to the appropriate newsgroup? I couldn't find one [quoted text clipped - 13 lines] > Many thanks, > Stephen McKeown <pre> You can use the following corrections for HP5+. I've included the corrections for TMY for comparison. It is a better choice for long exposures. A four minute exposure for HP5+ would require 40 minutes; for TMY, 13.5 minutes would be required. You could use Microphen for the developer, but "pushing" will only increase already blown-out contrast from the failure, and will not increase shadow detail. Ilford Reciprocity Failure Corrections: Metered Exposed Development (sec) (sec) Reduction (%) 0.1 0.1 0% 0.5 0.8 8% 1 1.96 11% 2 4.81 14% 10 38.8 20% 35 197 24% 60 396 25% 100 769 27% 120 974 27% 150 1301 28% 180 1648 29% 240 2394 29% 300 3197 30% Kodak TMax 400 (TMY) Reciprocity Failure Corrections: Metered Exposed Development (sec) (sec) Reduction (%) 0.1 0.1 0% 0.5 0.6 4% 1 1.4 5% 2 3.0 7% 10 20 11% 35 86 14% 60 161 15% 100 292 16% 120 361 17% 150 467 17% 180 578 17% 240 808 18% 300 1048 18% </pre> Thank you both very much. I will try TMax... either 100 or 400. Two quick questions if you don't mind: (1) Just out of curiosity, what did people do in this situation before new technology films? Just wait the 50 minutes? Just for grins I probably will do this once just to see what it looks like. And (2) I'm a bit new to developing, and I've heard TMax is harder to develop / less forgiving. Are there any special gotchas, or a link to a website discussing this, that you know? I very much appreciate both responses. Thanks, Stephen >Thank you both very much. I will try TMax... either 100 or 400. Two >quick questions if you don't mind: the reason i use tmx (100) is that its reciprocity failure is better than 400 (tmy). in the time ranges you're talking about, tmx and tmy require similar exposures, but the grain and sharpness of tmx is better. try both! >(1) Just out of curiosity, what did people do in this situation before >new technology films? Just wait the 50 minutes? either that or sacrifice depth of field >(2) I'm a bit new to developing, and I've heard TMax is harder to >develop / less forgiving. Are there any special gotchas, or a link to a >website discussing this, that you know? tmx is definitely less forviging that hp5+ (which i like using for middle of the day shooting in sun, since it is low contrast and high sharpness. i can also handhold with very large depth of field) in terms of developing. you could start a new thread here, asking about developing tmx. (specific to night shooting or not). you'd get a lot of responses. when im using tmx for night photography (which is a large portion of what i do), i will usually take 2 shots of each scene (3 if i think it is a very nice shot). one shot is about half stop below the suggested (reciprocity accounted for), and one is about 1 stop more than the recommended (depending on length of exposure) if i am using 3 shots, i will do something like: 1-stop under computed time at computed time 1.5 stops more i vary these vary by feel, so i dont even know if that's what i actually do :) when developing, ensure you're water temp is close the the time you're using it for, and be consistent with your inversions. i reduce the agitation of my tank in the later portion of the developing (in an attempt to control the highlights will still bringing up the shadows). Incidentally, You mention that TMX ~ TMY in this range, exposure wise. But as I'm gathering everything together I'm finding I don't have a ton of information on TMX. Can I infer that metering at 400 and using Mr. Gudzinowicz's table for TMY, for example, would work? Many thanks, Stephen P.S. (Yes, I need to just start experimenting now. I'm going to tonight, but since my schedule etc. forbids developing every day, I'd like to get a useful first batch in terms of learning. Thanks! -SM) > Incidentally, > [quoted text clipped - 10 lines] > tonight, but since my schedule etc. forbids developing every day, I'd > like to get a useful first batch in terms of learning. Thanks! -SM) I found one of my old posts on reciprocity failure and development corrections, and it's pasted below. Non-linear regression analysis of manufacturer's data was used to select the best data fit from more than a dozen different equations including those used in the literature. When comparing TMX and TMY, remember that TMY is 4X faster, so a fair comparison might be TMY metered at 15 sec. vs. TMX metered at 60 sec. The calculated times may be regarded as nothing more than suggested minimum exposure times. With TMX and TMY, I may expose 2X to 4X longer since the films have a tremendous latitude for overexposure if an active developer is used to maintain a "straight line" H&D curve. For instance, HC110B diluted 1+1 as suggested by Adams in the "Negative" is a good choice. Compensating or accutance developers usually provide poor high value separation especially when development is curtailed to reduce contrast increased by failure and by night scenes which often require N-3 development. Old post: The Schwarzschild equation has traditionally been used to describe reciprocity failure. It is: Tc = (Tm)^(1/p) where Tc is the calculated time, Tm is the measured time and p is the Schwarzschild coeficient. The equation assumes that Tm is much greater than 1 second. Years ago (early 1980's) I did curve fitting to published data, and programmed a calculator using the following modification: Tc = a * (Tm)^(1/p) where a is a constant used to get a better fit. That is the equation used for the table. The values for a and p are given below. The values for the development adjustments are calculated by converting the additional exposure time to f/stops of exposure and assuimg that the high values (well lit areas) are overexposed by this amount since they do not suffer failure to the same degree if at all. That is the way Kodak does the calculation: f/stops_over = log(Tc/Tm)/log(2) (log base = 10) The contrast reduction (%) required for paper's typical 8 stop scene range is: Contrast_reduction = 100% * (8/(8 + f/stops_over)) The development correction is 100% - Contrast_reduction (%) TMX TMY Old Kodak Ilford p= 0.90909091 0.85910653 0.73367572 0.77101002 a= 1.22743923 1.37088177 2.17770977 1.95884467 Tm 0.5 0.6 0.6 0.8 0.8 1 1.2 1.4 2.2 2.0 2 2.6 3.1 5.6 4.8 5 7.2 8.9 19.5 15.8 10 15.5 20.0 50.2 38.8 15 24.1 32.1 87.3 65.7 30 51.7 71.8 224.6 161.4 45 80.8 115.2 390.2 273.0 60 110.9 161.0 577.6 396.5 90 173.2 258.1 1003.8 670.9 120 237.7 360.7 1485.7 974.3 180 371.4 578.3 2581.9 1648.5 240 509.6 808.3 3821.4 2394.1 300 651.4 1048.0 5179.8 3197.6 420 943.1 1550.5 8193.9 4947.1 600 1396.3 2348.4 13323.6 7857.1 900 2181.1 3764.8 23154.3 13293.9 1200 2992.9 5262.2 34270.8 19306.3 1500 3825.6 6822.9 46452.9 25786.4 1800 4675.2 8436.0 59557.5 32665.4 Many thanks! I used this last night and had lots of fun. I'm looking forward to seeing the results. Stephen >> Incidentally, >> [quoted text clipped - 89 lines] > 1500 3825.6 6822.9 46452.9 25786.4 > 1800 4675.2 8436.0 59557.5 32665.4 Michael, I am truly sorry I did not see your post before I wrote the one below, and in fact did not know of that work before I wrote my article in Photo Techniques on reciprocal trade disagreements. I would certainly have referred to it if I had seen it. I'm sure you know that the equation can be plotted on log-log paper as a straight line. What I found by analyzing Howard Bond's experimental results was that the major difference between films could be attributed to the "a" coefficient with the exponent the same for all films to within experimental accuracy. > Thank you both very much. I will try TMax... either 100 or 400. Two > quick questions if you don't mind: > > (1) Just out of curiosity, what did people do in this situation before > new technology films? Just wait the 50 minutes? Just for grins I > probably will do this once just to see what it looks like. And People have been known to leave shutters open for a lot longer than that. One thing to keep in mind is that a stop or two of extra exposure rarely does any serious harm, so that if you are planning a really long exposure, it can be a good idea to make it twice as long as you calculate to be on the safe side. > (2) I'm a bit new to developing, and I've heard TMax is harder to > develop / less forgiving. Are there any special gotchas, or a link to a > website discussing this, that you know? Tmax 100 (I have no experience with Tmax 400) is about twice as sensitive to differences in time, temperature and agitation as the older type films. If you work carefully, use a reliable thermometer and always do your agitation the same way, you should not expect any special problems. It may take a few tries to get the development just the way you like it, but then you will be able to keep doing it the same way and get it right every time. When I first used Tmax 100, I used D-76. I didn't really like it despite its very fine grain and high resolution. I think my reaction might have had something to do with the acutance or apparent sharpness not being as good as the conventional films I was used to. I have since switched to using Xtol 1:1, and the film looks much better to me. Xtol appears to have a problem with sudden failure, but it hasn't happened to me yet. Peter.  Signaturepirwin@ktb.net > First of all, let me apologize for this off topic post. > Could you [quoted text clipped - 23 lines] > Many thanks, > Stephen McKeown Its right on topic! Ilford might be able to supply you with additional information, its worth contacting them. Otherwise its a matter of making tests and extrapolating from the published data for a starting place. As you can see from the published data long exposure reciprocity failure varies with the intensity of the light. What is happening is that the low intensity part of the exposure has less effect in comparison to higher intensity resulting in a rise in contrast (and change in shape of the characteristic curve). Long exposure reciprocity failure is a problem in astronomical photography. While most professional astronomy is now done with electronic sensors there is still a lot of data about ver long film exposure available. I would suggest searching amateur astronomy sites. I have, in the past, seem some tables of exposure going out to about half an hour but don't remember where I saw them :-( While 4 minutes is a long exposure it is stil quite parctical, I've made successful exposures longer than this (up to about 10 minutes) but I just guessed at development. T-Max films have less reciprocity failure than standard films so are a better choice for this. Probably the best off the shelf film for lack of reciprocity failure is Fuji Acros. While this is an ISO 100 film for normal exposure it might actually be faster than a conventional ISO-400 film when used for very long, low intensity exposure. The developer is not significant since you are not pushing but rather the opposite. Signature--- Richard Knoppow Los Angeles, CA, USA dickburk@ix.netcom.com > > [quoted text clipped - 57 lines] > > You can calculate the correction for reciprocity by the following: Tc = K * (Tm ^ 1.62) T = Tm + Tc this means raise the metered time, in this case 340 seconds, to the 1.62 power and add the result to the metered time. K for HP5+ is 0.09. For TMX or TMY it is 0.07. I got these constants by analysis of data published by Howard Bond in Photo Techniques. His data do not agree with Ilford , but the equation fits their data as well but with a K of 0.5 for every film they make. Howard's data are better. > You can calculate the correction for reciprocity by the following: > [quoted text clipped - 4 lines] > analysis of data published by Howard Bond in Photo Techniques. His data > do not agree with Ilford ... Looking it up in Mees, the original Schwarzschild relation is K = Intensity * (time ^ p) Where K and p are constants (different from Patrick's) and intensity is the light falling on the emulsion. Rearranging this becomes: T = (K / I) ^ (1 / p) The conditions are: o A constant density is produced on the film, i.e. works when photographing grey cards. o Time is > 1 minute For shorter times, and different densities, p is no longer a constant but is a function of intensity. Correcting for the intensity effect results in the hyperbolic equation: log T = C + a * sqrt ((log I/log Io)^2 + 1) Where C, a and Io are some constants that vary with emulsion. Though some prefer a catenary fit to the data: log T = C + log[(I/Io)^a + (I/Io)^-a] Where C, a and Io are also constants, only different. The only meaning I can dredge from this is that reciprocity failure is a function of light intensity and not one of time. Well, that really clears the air on the subject ... glad I looked it up. My conclusions: 1) I doubt two people can come up with the same reciprocity curves without a lab full of equipment, and probably not even then. 2) All curves and tables of that aren't generated by one personal testing are questionable. 3) As Richard states: at low light levels the normal contrast curve of the film goes out the window Advice: Bracket, expose for the darker portions of the scene, underdevelop for low contrast. Hope I take it. Using Ilford's curve correctly [and assuming it has any correctness] a scene with a seven stop range, needing no exposure correction in the highlights will need a 200x increase in exposure for the shadows. My experience is that the above is about right: My long exposures do produce gobs of contrast - to be expected as the reciprocity failure for the shadows will be greater than that for the highlights. And now I now why, or at the least, how to really muddy the waters. * * * OT can stand for 'On Topic' as well as Off Topic. SignatureNicholas O. Lindan, Cleveland, Ohio Consulting Engineer: Electronics; Informatics; Photonics. To reply, remove spaces: n o lindan at ix . netcom . com Fstop timer - http://www.nolindan.com/da/fstop/index.htm "Nicholas O. Lindan" <see@sig.com> wrote sophomorically: Please ignore: > Using Ilford's curve correctly [and assuming it has > any correctness] a scene with a seven stop range, > needing no exposure correction in the highlights > will need a 200x increase in exposure for the shadows. it is in error ... SignatureNicholas O. Lindan, Cleveland, Ohio Consulting Engineer: Electronics; Informatics; Photonics. To reply, remove spaces: n o lindan at ix . netcom . com Fstop timer - http://www.nolindan.com/da/fstop/index.htm >"Nicholas O. Lindan" <see@sig.com> wrote sophomorically: > [quoted text clipped - 11 lines] > > You missed my point entirely. The metered exposure time that serves as the input for my equation IS a function of illumination. My equation fits all available data I have gotten my hands on, and the constant 1.62 works for all within the accuracy with which you can measure scene brightness. The Ilford curve shown in all their film data fits with a K of 0.5. Try it. If you get the right K coefficient, you can calculate the addition to measured time. If everyone else including Schwarzchild got it wrong, what can I say? They, for the most part, did not set out to define a function of time, but a function of I*t. My equation applies to the right hand side of the catenary. > You missed my point entirely. The metered exposure time that serves as > the input for my equation IS a function of illumination. My equation > fits all available data .... Don't argue with me. I paraphrased Mees. And he paraphrased Halm who expanded on Kron who worked with Shepard's confirmation of Englisch who agreed with Abney who expanded on Swarzschild, who got it off an itinerant Tinker for all I know. > ... I have gotten my hands on, and the constant 1.62 > works for all within the accuracy Who said/says it doesn't? Maybe a pinch of bromide is needed ... SignatureNicholas O. Lindan, Cleveland, Ohio Consulting Engineer: Electronics; Informatics; Photonics. To reply, remove spaces: n o lindan at ix . netcom . com Fstop timer - http://www.nolindan.com/da/fstop/index.htm > Don't argue with me. I paraphrased Mees. And he paraphrased > Halm who expanded on Kron who worked with Shepard's confirmation > of Englisch who agreed with Abney who expanded on Swarzschild, > who got it off an itinerant Tinker for all I know. Frankly "Scarlet".... Who gives a darn about six significant figures? I don't! If your metering equipment says, "1 minute". make it 3. If "10 minutes" make it 40 or an hour and have a Guinness! Good Grief!!! Dr bob, unavailable light photographer. > > [quoted text clipped - 15 lines] > > Who said anything about 6 figures? Just because a little pocket calculator shows 10 doesnn't mean you have to use all of them. Exactly! dr bob wrote: Don't argue with me. I paraphrased Mees. And he paraphrased Halm who expanded on Kron who worked with Shepard's confirmation of Englisch who agreed with Abney who expanded on Swarzschild, who got it off an itinerant Tinker for all I know. Frankly "Scarlet".... Who gives a darn about six significant figures? I don't! If your metering equipment says, "1 minute". make it 3. If "10 minutes" make it 40 or an hour and have a Guinness! Good Grief!!! Dr bob, unavailable light photographer. Who said anything about 6 figures? Just because a little pocket calculator shows 10 doesnn't mean you have to use all of them. > "Nicholas O. Lindan" <see@sig.com> wrote > > I paraphrased Mees. And he paraphrased > > Halm who expanded on Kron who worked with Shepard's confirmation > > of Englisch who agreed with Abney ... > Frankly "Scarlet".... > Who gives a darn about six significant figures? I don't! What a lovely comment ... Who ever said anything about six sig fig.? Look, if I am that annoying put me in your kill file. The original post was to the effect that reciprocity failure is a function of light intensity and not exposure time. Crossing this pons asinorum makes, for me, the whole reciprocity-thing make sense and explains why contrast increases as light intensity decreases. Measuring the exposure time with a light meter is a good- enough method of measuring the light intensity on the film, as is Kentucky windage (if it reads 1 second, give it three ...). Never said it wasn't. And that's the way I do it. What a stupid subject to get riled about. SignatureNicholas O. Lindan, Cleveland, Ohio Consulting Engineer: Electronics; Informatics; Photonics. To reply, remove spaces: n o lindan at ix . netcom . com Fstop timer - http://www.nolindan.com/da/fstop/index.htm >"dr bob" <rsmith@dmv.com> wrote > [quoted text clipped - 34 lines] > > If you're talking about me, I'm not riled. I should have put my most recent post in place of that one. There is nothing Mees said or quoted from others that contradicts what I presented. None of them appears to have taken the same viewpoint that I did. If mine looks better on log-log paper, where's the beef? > > [quoted text clipped - 19 lines] > > Well, I guess that's where I went wrong. I didn't paraphrase anybody. Some years ago, I wanted to see if there was an equation that would work, so I did what most engineers would do. I plotted available data on various kinds of graph paper. Plots on log-log paper wer straight lines. Furthermore, the lines for all the different films were parallel. Now, of course, I had to find the right ordinate and abscissa, which took a little trial and error. I found that when I plotted the difference between measured and corrected exposure time against measured exposure time I got those straight parallel lines. Why Mees et al did not do that, I'll never know. Perhaps it wasn't scientific enough. I must admit I do not know why it works, but I know that it does, and is easily done on a pocket calculator that you can get most anywhere for less than $20. If you can remember 1.62 and the K factor for the film you want to use, you don't even have to carry a chart. I read the chapter on reciprocity in "The Theory of the Photographic Process" just to make sure no one else had done the same thing before I published my thing in Photo Techniques. Thank you, this was very interesting. I'm curious though about the large difference between K = 0.5 and K = 0.09 for HP5+. Why the huge difference? Wouldn't K = 0.09 suggest that HP5+ is nearly as good as TMX/TMY for reciprocity? Many thanks, Stephen > >>First of all, let me apologize for this off topic post. > >>Could you [quoted text clipped - 65 lines] > do not agree with Ilford , but the equation fits their data as well but > with a K of 0.5 for every film they make. Howard's data are better. >Thank you, this was very interesting. I'm curious though about the >large difference between K = 0.5 and K = 0.09 for HP5+. Why the huge [quoted text clipped - 90 lines] > > Well, it's a little more than 3/4 as good. Ilford' s data are surely conservative if getting more than enough exposure is conservative. It may also be true that the numbers should be conservative because of batch-to-batch variations. Accoring to Bond's data, 100Delta is better than either. |
Reply to this Message |
 Sign In
 Join
 My Latest Posts My Monitored Threads My Blog My Photo Gallery My Profile My Homepage Start New Thread Enable EMail Alerts Rate this Thread
|
©2009 Advenet LLC Privacy Policy - Terms of Use
This website includes both content owned or controlled by Advenet as well as content owned or controlled by third parties.