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Photo Forum / Film Photography / Darkroom / April 2004b+f of TMAX 400 and my so-called 'densimoter'
In a previous thread (http://groups.google.com/groups?hl=en&lr=&ie=UTF-8&oe=UTF-8&threadm=b379902d.040 3171641.474a2dd3%40posting.google.com&rnum=1&prev=/groups%3Fq%3Dglaser%2Bgroup:r ec.photo.darkroom%26hl%3Den%26lr%3D%26ie%3DUTF-8%26oe%3DUTF-8%26group%3Drec.phot o.darkroom%26selm%3Db379902d.0403171641.474a2dd3%2540posting.google.com%26rnum%3 D1) we discussed the possibility of using the Ilford EM10 exposure monitor with a step-wedge as a densitomter. At $23 at B&H, this unit seemed like a worthwhile investment and I've gone ahead and tried using it. In general this methodology seems to be registering meaningful results, and when I have more leisure I shall elaborate. For now, I am stuck on base-plus-fog. With my enlarger at 16.5 inches and aperture at F16, I used the EM10 to take the following readings from my step-wedge. Step 1 (.05) reads 43 and Step 2 (.20) reads 53. For interpolation purposes, this gives us .015 desnsity units per EM10 calibration unit within this step (you have to use a different interpolation scale for different steps due to the non-linearty of the EM10's gain control). Now I left a frame on my test role unexposed for measuring base-plus-fog. The unexposed frame made the EM10 go green at calibration number 51. Doing the math, and adding the result to .05, gives a density of .17. I'm sure that the EM10 is not _that_ accurate, but even making an impressionistic guestimate, you can see that the unexposed frame comes out a lot closer to the .20 step than to the .05 step. The film in question is TMAX 400 developed in HC-110 dilution "H" (1/63). One roll was developed for 10 minutes, another for 12 minutes, both giving equivalent base-plus-fog readings (as I suppose you would expect.) Does a desnity of .17 for TMAX 4000 sound plausible? I've always heard that b+f should be around .10. On the other hand, I've also read that fog is affected by different developers. Is it possible that this development regime could result in b+f of .17? If it seems that .17 (or thereabouts) is just utterly impossible, I would be inclined to discard the approach of interpolating the EM10's readings. Thanks. --Phil Phil From my EM-10 reference curve (not measured, found on the NET), the region from 40 to 50 in the dial is acceptably linear, so maybe there's some other reason - stray light? Jorge > In a previous thread > (http://groups.google.com/groups?hl=en&lr=&ie=UTF-8&oe=UTF-8&threadm=b3 [quoted text clipped - 38 lines] > > --Phil Jorge Omar <jorgeomar@ieg.com.br> wrote in message > From my EM-10 reference curve (not measured, found on the NET), the > region from 40 to 50 in the dial is acceptably linear, so maybe there's > some other reason - stray light? Hi Jorge, You know what, I neglected to search the archives before posting my question (mea culpa!!!) and discovered some earlier postings that are relevant to this question, and discovered that I left out the very important point that I currently working in 35mm!!! http://groups.google.com/groups?hl=en&lr=&ie=UTF-8&oe=UTF-8&selm=QbZn9.11514%24O B5.1197856%40newsread2.prod.itd.earthlink.net http://groups.google.com/groups?hl=en&lr=&ie=UTF-8&oe=UTF-8&selm=99qj38%24tgq%24 03%241%40news.t-online.com http://groups.google.com/groups?hl=en&lr=&ie=UTF-8&oe=UTF-8&selm=35trj6%245ps%40 antares.lu.erisoft.se While I suspect there would be disagreement about various numbers, all seem to agree that the "anti-halation" layer of 35mm makes its b+f greater than what you find in 120 and in sheet films. One of the posts suggests that it can be as high as .29!!! The observation that Tri-x has a denser base than TMAX is borne out by some additional tests I did on film that I had developed a while back in a different darkroom, using different tanks, different developer, different everything. The b+f fog of Tri-x was indeed .29 and that for TMAX-400 was .21. I dont' know how to account for the difference in density of the TMAX b+f then (.21) versus now (.17) except to say that it was a different developer (Tmax developer) and fixer (don't remember) combination. I'm also wondering if fixing can affect b+f. Since I'm a little trouble with color distinctions, I'm leary of depending on my own judgement about the pinkness of TMAX as a measure of its having completely cleared, so I fix for 7 minutes (in Kodafix), two minutes longer than the manufacturer's recommendation. Perhaps that might account for the difference? Any additional comments would be welcome. Thanks!!! Hi, Phil Developers may change base fog due to chemical fog. I've never used TMAX dev, so I cannot comment in it, but Diafine WILL give more base fog (compared to others). Fixing/washing may give slightly different densities also, depending on the removal or not of the anti-halation layer ('pinkish look'). So, from the links you posted and the above, I would not worry unless someone post some disagreement data. Jorge > I dont' know how to account for the difference in density of the TMAX > b+f then (.21) versus now (.17) except to say that it was a different [quoted text clipped - 9 lines] > > Thanks!!! : Hi, Phil : Developers may change base fog due to chemical fog. I've never used TMAX : dev, so I cannot comment in it, but Diafine WILL give more base fog : (compared to others). : Fixing/washing may give slightly different densities also, depending on the : removal or not of the anti-halation layer ('pinkish look'). : So, from the links you posted and the above, I would not worry unless : someone post some disagreement data. I always thought that the reason for the higher base density of 35mm compared to sheet film and 120/220 was the addition of something to prevent "light piping" into the canister through the exposed leader. The theory being that if the base was clear the light would be transmitted through the base not unlike light through a strand of fiber and fog the emulsion. This cannot be removed during processing. There is also as you and others have mentioned the issue of chemical fog and incomplete removal of the pink anti halation coating. : > I dont' know how to account for the difference in density of the TMAX : > b+f then (.21) versus now (.17) except to say that it was a different [quoted text clipped - 9 lines] : > : > Thanks!!!  SignatureKeep working millions on welfare depend on you ------------------- fwp@deepthought.com > In general this methodology seems to be registering meaningful > results, and when I have more leisure I shall elaborate. For now, I am > stuck on base-plus-fog. I'm pleased the method is working for you. I would'nt want to give anybody a bum steer. > Does a desnity of .17 for TMAX 400 sound plausible? That sounds very good. The lowest I've read on my well calibrated Tobias TB+ with Pan F is .11 . Readings in the upper teens and lower 20s are quite in line. Upper 20s readings are commen. Although I've read of fb+f in the 40s I think that is generally considered quite high and associated with pushed high speed film. Dan > > In general this methodology seems to be registering meaningful > > results, and when I have more leisure I shall elaborate. > > > I'm pleased the method is working for you. I would'nt want to give > anybody a bum steer. Yeah, I'm quite happy with this approach. There were two things that I came across that helped with the consistency of ther results. My first few trials were done with a home-made cardboard "negative" carrier for the test tablet so that I would not have extraneous light -- i.e., it was cut to size for the step tablet. The mistake here was that the position of the strip was inconsistent, so that at times it was being projected from the edge of the enlarger's light beam. This resulted in fall-off, so that readings were noticably different from one area of the same step to another. I therefore created another mask that fits into my normal negative carrier and readings are now consistent across the frame. The second bit was to understand that its best to get the range of readings up into the 40s and 50s because, as Jorge points out, that's where the readings are more linear. So for the Zone VIII reading I lower the enlarger to 6 inches and stop up to 5.6. For the Zone I reading I raise the enlarger to 16.5 and down to F16. I still find that from one session to another there are variations and I need to recalibrate each time. I suspect that this is due to the battery in the EM10 draining or perhaps to power-fluctuations in the enlarger. When I get around to some kind of votage regulation for the enlarger I'll see how that changes things. I might also try one of those power supplies that has a 9v connector for replacing a battery. In any case, this system works quite well enough for me at this stage of my learning process. I am grateful for the suggestion, and for all the additional information in this thread about b+f. Many thanks! --Phil > The second bit was to understand that its best to get the range of > readings up into the 40s and 50s because, as Jorge points out, that's > where the readings are more linear. So for the Zone VIII reading I > lower the enlarger to 6 inches and stop up to 5.6. For the Zone I > reading I raise the enlarger to 16.5 and down to F16. IIRC, your reason for using the "sub.-dens." EM10 is to evaluate film/developer combinations. You might consider Zone III - VII. Those are the five Zones which show in a print. Also you will be able to see the density vs exposure curve. When I do that I need not reset my lens f stop when exposing the film. Resetting the stop introduces a variable which I feel is best handled with resets of the ETRSi electronic shutter. I have done ten exposures for nine zones doubleing up at Zone five with no f stop variation. I don't think that can be said of all lenses. I avoid exposures greater than 1/4 or less than 1/125. > I still find that from one session to another there are variations > and I need to recalibrate each time. I suspect that this is due to > the battery in the EM10 draining or perhaps to power-fluctuations There may be some play involved when changeing stops. Other than the old fashioned way of slipping in stops the only way we've been left with is turning the ring. Dan > In a previous thread > (http://groups.google.com/groups?hl=en&lr=&ie=UTF-8&oe=UTF-8&threadm=b379902d.040 3171641.474a2dd3%40posting.google.com&rnum=1&prev=/groups%3Fq%3Dglaser%2Bgroup:r ec.photo.darkroom%26hl%3Den%26lr%3D%26ie%3DUTF-8%26oe%3DUTF-8%26group%3Drec.phot o.darkroom%26selm%3Db379902d.0403171641.474a2dd3%2540posting.google.com%26rnum%3 D1) [quoted text clipped - 34 lines] > > --Phil For 35mm with its grey base, my understanding is that FB+F is about 0.40. For 120 film, which has non-tinted base, it is quite a lot less. There must be some figures somewhere on the web. I quote below some lines from an article by Geoffrey Crawley in which he compares the new Delta 400 to the older 400 Delta, and also to HP5+, and their suitability for pushing. This indicates FB+F figures around 0.40. <begin quote> ..... The new film has a noticeably lower base/fog level than its ancestor. Processed to 400, 800, and 1600 gave Dmins of 0.38, 0.4 and 0.42, compared to 0.45, 0.48, and 0.54. HP5 gave 0.4, 0.42, and 0.44 again proving the quality of the popular traditional material. <end quote > > In a previous thread > > (http://groups.google.com/groups?hl=en&lr=&ie=UTF-8&oe=UTF-8&threadm=b379902d.040 3171641.474a2dd3%40posting.google.com&rnum=1&prev=/groups%3Fq%3Dglaser%2Bgroup:r ec.photo.darkroom%26hl%3Den%26lr%3D%26ie%3DUTF-8%26oe%3DUTF-8%26group%3Drec.phot o.darkroom%26selm%3Db379902d.0403171641.474a2dd3%2540posting.google.com%26rnum%3 D1) [quoted text clipped - 50 lines] > again proving the quality of the popular traditional material. > <end quote> Soak a piece of film leader in Clorox or equivalent chlorine bleach to remove the emulsion. Measure the density of this piece to find the minimum you could possibly get with that film. I think 400TMax, 400TX, and HP5+ are all different, HP5+ having the most dense base. Next, measure an undeveloped, fixed piece of film to find the component of B+F due to gelatin without silver. A higher density than base + gelatin is to be expected after development of an unexposed piece due to chemical fog. It is the chemical fog that can cause increased grain. |
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