T-Max film -- EXPOSURE INDEX AND DEVELOPMENTgreenspun.com : LUSENET : B&W Photo - Film & Processing : One Thread
I've been runnning some film processing tests of T-Max 400(8x10in.) with T-Max RS Dev.(1:9) using JOBO rotary processor, and I have some questions about the results.
First of all, Exposure Index which came out was 560. Is this pretty normal?? Here is how I found my EI. (I followed the article, "exposure test" in the KODAK book. 1. I set the manufacturer's recommended ISO film speed. That is 400. I exposed 5 sheets of film shooting a gray card (focus at infinity). 2. In the first shot I underexposed 3 stop so that the gray card is placed at Zone 2, and the second shot is -3 1/2 stops (Zone 1.5) , and the third is -4 stops (Zone 1), and so on. 3. I develop the films with T-Max RS (1:9) for 9 min at 75F using JOBO (rotation speed 3 1/2) 4. I read the density of the negatives. Base+fog was 0.06. The negative which is 0.16 was the one which was underexposed -4 1/2 stops. 5. I multiplied film speed(400) by the factor(1.4) on the article. 400 x 1.4 = 560 EI=560 Next, the result of the Development test shows that the normal dev. time is 10min. I set my new system-speed number(560), and shoot 4 sheets of films--which were overexposed 2 stops (Zone 7)and--process them in defferent dev. times, 8min, 9min, 10min, and 11min. The density of negative which is 1.11 was the one was deveoped for 10 min. 5. Thus, the result was EI 560 and 10 min development for grade 2 paper printing. Is this the right way to figure out?? Also, I read the article by J. Sexton about T-Max film ,and his current starting recommendatin for T-Max 400 in a JOBO with T-Max RS 1:9 at 75 degrees is EI 320 for 7.75 minutes and rotation setting on 3 1/2. My result is very different from his recommendation. So, I shot normal subject and processed both in my way (EI 560 for 10min) and in his recommendation (EI 320 for 7.75min) The negative processed by my deta looked OK whereas the negative processed by his recommendation looked a little flat in terms of contrast. Therefore, I thought that what he is saying in the article is that make a little flat neg. and add some contrast later when printing, which yield more beautiful print in stead of adjusting contrast when making neg. Am I misunderstanding completely?? How come my deta is away different from his recommendation?? I used sekonic meter and shunider lens --they are pretty new!! Anyone can help me?? I am beginner of large format. Thanks Anausagi
-- anausagi (email@example.com), November 03, 2000
What sort of densitometer did you use, and are you sure it's accurate?
I'm very suspicious of your base+fog reading of 0.06, this is far too low to be real. Most base+fog density readings come out in the 0.12 to 0.15 region. I doubt if the film base alone would give a reading of less than 0.1.
Aha! I see you mention a Sekonic meter in conjunction with the enlarger lens. If you're trying to read density from the enlarger baseboard, forget it. It's almost impossible to get sensible density readings like that, for the simple reason that all manufacturers data is based on diffuse density readings, which you simply can't get from a projected image.
Why not use Kodak's published curves for Tmax and RS? They're readily available from Kodak's website, and have been measured using equipment and methodology far more accurate than the average user has access to.
-- Pete Andrews (firstname.lastname@example.org), November 03, 2000.
Oh boy! Think of how many nice photos you could have taken with all that film if you had just done a couple test shots to adjust exposure for adequate shadow detail and development for good contrast. One probelm with testing the way you did (full frame grey card) is that it neglects the effect of flare. Why make this more complicated than it needs to be?
-- tim brown (email@example.com), November 03, 2000.
I am one to recommend some testing, but the minimum necessary to get what you want. I just test for Z 1 to get film speed and Z VIII to get contrast, and don't worry about the curve in between. Furthermore, I don't believe it is useful to test your film with a densitometer if you don't also test your paper. This is all very expensive and, unless you plan to be doing this regularly, is not worth the effort.
Good information can be found on circada.com bout the theory of testing, the process and building and using a diffuser, which is quite useful. I don't, however, believe that their sensitometric approach using a densitometer is worth the time or effort. Very different is a Shutterbug article which you can find on Tom Halfhill's homepage http://www.hooked.net/~halfhill/speed1.html and a part 2 on http://www.hooked.net/~halfhill/speed1.html. It deals with the very basics, is very simple and that is what is good about it. I have used these two sources, plus a dozen other books, to devise a simplified approach to testing.
Since I shoot 6x7, I have 10 shots on a 120 roll. I thus shoot the first frame of a piece of paper on which everything is written (this is not really necessary, but just a convenience), the second one by putting the lens cap on and closing the lens to the lowest aperture with fastest shutter speed (thus achieving 0 density above fb+f). Then I shoot the next four frames to get Z1 (four stops below an average reading) and bracket around what I guess is the approximate speed of the film. Thus for an ISO 400 I might guess that the real speed will come out 250 or 320 and shoot the frames at 4 stops below 200, 250, 320 and 400. This is followed by shooting the next four frames to get Z 8, and therefore 3 stops above the approximate speed I estimated above. All of this is processed at a standard time. The maximum black negative, the second one on the roll, is put in the enlarger carrier. I focus and make a series of test prints to get the first exposure that is completely black when dry. Then I choose from the Z 1 negatives to find the first one that gives the first hint lighter than complete black on the paper when dry. If this turns out to be the negative shot at 4 stops below ISO 320, I then take the negative shot at 3 stops above ISO 320 to get the Z 8 reading, and thus the contrast. If that turns the paper white I reshoot and develop for a lesser time. If it turns out a little too much darker than paper white (this is very subjective and probably a slight flaw in the system, although you should be able to make an educated guess), I increase the time. A modified procedure is used to achieve N- and N+ contrast. I am sure that my explanations appear very complicated to anyone who does not already know what I am talking about, but the Shutterbug article is much much clearer. The advantage of this technique is that it calibrates your negs to the paper that you are using. To calibrate various papers to each other, see The Variable Contrast Printing Manual by Anchell for VC papers (the calibration technique also works for non-VC papers). Good luck.
-- Raja A. Adal (firstname.lastname@example.org), November 06, 2000.