Stouffer Step Wedge, How do I use this for Zone Systemgreenspun.com : LUSENET : Large format photography : One Thread
I just got a Stouffer Transmission Projection Step Wedge in 4x5 size. It did not come with instructions, and I am not sure I know how to use it. I want to use it to determine the characteristic curve of film/developer combinations and to find Zone I and Zone VIII densities. I have a densitometer. The first step has a density of .04. If I expose on Zone X with the step wedge over the film, can I ingnor the .04 denisty of step one and consider step one to be Zone X. Then would each progressive step be a half zone reduction: Step two is Zone 9.5. Step three is Zone 9. Is this correct?
-- William Marderness (firstname.lastname@example.org), January 19, 2000
Get a copy of Beyond the Zone System by Phil Davis. He explains how to use sensitometry using the step wedge for both the Zone System and his BTZS method.
-- John Hoenstine (email@example.com), January 20, 2000.
Phil Davies book is a great reference. Step wedges can have many applications. The basic idea is to use the step wedges to perform film and paper tests. I used mine to do some paper tests to calibrate variable contrast paper to my cold light i.e., my cold light is extremely blue heavy and gives harder contrast on variable contrast paper than condensor light sources - a no.2 filter would give a harder contrast than a grade 2 paper. Print the Stouffer step wedge onto the paper you use regularly, at some size you use regularly, like 8x10. Try to work in the middle of the range of the step wedge i.e., you should have pure white and pure black at the ends. Now look for the density range from the last white to the first black. This now tells you the density range on film which each contrast grade of paper can handle. Now you can look to expose and develop your film to give you these required densities. Performing film tests is similar, except that it might be easier to contact print the step wedge onto film. Also, with film tests, you vary the development time as well to see how that affects the densities. Contact print the wedge onto your film (again try to work in the middle of the range of the step wedge). In this case, each 0.3 units of density corresponds to 1 stop i.e., both the density and the exposure scales are logarithmic. Perform your tests and see how many stops of light gives you what densities on film for your film/developer/exposure/development combinations. Now you can relate these densities back to what you need for each paper grade. Of course, you can skip paper tests if you have a good idea what the densities required on the negative are. Then you only need film tests to obtain working methods i.e., what deeveloper, what time etc. The densities on the step wedge typically have an error margin, so 0.15 may actally be 0.15 +/- 0.01 or something. Stouffer offers to read your step wedge with a densitometer before mailing it to you i.e., a calibrated step wedge. If you have a densitometer, you can do exactly the same thing. Feel free to contact me if any of this is unclear or if you would like more details. Phil Davies book should be high on your list though. DJ
-- N Dhananjay (firstname.lastname@example.org), January 20, 2000.
All the replies have been dead on. Buy the Davies book. I use my enlarger for a light source and mount one of my lenses with shouuter in place of the enlarging lens so I can replicate the exposure. Make sure your exposure gives you at least 2 clear steps before there is any reading above Base+fog. That way you know where to start your readings. You plot the exposure against the density for each developing time and viola your curve. It's a piece of cake but each step must be done precisely. Temp/agitation/method of development must be the same as used to normaly dev. your film. I use a cold light in my enlarger and I have wondered if the color affects my curves. I don't know. Also to insure that the only light that reaches the contact printed film is from the lens, I wrap the enlarger head with a towel so there are no light leaks. George
-- George Nedleman (email@example.com), January 20, 2000.
I agree with the advice about BTZS. To answer another question, if you want to meter the step wedge using a zone system approach, you should meter for what would be a shadow or even zone I. To work the other way will be effected greatly by development and probably be different with each new try. Also, to photograph the step wedge you would have to factor in bellows extension which if done incorrectly would skew the results.
-- Jeff White (firstname.lastname@example.org), January 20, 2000.
Expose for zone I to establish a film speed. Your film speed will be the frame .10 over film base plus fog. Contact print the step wedge on your sheet film you use, develop it. look, check it, make sure you have at least 2 completely clear segments. if not. go back to the darkroom and give the copy film less exposure. if it's much more than 5 or 6 clear segments, go back and give it less exposure. Once you got the exposure for the test film, you are ready to do your development tests. Expose 5 sheets and put them in a box. develop each of the five sheets at different times. I used tmx in xtol in a jobo processor, and used times of 4.5, 6.5, 8.5, 10.5 and 12.5 minutes and got the data I needed. If you are using a process such as a jobo, be sure to put in some fully exposed (fogged) sheets so the develper does not get over active. my tank holds 6 sheets. so I put the test sheet and two fully fogged sheets. Temperture and agitation are important. consistency is essential, if you cannot be consistent in controlling the temperture, agitation and time, you're wasting your time. Develop the sheets, make a graph of exposure (step wedge value) vs density (test film value), read the values of the ares on the test film and graph it. graph all five. draw a line at dmin, film base + fog + .04, and (to follow Ansel Adam's method) a line at 1.35 density. look at the range for each development time. Your normal dev time will be 8 stops from dmin to 1.35, n+1 will be 7, n-1 will be 9, etc. My graphs, and the data I used for my zone system testing is online, at http://darkboidy.tripod.com/ref/index.html . I also have a graph of paper curves for ilford contrast filters 00,0,1,2,3,4, and 5 on ilford mg iv fb glossy, developed in dektol.
To answer your question though, no. The step wedge does not have zone values like you are trying to assign.
If your fb+f is .04, I'd be amazed, Mine was .06-.07, and 35mm it's often 0.10 or higher. And remember, your zone I is film base + fog + 0.10.
-- Michael Jones (email@example.com), June 13, 2001.
I made an error in my first few lines, the segment should be: if you do not have at least 2 clear frames, go back and give less exposure. if you have much more than 5 or 6 clear frames, go back and give it MORE exposure.
I apologize for this error.
-- Michael Jones (firstname.lastname@example.org), June 13, 2001.
What about using a calibrated step wedge for color printing?
-- Steve Silver (STEVE477@YAHOO.COM), June 24, 2002.