calibrated negative step tabletgreenspun.com : LUSENET : Large format photography : One Thread
I am thinking to run some tests of exposure and development of film using a calibrated negative step tablet ( I cannot buy a densetometer.that's too expensive!!) On the book"Negative" by A.Adams he wrote "You can secure fairly accurate density measurements using the tablet." However, I've never seen the step tablet before, so I have no idea how it looks like and how it works. I found that the company named "stouffer" makes Transmission Step Wedges and Transmission Projection (TP) Step Wedges, and I am wondering which to buy for measurement of density. Also, I found that there is an unclibrated negative step tablet avairable on a market. What is the difference between calibrate and uncalibrate. If anybody knows the way of measureing a density of negative using a calibrated negative step tablet , please give me some advice. I am using 8x10 T-Max 100 film and T-Max Dev. using JOBO CPA-2 processor. Thank you Ric Yama
-- Ric Yama (email@example.com), July 06, 2000
I would recommend that you read Phil Davis' book "Beyond the Zone System", which describes in great detail a process for testing both film and paper, using step tablets exposed under an enlarger. He also describes how a spotmeter can be used to measure negative density.
Overall, I am persuaded that his approach does enable you to understand very clearly the response of film and paper under different exposure and development conditions ; indeed, the most interesting thing in the book, in my opinion, is that it demonstrates how film speed changes as these conditions change. I am intending to carry out my own rigorous tests with the film / developer combinations I have decided feel right to me (based on subjective "feel" only) ; (1)TMax100 & Rodinal 1:50 (2)Delta100 & PMK Pyro (3) Fuji Neopan 400 & Microphen (4)Tri-X & HC110/D-76.
I am less persuaded by his recommendation to keep everything important in a range between Zones III and VII. This certainly will work in many circumstances, but you need to be able to be more "fuzzy" in your approach if you're really going to be able to respond aesthetically to the quality of light.
-- fw (firstname.lastname@example.org), July 06, 2000.
A few years ago I needed a step tablet to calibrate a densitometer; I found that calibrated step tablets were ridiculously expensive.
I got a step tablet from Fred at Darkroom Innovations (www.darkroom-innovations.com); he simply contact-printed a step tablet on 4x5 Tech Pan, then read a noted the densities using his often-calibrated densitometer.
I forgot how much it cost, but it was _lots_ less.
Now....I strongly suggest that this really isn't the way to go because you're ignoring the rest of the system.
For an EI test, make a couple of test negs, exposing only half of the neg for what should be a Zone I exposure. Zone I, if that's defined at .10 DU above fb&f, should be the first step that clearly shows density above film base and fog density. Not just a hint of density if you squint at it, but clearly.
If you go by that, if there's an error then chances are that it'll be on the side of overexposure, which is fine.
Are your negs printing ok?
If they are, then make your own standard by which to compare future film/developer combinations; shoot a strip of exposures from Zone I through Zone X or higher. Develop normally and you'll have your own standard. It won't matter what the actual densities are, although you could get a lab to read the negs if you want.
For future film/developer combinations, do the test strip again; compare it to your standard and you'll be able to tell what the real EI is compared to your standard, and whether the new material is of higher or lower contrast.
A great book; _Beyond the Zone System_ by Phil Davis.
-- John Hicks (email@example.com), July 07, 2000.
The way you "measure" the density of a negative with a step tablet is by visually comparing the density on the negative to the various densities on the step tablet. Pick out the step on the tablet that is the closest match, or estimate that the density on the negative falls in between two steps.
The difference between calibrated and uncalibrated is that the calibrated step tablet has been individually measured so that exact density values are provided by the seller. For the purpose of visual estimation, you don't this level of accuracy.
-- Michael Briggs (MichaelBriggs@earthlink.net), July 07, 2000.
Can I just add to Michael's answer that you should use a diffuse light source, such as a light-box, for the comparison. Add a low power magnifier, a small tube to keep out extraneous light, and you've virtually got yourself a densitometer.
-- Pete Andrews (firstname.lastname@example.org), July 07, 2000.
A calibrated step-tab has been read with a densitometer. An uncalibrated one has not. I suggest you buy a densitometer. I bought one on ebay last summer for about $250. When you are done using it, you can sell the densitometer on ebay and get most, if not all or more, of your money back. I use my densitometer enough that I decided to keep mine.
-- William Marderness (email@example.com), July 07, 2000.
Hi Ric, I don't think anyone clearly answered this for you, so let me say a few words. The regular step tablet you'll probably be getting is essentially just a piece of film, typically about 1" wide by about 5" long, with (typically) 21 exposure "steps" on it. For example, the first <" is clear, the next <" is slightly dark, etc, etc, until the last one is REALLY dark (dense). The densities of the steps have been accurately controlled.
The way you normally use these is to contact print them onto a test material; this give you a series of known exposure changes. Then, you measure (with a densitometer) the result on your test material; this tells you how your test material responds to various exposure levels. This test, if lens flare did not exist, would be exactly the same as making a series of camera exposures of a neutral target where you changed the exposure in equal f/stop increments. It's just that the step tablet method is far more accurate.
My best guess is that Ansel is suggesting exactly what Michael Briggs has described.
My own advice would be to follow John Hick's recommendation. I know a lot about the sensitometry end, and on this basis can assure you that John understands what he's talking about with B&W films. Have fun!
-- Bill C (firstname.lastname@example.org), July 07, 2000.
Or, you could cut to the chase and use a simple procedure that involves your whole system: camera/meter/film development/enlarger. 1) Make a test strip through unexposed, normally developed film, using 1/4 - 1/3 stop time increments. When you have a strip with two adjacent patches that appear equally black, note the shorter of the two exposure times (and the enlarger head height, lens aperture, etc). These settings will become your standard set up for testing. Make a control print using these settings. Next, make Zone I placement exposures at different EI ratings, develop the film, and print the negs with the standard set up. Your EI is the fastest that yielded a print that, when compared to the black control print, shows a subtle but not imaginary difference. For N, N+, etc., development times, test for the highest non-white zone wanted. The development time is correct when a print made using the standard set up and previously determined film development time just shows density in an area placed in the highest non-white zone. Works for me. njb
-- Nacio Brown (email@example.com), July 07, 2000.
Oops. In the next to last sentence in my note above, "previously determined film development time" should have been "previously determined film EI." njb
-- Nacio Brown (firstname.lastname@example.org), July 07, 2000.
I have tried to email you but AOL says that your address is invalid. I have a densitometer and a step wedge that I would sell at a reasonable price. Write me if you are interested.
-- David Ingalls (email@example.com), July 08, 2000.