Has anyone used a Photographers' Formulary step wedge to determine exposure parameters? What information can you get, and what advice might you have for using this device? Thanks!

-- Jim Poehling (poehling@tranquility.net), June 05, 1999

Answers

I'm not familiar with that one (I use an Ilford step wedge), but they are used generally to derive characteristic curves for film and paper. From these curves, you can get ISO ratings, your own EI and contrast information. Ideally, you also need a densitometer, to check the wedge, and measure your results.

For film testing, you can photograph the wedge. Do ensure it is entirely back-lit, and don't forget to allow for the lens extension.

For paper testing, you might be able to enlarge the wedge, or contact- print it.

For lots of details, see Phil Davis 'Beyond the Zone System'.

-- Alan Gibson (Alan.Gibson@technologist.com), June 07, 1999.

For a complete discussion, see "Photographic Sensitometry" by Todd and Zakia.

-- tony brent (ajbrent@mich.com), June 08, 1999.

In the event you do not have the two books suggested in earlier answers: a step wedge is nothing more than a range of densities on a piece of film, and for black and white photograph at least, substitutes for you making a whole bunch of test negatives to print to find out what density range your paper will take before you lose detail at the high and low ends of the scale. for example: since most zone system books recommend testing for zone 1 at .10 above film base plus for, you could locate that density on your step wedge and then print it so you just just have black. then locate the density that next to paper white. measure it, and then you have the density range that the paper will handle. you then tailor your negatives to that range. You then know, when you are out "crusin for snapshots" that if you find situations that are either less or more than your density range you either need to expand compact the range if you want to use the same paper grade. Other wise, you can also test the step wedge on grade 1 and grade 3 papers the same way and you will then know how much density difference those papers will handle. It actually is much easier to do than it is to tell about it. But you should find someone who has a densitometer. Kevin

-- Kevin Kolosky (kjkolosky@kjkolosky.com), June 12, 1999.