Step wedge use for film testing?

Is there a way to use a step wedge for testing the tonal gradation of film? If so, how is this done? Do I put a (transparent) step wedge on a light table and photograph it?

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Thank you, /Peter

I contact print the step wedge on 4x5 film under the enlarger. They

also make step wedges that will fit 120 and 35mm. You can photograph

a step wedge on a light table but if your plan is to then read in on

a densitometer make sure that the image is large enough on the film.

I have <a href="http://www.jeffsphotos.com/zonegraphs.html">my test

results</a> on my web site from testing using the contact method.

Thank you Jeff. Are the results from enlarger light the same as those

from flash/daylight? I mean, does it matter what kind of light source

that is used for the contact printing?

Yes the results are the same. I use a 4/10's of a second exposure to

avoid any reciposity. I have used the system with a cold light and

now use it with a dichroic head with the same results.

The light source should make absolutely no difference to the

result.<br>However, if you photograph the step wedge, then the flare

factor of the camera and lens will affect the results quite

noticeably, reducing the contrast range of the step wedge from its

specification.<br>For instance, if you use a light box, then the

amount of white light surrounding the step tablet will alter the

contrast of the image on film. You'll get a truer representation by

masking off all but the area of the step wedge itself.<p>If the object

is to find the transfer function of the camera/lens/film combination,

then photograph the step tablet. If you want to only test the film,

then you should contact print, using a diffuse light source for

exposure.<br> (Photographic density is always given as diffuse

density, unless stated otherwise. Using a collimated source, such as

an enlarger, for the exposure may give a misleading result.)

I remember Kachel mentioning (maybe in Darkroom Techniques) that

color of light does influence an emulsions response. A traditional

emulsion gains contrast when exposed with strong red light, (as when

exposed through a 25 red filter), which is what I found in my tests

and, if memory is serving me right, new technology films lose

contrast. Might be worth keeping in mind if you're exposing under a

color head. Good luck. DJ