using a stouffer stepwedge and film

[pellicle]

Hi

I feel like I keep asking silly questions here, but anyway I didn't go to the right courses at Uni

Would I be right in assuming the main use of one of these things is to put over the film and then contact print that for checking your contrast and development times?

If I was going to do this with mine, would I then place it over a sheet of 4x5 and then place it in the camera and expose it by photographing something white and evenly illuminated? I also don't have an enlarger (contact printing by bulb here) even so I could perhaps use the bulb and a timed exposure in the dark room for the same effect right?

When checking the film density I was intending to use my film scanner, as I've already tested that this will record linearly within the densest negative I can get (approx 10 stops over exposed sheet of ADOX CHS 100 although perhaps other negatives might go denser I have not tested this).

How then should the density of the negative compare with the Stouffer wedge? Clearly the 21st step will be nearly perfectly clear on my negative, and the 1st step should be close to the densest. However I'm fairly confident that my film (from previous testing) will cover greater than a 10 stop range (-5 to +5 being well within tolerance).

Hmm ... why is this chapter of Davis's book confusing me?

<frown/>
Thanks for your time.

 

[Mike Wilde]

my step wedge system approach

I'm a wet darkroom user. Here is my method.

For B&W, most VC papers are capable of going from white to darkest black at grade 0, the softest end, in about 7 stops of dynamic range ( 14 steps on a 21 step step wedge). They get there faster - like in 3 stops (6 steps) or less at the hard end. I use the step wedge to calibrate for constant grey exposure when dialling in different contrasts on my dichoic enlarger.

To achive a full tonal scale that fits my papers, my aim in making a negative is to have a dynamic range of about 5 stops. For me this means a target denisty range of about 1.00 or a bit more in a densitometer. This puts me into a #2 contrast on the paper, with room to print it harder or softer if that is how I want to interpret that image.

If you are exposing film though the step wedge there is the film base of the step wedge that will screw your numbers up. Don't expose throught the step wedge for now.

The dark areas of the print - thinnest area of the negative- is almost excusively a function of exposure, and the degree of development has little effect.

Figure out how much light exposure is needed on film to get some density above the noise floor ( film base plus fog for the non electrical engineers). Meter an evenly lit flat wall scene, etc. with your camera, with film speed on you meter set to the speed shown on the box. Stop down 4 stops on the camera from the recommended meter reading. This gives you zone 1 in zone system speak. Then expose with lens openned one stop (zone 2). Develop both exposures. Scan. Compare to the scan density of step one on your step tablet (.15 plus film base) to the exposures that you made for zone 1. You want something a bit lighter than the first step. My experience is that the box speed usually doesn't indicate what it takes to get zone 1 off the noise floor.

Once you find the right speed for the thinnest part of the negs, set your camera's meter to match that speed. Meter that flat scene as before. This time open up 3 stops - to expose for zone 8. Then shoot the rest of the roll with everday scenes. The search for the right developer time is dependent on overall developer activity as it relates to developing the whole roll.

Develop per the film manufacturers recommended time. Measure the density of the test exposure shot to simulate white on your scanner. Look at the density of the step wedge. If you want to follow my example, then my zone 1 starts at step 1 (more or less). I want my zone 8 to land at about a density range (Dr) of 1.0, so .90 plus the first step of .15 is close enough. If step one on a 21 step step wegde is .15, then my 'white' in the print will have to have the denisty of step 8 (7x.15Dr steps from step 1). If the negative is too dense, then develop less on the next test, if you want to print on a grade 2 filter or with grade 2 paper. If the negative is too flat, then develop more.

Hope this helps. There is a simpler way - look up the late barry thornton's article that I think is called 'the unzone system' that desribes how to do all if this visually.