How do you determine the exposure for contact printing a step wedge to film?

[williaty]

Now that I finally have a densitometer that works, I want to contact print my Stouffer step wedge to a sheet of film to check on my developing. My plan is to have my Gralab 450 timer flip an LED light bulb on and off rapidly to provide the exposure. At this point, I'm more interested in just getting all the steps recorded so I can look at the characteristic curve of the film than I am about knowing precisely to the photon how much light I gave it (in order to determine speed point).

How do I determine the correct exposure before making the first test?

Thanks as usual.

[stawastawa]

give it some light! turn on that LED and expose the step wedge over your paper of choice for some 10 seconds to 2 minutes. Depending on how many steps you have you can grossly over expose and still get information from the step wedge.

[Jac@stafford.net]

We made millions of good contact print tests before densitometers and similar technology.
Stick your chest out and try some test exposures using strips.
.

[williaty]

I don't want to spend god knows how many sheets of film (at ~$2/sheet) and who knows how many hours babysitting development, to arrive at the correct exposure. There's clearly some math applicable to this situation, it's just a matter of finding someone who knows the math and can explain it to me.

[djdister]

This doesn't require math, it requires an exposure meter. Set the ISO of your film on the meter and take an incident meter reading from the location of your contact frame pointing back at the light source (turn it on). Take the incident exposure reading and expose and process one sheet with the step wedge. Looking at the step wedge on the exposed film, adjust your exposure until you reach d-max without over exposing the film. Shouldn't take more than 3 tries to get there, more or less. Your new densitometer should help determine how close you are to a properly exposed sheet of film without wasting too many sheets.

[williaty]

With no lens involved, how do you translate f/8 at 1/8 to a time-only exposure?

[Erik Larsen]

You can tape the step wedge to you film and put in a film holder and use you camera with a lens and shoot a grey card or white card, shouldn't that work?

[williaty]

Only to the extent to which the shutter is perfectly repeatable. Mechanical shutters run +/- 1/3rd of a stop, if not worse.

[djdister]

With no lens involved, how do you translate f/8 at 1/8 to a time-only exposure?

Oh right. You need a light meter which also has an EV (exposure value) scale. EV values are a combination of a shutter speed and f stop, so using an EV scale will give you a time option that works for you. Check out the Wikipedia page for Exposure Value (it has some math stuff too).

153264

[Harold_4074]

While your interest in photometry is admirable (and I confess to sharing it) I suspect that pretty soon you will discover that knowing the characteristic curve for one film, developer, time, temperature and agitation will not lead directly to a perfect print. Placement of the important values on the film curve depends to some extent on the paper curve, which is one reason that there are so many different papers and paper developers out there.

To be scrupulously correct, you need to expose the film using the light spectrum appropriate to your subject matter, and exposure times that keep you out of reciprocity failure. Putting the Stouffer wedge in front of a sheet of film is probably the best place to start (this is presumably the reason why they come in standard film sizes).

That said, one of the better ideas from many years past is to "shoot around" the box speed and "normal development". That is, make exposures of "normal", high and low, and then develop them for times of normal, high and low. This implies nine sheets of film, but since this is the Large Format Forum ( :) ) you should be able to make do with three sheets of film and a pair of scissors, clipping corners as needed to keep the pieces identifiable. When you have the films, use one of the rebate portions to determine the maximum paper black for your chosen light source and processing, and the print all nine samples identically. Adjust as indicated, and repeat until your normal/normal negative prints the way that you prefer---if you don't converge pretty quickly to a reliable process, it probably means that your process isn't repeatable enough for numerical data to be useful anyway.

Densitometers have their uses (which I find comforting, because I have two of them...) but in my experience they really earn their keep for process control as opposed to process development. If your print contrast drops, for example, the machine can tell you objectively that the problem either is, or is not, with your light meter, thermometer, film, paper, chemicals or perception.

[Jac@stafford.net]

I don't want to spend god knows how many sheets of film (at ~$2/sheet) and who knows how many hours babysitting development, to arrive at the correct exposure. There's clearly some math applicable to this situation, it's just a matter of finding someone who knows the math and can explain it to me.

Well, you got some very good solutions, but the cost of film is probably insignificant compared to the other gadgets you purchased to get around it. A step-wedge transparency makes it easy. Besides, you will have to come to a development standard anyway.

[Drew Wiley]

Gosh. Talk about doing things the hard way!

[ic-racer]

Now that I finally have a densitometer that works, I want to contact print my Stouffer step wedge to a sheet of film to check on my developing. My plan is to have my Gralab 450 timer flip an LED light bulb on and off rapidly to provide the exposure. At this point, I'm more interested in just getting all the steps recorded so I can look at the characteristic curve of the film than I am about knowing precisely to the photon how much light I gave it (in order to determine speed point).

How do I determine the correct exposure before making the first test?

Thanks as usual.

Use trial and error, just like making a test print. You want to record the toe and as much of the rest of the curve. You may not be able to fit it all on. Let it fall off the shoulder.

For example, when using a 21 step wedge, your resulting negative might have two clear steps before measurable density. So, plot that out and if you still are missing all of the straight line then up the exposure for your next test one-half stop at a time, but at least try to keep the lightest film density above 0.1 log D.

To see that you are in the 'ballpark,' I use diffusion enlargers with multicoated lenses. I most frequently print on Ilford Multigrade. My best prints are from negatives that were processed to a gamma or contrast index around 0.65 to 0.75.

[Luis-F-S]

I would do a test strip of the clear edge base increasing the exposure until the paper doesn't get any "blacker". Picker's proper proof, then expose the step wedge for that exposure. L