ZS: In what zones would you place white and black cards for N?

[ProfessorC1983]

I'm doing some ZS-inspired sensitometry work on a homemade dry plate emulsion to be used for alt-process contact printing. I'm attempting to determine what "normal" development time is for a typical SBR, so that I can then expand and contract as needed.

In my current method I take exposures in diffuse daylight of a set of black, white and 18% gray cards (the cheap ones from B&H), while metering on the gray (i.e. placing it on Zone 5). This lets m determine correct exposure, but I'm not quite sure where I should aim for the white and black cards to fall, so I'm still guessing a bit at the right dev time.

Looking back at my notes, most often there is a 4-stop difference in spot meter readings between white and black. If a "normal" SBR is 6 stops (right?) and I want to expose for shadows, then should I be placing the black card on say Zone 2 or 3 and developing until white falls on say Zone 8 or 9?

Or maybe another way of asking is, what print values would you expect from black and white cards in a full-dynamic range print? I could then work backward from there based on the exposure scale of the print process to determine N.

 

[Doremus Scudder]

You need to read up on the Zone System before you do testing.

In a nutshell, you're supposed to be basing your exposure on a shadow, not on the 18% gray card. Find a textured black (black fabric that you want to show detail in, for example) and use that in place of, or in addition to, the black card. Place that in Zone III (two stops less exposure than the meter reading). Then check the gray card and the white card (a textured white would be better maybe) to see where they fall. Adjust (or find) lighting that allows them to fall in Zone V and Zone VIII, respectively.

Once you have that, then you have "normal" lighting. Now you need to determine your E.I. and development time. Since you're working "down-and-dirty" and likely don't have a densitometer handy, make an exposure at your best guess for E.I. and develop it at your best guess for proper development time.

Print this negative so that the clear, unexposed areas of the negative are rendered just an almost-imperceptible bit lighter than maximum paper black. Then check your test areas to see how you did in what you consider ideal lighting (not too bright or too dim). The black should be a Zone III textured black. If not, adjust your E.I. for the next test. The gray card should be Zone V (but don't stress out about this much, Zone V is a bit "flexible") and, more importantly, the Zone VIII should print just a bit grayer than pure paper white. If that's not the case, adjust your development time (more for more contrast and brighter whites and vice-versa).

Repeat this till you are satisfied with the results. Now you have your personal E.I. and development time for normal. It isn't ISO standard, nor will it necessarily apply to others with different meters and developers, etc.

If you need real scientific accuracy, take up sensitometry and read up on the ISO standard tests.

Best,

Doremus

 

[Bill Burk]

A 2-D scene will yield roughly 5 stops of subject luminance range. Make something that casts two stops’ worth of shade and then put the black card in the shade. Now there’s seven stops of subject luminance range.

Or you can stop down two stops and make another exposure and look at the two plates as a set.

Most Zone System tests ask you to stop down four stops from gray, etc.