In his book The Book of Pyro, Gordon Hutchings describes a zone board which permits a full test of 10 zones with one exposure. It sounds intriguing and I'm in the process of building one. Has anyone out there built and used one? If so what is the experience with it?

-- Alan Shapiro (ashapiro@yorku.ca), December 29, 2000

Answers

Well I haven't but it sounds interesting. I've printed out scales which give me 5 or 6 zones, but under even illumination you can't get 10 zones. How does he do it? Half in shade, half in open illumination?

-- Bob Atkins (bobatkins@HOTMAIL.COM), December 30, 2000.

Picture this. He has a board, about 6 inches wide by about 7 feet long, painted a flat grey. At one end he has a blue 500 watt daylight bulb enclosed in a canister (e.g. a very large coffee can, open at one end. I am using a new, empty, gallon paint can). The light shines down the length of the board. With room lights off, there is intense illumination near the light source and the illumination falls off as one moves down along the board.

Using a light meter he assigns zone values (using markers) which are high near the light source and then go down. In my experimentation so far I can achieve about 10 or 11 zones. The board is then photographed using the zone V exposure meter reading. For example, if the reading on the meter is EV 12 near the light source, mark that point on the board (at the side of the board) as, e.g., zone 10. Read down the board until the meter shows EV 11 - that will be zone 9, and so on down the board. Set the exposure meter with EV 7 opposite zone 5 and expose the film at the indicated exposure. You then have a negative that is quite dense near the light source and then becomes less dense as you move along the board. The markers indicate where the different zones are and you can then take densitometer readings at those points and you've got yourself a film curve!

I have simplified the whole thing and anyone interested is advised to read Hutchings' The Book of Pyro.

So far the problem I am having is that the top few zones (zones 10 to 8 or 7) are very close together on the board and the meter and densitometer readings have to be very careful to distinguish among them. This is using medium format film. It should be easier, at least to read the negative, on 4X5 film.

But note that one film exposure (one sheet or frame) gives you all the zones you could want for curve ploting.

-- Alan Shapiro (ashapiro@yorku.ca), December 31, 2000.

That would work!

If I was going to do it though, I think I'd prefer discrete areas for each zone rather than a continuous transition from 0 through 10 and up. The only way to do this would be with two step charts on the same frame shot under different levels of (uniform) illumination. Easy enough to design in theory but probably more difficult in practice!

-- Bob Atkins (bobatkins@hotmail.com), January 01, 2001.

I have a different approach to the same problem. I built a mask to put over the dark slide of a sheet film holder. The mask has 15 holes, each 0.5 inches square. I have a means to cover each hole independently. With the mask taped to the film holder, and the camera aimed at a fairly large evenly-illuminated surface, take the cover off of one hole, put the filmholder in the camera, pull the dark slide and make an exposure. Then replace the dark slide, take the filmholder out of the camera. Cover the first hole, uncover a second, etc. This is described in more detail on my website www.vsta.com/~alrob, Appendix E.

Al Robinson

-- Al Robinson (alrob@vsta.com), January 07, 2001.