What do you do if the light changes between exposures?Hi folks,
As a Zone System practitioner I would like a relatively quick way to ensure that the process variables for my camera, film and film developer are "in control". I would like to propose a method to do this and would appreciate your feedback on its pros and cons.
BTW I don't (yet?) own a sensitometer nor have I purchased any KODAK Black-and-White Film Process Control Strips (CAT 180 2990). They would only test out that my film development process was in control, so instead with the following suggestion you can widen the net and include your own film plus camera system too.
Aim:To expose a roll of film with 3 frames, each frame being a shot of the same grey surface (not necessarily 18% grey) exposed to Zones III, V and VII by only varying the camera's aperture. Process the film for N development, then measure the density of each frame to see if it matches your previously determined density targets for those zones at N development. You of course will need to have previously determined these densities using your favourite ZS methodology, and thus be in possession of a densitometer.
Method:1. Find any mid grey surface to mostly fill the frame of your favourite format.
2. Expose frame 1 for Zone III using your light meter. Choose a shutter speed on your camera that you have measured to be within 10% of its nominal value. Use either f22 or f16.
3. Expose frame 2 for Zone V using the same shutter speed as step 2 and opening up the aperture to either f11 or f8.
4. Expose frame 3 for Zone VII using the same shutter speed as step 2 and opening up the aperture to either f5.6 or f4.
5. Ensure the light level hasn't changed between steps 2 and 4.
6. Process film for N development.
7. Measure the transmission density of each frame and ensure it matches your expectations to within your acceptable margin of tolerance (say +/- half a zone). You should understand the Zone system to know where those densities should fall.
A possible variation is to take 3 frames of each zone to check for variability of your shutter timing.
The advantage of this method is that:
- It is less sensitive to flare you would get by having say a test surface/card with the three different Zones on it at once.
- You also don't have to create or maintain such a 3 zoned surface which takes more time and relies on the accuracy of your light meter in high flare conditions to ensure the surface was calibrated.