Kirk Keyes said:
Last year, I was in Death Valley, trying to take photos of patterns in the sand. I've got one of those newer Minolta Flashmeter VIs that can do both incident and reflected measurements. I used the spot meter while there and some of the scenes were only about 3-4 stops (reflected) between the darker and lighter portions of the scene. Using Acros and Xtol, I was able to develop the film enough to expand it out to where it prints well.
Today, I was flipping through my copy of the BTZS book (3rd Ed.), and I thought back to the Death Valley stuff. So I was looking for a description of how to meter scenes of low contrast using BZTS. Using an incident meter, it looks to me that the BZTS system can't measure scenes that have SBR's less than 5. It also seems that it can't differentiate between a 5 SBR scene and a 3 or 4 SBR scene.
I know you can determine development times for SBR ranges this low, but how do you actually measure them with and incident meter. Does photographer's discretion (i.e. override meter readings) kick in here?
Kirk
The important thing to understand about the scene you describe is that neither a reflected reading nor an incident reading will give you the correct exposure to reproduce the tonal values as you want them without interpretation. In other words, whether you use the Zone system or BTZS you have to make interpretative decisions as to how you want to the tones in the scene to reproduce on your print. You understand this with the Zone system and know how to accomplish what you want so no point to comment further about this.
But what about BTZS. If you use an incident meter the reading will suggest an SBR of 5, and the reading will be the same regardless of where you point the meter. Such a reading if developed for an SBR of 5, will give you an overexposed and underdeveloped print. You will have a lot of detail in the shadows, with good separation, but muddy blacks. You can do one of two things to approximate an SBR that will suggest better exposure and development. One option is to go to one of the shadow areas of the scene and take a meter reading at that spot, note how much this EV values differs from the EV value of the first reading, and subtract from the SBR of 5 to give you a new SBR value, which could be 3 or 4. If there is not a real shadow area large enough to use for the reading you can simulate the shadows by shading the cone of the meter, take a reading, and then do the same calculation as above. Base exposure on an average of the shadow (or shaded) reading and the reading taken in full light. Or you could just double the EFS of the film and make the exposure based on the shadow reading.
Development is another issue. Most developer/film combinations will easily allow for development of SBR values of 5 or less with regular silver gelatin printing, where the desired CI is about 0.60 and the exposure scale of the process is about 1.10. However, with AZO #2 and alternative processes, where the desired CI for the negative is 0.75 or even higher, and the exposure scale of the process is 1.5 or higher, the practical reality is that very few films are capable of development for a SBR of less than 5. So in a scene such as the one described by Kirk, unless you happen to be using one of the films that will allow a CI of up to 1.15 or 1.20 you are just as well off to expose and develop for the SBR of 5 and make adjustment with the process for more contrast. And the problem is not the developer, but the fact that most films have a maximum CI so that no matter how long you develop, or high much energy your developer has, the film reaches a point beyond which further contrast is not possible.
Sandy