Ok I'm stupid, what is SBR?
Ok I'm stupid, what is SBR?
SBR indicates Scene Brightness Ratio. This is one of several different terms that Phil Davis' Beyond the Zone System uses. This system is more extensive and inclusive then the Zone System.
SBR = "Subject brightness range". From Mako's article in Photovision (9/03), the SBR is calculated as # of stops divided by # of zones times 7. His articles may be an easier intro to BTZS than Davis' book.
SBR stands for subject brightness range, or subject luminance range. Davis uses SBR rather than SLR so as to not to confuse with single lens reflex.
SBR is determined with an incident reading of the shadows and highlights of the subject, and provides us with an idea of the contrast range of the subject, and therfore what kind of development the film needs for the lighting conditions.
It provides the same kind of data that we get from the Zone system and can rougly be equated to N numbers as followsl.
SBR 9, = more or less N-2
SBR 8, = more or less N-1
SBR 7, = more or less N
SBR 6, = more or less N+1
SBR 5.5, = more or less N+2
I prefer the SBR method of metering to the Zone system and use it for most of my work.
Now you've got my interest up Sandy. Whats the best recommended reading on this system?
The best reading, buy maybe not the easiest, is Phil Davis in Beyond the Zone System, either 2nd, 3rd or 4th editions.
You can also follow the articles in Mako in the last several issue of Photovision, which are easier reading but lack the theory and background in Beyond the Zone System.
I'll second the recommendation for the book. It is not the easiest going for the non-mathematically inclined, but I can say for certain that what it offers really works and lets you concentrate on making pictures. I can honestly say that when I have used the incident method described in the book, I have not had an exposure or development 'failure'. I'll also put a plug in for the palm pilot program that Phil Davis markets through the View Camera Store: it makest the whole process painless, and if you want to skip all the testing stuff, you can just use the built-in database if you use some common films and developers. I have found his data on Tri-X, FP-4 and HP-5 souped in DDX and D-76 1:1 to be very accurate right out of the box. In my opinion, Knowledge == Freedom.
If you approach the book with an open mind it is not that hard of a read, the problem rises in the chapters dealing with logs, etc. Which essentially are good for background but not essential to understand. I and many others urged Phil to publish a BTZS "light" but in the end he declined because he felt a thorough understanding of the background is better to use the system to its outmost capabilities.
The actual concept of the system is so simple (like all great ideas) that sometimes it gets lost in all the information. In essence what you do is make a print of a step tablet and measure the ES (exposure scale) that the paper can represent, then make 5 or 6 contact negatives from a step tablet and develop them at different times. Mark the points in the negative that show the same SI (Scale index, what is normally known as contrast range in the ZS) as the ES of the paper and then you are assured to be able to repoduce the all information in the negative onto the paper.
Its brilliant, and I have to tell you that without this methodology, doing alt printing would cost 3 times as much and it would be a lot harder.
I am not saying this will produce "perfect" negatives that you just put on your easel and expose and you will have a master print. But I can assure you that the first test print will be damm close without having to go through all that test strip, contrast descisions normally made with the ZS. Some times you even get lucky and do get a print that comes out perfect on the first try!
Another great thing about the system is the information flow, if you calculate the average gardient, what Phil calls G bar, then anybody, even though they might have different times and temperatures can develop the film using your information to get similar results. For example if I develop my pd negs for a G bar of .8 at 75º for 11 minutes and another BTZS user wants to start making negs for pd all I have to tell him is do it for a G bar of .8 and he can go back and see his tests and adjust his developing so that, for example, he knows that in his system he can get a G bar of .8 by developing at 71º for 16 minutes.
Well, I will close this by saying that I feel like a fool having Phil's book for 10 years on my shelve and never giving it a chance. If I had I would have saved me a lot of agravation and wasted film.