[Leica] zone system, BTZS

[john.hopkins@chemserv.chem.lsu.edu]

     There are obviously many different approaches that can be used for 
     exposure, development, and printing.  Often times methods that seem 
     radically different really boil down to the same thing.  The correct 
     one to use is the one that works for you. BTZS tubes are nothing more 
     than an inexpensive but effective development system designed to hold 
     sheet film.  In principle any system of development can work with the 
     zone system---you just have to calibrate the delopment times.  If you 
     develop all your negatives for the same time/temperature, then you are 
     really using the zone system and have worked out a way where the 
     exposure/development times work for you in your system.  i.e. 
     something near the zone system N or N-1/2 development.  I do precisely 
     this.  Over the years I have adopted a system that many others have 
     taught me.  For large format negatives I push and pull the development 
     times to adjust the negative contrast to fit the light I find in the 
     field.  Obviously this isn't so easy for 35mm film.  However, push 
     processing has the added effect of increasing the grain of the film.  
     For large format film where the degree of enlargement is minimal this 
     is often of little concern.  It is however for 35mm film.  For 35mm 
     film if I need a little extra contrast in the negative, beyond what 
     can be obtained with the printing paper, I selenium tone the negative. 
      This provides about 1/2 a grade of contrast expansion (N+1/2 in zone 
     system terms). In this case expansion occurs without increasing the 
     grain as much as by doing the same thing using a longer negative 
     development time.  To achieve N-1 compression I use the following 
     strategy:  I don't worry about it.  Unless, the image I just took may 
     be something very special.  If there is the slightest possibility that 
     the image of concern is one of my best 10 for the year---I'm going to 
     cut the film and sacrifice a few images to develop properly the image 
     I hope is special.  Note that the decision to develop N-1 can usually 
     be decided after the fact, as long as you have given the low values 
     enough exposure which presumably an experience photographer would have 
     done.  The decision to tone the negative is also decided much later in 
     the darkroom.  Not very scientific but it works for me. Some people 
     get scared off by the zone system because it may sound difficult at 
     first or too artsy.  But if you understand what is going on it's 
     probably not too different from what you are already doing---simple 
     commnon sense knowledge of exposure and development.
     
     John Hopkins
     john.hopkins@chemgate.chemsu.edu