Sunday, November 21, 2010

Variable Contrast papers and the Variable Contrast Light Source.

My experimentation with the Zone VI enlarger continues but I am not sure if it is progressing.  The enlarger uses two special made florescent lights each with a separate rheostat attached to a timer that has a photo cell which controls unit exposure by light intensity. If you measure the timer against a source that measures actual time a "unit" of exposure can go from a fraction of a second to several seconds depending on the light intensity . You dial in a unit of exposure  by 10's, 1's, and .10's.  The green light is for "soft" contrast the blue light is for "hard" contrast.  I've noticed that  the soft contrast light is much brighterand therefore reduces the time for each unit of exposure because the photo cell reads the greater light intensity but the photographic paper is much less sensitive to the soft contrast light source than the hard contrast light source.  Printing with the soft contrast light alone in theory equals a contrast grade of "0". Using the hard contrast light alone in theory equals a contrast grade of "4".

 The hard contrast light source appears much dimmer to the eye and to the photo cell so the exposure unit is lengthened but the photographic paper is much more sensitive to the light. Even if I were to dial an equal light intensity  for each bulb where each light source when used alone matched the duration of the unit of time of the exposure the soft light exposure would need to be much longer than the hard light exposure to produce a visible image on the print. When working with graded papers you only need to use the "hard" contrast light source.  When working with variable paper you use both in a combined exposure or two separate exposures from each light if you want a wider range of values of black, gray, and white. One way of printing with this enlarger is to run two separate test sheets using each light alone and then looking for the exposure duration fir each light that looks correct and then run a test print and look at the results.  Dialing in contrast with this type of light source though isn't the same  as printing with filters.  I thought at first it would be that easy but the more I work with it the more complicated the process becomes.
  Contrast grades  are kind of subjective when using only the eye.  Certain papers and certain types of paper surfaces can appear to have a higher contrast.  A wet print will also appear lighter and more contrasty than a dry print. When I print with a semi-matte ilford paper of variable contrast and use say a filter, or contrast setting equal to a grade 2 and then use the same settings and make a print with a gloss surface ilford paper the glossy print will look (to me anyway) like the higher contrast print.  My eye prefers the warmer tone papers to the colder tones but the colder tone papers produce a more pure white in the paper base and to me look higher in contrast.
Lately I have been experimenting with some graded  papers I have.  Zone VI brilliant fb grade 2, Bergger glossy fb grade 2, Ilford Pearl RC grade 2 and a Forte paper semi-matte grade 3.  The Zone VI paper is a cooler tone than the Bergger or Forte paper looks more "contrasty" than the Bergger paper and does appear a grade lower in contrast than the Forte paper based on the gradae. Of all of the papers though I liked the results from the Ilford RC pearl.  Once I produced about as good a print as I could get with each paper I tried to figure out what settings on the Zone VI enlarger would give me a similar contrast with a variable contrast paper, Ilford warmtone semi-matte with the same negative.  I started off with using the minimum setting for the soft contrast light and a setting of "E"for the hard contrast light. The dial on the light control goes Minimum-A-H-Maximum so a setting of "E" is about mid-range.  Once I had what I thought was the proper exposure for the first print at that setting I then adjusted up the soft setting going from Minimum to E.  The prints went like this; Min./E, A/E, B/E all the way up to E/E.  As I increased the soft light I also had to reduce the exposure by about 10% even though theoretically the timer would shorten the exposure unit the brighter the light became to produce a similar exposed print.  In the end it was difficult really to tell much difference in any of the prints that could really be attributed to a change in contrast.  The scans were done separate with equal settings but still look pretty identical.  The scan on the left should be more contrasty since it was made with a low soft setting and higher hard setting, the print on the right had an equal setting if the same dial setting for each light could really be called equal which I don't think it is.

My conclusion from this little experiment is that I really still do not no enough about the way the lights work in combination to make a print of a particular contrast grade there are just too many other factors but I hope with further experimentation I may someday learn the best way to control contrast with this enlarger when using variable grade papers. 


Anonymous Progress Lighting said...

really good blog!!! Thanks

2:16 PM  

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