Sunday, September 13, 2009

Agfa MultiContrast FB paper ISO and ZoneMaster meter calibration

What I used to calibrate ZoneMaster enlarging exposure meter (made by RHdesigns UK), is different with the way written in ZoneMaster manual. Manual said you have to set the exposure compensation, which gained from test stripe, then find out the paper contrast range to set paper ISO.
Well to me these sounds complicated and troublesome, I always trying to solve the problem in one shot, so I did it, with help of Stouffer TP-41 4x5 step wedge(looks like they do not produce it anymore, but TP-31 is OK), and ZR9 Zone system chart, on Agfa FB paper.
First, I put TP-41 over the meter, with #5* wedge on top of the meter circle. under the enlarger, I measure it and get the reading, it is for mid-grey, so I press the darker button, to push the readout to darkest end of greyscale, it is for ZONE II.  According to the readout, I made contact print for each grade, so I got 7 contacts, from #00, #0, #1...#5. for 8x10 paper, it only need two pages of paper to finish all the test.
I developed and processed the paper as usual, then inspected the print under the light. use RZ9 as reference, find out the best match grey scale as Zone II and Zone VIII as on RZ9.
Here is the data I got from prints.
Grade       II~VIII Range    ISO      Offset
#00           #2~16             225      0   **
#0             #5~36               160      0
#1             #6~35               150      -1
#2             #4~29               130      +1
#3             #4~24               105      +1
#4             #4~22               95        +2   
#5             #5~18               70        0

take #1 as example, the grey range from #6~#35, totally 30 steps in count, and each step represents Dlog0.05 on TP41, so it means grade #1 paper can handle 0.05x30=1.5 density range on negative, place it between Zone II and Zone VIII, we define it as ISO 150 for this grade.
And since we use step#5 as reference to make the meter, but now it moves to step#6 on contact print, so we need to make exposure compensation -1, to adjust the ZoneMaster meter.

* TP41 got 41 wedges and each one in 0.05 density increments, total 2.0 density range, fully cover the d.range a normal negative will have. using #5 instead of #1 as start point, for leaving spaces for calibration if needed.  
** Due the long slope of the grade #00, it is tested by TP-21, which has a logD=3.0 density range. and used #3 as start point. each step on TP21 represent 0.15 density range.

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