November 18, 2010

Measuring enlarger's light falloff

I have measured the light falloff of my enlarger (a DURST M605).
All measures have been taken with a RH Designs Analyser Pro, in densitometer mode.
Four measures have been taken, on the diagonals of the projected image at ~3cm from the corners, and averaged. No film was in the negative carrier. The meter has been oriented the same way radially for each measure.

Results are summarized here (1 stop = 0.3 log units)
  • 24x36 - Rodagon 50mm @f11
    • Diffuser Head: 0.09    (~1/3 stop)
    • Condenser Head:  0.24  (between 2/3 stop and 1 stop)
  • 6x6 - Rodagon 80mm @f11
    • Diffuser Head: 0.11  (~1/3 stop)
    • Condenser Head:  0.16  (~1/2 stop) 
Considering that 1/4 stop is the typical light falloff of most enlarging lenses, results seem OK, except for the 50mm with condenser head.

Some time ago I measured the light falloff of a Kayser System V enlarger with condenser head and Nikkor 80mm lens, obtaining a light falloff between 1/2 and 2/3 stop. Adding a 3cm spacer to move up the lamp housing, the falloff decreased between 1/3 and 1/2 stop.

References:

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