September 16, 2010

Comparing lightmeters

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[this page was updated on April 11th 2012]

Being a bit concerned about the precision of my Pentax Spotmeter V, I ran a quick comparison test with other lightmeters, measuring a white wall in artificial light (EV 5 at 100 ISO).
I set all meters at 400 ISO and mounted a 135mm lens on my SLRs, in order to avoid staying to close to the wall.

According to the spotmeter the right exposure was 1/4 s @ f5,6.
I measured the wall with other meters and annotated the deviation.
A positive deviation means that, assuming the spotmeter is right, the meter would produce an overexposure. A negative deviation means that the meter would produce an underexposure.

Here are the results:
  • Nikon FE2:               same exposure as the spotmeter
  • Nikon F2:                  same exposure as the spotmeter
  • Nikon FM2:              -1/2 stop
  • Nikon D40:               +1/3 stop
  • Nikon D700:             +2/3 stop
  • Panasonic GF1:        -1/3 stop
  • Sekonic L-208:         -1 stop
  • iPhone light meter (free app):  +2/3 stop
On digital cameras (D40, D700, GF1) the exposure was chosen so that the peak of the histogram is centered.

Results are quite comforting, also considering that the D40 and D700 meters are prone to overexposing (I usually set a -1/3 or -2/3 exposure correction on my D40).

Note that the comparison test is not a procedure for calibrating meters. However, it can make you more confident in your equipment (or at least more aware of defects).

The most important thing is calibrating your meter against the film you use. At that point it makes little importance knowing that your meter is right against an absolute reference.

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