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A2/10 How to Use a Digital Camera as an External
Light Meter
see also
Light Meters (page 77)
The Zone System (page 69)
Using the Nikon Spot Meter (page 68)
EV & LV (page 75)
Why buy a separate meter when you can buy a complete camera with a built in meter for
less than a separate professional meter? Yes, for the same price or less as a pro meter
you can buy a digital point-and-shoot that weighs less and lets you preview the images for
color and contrast.
As of October 2004 I no longer use my Pentax Spotmeter. Instead I look at the LCD screen
of my Nikon D70 and copy that exposure for use with my film camera, presuming the LCD
image looks as I want it. This is better than any meter; it shows me the effects of lighting
and color temperatures and simulates my chromes on a light table.
Watch for these issues:
1.) Overall camera calibration. My Nikon D70 is right on, and my Canon A70 is one stop
more sensitive than rated. That means that my A70 set to ISO 50 is really at ISO100, so for
Velvia I have to add a stop to what the A70 at ISO 50 says. Make a few shots at various
ISO variations to see which one matches your film.
2.) Filter factors. Put the same filter over the lens of the digital camera. If you have
different or no filters on one camera then be sure to apply the differences in filter factors.
3.) Light Transmission. Not all lenses transmit all of the light, so you may also have to
take "lens factors" into account as well as any aperture calibration variations in lenses.
Zoom lenses, especially older ones, may lose as much as 2/3 of a stop compared to fixed
lenses due to light lost as internal reflections. This is never a problem with TTL SLRs
because TTL metering automatically corrects, however it will alter the reading if you are
trying to use the reading from one camera on another.
4.) Differing ISOs. It's unlikely that your preferred digital ISO setting will just happen to
match your preferred film. You'll be shooting photos with your digicam and not just using it
as a meter. It is cumbersome to keep swapping ISOs between what matches your film and
where you prefer to shoot the digicam. If you swap ISOs you are likely to forget and use
the wrong setting and waste film. I suggest leaving the ISO of the digicam where you prefer
and calculating exposure conversions in your head or use the calculator dial on a light
meter. You even can use a broken old meter for this. I use the scales on my Pentax
meters. Here's how:
© 2007 KenRockwell.com 87 converted by Sándor Nagy