tab@ihuxl.UUCP (Thomas A. Burrows) (06/27/84)
.
A question was asked about the sensitivity and price of the Luna-Pro
SBC variable angle attachment (7.5 and 15 degree). The variability
is achieved by shifting in different diameter apertures, so the smaller
the angle the less the sensitivity. However, the SBC is so sensitive
that even with the 7.5 degree attachment I can accurately measure
very dark shadows in nearly unlit church interiors. Most (all?) one degree
meters will not work in situations this dark. In very dark situations
the 15 degree setting can be used to get two more stops of sensitivity.
The 7.5/15 degree attachment is $50-$60, which is cheap considering
the fact that it makes the meter an order of magnitude more useful.
There is a 1 degree attachment for the SBC. I tried one out in the
store and found that light leaking in through the eyepiece (!) caused
large errors. It was not particularly selective and was also quite
bulky. You are probably better off with a real spotmeter. For example,
I found that Minolta's best spotmeter has an error of only about 1/10th
of a stop when a bright light fixture is just outside of the 1 degree
circle. Lesser spotmeters can exhibit errors of two or more stops in
such a situation. The Minolta also takes screw-in close-up lenses so
you can meter objects down to 1/10th of an inch across. This is good
for macro photography or situations where the contrast of fine details
must be known.
Tom Burrows
AT&T Bell Laboratories
Naperville, IL