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Just finished another
round of photographing a couple of oil paintings with my
Cambo 4X5 camera (shooting both VPS and E100S film). Even
after using a polarizing filter for both the camera lens
and Speedotron M11 lights, there still was significant
glare or reflections. Could it be the angle of the lights
which was 45°, or the distance between the lights and
subject which was approximately 60". I did alter the
angle to a 35-40° for a second round and am waiting for
the results next week. I should add that I wasn't
thrilled with the VPS film; is there a better film for
this kind of work, something with better resolution?
Thanks for your help.
Kevin
Dear Kevin:
Doing copy work on oil paintings is not really difficult
if you know a little about the physics of light. Once you
do you can apply this along with a few standard, logical
techniques and get perfect results every time without
using special film, lights or anything else. This is
about the physics of light. Nothing more.
First we must understand that light falls off in
intensity more rapidly when the light source is closer to
the subject than when it is farther away. In my classes I
demonstrate this by holding my meter high over my head,
toward the sun and take a reading. Then I move the meter
to the ground (still facing the sun) and ask my students
if I will get a different reading in this position.
It’s always unanimous. The reading will be the same.
I ask them why? It’s now further from the sun than
it was a moment ago! They explain that the distance to
the sun is so great that there will be no measurable
difference in the two readings. With that they prove that
they know more than they think they do about light and
it’s fall off characteristics. This is the principle
that many photographers fail to apply on a daily basis.
The principle that the distance from the light source to
the subject affects the rate of light fall off on the
subject is a very useful one.
The old idea that putting your copy lights at 45 degrees
to the subject just don’t work. You are asking for
reflections when your lights are at 45 degrees because
your surface is not flat and at that angle it is quite
possible to see many specular reflections if your lens is
any where near the painting. Oil paintings have many ups
and downs with the thick paint applied by the artist. Yes
I understand that these mountains and valleys of paint
are to be free of harsh shadows but this problem will be
very small when you have the two lights coming from
opposing sides of the painting. The shadows, tiny as they
are will cast shadows that at there very worst will be
only one stop less than the vast surrounding area. This
is far less significant than most people think and is not
worthy of concern. Making your lights larger will only
add to the reflection difficulties. It is simply not
necessary.
Ok, first let’s discuss the position of the
painting. Hopefully it is not in a picture frame. This
would be a big hindrance. Position your painting on a
platform so it is safe from falling and where you can
adjust the angle as it faces the camera. Select a camera
angle that is comfortable to work at and position your
painting so that it is perpendicular to your lens. If you
do a lot of this work, you might consider building a
large T square to hold near the painting. The long end
points toward the lens and should not reveal any
observable angle difference from the lens.
Now, to minimize the effects of light fall off, position
your painting so that the long dimension is up and down.
In other words, stand it up on end. If it is a square it
don’t make any difference. Now when positioning your
two lights, select a position that is even with the
center of each side of the painting. You don’t want
to have your lights closer to the top or bottom ends.
They need to be centered. The strobe heads should be a
significant distance away from the painting. A good rule
to follow is double the width of the painting. If the
painting is three feet wide from left to right then place
each of your lights at a distance of 6 feet from the
nearest edge. If you were to place the lights in closer,
the rapid fall off caused by the close proximity would
make it very difficult to achieve even lighting.
Now check the angle of your lights. Contrary to popular
opinion, 45 degrees out from the plane of the painting is
too much. Take it back to about half that or 22 degrees.
This will minimize the chance of glare from the strobe
coming back to the camera. Here is another secret to
eliminate the reflected light. Use a longer lens. Think
about it. Put yourself in the position of the camera.
Keep moving in closer and closer. When you get to where a
wider lens would be if attached to the camera you can
probably see the lights reflected in the painting. Now
imagine backing up to the back of the room. You will
never see the lights reflecting from way back there AND
as a bonus, you have much less chance of recording any
sort of architectural distortion because you are so far
away. A subject to camera distance of 15 feet with a
longer lens is far more desirable than 5 feet with a wide
lens. I am sure you have heard portrait photographers
talk about the flattening effect on a face when using a
longer lens? Flattening. Nice idea for photographing a
flat subject, wouldn’t you agree?
Now check the angle of the strobe heads to be sure that
they are pointed toward the center of the far side of the
painting rather than the near side. Your light sources
should be small and with no umbrellas. (Be certain that
the lights are shielded are not seen by your lens).
For nearly 20 years I have been doing this with perfect
results and have never needed a polarizer, simply because
there is no specular light coming back to polarize.
Meter readings are important. They should be within 3
tenths of a stop from corner to corner, top to bottom,
side to side and across the center. This is not that hard
if your lights are far enough away because the fall off
is so gradual. Just make small adjustments to the
position and distance. Barn doors really help out a lot
with fine adjustments.
Once you have metered and your lighting is even you can
make your exposures. It is indeed advisable to cover up
any light objects near the camera with a dark cloth (this
includes your clothing and tripod). You should always
work in a darkened room and be sure that there are no
light sources behind you that could be “seen”
by the painting and reflected back to the lens.
When doing copy work, many photographers rate their film
as if they were doing portraits. Most of us have rated
Kodak VPS III in the 80 to 100 range even though Kodak
says it is ISO 160. When doing copy work, rate your film
at the recommended ISO because you are photographing flat
art and the dynamics of the tonal range are much less
than in the real world. Over exposing will unnecessarily
add to the contrast and make your subject look harsh and
unlike the original. The subject by it’s very nature
has a much lower contrast range than an actual scene in
nature. The brightest it will ever be is the lightest
white paint that is used. The darkest it will ever be is
the color of the blackest paint used. Unlike nature where
you have dark objects with little or no light striking
them at all and other lighter areas which are lit by open
sky or even the sun, the painting is a much more
dynamically conservative subject. It is still wise to
bracket a bit when doing copy work. A little extra film
is well worth not having to reset things from scratch but
always be sure to photograph it at the recommended ISO of
the film you are using and then do your bracketing. The
new Kodak Portra 160 VC will provide more vivid color and
better contrast for copy work than the NC or normal
contrast film. You may wish to test them both to
determine which you feel produces a more realistic
rendition of the original painting.
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