[Leica] Dynamic Range of Film (long)

[Myers Pete <MyersPete@aol.com>]

Dear Greg:

Your question in regard to the dynamic range of commercial film is a good
question to ask. I get LUG in digest form, so it might be that you have
already had a complete answer. But, in case not, I will try to provide you
with a few numbers to mull over.

If you place a piece of black velvet on a white card out in the full sun, you
will get a contrast between the two levels of about 50 to 1. If landscapes
were that simple, we could all shoot slide film. But, it is not. 

What happens in real life is that typically the shaded area of say the back
side of a mountain is 8 to 1, between the direct light and the diffuse sky
light. However, within the shade, other objects produce more shade. So now,
the same black velvet on a white card on the shade side of the mountain would
be down 400 to 1 in comparison to a white card on the bright side of the
mountain.

There have been many studies of 'typical' landscape lighting, but the best
data I know of is as follows: The dynamic range of light in a landscape varies
from as low as 27 to 1 to as high as 750 to 1 in 'typical' scenes - with an
average of 160 to 1.

But, 'typical' is not an extreme. Often, light can get into the 1000 to 1 or
even 10,000 to 1 range and even higher. Fortunitly for us, artistically
dynamic light beyound  about 1000 to 1 is not all that useful. However, the
dynamic range of a TRUE 12 bit digital camera is 4096 to 1 and represents a
useful tool in the real world. Unfortunitly, we are not quite there yet - it
may say '12 bits', but only peltier cooled CCD cameras made for scientific
applications can live up to it. Kodak's CCD SLR cameras have about a 256 to 1
or 8 stop dynamic range on the large area CCDs like the EOS 3.

So, that gets us back to using film. I am looking at my Kodachrome 64 data
sheet and it says that it can barely pull a dyanmic range of 100 to 1.
Therefore, if the 'average' scene has a dynamic range of 160 to 1, your scene
is not going to fit the film. Hence, why most slide shots are made in the
early or late parts of the day when the light tends to tone down. Or, if the
light is partially in range, graduated neutral density filters are used to
knock down the sky values to those of the land values. Obviously this is not
easy to do.

Pressing on to color print film: I am looking at a Kodak Royal Gold 100 data
sheet - not atypical of most color print films. It has a dyanmic range over
1000 to 1. Not only is this true on the data sheet, but I have shot such 'hot'
scenes with color print film many times (lots of Fuji Reala and other Fuji
films, some Kodak) and have measured these types of light values as density
levels. 

While color print film has the dynamic range to capture the most useful range
of a landscape, unfortunitly, your color printer has no tools to make a print
that will show it. That is because color print paper is not variable contrast.
It is designed to print a typical contrast scene. Beyond that point, a hand
print must be made that uses all the light masking tricks possible to compress
the dynamic range down into a print of fixed contrast.

Now, comes black and white film: while the film type has an effect and creates
certain limits, it is possible to use developers that will allow a contrast of
over 15 to 20 stops! That is up to a dynamic range of 1,000,000 to 1.
Developed for photographing nuclear blasts.

But, down to earth, 1000 to 1 is typical of a 400 speed film with
'performance' films, like Delta 100, starting to roll over at 250 to 1. Using
special developers, like PMK Pyro, can bring a 400 speed film into the near
10,000 to 1 range.

Obviously, with variable contrast or graded paper in black and white, you can
use a lot more of the full dynamic range of the light on these negatives,
while minimizing the gymnastics of extreme light masking. Dodging and burning
at the right grade can get the image solidly printed.

The best news is in using the computer for color negative film or in black and
white. The dynamic range of a scanner and computer can easily handle the data
on a color negative or black and white negative and allows the photographer to
change the dynamic range of the raw image to match the output media.

This is my own forte' as a fine arts photographer - my sole profession. I have
been one of the pioneers in using the computer in straight image making for
landscape work. This stemmed out of my work at NASA, where I picked up the
math and knowledge about digital imaging. (See Photo District News, November
1996, pp 115-120 for an article on my work).

There is a lot of confusion about film, dynamic range, grain size, etc. in
image making. I hope I have helped answer your question a bit. 

Pete Myers