Greetings Nikon-a-holics
There have been a few entries about the colour matrix meter in the F5 and its
ability/inability to actually detect colour.
For those with photo secretary there is an option to show the colour information
being processed by the meter, (I don't have the software in front of me at the
moment so I can't give the exact menu location). Have a look at this display
while you move different coloured objects in front of the lens (while metering
of course). BTW, I have found that this will flatten the batteries in your
camera rather quickly, so if you're paranoid about your batteries, you better
skip this.
Now, let's consider the 1005 elements of the RGB meter. This equates to 335
elements for each colour specific sensor, red/green/blue. I would imagine that
these sensors would be arranged in groups of 3, one of each colour.
We now need to consider the meter, not as we see colours, but as a computer
represents colour, as numbers. Each sensor represents the light falling upon it
as a number between 0 - 255. So for each sensor GROUP there is 256 x 256 x 256
or roughly 16 million different values that it can represent. The red sensor
gives the red value, the green sensor the green value and the blue sensor the
blue value.
Using this scheme, 16+ million different colours can be represented. Black is
given as 0,0,0 (R,G,B) while, white is 255,255,255. If the values are moved up
together, 25,25,25 or 100,100,100 etc you have grey scales. Most computer paint
programs will allow you to create new colours in this way, try it out and see
the results.
While 16 million colours is less than we can see and probably what can be
recorded on film, it is enough to evaluate the PREDOMINANT colours of the scene.
This is how the F5 determines the camera orientation. In the F4, the finder had
mercury switches which changed the bias on the metering cells when the camera
was rotated. In the F5 if the meter detects that the top half is blue (r,g,b
values within certain parameters) it assumes this is the sky, either the long or
the short side of the frame.
Once this information is combined with the brightness and contrast (as in any
other exposure meter) and distance (with D-type lenses) a table of values is
formed (a matrix - hence the name, matrix metering). This matrix is compared to
a database (30,000 values is the going number I believe) the result of this
compare is an exposure index. Once an exposure value is determined it can be
translated into aperture and shutter speed values.
As many contributors have said and I'll re-phrase a bit, the camera can't think.
It can only interpret the information that is presented to it's computer
processors and determine an exposure index which complies with it's programmed
logic. It is basically a purpose built computer with a light tight compartment
in it.
I hope that this clears up the various questions about the F5 meter, how it can
"see" colour and how it determines it's exposures.
For mine, I believe Nikon has done a bloody good job on the exposure meter, I'd
like to know what they plan to do to top it.
Keep the great shots coming.
Best,
Eric
