ISO Collaboration
Prepared 2007-12-02 by Bill Claff
Revised 2007-12-31
The purpose of the collaboration is to collect native ISO information on all Nikon DSLR models.
The native ISO of the sensor is seldom exactly a standard value such as ISO 200.
Knowing the actual native ISO helps us understand metering discrepancies and is used to compare Quantum Efficiency (QE) between camera models.
The native ISO is determined by measuring the average number
of ADUs recorded for a “correct” exposure.
Since the sensor is far more sensitive than the 1/3 EV metering multiple
samples must be averaged to acquire the value.
You need to be
running a Windows system and to get the following from my web site:
(You should be able to right‑click and save from these links.)
Place them all in
the same directory.
Choose your fastest
prime lens.
Use a 50mm f/1.8D AF-Nikkor if it is available as this is what I used to
collect my data.
Use default noise
reduction settings. In particular do not use long exposure noise reduction.
Use RAW or RAW+JPG.
If your camera does
both 14‑bit and 12‑bit then use 14‑bit.
You will be using
Manual mode, Manual focus, Spot metering, and ISO Auto On and the camera set
for the lowest numbered ISO.
Using a ‘DOS box’
run the flat_target program with parameters as follows:
flat_target 2 128
This puts a window
on the screen with the RGB value of (128, 128, 128).
The values are shown in hexadecimal. So at this point you will see 808080 @ 2
in the title bar.
The ‘a’ or ‘-‘ keys will reduce the gray value by 2 on each keypress.
The ‘z’ or ‘+’ keys will increase the gray value by 2 on each keypress.
Enlarge or maximize
the window.
Note that all
readings and images are taken wide open in manual focus with the lens set to
infinity and touching the computer screen.
(If your screen curves a lot then be sure to use a lens with a recessed from
element.)
Set the shutter
speed for a proper exposure with the initial image on the screen and at the
lowest numbered ISO for your camera.
Use the slowest shutter speed that doesn’t cause ISO Auto to start flashing.
Take 32 images
pressing the ‘a’ or ‘-‘ key between each image.
(Note that because ISO Auto is set they will all be “correctly” exposed.)
When you will finish the title bar will read 404040 @ 2. There is no need to go
to 000000 @ 2.
Transfer the images
into the directory with the downloaded programs and batch file using your usual
procedure (although a card reader is preferred to Nikon Transfer).
Using a ‘DOS box’ in
the directory with the images run the ISO_gather batch file.
ISO_gather will use
stat_analyse to extract information from the NEF files in the directory.
A summary file
called ‘ISO.txt’ is created.
Simply e‑mail
the ISO.txt file to me at Bclaff@Comcast.net
and I’ll add your data to the collection.