Digital BW, The Print

I've had a few responses about my method of
determining effective ISO for the digital realm - so
here goes:

This testing is very similar to that done with
conventional photographic materials.  I use a
hand-held meter, even toned card (white or grey), and
a zone dial (the sticker from calumet that attaches to
the pentax spotmeters).

To determine effective ISO of the camera, read your
cameras manual for the default ISO setting, and set
your camera as such.  Most digital cameras default at
100, but still check.

Use a tripod and fill the viewfinder with the white
card - I typically will make sure that the light is
even across the card, and the sun is at a 45 degree
angle to the card itself.  At this point, set the
focus at infinity.  

Meter the card, and do a series of Zone V exposures. 
I shoot a series in 1/3 increments from 1 stop below
to one stop over ASA 100.  This gives me a set of
seven Zone V values from ASA 50 - 200.

At this point, I convert all images to 16 bit
greyscale files in photoshop as stated in my previous
post.  Using the eyedropper tool, I choose the image
that is closest in value to 50% (zone V value).  

If you have taken notes, you should be able to line up
what image is the correct ISO for your equipment.  My
equipment sets my ISO as 80 - but most likely your
results will vary from mine. 

This is a very simple and quick method in determining
ISO - and is extremely helpful when you want to place
a specific zone for imaging.  As I stated before, this
does not allow for any processing functions of the
zone system (such as n-1, n+2, etc.) but does allow
specific placement of the important values.

Good luck,
Don

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