Digital BW, The Print

On Wed, 10 Sep 2003, Loring Palleske wrote:

> 
> Don't confuse zones with f stops. zone 0 is always black and zone 10  
> white. Even a 5 stop latitude will have 11 zones.

Yes, you are correct.  I should have said stops instead of zones.  

The beauty of the zone system though is that it calibrates your film's dynamic range into zones which happen to be one stop apart.  If they weren't a stop apart, it would be very difficult to place items in a particular zone using a spot meter.  In fact, in The Negative, Adams defines the zones to be a stop apart.

> >
> > 2) At what zone does your camera overexpose and blow out the highlight  
> > detail.
> 
> Always zone 10
> That is the definition of zone 10
> 

That is true for film only once it has been calibrated to that by finding your standard development time.

With film, it's the toe of the curve (shadows) that determines your ISO.  My point was with digital, I think the highlights should determine your ISO.

For example, say you have a scene with both a white and gray object in it, and you meter the white object and placed it in zone 10 (paper white) which corresponds to a digital value of 255.  You meter the gray object at that exposure and it happens to fall exactly on zone 5, so you make an exposure.   I doubt that the gray and white objects in the digital file will have values of 128 and 255 respectively.  In fact, no matter what values they fall on, I doubt that their difference will be anywhere near 127.

So, by using an ISO based on zone 5, objects that fall into zone 7 (where you would expect full texture) may in fact turn out to be a value of 255 (paper white) in the digital file, and so will zone 8, 9, ...

--Tom