Re: digital stops calibration

[Elgenper <elgenper@xxxxxxxxxxxx>]

I fear it´s even more complicated than that....

Some time ago, I got the idea of making a zone calibration of the DSLR I used then (I´m an old Zone System aficionado since the Silver Age...).  I used the same procedure as with, say a Hasselblad: put the camera on full manual, set up a gray card in even daylight, measure it with a handheld meter, compute a series of exp time/f stop combinations, and shot away. Then I opened the bunch in PS (for once, no worries about dev temp&time, I thought).

Surprise, surprise...  Something in the camera firmware (I presume) had been VERY helpful with those "off" exposures at the outer parts of the intended scale, and "compensated" them all towards the center of the histogram.  I did get a step scale, but comprising only an interval of 3 - 4 steps.  Built-in minus development, so to say....

I gave up; now I simply trust the histogram....  (St. Ansel would have been euphoric if his 8"x10" had had a live histogram!).

Per

16 sep 2005 kl. 03.47 skrev Herschel Mair:

I suggest the following: (Off the top of my head)

 

My take on a digital zone system

 

Use an off-white subject with fine texture. Like a bath sheet, taped up on the wall.

 

Set up a digital camera on a tripod about a meter away and take a reading off the towel.

Shoot an exposure at that reading it should give you zone 5 right?

 

Shoot, successively, in 1-stop increments, 5 stops down and 5 stops up. That will give you 11 stops of exposure range.  From these you can make up a greyscale in PS which increments at exactly 1-stop.

 

Don't do any image processing to the raw files. Or, I should say do the same to all of them.

 

Take a few readings, (INFO) find out how it relates to the 0-255 thang. You can plot it out.

See where detail disappears at each end etc.,

 

See what happens when you shoot JPG and compare.... etc., etc.,