[alt-photo] Re: Your Approach to Making Negs for Platinum Printing? Ideal Negative Contrast and Dmax?
photographeur at nerdshack.com
Sun Oct 9 01:07:08 GMT 2011
>When you say DR do you mean the range between
>FB+F and the most dense tone in the negative?
Yes, for transmission media. For reflective media [prints], it is
the difference between image area base white and Dmax (although any
particular image may not have areas that go to both extremes, so the
DR for a particular image may be less).
> I have a X-Rite transmission
>and reflection densitometer at home and I'm unsure of how to read a neg to
>determine is DR or a prints ER. Is it simply reading most dense area and the
>least dense area and taking the difference?
Yes, that will give you the DR of the particular negative or
print. I don't know what you mean by ER. An individual print's DR
is the difference between the lightest and darkest reflection
densities in the image area. A print media's [potential] DR is the
difference between the lightest and darkest reflection densities you
can obtain with that media, if you expose with a step wedge that
shows at least two indistinguishable steps at each end. (Really,
this is the DR of the medium + processing. You may be able to adjust
this by different processing.) A print medium's ES is the DR of a
negative that will just produce the full range of DR in the print
when optimally exposed.
>I am specifically interested in figuring out how to properly measure the
>density range in a negative so that I can match my visual understanding of
>what these negatives look like to the actual measurement of the negatives
>density range. I hope that makes sense. I suppose I'm just looking for a
>little clarification on the best practices for using a densitometer and how
>to relate the measurements to density range and exposure scale.
(1) Start with the printing process. Use a long-scale step wedge,
and expose so that you have at least two indistinguishable steps at
each end. (If you don't get at least two indistinguishable steps at
each end, you need a wedge with a longer scale. This can be a
problem with long-scale printing processes like traditional
Pt.) Once you have this, your ES for that medium/process is the
number of distinguishable steps in the print multiplied by the step
size (24 steps of a 0.1 per step wedge is an ES of 2.4; 14 steps of a
0.15 per step wedge is an ES of 2.1. Etc.).
(2) Adjust your negative exposure and processing to give a negative
DR equal to the print medium's ES. (This assumes that you want a
print that ranges from Dmin to Dmax for the print medium/process. If
you want a print that doesn't go all the way to Dmax or Dmin, make
the negative DR equal to that portion of the ES that produces the
print densities that you want.)
(3) Adjust your printing exposure so that you get print densities
from Dmin to Dmax. Overexposure will get you to Dmax, but not Dmin
(shadows will look blocked, highlights will look
fogged). Underexposure will get you to Dmin, but not to Dmax
(highlights will look blocked, shadows will be too light).
That is all there is to it.
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