[pure-silver] Re: Pure Black and Golden.
- From: Richard Knoppow <dickburk@xxxxxxxxxxxxx>
- To: pure-silver@xxxxxxxxxxxxx
- Date: Wed, 2 Feb 2005 02:51:37 -0800 (GMT-08:00)
-----Original Message-----
From: Peter Badcock <forums@xxxxxxxxxxxxxxxx>
Sent: Feb 2, 2005 12:34 AM
To: pure-silver@xxxxxxxxxxxxx
Cc: Richard Knoppow <dickburk@xxxxxxxxxxxxx>
Subject: [pure-silver] Re: Pure Black and Golden.
Richard,
thanks for taking the time to explain this.
> -----Original Message-----
> Because the current
> ISO speed method yields about the minimum exposure that
> will result in good shadow detail there is practically no
> underexposure latitude for B&W negative films. OTOH, there
> is lots of overexposure latitude, many stops for most
> films.=20
I was hoping to rely on this fact with the Delta 400. In
fact by exposing it at the rated ASA and developing for the
recommended time I was also assuming that this would
increase the contrast on the neg. (in comparison to exposing
for longer but developing for less). BUT read on below,
where I think I have realised the error of my ways.
> One can render long scale subjects by lowering
> either negative or print contrast but the visual
> appearance may be unsatisfactory; the eye wants to see
> about normal contrast in the mid-tones.
OK, I think I've got it now, I stupidly assumed that because
I was taking the shots on an overcast day that the
brightness range between the black and golden lab would be
less somehow - when in fact they will ALWAYS be 4 stops as
metered whether in full sunlight or indoors!! So maybe what
I need to do is to develop the film for less time to cater
for the 'long scale' between the 2 dogs.
I will also check out the response curves for the film and
compare them to other films with different exposure
lattitudes to see if I can accomplish a brightness range of
4 stops between my zone III and zone VII while retaining
sufficient local contrast.
regards
Peter Badcock
Contrast is almost completely a function of the degree of development. I=
ncreasing exposure beyond the minimum will not increase overall contrast bu=
t will push the shadows up the toe increasing the contrast there. Eventuall=
y, if one exposes enough, you will reach the "shoulder" of the curve where =
the contrast again becomes less. Most modern films have a tremendous range =
before this shoulder is reached. Its usually safe to increase exposure a bi=
t. It often results in better shadow detail.=20
In the case of the two dogs I think the problem is that the brightness =
range is greater than can be accomodated by the print. Reflection prints ha=
ve quite limited range, perhaps 30:1. Note that this is not the contrast gr=
ade of the paper, all papers with similar surfaces have about the same brig=
htness range. It is limited by the maximum visual density on the one end an=
d the maximum reflectivity of the paper on the other, the absolute limit of=
highlight brightness being the ambient light illuminating the print. Maxi=
mum visual density is around 1.8 which is available only on glossy surfaced=
paper. Any texture or matting scatters light and raises the brightness of =
the minimum black. Matte and textured surfaces also lower overall contrast =
because they limit the brightness range of the paper even further. Film is,=
in general, capable of recording a much greater range of brightness than c=
an be reproduced on a reflection print. About the best one can do is to cho=
ose the part of this range that is to be reproduced as mid- grays and choos=
e print contrast and exposure so that it prints as such. The eye wants to s=
ee "normal" contrast in the mid grays. Increased or decreased contrast is u=
seful as a special effect, but, for instance, printing a picture of a very =
long range subject so that its compressed to fit onto a reflection print wi=
ll look dull and grayed down. Sometimes prints like this are useful, for in=
stance for scientific work or as evidence photos, but generally they will b=
e seen as defective.=20
Burning and dodging allows placing parts of the image with varying aver=
age brightness so that they are mid-gray, or near it. Variable contrast pap=
er gives one the further option of changing the printing contrast as desire=
d for different areas of the picture.=20
A great many very different prints can be made from the same negative; =
its an interesting excercize to try it. You may find that you can get a var=
iety of equally desirable images this way.=20
--
Richard Knoppow
dickburk@xxxxxxxxxxxxx
Los Angeles, CA, USA
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