"UC" <uraniumcommittee@[EMAIL PROTECTED]
> wrote in message
news:1193681451.045599.275160@[EMAIL PROTECTED]
> On Oct 28, 9:23 pm, t...@[EMAIL PROTECTED]
(Thor Lancelot Simon)
> wrote:
>> In article
>> <1193589625.019232.237...@[EMAIL PROTECTED]
>,
>>
>> UC <uraniumcommit...@[EMAIL PROTECTED]
> wrote:
>>
>> >No, I test the materials I use.
>>
>> Do you? Because you referred to a H&D curve you had,
>> pur****tedly,
>> generated yourself, but then when I challenged you to
>> post it, you said
>> to look at the published Kodak curve (which does not
>> appear to show
>> anything like the effect you originally claimed). So.
>> Let's see some of
>> this data from the testing you supposedly do of the
>> materials you supposedly
>> use.
>>
>> Oh, I forgot, you just like to hang around here and
>> _talk_ about all the
>> photography you do. One wouldn't expect less from a
>> famous Usenet kook,
>> I suppose.
>>
>> --
>> Thor Lancelot Simon
>> t...@[EMAIL PROTECTED]
>>
>> "The inconsistency is startling, though admittedly, if
>> consistency is to
>> be abandoned or transcended, there is no
>> - Noam Chomsky
>
> I said I had tested the films. I did not say I generated
> H&D curves.
> You need special equipment for that.
>
> Here is the curve for TMY:
>
>
http://www.kodak.com/global/en/professional/sup****t/techPubs/f4016/f002_0507ac.gif
>
> Here is the curve for Tri-X Pan:
>
>
http://www.kodak.com/global/en/professional/sup****t/techPubs/f4017/f009_0490ac.gif
>
> Do you see the difference?
>
The curves are quite interesting. Kodak does not appear
to smooth their film curves, otherwise there would not be
the slight uneveness exhibited by several of them including
those for 400T-Max above. Neither of these curves shows
much shouldering, it would appear that both films are
capable of considerably greater density than the log 3.0
shown as a maximum on the curves. The question is how much
the contrast is falling off at high exposures and high
densities. Note that the curves show a large range of
contrast indeces. What shouldering there is seems partly
dependent on the degree of development as one would expect.
Also note that the range of exposure is quite wide. Assuming
the minimum usable gradient is somwehere around log -2.5 the
arithmetical range is around 1:400 or a bit less than nine
stops. If we assume an average scene brightness range of a
little less than this both films are pretty linear. For the
most part highlight compression in both B&W and color is due
to the limitations of the printing medium and method of
illumination, that is reflected light. Transparencies can be
illuminated at levels much exceeding the ambient so can
reproduce very bright highlights, reflection prints do not
have this advantage unless illuminated in a light box and
printed especially for that purpose. In general reflection
prints have more shadow detail than can be seen by reflected
light but highlight detail is compressed because the print
is made to make the mid-tones right by reflected light. One
can usualy see some additional shadow detail in a print by
looking at it with transmitted light. A print can have a
range similar to a transparency if its illuminated by extra
bright light in a light box and printed to the right
contrast and density for the purpose.
The point is that film is seldom responsible for lack of
highlight detail. The eye generaly judges the "correctness"
of tone rendition by the reproduction of mid gray values. In
some cases there will be more detail in both shadows and
highlights than can be accomodated on a reflection print if
the contrast and overall density is chosen to meet this
criterion.
Getting valid characteristic curves for film is not
trivial. The method used by manuacturers uses a special
device for exposing called a sensitometer. This gives a
known and controlled exposure and uses a method suited to
the end use of the film. Processing must be done precisely
to eliminate as many errors as possible and the resulting
film is read on a densitometer, again matched to the use of
the film.
It is quite possible to get useful curves by simpler
means but they will include variables other than the
emulsion. Sometimes this is desirable, for instance, testing
in a camera will yield a curve showing the effects of flare
_in that camera_.
In any case, the developer will also have some effect on
the curve shape and presence or lack of a shoulder because
the maximum density possible with a given emulsion will vary
with the developer. For instance, active developers like
T-Max and Microphen (which is similar) will yield quite high
maximum densities, generally higher than can be used in
practice.
--
---
Richard Knoppow
Los Angeles, CA, USA
dickburk@[EMAIL PROTECTED]
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