[rollei_list] Re: OT Infared film and shooting with it.
- From: "Richard Knoppow" <dickburk@xxxxxxxxxxxxx>
- To: <rollei_list@xxxxxxxxxxxxx>
- Date: Tue, 25 Sep 2007 19:42:58 -0700
----- Original Message -----
From: "Eric Goldstein" <egoldste@xxxxxxxxx>
To: <rollei_list@xxxxxxxxxxxxx>
Sent: Tuesday, September 25, 2007 6:43 AM
Subject: [rollei_list] Re: OT Infared film and shooting with
it.
You are correct that what is needed is a working EI (not
ASA as
stated), but to my knowledge you will not now find
anything but as ISO
speed designation on a film box...
Eric Goldstein
--
I looked for my copy of the Kodak HIE data sheet but
can't find it just now. Its probably on a zip disc
somewhere. I am pretty sure Kodak never published an
exposure index for it but rather advised about test
exposures under certain common lighting conditions. There
are a lot of variables to IR film plus standard exposure
meters are not intended for measuring IR.
Its possible the ISO has some sort of standard for IR
film but I certainly don't have it. There is no single ISO
speed standard. Individual standards are published for
various kinds of film. The one most of us refer to is for
black and white silver-halide negative film for still
cameras for pictorial purposes. That's a lot of
qualifications. There are separate standards for color
films, for reversal films, for special application films
like aerial films, etc. And again all are parsed up into
catagories, i.e., color vs: B&W aerial films, etc.
The reasons have to do with the differences in
processing and in the desired results. For example, aerial
films and motion picture films are generally processed in
machines with fairly standardized methods. This is also true
of all types of color films. Negative B&W and color films
are usually processed to quite different contrast values.
In addition the ISO standards try to account for the
normal handling films get in various applications. The B&W
negative standard, for instance, requires the film to be
stored under specified conditions for a time prior to
testing. This assumes that in normal use film will not be
processed immediatly after exposure.
The idea is to give some idea of the performance of
each type of film under controlled conditions, which,
presumably, have some relationship to the way the film is
actually used.
The B&W standard in current use is an ammended version
of a standard adopted about 1958. This was based on the then
new DIN standard but modified to move the speed point up the
toe so that it would correspond to the point found using the
older ASA method which was based on the system worked out by
Loyd A. Jones of Kodak Research Laboratories. The current
standard is essentially the same but has some changes in
detail.
The information I have on other speed standards in use
is not current but rather what is in some of the text books
of around the 1960's to 1980's. Its probaby valid for method
but not for details.
AFAIK, there has never been a standard for IR film used
pictorially although they may be one for aerial film.
Variation of focus: Most normal camera lenses are not
corrected for IR. The IR correction varies all over the
place. Some are pretty well corrected, some not. Some lenses
have an offset for IR but I suspect that is not really a
constant with distance although so marked. Some lenses have
a specification for IR off set even though its not marked on
the lens. Higher quality Kodak lenses had such a spec on
their data sheets. Here the advice of using small stops is a
good one but experimenting will also give some idea of how
much the IR focus deviates from visible light.
The type of filter will also make a difference. Filters
which cut out visible light mostly or completely may show
the focus deviation more than using a filter that simply
reduces blue and green.
Note that all IR film is sensitive to blue. The dyes
used for IR sensitization, particularly into the far IR,
often have a gap in the green region. There is a difference
between films which simply have extended red sensitivity and
those which are sensitive to non-visible IR such as HIE.
IR films also tend to be somewhat grainy and are have
relatively short shelf lives. Films of any sort are
perishable so making anything which is low volume and extra
perishable, like IR film, can be uneconomical.
---
Richard Knoppow
Los Angeles, CA, USA
dickburk@xxxxxxxxxxxxx
---
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