Re: ISO for meter w/infrared

[William Rivelli <rivelli@xxxxxxxxxxxxxxxxxxx>]

Charles Jay Pilzer <cjp@xxxxxxxxxx> wrote:

>I am using a Hasselblad with has no built in meter.  I have a Sekonic L-508
meter.  I would like to know what ISO to use on the meter for HIE when I
have one of the following filters on the camera and no filter on the meter.<
***
   Andrew Davidhazy gave you the basic right answer: Begin by following the
info on the Kodak film data sheet, then adjust from there, depending on
development and other factors.

There is a lot of confusion about all this which I'll try to help clarify
by going into more detail:

The recommended speed of Black & White Kodak IR films (HIE and HSI) is ISO
80 without a filter. This is the speed at which you would set a HAND-HELD
meter (NOT an in-camera meter).

When you use the #25 filter with HIE/HSI you need to give 2/3 of a stop
more exposure because the filter blocks some of the light to which the film
is sensitive.  Therefore the film speed should be set at 50 on your
hand-held meter. (All these speeds are approximate; they may vary a bit due
to your equipment and processing).

Now here's where the confusion begins:

Many people are using 35mm cameras with through-the-lens meters and they
have found that the meter must be set to a film speed of around 200 to 400
to get proper exposure when the meter has to read through the # 25 filter.

The reason is this: with regular B&W film such as 400 speed Tri-X, you have
to give 3 stops more exposure when using the # 25 filter, since the filter
cuts off a large amount of the light to which the film is sensitive. If you
keep your camera meter set at 400, the meter-which is looking through the
filter- will compensate, and indicate that you have to give 3 stops more
exposure and the photos will be properly exposed.

BUT when you load the camera with HIE film and set the film speed correctly
at ISO 80 and have the meter look through the # 25 filter, the camera meter
doesn't know what kind of film is loaded and it still says that you have to
give 3 stops more exposure. BUT THAT'S WRONG! With HIE film you only need
to give 2/3 of a stop more exposure, so your negatives will be overexposed
by 2 1/3 stops.

YOU CANNOT SET THE IN-CAMERA METER FOR THE TRUE FILM SPEED. You have to
fool it so that it will indicate the right exposure. That's why a lot of
people set their in-camera meters to 200-400. But no matter where you set
your camera, the actual film speed is still 80 with no filter and 50 with a
# 25 filter.

Since you have a hand-held meter, things are much simpler. Set your meter
at 50 when using the # 25 filter and take a reading. That's all.

Happy photographing,

Bill

PS: One thing I'm curious about-you said you are using a Hasselblad with
HIE film. Are you using 70mm film?

      William Rivelli
WILLIAM RIVELLI PHOTOGRAPHY

rivelli@xxxxxxxxxxxxxxxxxxx
    www.rivelli-william.com


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