100 ISO - Best Film Speed?

[P3D Dr. George A. Themelis <fj834@xxxxxxxxxxxxxxxxxxxxx>]

After using slide films with speeds from 25 to 400 ISO, I am convinced that
100 ISO is the BEST all around choice for classic stereo cameras.  Here is
why:

1. It can handle the brightest natural light (usually one fstop above sunny
day).  The sunny day rule for this film is f16 @ 1/100.  Most stereo
cameras have f22 max aperture and 1/200 max shutter speed, enough to handle
1-2 steps above that.

2.  On the other extreme, it will allow you to shoot indoors hand-held
using f3.5 @ 1/25.  This is typical for offices or brightly lit interiors
(like the church I was photographing during service in Greece).  f3.5 is
the usual maximum aperture of a typical stereo camera and 1/25 is the
slowest safe (with some practice) handholding speed.

Faster films (like 400 ISO) will let you work in less light but come with
plenty of (noticeable and disturbing in stereo) grain.  Slower films (K25
for example) will work OK on a sunny day but with less light you will get
the 50s syndrome, i.e., out of focus backgrounds and lack of sharpness due
to camera shake.  Flash or tripod are always an option for slow films but
photographing scenes with people, or moving objects, at slow speeds can be
a problem (in a couple of pictures from the church, the priest is blurred
while the surroundings are sharp).

I am personally glad to see that film companies are constantly improving
the quality of the 100 ISO slide films!

-- George Themelis

PS. I have seen plenty (too many) of slides from the 50s suffering from
lack of sharpness as a result of the slow film speed. The only color slide
film for a long time was Kodachrome with rating of 10 (or 8).  With a sunny
day recommended setting of f6.3 (between 5.6 and 8) and 1/50s it is rather
remarkable that sharp pictures were taken without the use of a tripod on a
not-so-sunny day.


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