RE: [pct-l] Film ASA

["Kelly Miller" <aj7x@amsat.org>]

I'm not familiar with the actual manufacturing process of different ASA film
speeds.  In the most basic sense, the lower ASA speeds will offer higher quality
and sharpness and less grain.  They in return are less sensitive to light, which
is no big deal, it just means that a slower shutter speed and larger (smaller
number) f:stop is needed.  Shooting conditions dictate whether a certain
combination of these is feasible.  A handheld shutter speed needs to be at least
1/focal length of lenses.  As an example, a 50mm lens would need a 1/50 shutter
speed to offset any vibration from the user.  Of course this is just a
guideline.  A larger f:stop (larger lens opening) has a smaller depth of field
or focus.  This is usually not a concern with long distance scenic shots, but is
nice effect with portraits.  As a rule, if you had control over the exposure,
you would use something like 1/ASA at f:11 or f:16 in open daylight shots in the
sun.  With your ASA 25 film this means that you should chance exposure from 1/25
@ f:16 to something like 1/100 at f:8 to have a faster shutter speed.  You have
many choices since each change in f:stop to a larger diameter opening, such as
f:16 to f:11 or f:4 to f:2.8 lets in twice the light.  This means you cut the
shutter speed in half to compensate.  Also, if you have a tripod, the need for a
higher shutter speed to offset motion is mute - though it may be necessary for
action shots - and you have even more possibilities to choose from.

Well, that was the short answer.  If you need more details, let me know.

...Kelly


> A question about ASA.  I have always taken slides, and used 25 ASA film
> in my old Olympus XA-1.  My assumption, which may be wrong, is that the
> lower the ASA, the richer the "burn" of the image on film.  I have also
> assumed that the kind of shots I take, usually from the tops of passes
> to chronicle where I've been and where I'm going, are best taken with
> low ASA film.
>

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