Jason Lay wrote:
>
> That helps Skip, but can you explain how 2 stops would equate to ISO...It
> appears as if you multiply your ISO by 2 then do it a second time or divide
> by 2 then do that again to get 2 stops either way...If I was shooting 800
> speed film, could I then set the ISO at 400? This would then open up the
> aperature more? Would this affect the speed of focusing? Which direction
> would be overexposed and which would be underexposed? Thanks for your help
>
If you double the ISO, that is equal to one stop, i.e. ISO/ASA 100 is
one stop faster than 50, 200 is one stop faster than 100, 400 is one
stop faster than 200, etc. ISO 160 is 2/3 stop faster than 100. If you
are using 800 film, and set the camera at 400, then you fool the camera
into letting more light hit the film than is required, thus you are
overexposing. The camera will usually default to slowing down the
shutter speed, but not always. It may speed up focusing as a result,
but one stop isn't going to make a noticeable difference.
In direct answer to your first question, if you overexpose 800 by 2
stops, you'd set your camera at 200, to underexpose by 2, you'd set it
at 3200.
Skip
--
Shadowcatcher Imagery
http://www.shadowcatcherimagery.com
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