----- Original Message -----
From: "karol" <dzikamal...@interia.pl>
> i've got an Zero Image pinhole camera
> and i've got a question concerning sth called 'reciprocal failure'.
> In a instruction added to a camera it's written
> that it means that i need to multiply the speed by 2 when it's 1-2seconds,
> by 4 when it's 2-4...by 12 when it's more then 10 or sth like this. anyway
> it's written in a very simplified way so i'd like to know some details.
the
> aperture in this camera is 138.
Karl,
Exposure is given by a pair of parameter, they are: Time and
Aperture, there is a reciprocal relationship between them. That means that
if you increase one of the values by a factor X and decrease the other by
the same factor X, the exposure will be the same. An example: 20 times 40
is equal to 800, but if you halve 20 and double 40, their product will also
give you the same result 10 times 80 equal 800. Another example: f/60 @
1/200 secs = f/90 @ 1/100 secs.
Unfortunately, when your exposure time gets (usually) bellow 1 sec or
higher than (usually) 1/1000 sec, that reciprocity between Time and Aperture
fails, hence Reciprocity Failure. The effect is that you will need to
expose for longer than what the reciprocal relationship is telling you.
Each film has its own characteristics, therefore, each film FAILS in a
different way.
Guillermo
