Re: [APML]: 37 films tested (was Gold Max)

[Jerry Lodriguss <jml@astropix.com>]

>The f/stop speed loss was determined by photographing a Kodak gray
>scale/color patch card under blue flood lights at 1/8th second and around
>f/11 or f/16.  The lighting was varried to keep the f/stop in this range
>regardless of film speed.
>
>The same card was then rephotographed at the same f/stop for 128 seconds
>through a 1000X neutral density filter.  This is a 10 f/stop difference,
>requiring a factor of 1000 in additional exposure.  (On five of the films, I
>repeated this for 256 and 512 seconds as well.  I think they were Royal Gold
>400, Royal Gold 1000, PJ400, PJC-1 and PMZ)  The extended exposures were
>repeated at 1/3 f/stop wider apertures until a full 3 f/stops had been
covered.
>
>The resulting negative strips showed the original 1/8th sec. baseline, or
>control exposure at "normal" density while the time exposures showed a
>progresive darkening as the f/stop was sequentially opened.  The strips
>typically started off lighter than the baseline exposure, then got darker at
>the 3 f/stop point.  The point where the additional extra aperture gave me
>an image density EQUAL to the baseline 1/8th second exposure told me how
>much speed in f/stops the film had lost in the 128, 256, or 512 seconds of
>exposure time.


Robert,

Interesting tests! The reciprocity failure data is very useful.  Thanks!

Couple of questions:

You say you varied the lighting to keep the exposure at 1/8 second at f/11
or f/16. I'm assuming you did this to compensate for the film speed
differences?

Did you also vary the lighting the same amount for each film speed
difference at the 128 second exposures?




    
Thanks,

Jerry