Shannon,
Numerically, an EI of 1000 may seem as a big jump from ISO-400,
but it is really just 1 1/3 stops faster, which probably can be accounted by a
combination of factors like: "how thin you want the negatives low zones to be",
a bit of anomalies in the reciprocity correction (I am not saying your method is
incorrect) and the pinhole actual diameter being a bit bigger than what you
think it is. Beside the above, 400 is the ISO speed of HP5 when processed as
per the ISO standards, but it could prove to be a bit faster with your specific
processing. An small contribution from all or several of the mentioned factors
could easily make your 400 film appear to be 1000 film, instead.
Guillermo
----- Original Message -----
From: "Shannon Stoney" <shannonsto...@earthlink.net>
> I have been testing with HP5+ film to see what film speed to shoot it at.
> To my surprise, it seems as if its speed in my pinhole camera is about 1000!
> It's rated at 400. The way I figure exposures is based on the fact that my
> pinhole is f352. That's supposed to be 30 times whatever f64 is. So I
> multiply the f64 time by 30 and then adjust for reciprocity failure, using a
> formula I found online from Ilford: raise the metered time to the 1.48
> power. This accords with most reciprocity failure charts that I've seen.
>
> But to get my shadows thin enough, I have to shoot this at 1000. I have had
> a lot of old cameras with old shutters that required different speeds than
> the regular one because, I assume, the shutter is a bit slow. But a pinhole
> doesn't have a shutter really! So, I wonder why you end up having to shoot
> as if the film is much faster than it is? Has anybody else noticed this?
/
