You should also take into account long exposure reciprocity. Short: The longer your exposure time gets the less sensitive your film is. Depending on the exposure time that can be another few stops, especially with Foma 100.Do I need to take something else than normal aperture + exposure time + film ISO into account? The aperture of the pinhole is f/207 so it's about 9.5 stops from f/8. Do I just extend the exposure times by 9.5 stops (if I meter at f/8) and get good results?
How about a slower film, like Rollei Pan 25?
/Minna
Click!... Mathematically, I wonder what a graph looks like for a given film and f-stop. That is, if you were to plot points for all exposure values and did some sort of curve fitting, what sort of function would you end up with?
With a 6x12 format you won't be enlarging all that much, if at all, so you may as well use a faster film. The natural softness of a pinhole image will outweigh any grain issues. If you need long exposures, use slower film. I mostly use Delta 400 at EI 200 for my roll film pinholes.
There are several pinhole sites out there with lots of information. f295, pinhole resource & others. F295 has an active group like APUG.
In my pinhole forays, I found that fast films called for too short an exposure in bright outdoor scenes to time reliably with a human-powered shutter (a true digital shutter -- operated by thumb and forefinger). So I have gone toward the slower films to get exposures out towards 4 or 5 seconds with my gear. There has also been some suggestions that high reciprocity failure in some of the fast films actually results in longer exposures than some of the better behaved slower films like ACROS 100.
I've been fiddling with the idea of an electronically timed shutter activating a small solenoid. The difficulty seems to be availability to timers with short(1/30-1/2sec) ranges. I found one source that could provide custom timing in that range for about an extra $100 + the timer($50)
The other thing is operating voltage every thing seems to be 9-12-24V
1) First, make sure you know the ISO of the film or paper you're using.
2) Set the ISO value into your light meter.
3) Meter your scene and reference the exposure time for the largest f-stop that your meter will read.
4) Use the following formula to convert the exposure time for your camera's f-stop value:
(f/R)^2 x Tm = Tc
f=Your camera's f-stop
R=the reference f-stop used on your light meter
Tm= The uncorrected exposure time recommended by your light meter
Tc= The corrected exposure time you'll actually use
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