In this tutorial is explained in which way it is possible take advantage by sensors installed in a digital camera and measure the exposure time of your pinhole camera without the use of an expensive light meter.
Starts to place your pinhole camera in front your subject, will be better if the sun remain rear the camera.
In this case the pinhole camera mount a film ISO200, thus must be set the digital camera with the follow parameters:
- Stop number= f16
- ISO 200
placing the digital camera close the pinhole camera to focusing the subject and then press the button only to display the exposure time.
The digital camera displays the opening time according the setup f16 and ISO200.
The opening time is valid for the stop number f=16, but our pinhole camera CURVA-45 own a stop number of f=230, but this isn't a problem it is possible convert the digital camera opening time suitable for the pinhole camera thanks to the follow formula:
POt = ((fp)^2/(fd)^2)*DOt
POt = Pinhole camera opening time
fp = Pinhole camera f stop number
fd = Digital camera f stop number
DOt = Digital camera opening time
In our case the formula results:
POt = ((230)^2/(16)^2)*(1/320) = 0.64 s
In this case the opening time is very short, the white wall reflect a lot of light, this produce a negative effect to shot the photo because the photographer will going to open and close the shutter in a time lesser one second. In this case is better wait a reduction of the light intensity as in the sunset or by the aid of some panels.
Below you can see the final result, 0.64 seconds to open and close a pinhole shutter depends mainly by the photographer ability, in fact in this case the picture results a little bit overexposed.