How calculate pinhole exposure time by a digital camera

Use your digital camera to measure the light

How calculate pinhole camera exposure time by a digital camera



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.



pinhole in position
"In the picture the pinhole camera is placed in front at the tiles, the subject is the number 1074 in the wall"


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.



digital camera close a pinhole
"After the digital camera setup, the photographer focusing the subject to obtain the opening time at the same light condition"


The digital camera displays the opening time according the setup f16 and ISO200.

digital camera display
"The opening time displayed is 1/320 seconds"


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

Where:
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.

pinhole shutter
"The CURVA-45 shutter is guided by a dovel profile and aid the photographer to execute fast shot, however an opening time of 0.64 seconds reduce the possibility to execute that."


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.

pinhole photo
"The picture above was be executed by a pinhole camera CURVA-45 and the film used was be a Kodak Color Plus 200®. The picture format is 10x15 cm