500mm pinhole camera "lens"

The focal length or projection length is determined by how far the pinhole is from the negative. In this case I have built a "tube" to have  the pinhole at 500mm from the negative.


The photographs are of Kingsnorth Power station taken from the shore line 3kms away the other side of the river.

As with pinhole camera the focus is soft but the depth of field is from in front of the camera to infinity.

A different view with closer foreground

The exposure was 6 minutes with a pinhole of 0.89mm giving an aperture of f/561.

The Calculation

I established the size of lens needed by measuring the width of the power station and the distance away on an Ordnance Survey map.  Then by the use of simple trigonometry I established the Tangent of the angle for half the width of the station. Knowing the half width of the image and now the Tangent of the angle I calculated the distance of  the lens to negative and made the necessary tube accordingly.  It created a photo exactly as expected.