Testing focus

Now that a lens had been incorporated into the filmable pinhole camera system I needed to know how much of the image would be in focus due to the fact that using a lens creates what is called Depth of Field. I also needed to test how to set the focal distance by moving the lens nearer and further away from the image plane. To determine this I decided to create a basic test outside my house using some homemade distance markers and a brick wall.

Focus Markers on brick wall

Filmable Pinhole Camera Focus/Depth of Field test

By measuring in five feet increments I could get a rough idea of how close or far the subject of our film should be for a good focus to be achieved. I started by setting up the first marker five feet from the box and then the others in further five feet steps as shown in the picture above.  I then took a series of photographs of the resulting image created inside the box moving the lens each time.

Focus Test 1

The first photo above clearly shows the focus to be around the first marker placed at five feet from the box. The wall around the marker is a good way of seeing the depth of field - what is in focus. I marked the position of the lens from the image plane and moved it a few millimeters to see how the focus changes in the next picture bellow.

Focus Test 2

The second photo at the new lens position shows how the focal length was affected as the 10 and fifteen feet markers are now sharper focus than the five feet marker. Also the depth of field appears to be larger in this photo.

Focus Test 3

In this photo I have moved the lens once more increasing the focal distance. All markers are now soft focus and the road and houses in the background are sharp focus. Both the focal distance and the depth of field have increased significantly in this photo.

This test, although very rough, did help cement a few issues with the system. I now knew roughly how far the box would have to be placed away from the subject of our film. I also knew the light level of the image would be sufficient for the Sony EX1 we had planed to use for filming inside the box. The introduction of a lens with a small pinhole style aperture in front of it meant we now had an adaptable system capable of capturing an interesting image.