The wooden block with two boreholes on its central width.

The hole on the left is inclined whereas the hole on the right is perpendicular to the surface of the block.

From above the geometry of the boreholes can be seen more clearly.

The block is affixed in a dark chamber on the right, and on the left a second dark chamber has a red circular marker on its wall which gives the exact area visable through each of the boreholes from inside the right chamber.

A closer view of the void between the chambers

Cross section of the two chambers and the block. The hole drilled into the left chamber is the same size as the red marker.

It is crutial that the view through each of the boreholes is the same (the red circle), so this view shows how this works.

The maximum visable area from each hole is the same. The straght hole is on the top, and inclined hole on the bottom.

View through the straight hole. The view is completely occupied by the red circle, but the circle does not exceed beyond the area in view.

View through the inclined hole. Note that there are very small sections of wall on the left and right visable. This is because the red circle is now being viewed at an angle so appears as an ellipse.

Now with the camera positioned inside the dark chamber at the exit of the two boreholes looking back onto a wooden plank the illumination of the plank as the light passes through the straight borehole can be seen. The red marker has been replaced with a opaque white sheet of paper.

Looking on the other side where the light has passed through the inclined borehole and illuminated the wooden plank in a similar manner.