Depth of Focus
Safety Warnings
Warning: Bright Light Precaution
Purpose
Demonstrates how aperture size controls depth of focus. Students observe that reducing the aperture of a camera allows pinholes to remain in focus over a wider range of image-plane positions, illustrating the tradeoff between light gathering and depth of focus.
Figure 1:
The large-format camera with adjustable aperture and ground glass plate, alongside the lamp with pinhole-patterned aluminum foil covering.
Figure 2:
Top: wide aperture with ground glass away from the focal plane — pinholes appear as large circles of confusion. Bottom: at the focal plane, the same pinholes appear as sharp points.
Figure 3:
Top: small aperture — pinholes remain sharp even with the ground glass displaced from the focal plane, but diffraction spikes appear. Bottom: at the focal plane for comparison.
Figure 4:
Top: wide aperture, significantly out of focus — each pinhole produces a large circle of confusion. Reducing the aperture shrinks these circles even without moving the ground glass. Bottom: at the focal plane for comparison.
Equipment
- 1
Demo Apparatus
- 1