UofT ECE516 Large Pinhole, Small Pinhole, and Lens Based Cameras

Cameras have been around since approximately 400BC. Basic pinhole Camera Obscura (Dark Rooms) can be built without the need for electrical input. This experiment explores the fundamental principles of cameras and how they work through investigating mathematical concepts surrounding the camera obscura or “Dark Room”. To begin, the relationship between aperture size and focal length, or the f-stop will be explored using a large-box camera obscura. Additionally, the same concept will be used when building a small form factor camera from a box about half the size of the first. Finally, parts from a home-assembled non-electric projector will be re-purposed to make a lens-based camera obscura.

Large Camera Obscura

1. 1 large box this experiment uses a 42.5cm x 33cm box
2. 2 regular (55.8 x 75.1cm) matte black poster boards
3. black masking tape (this procedure uses black Duct Tape)
4. 1 sewing needle (large quilting needle)
5. 2 sheets of white printer paper
6. 1 stick of glue

Small Camera Obscura

1. 1 small box (this experiment uses a 22.5cm x 12.5cm
2. 1 small bottle of black acrylic paint
3. 1 roll of black masking tape (or black Duct tape)
4. 1 sewing need (small stitch needle)
5. 1 sheet of white printer paper

Lens Camera Obscura

1. 36 x 36cm piece of corrugated cardboard
2. 1 small 1.5 inch Plano (convex) lense
3. 1 sheet of white printer paper
4. 1 roll of black masking tape (or black Duct tape)
5. 20 x 20cm piece of black cloth
6. 2 sticks of hot glue refills
7. Toilet paper liner
8. 2 8-cm rubber o-rings

Using f-stop calculations as well as the box dimensions from the materials above, calculate the optimal pin size for each camera The general formula for optimal aperture size is shown above.

1. Clear a working space and collect the required materials
2. Using aperture formula, determine the optimal aperture diameter for the corresponding focal length (box length)
3. Cut black poster board to fit inside the faces of the large box (the entire inside of box should be black)
4. Use a glue stick to temporarily secure poster board pieces to inner faces
5. Apply 2 x 5cm pieces of black tape to the corners. There should be 16 pieces of tape holding the poster board in place, two in each corner)
6. Assemble the top and bottom of the box using tape, ensuring all gaps and holes are sealed. For the center gap on each face, use excess poster board to cover the openings before securing everything with tape for a light-tight seal.
7. Cut a 5cm x 5cm inch hole in one of the end faces (small sides) of the box. This will act as the first aperture stage
8. Use a large sewing needle to poke the hole according to the sized calculated using the corresponding focal length (0.91mm in this case)
9. With a smartphone, take a photo of the inside of the box when in front of a bright environment with a subject in the background

1. Clear a working space and collect the required materials.
2. Using the f-stop calculation, determine the optimal aperture diameter for the corresponding focal length (box length).
3. Paint the inside of the box black. Apply multiple coats if necessary.
4. Using black tape, assemble the top and bottom of the box. Cover any holes with several layers of black tape to block out light.
5. Cut a 5 x 5 cm hole in one of the end faces (small sides) of the box. This will serve as the first aperture stage.
6. On a hard surface, poke two small pinholes in two separate 6 x 6 cm pieces of aluminum foil. First, create a 0.3 mm pinhole, then create the specified 0.67 mm pinhole. Use a ruler with millimeter markings for precision (see Figures 5 and 6).
7. Tape the 6 x 6 cm piece of aluminum foil to the inside of the box, ensuring the pinhole is centered (or use poster board as shown in Figure 6).
8. Cut a hole large enough to fit a smartphone camera.
9. Take a video of the reverse image on the screen while in a bright environment with nearby subjects.

1. Clear a working space and collect the required materials
2. Fit the plano lens inside a toilet paper role liner (inside cardboard), use tape to increase diameter if necessary.
3. Mark cut points on cardboard according to Figure 9
4. Cut out main housing.
5. Cut the solid lines and fold the lines with arrows in the direction of the fold as seen in Figure 9.
6. Mark cut points according to Figure 10 for focal point slider (FPS)
7. Using the toilet paper liner as a trace, cut out a hole in the end of the main housing
8. Insert lens piece (with liner) into the hole on main house, wrap o-ring on the both the inside and outside parts of the lens piece to hold it in place
9. Cut out FPS
10. Slide FPS cut out into main housing to secure while taping
11. Tape with black tap, cover any holes on taped edge
12. Apply hot glue to all from edges of FPS and fasten wax paper to front edge
13. Cut jagged edges of wax paper
14. Cute fastening holes for “dark cloth”
15. Using Xacto knife, push fabric into fastening holes
16. Apply hot clue to edges of “dark cloth”
17. Apply black tape to edges of “dark cloth”
18. Slide wax paper side of FPS into main housing
19. Slide FPS and look through the camera until image becomes clear

Large Camera Obscura

Observations:

1. Brighter images than small camera
2. Same detail if not more than small camera as certain focuss distance
3. Easer to position smartphone and capture a subject
4. The pinhole size was almost the exact same size as calculated for clearest image. In the experiment we used two different pinholes one too small and one at 0.91mm to prove that
5. Harder to focus, depth of view was less than small camera

Small Camera Obscura

Observations :

1. Much dimmer image
2. Slightly sharper in correct angles
3. Much harder to position smartphone and capture a subject
4. Pinhole appeared to be close to the same width as calculated for a clear image

Lens Camera

Observations:

1. Best image quality of all three
2. Adjusting the focal length to acquire a desirable depth of field is an advantage for image quality over the other two cameras
3. As expected away from or towards the subject had an affect on image clarity
4. There is a large amount of space for modifications if photo paper insert or were used or focal length measurement via a mechanism on the side of the main housing.
5. The “dark cloth” did have an affect on the image quality or brightness
6. Image orientation is inverse of our normal sight as expected

Large vs Small Cameras

The large format pinhole camera provided a better picture overall. There was greater contrast due to the larger amount of light entering through the aperture. The larger pinhole seemed to have a clear image. However, it was harder to position the camera as the depth of view was less than the small camera. This should be expected as the diffraction effects are less as the pinhole size increases in diameter. This is the purpose for the general formula to approximate the optimal aperture hole size (as seen in the chart above). I have also included a chart to show the different between scaling the pinhole size proportionally vs using f-stop calculation. You can see that the maginute of diameter of holes increases at almost double the rate if one does not calculate it using d=c*sqrt(f*lambda).

From these findings we can see that large cameras require a larger aperture size. This affects brightness while lowering the depth of the field of view. The angular resolution (theta min) gets better as the size of the aperture increased due to the lowering of diffraction.

Lens Camera

The lens-based camera produced the sharpest and brightest image. This is due to the amount of light allowed through by the aperture, combined with the focusing properties of the convex lens, which creates a clear and focused image. However, after the fact, I realized I had forgotten to measure the size of my subject while testing the lens camera. I know I was standing about 1.5 meters away from my TV, which was capturing all four corners of the screen. The TV is 55 inches, and the average height of such devices is around 73 cm. As seen in the calculation above, we can use the relationship between focal length and the image plane to estimate the size of the TV in the image. Using this relationship, we estimate the image size to be around 75 cm (see calculation above).

This document has successfully outlined how to make three different sizes of cameras using the same basic principles. First, a large pinhole camera was built to demonstrate the basic concept of how pinhole size affects image quality and exposure. By adjusting the aperture size in relation to the focal length (or box length), the resulting image sharpness and brightness can be controlled. Next, a smaller version was created, illustrating how scaling down the camera and pinhole's size impacts the overall functionality and image formation. Finally, was the development of the lens based camera. The lense camera proved that the size of the subject and focus distance is directly proportional to the size of the image plane and focal length. Through these examples, the fundamental relationship between aperture size, focal length, and image quality was clearly demonstrated, allowing for a deeper understanding of the physics behind pinhole cameras.