UofT ECE516 Pinhole Camera

Pinhole camera report

Chuanzhi Li/ imadeaccount：lichuanzhi05

1010822273

1 introduction

In this lab, the experiment will be performed to help understand the basic theory of pinhole cameras. The pinhole size can be calculated based on the formula, and the image of the best pinhole size will be used to compare with the none-optimal one to evaluate the functionality. Two pinhole cameras will be designed and made to determine if the large camera provides a better image.

2 Ideal Pinhole size

The basic principle of pinhole cameras is using the pinhole to limit the light that goes into the camera, catching a point of view of each point of the object. So there is a contract image catched in the screen, shown in Figure 1. The size of the pinhole decides the clarity of reflection: Figure 2, the big pinhole brings large but fuzzy reflection. So the pinhole should be small for better clarity. However, another view of light showing a small hole will cause diffraction that makes the light fuzzier, so the Optimal pinhole size is a balance of these two facts. According to material:

d=c √(fλ)

where

d = optimal hole (aperture) diameter;

f = focal length (distance from aperture to image plane);

λ= wavelength of light, e.g. pick something around the middle of the range of human vision such as green = 550nm (which is also the wavelength to which human vision is most sensitive), or to which your sensor or film is most sensitive;

c = 1.56 according to Kjell Carlsson(2004)

Figure 1: Principle of pinhole camera Figure 2: Different pinhole size

Camera optimal pinhole size selection:

The focal length of a big camera is 50 cm while for a small camera is 10 cm.

Camera design

A pinhole camera should have a box with thick or special material to block the light out. It also needs a black inside to maximally reduce the reflection light inside. Both these two requirements mean to filter the light noise inside the box. The opposite side of the pinhole designed a white paper for both big and small cameras to catch the image. And I opened a side hole enough to fit my phone to take pictures.

The size of captured image follow the formula:

Small camera:

The small camera used a Garbage bag packing box from dollarama. The inside has been painted black using dark color. The box is thin so the outside is using tin foil to prevent unexpected light sources. A half paper tube used to extend the focal length.

The optimal pinhole for a small camera failed to achieve.

Big camera:

The big camera used a big packing box from T&T. The inside was also painted dark. A cap used tin foil plus black paper. The wall is thick enough so no extra block is required.

Experiment:

The first experiment is using two cameras to catch the view outside my room's windows. Each of them takes pictures with a different pinhole.

The view outside my window

Shot by small camera with 1 mm pinhole

shot by small camera with 2 mm pinhole with lens

shot by big camera with 3mm pinhole with lens

shot by big camera with 1.5mm pinhole

shot by big camera with 1.5mm pinhole and lens with lens

Here is some discussion on the result:

1. The pictures from the big camera all get adjusted(exposed by the phone image editor) or are hard to observe. The light(brightness) should be more than the small camera, but the picture is darker. The light separates in the large screen.
2. The orientation of the image is reversed up-down and left-right
3. The result shows the small pinhole size does provide a better resolution.
4. Cannot test the deflection due to the pinhole which is smaller than the optimal pinhole(even the optimal pinhole itself) did not bring enough light, so the picture is dark. Which also proves that the bigger ping hole brings more light.
5. The lens reduced the resolution somehow. It also brings more scope of view to the screen.
6. The best picture is the big camera with a 1.5mm pinhole, So the big camera seems to bring a better picture.

Base on the idea professor shown in the lecture. Lens Camera require a just distance for the forcal lenth. So I modify the large camera from the reflection catch to the transmission catch that I can control the distance easier. The image cathcer using a toilet paper from Uoft which is white and thin. Here is a video to show the lens camera functionality.

As We can obeserve, even with a large hole(way more brightness than the camera without lens), the lens camera can still produce a clear picture.