1. PW2 - Reflection
02 – Pinhole Cameras

2. History The pinhole camera idea has been around for over 1000 years.
As early as the 16th century, people were using this device to create permanent images on a sort of photographic paper. These were the first pictures.
Scientists who studied optics and other philosophers were aware of a certain phenomenon with light and a pinhole creating an image.

3. History
pinhole
object
image
The image on the other side of the pinhole appeared upside down and most often smaller than the object itself. Why? 
Light travels in straight lines, it reflects off of an object and only those certain rays that are in a direct path to the pinhole make it through. They do not bend, they are straight

4. Explanation do - is the distance of the object (from the pinhole)
di - is the distance of the image (from the pinhole)
ho - is the height of the object
hi - is the height of the image

5. Explanation
Just by geometry we can see that light reflecting from the bottom of the object will pass through the hole and end up at the top of the screen.
The light reflecting off of the top of the object will pass through the hole and hit the bottom of the screen
What results is an INVERTED image
Note the arrow for the “object” is pointing up and the arrow for image is pointing down

6. Formula
Drawing ray lines (red lines above) results in similar triangles, so we get:
This is known as the magnification formula which is simply written as:

7. Magnification
Magnification tells us if an image in a pinhole camera is the same size, smaller, or larger than an object. Magnification is calculated by:
Magnification, M, has NO UNITS (yaay )
By calculating M, we discover that when:
M = 1, image is same size as object M > 1, image is larger M < 1, image is smaller

8. Example
What is the height of an image if an object 8.0cm high is 125 cm from a pinhole camera that is 21 cm long?
di = 21cm
do = 125cm
ho = 8.0cm
hi = ?
hi = di ho do
hi = (21cm) (8.0cm)
(125cm)
hi = 1.3cm

9. Example Continued What is the magnification from the previous example?
Note: if possible, use info that is KNOWN to calculate this up.
Use di/do since both of those values are known
M = di/do
M = 21cm/125cm
M = 0.17
By using info that is known, there is less error in your final answer. If we had used hi/ho, the answer should be identical, but it is slightly different due to the rounding of it when it was calculated
M = hi/ho
M = 1.3cm/8.0cm
M = 0.16