• Office hours are posted on the website.– Molly: Tuesdays 2-4pm– Dr. Keister: Wednesdays 10am-12– Prof. Goldman: Wednesdays 2-3:30pm

• All office hours are in the help room downstairs.

• I have unclaimed homework at the front.

Homework Policies

• Homework is due at the beginning of class. It will be collected 15-20 minutes after the start of class.

• Homework will be accepted until the end of class, with points deducted for lateness.

• No homework is accepted after class is over, because the solutions are posted on the website.

Exam 1!

• First exam is next Thursday, October 4th. • It will be in class. • It will cover chapters 1-3.• There is no homework due next week.

• We will try to post a practice exam this week. Check the website.

Chapter 4: Cameras and Photography

• Pinhole Camera– Review image formation– Focusing

• Lens-based Cameras– Essential parts– Focusing the image– Depth of focus– Depth of field

• Types of cameras– View camera– Single lens reflex– Rangefinder

Pinhole Cameras

Light rays from each point on the object reach one point on the screen, and no rays from other points on the object reach that same point on the screen.This produces a focused image.

Pinhole camera

Image

Object

Clicker Question

• Which camera will produce the smallest image of the light bulb?

• A• B• C• D, they are the same size

A

B

C

Clicker Question

• Which camera will produce the smallest image of the light bulb?

• A• B• C• D, they are the same size

A

B

C

Pinhole Cameras

Remember that the object does not have to be self-luminous. The rays reflected from a light source will also enter the pinhole and can image the object.

Pinhole camera

Image

Object

Pinhole Camera

blurryimage

Object

If we increase the size of the hole in a pinhole camera, we get more light, but the image gets blurry, because rays from each point on the object hit more than one spot on the screen, and rays from more than one point on the object reach the same spot on the screen

Camera with LensObject

Adding a lens bends the rays so that rays from each point on the object reach only one point on the screen, and no rays from other points on the object reach that point. This produces a focused image on the screen.

Image

Image Size and Zoom

To produce a larger image with a pinhole camera, you can either decrease the distance from the object to the camera, or increase the distance from the pinhole to the back screen of the camera. The image stays in focus because only one ray from each point on the object gets through the pinhole and reaches the screen

Camera with Lens: Zoom

Just increasing the distance between the lens and the back of the camera does not increase the size of the image. The image no longer focuses on the back of the camera.

Camera with Lens: Zoom

To produce a larger image, in focus, with a camera that has a lens, you have to both move the position of the screen and change the focal length of the lens.

FocusingAs we’ve seen, objects at different distances from a lens will result in focused images at different distances behind the lens.

This means that a camera has to allow the lens to move so that the image will be focused to the plane of the film for different object distances.

Essential Parts of a Camera

lens

shutter

diaphragmfilm or screen

The components are all mounted in a light-tight box. The bellows allow the photographer to change the distance between the film and the lens.

Focusing

• We have thus far been drawing lens diagrams as if the lens focuses to exactly one spot.

• In reality, film and digital sensors have limitations that prevent them from recording a perfectly focused image.

• In addition, there is some amount of blurring that is not detectable even by your eyes.

• Thus there will be a range of image locations that will be acceptably focused.

Depth of FocusIn a pinhole camera, the object is in focus at any plane behind the pinhole. This is an infinite depth of focus

size of acceptable blur

depth of focus

Depth of Focus

If we reduce the size of the lens, but do not change the focal length, the depth of focus that generates the same size blur becomes larger.

depth of focus

depth of focus

Depth of Field

Depth of field refers to the range of object distances that will produce an acceptably focused image at a given film positionIt is a measure of how far apart two objects can be and still both be in reasonable focus on the film

depth of field

size of acceptable blur

Depth of Field: Object Distance

As the distance to the objects increases, the depth of field increases. Here the two objects are farther apart than before, but they focus to almost the same film position.

Finding Focusing Distance• A camera is focused by changing the distance between the lens

and the film or CCD at the back of the camera• Let’s say our camera has a lens with focal length 1 cm.

• We want to take a picture of a friend 100 cm from the camera. Where should we put the film?

• Note that the image distance is very close to the focal length. This is because the object distance is much larger than the focal length

• What if we are looking at a flower 5 cm from the camera?

Camera Examples: View Camera

Camera Examples

Some old cameras did not have an adjustable diaphragm, and could only be used in bright outdoor conditions

Camera Examples

Rangefinder and Viewfinder Cameras

Single-lens Reflex (SLR)

Point-and-Shoot Digital