Lesson 8 - Photography course for kids

Focal Length and Depth of Field

photo taken by Aimee aged 15 years

​ From now on the photography lessons require a camera where you are able to change the F.Stops, shutter speeds, ISO's.
If your child does not have one they can still have fun taking the different types of photos in the challenges.


FOCAL LENGTH
Choice of lens dictates how much of a scene you are able to include in a photo.  
This is described in the terms of lens ‘focal length’.  These lengths are written on the side of the lens in millimeters, (mm).
Shorter focal lengths (wide angle lenses) give a wide angle view.
Longer focal lengths (telephoto lenses) give a long narrow view. 
 
Lens Focal Length
Lens Type
Possible Use

Less than 21mm
Extreme wide angle
Architecture

21-35mm
Wide angle
Landscape

35-70mm
Normal
Documentary

70-135mm
Medium Telephoto
Portraiture

135mm-300mm
Telephoto
Sports, Wildlife

 
 
     APERTURE

• The aperture in a camera is like an iris of an eye, widening and narrowing.
• The aperture settings are called ‘F stops’. The smaller the f stop number the larger the aperture opening is.
• Aperture settings will allow more or less light in your photo.
• Aperture setting will also alter the depth of field.  Depth of field is how much of the area from far to near that is in focus.

 
An easier way to remember F stop settings:
      
A big f.stop number means you want a big amount of the picture in focus.  You also need a larger amount of light (because the opening is small, need more light.  You may need to use a flash or a slower shutter speed).   

So Big F stop, Big area in focus, Big amount of light needed.                                      
 
A small f.stop means you want a small amount in focus, more blur around the subject. So Small F stop, Small area in focus, Small amount of light needed.
 

The smaller the F Stop, the bigger the aperture is opened, letting in more light, but also blurring more of the photo, (narrow depth of field).

APERTURE PRIORITY MODE
                                                                                                                                       
Some cameras have an AV or A setting. This is the aperture priority setting.  This lets you control the depth of field without you having to worry about the shutter speed, the camera will automatically take care of that.  You can focus on your depth of field and let the camera take care of the producing the correct exposure.
 
Remember also how distance can help your depth of field.  The further the distance between the subject and the background, the more blurred the background will be. The more you zoom in on a subject, the more blurred the background will be.
 
 
Depth of Field Photo Challenge:
 
Choose a subject to photograph.  A row of something, near to far works really well.
Take a photo with a big f stop number to keep most of the picture in focus.  
Then do a photo of the subject  using a small f stop number and see if you achieve more blur and a smaller amount in focus.
Use the distance rule too to create more background blur.

Photo by Madelyn aged 14. Using a small f stop. Notice the small amount in focus. A narrow depth of field.

Take note of the background flowers in these photos.  The first photo, the camera is set to f.stop 29.  The photo on the right is f.stop 4.5