This probably belongs in a tutorial of some sort but I think that it should have some critiquing first and I also don’t have authority to create new articles so let me know what you think.
Understanding Depth of Field
Depth of fieldFocal Length
is the range of distance, in front and behind the exact plane of focus that appears acceptably sharp
. Note that depth of field
is our perception of acceptably sharp
not what is exactly focused. Depth of field
does not change abruptly from sharp
to blurred but transitions gradually as the distance increases in front of and behind the focal plane.
There are a lot of aspects that affect depth of field
including: focal length of the lens
setting, distance to focused object and the size of the print or viewing media. (The bigger the photo the more noticeable are the effects of depth of field
To achieve optimum performance, a modern photographic lens
has many elements. If these elements were to be replaced with a single lens
to give the same magnification, the focal length would be the distance from the centre of that single lens
(focused at infinity) to the focal plane where the film or sensor is located.
The longer the focal length the more depth of field
will have an effect on the outcome.
Distance to the Object
If the objects of focus are at a considerable distance (like on the horizon) the depth of field
is considerable. For example: a mountain in the background and a tree in the foreground some thirty metres away. Both objects would appear pretty much in focus. But say we focus on a flower only 300mm away from the camera; the effect of depth of field
becomes very apparent.
Aperture or “f stop”
is essentially the size of the hole that lets the light
in through the lens
and into the camera to enable the photo to be taken. The “f” number if determined by the focal length divided by the size of the opening.
The larger the aperture
(smaller “f number”) the tighter depth of field
and the more blurred unfocused objects will appear. The smaller the aperture
(larger “f number”) the greater depth of field
and the less blurred unfocused objects will appear.
is usually the most accessible attribute that can adjusted quick and easily to change the depth of field
, however it should be noted that reducing the aperture
(increasing the “f number”) will also reduce the amount of light
entering the camera, therefore more time will be required to obtain the same amount of light
to expose your film or sensor: increasing your “f number” will reduce your shutter speed
The Cooperative Dragonfly
Macro photography is greatly affected by depth of field
. Below are a number of photos taken of a dragonfly that was most cooperative as it stayed still long enough for me to take a few photos with different aperture
settings. All photos are taken with a Canon
100mm macro lens
Using Depth of Field to Your Advantage
Having the background out of focus so that the object stands out can add a three dimensional aspect to the photo, so use this to your advantage. Also annoying objects in the foreground can almost be removed with good placement of the camera and use of depth of field
. Say for example birds in a cage. If you push the lens
right up to the cage, block most of the light
that would illuminate the bars in front of the lens
and select a suitable aperture
size, the bars of the cage will disappear.
Most modern SLR cameras have a depth of field
preview button which will show you what the depth of field
will be like before you take the photo. Your homework is to read the manual for your particular camera find the depth of field
preview button and learn how to use it well.
Below are a number of photos taken of a test sheet that was printed and laid on the table and photographed at a steep angle to demonstrate the effects of different aperture
settings on depth of field
. All photos are taken with a Canon
100mm macro lens
If you would like try this out for yourself, a "PDF" version of the test sheet can be obtained from:
"Future link to pdf file"