Depth of field - the simple explanation....

Thread starter #1

rip18

Senior Member
What do we mean when we say "Nice use of depth of field?"

Depth of field refers to that part of an image that is acceptably sharp focus. This usually ranges from some distance in front of the subject to some distance behind the subject.

We have two basic ways to control depth of field: 1) aperature or f/stop and 2) how far in front of the lens the subject is.

With smaller aperatures (larger f/stop numbers), we have more depth of field. For most lizards, snakes, etc., I like to use an aperature of f/11 or larger. For most landscapes, I like to use as small an aperature as I can (f/22 or f/25).

The closer a subject is to the lens, the shallower the depth of field. This is one reason that shooting macro is such a pain. There are really shallow depths of fields, which means you usually need LOTS of light so that you can use smaller aperatures. One reason we can get away with using f/2.8 or f/5.6 to take bird pictures is because the birds are further away from the lens than most lizard pictures for example. If I take a full frame picture of a Coke can with my 28 mm at f/5.6, it probably won't be sharp all the way through the can because I am so close to it, but if I take the same full frame picture of a Coke can with my 400 mm at f/5.6, it will likely be sharp all the way through - because I am further away & will have more depth of field.

Longer lenses don't have more depth of field inherently than shorter lenses at a given f/stop, it is just because we are further away from something...

So, how do we use these facts?

1. We use shallow depths of field (low f/stop numbers) to "hide" messy backgrounds. If we have a critter in front of a jumble of sticks, we can focus on the critter & use f/2.8 or 4.0 or 5.6 to "hide" some of the mess.

2. We can use deep depths of field to show two animals close togather (like this one: http://www.forum.gon.com/showthread.php?t=161620). Notice the use of f/8. Note that the near edge of the buck's leg is just a tad "soft" or out of focus and the far tree line is out of focus. Almost all of the two deer is in nice, sharp focus. If he had shot in program or automatic mode while focused on the doe, it is likely that the nearer buck would have been completely soft because the camera would have selected f/5.6.

3. Deep depths of field (high f/numbers) are nice for landscapes, particularly with wider angle lenses with a point of interest (flower, rock, tree) close to the subject. Here is another example of that:http://www.forum.gon.com/showthread.php?t=160024 . Note that a tripod is almost a necessity when using small aperatures (high f/numbers).

Here is a link to a depth of field table & depth of field calculator:

http://www.dofmaster.com/doftable.html

http://www.dofmaster.com/dofjs.html




There is also something called "hyperfocal distance" which is where the widest distance possible is in focus. To get the "best" depth of field, you may not want to choose f/22 and focus on your primary subject. You may want to focus elsewhere to get the "most" out of your image. I'm not even going to try to explain it because I don't understand it good enough to try to explain it, but here is a link: http://www.dofmaster.com/hyperfocal.html

Note that all of those pictures of bucks standing in front of a moon or ducks flying across a moon are either slide sandwiches or digital composites because there is not a lens made with enough depth of field to have both a sharp moon and a sharp something closer to the lens...
 

jason308

Senior Member
Great post Rip. This one needs to get in the techniques sticky.

Hoss
I'll second that.....Nice explanation and links Rip!!!
 

Smokey

Senior Member
Looks like that there Picture Taking Greenhorn has been asking questions again....geesh!!!:crazy: .....aint he supposed to be on the way to Tennessee to get his horse and go to a match:huh:
 
Thread starter #7

rip18

Senior Member
Thanks, y'all. Feel free to add to the discussion!

Okay, I took our recent discussion threads that were suggested to be made "sticky" and added links in the "Photo Tricks of the Trade" sticky that is already at the top.
 

Hoss

Moderator
Thanks for sticking em Rip. I was going to do that this evening when I had more time. If anyone hasn't visited this thread, it's worth the time to check it out.

http://forum.gon.com/showthread.php?t=20095

This thread was started some time ago. You'll see at the end, we've started putting links to informative threads in it. So if you've got some good stuff to discuss, start a thread and we'll get a link put in so it's always easy to find the thread.

Hoss
 

leo

Retired Woody's Mod 7/01-12/09
Another informative

explanation rip, thanks for sharing your knowledge with us :clap:
 
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