Depth of field and aperture selection question.

[s_erez]

Hi,
I am relatively new to digital photography and I have a question related to aperture selection.
I am familiar with the theory behind the depth of field, the larger the aperture the more of a shallow depth of field and vice verse.
This is very simple to understand, however my question is how do you know which aperture to use for a specific situation?
I know about the depth of field button on the camera, but I could never see what my picture will come out when I used it.
Any techniques or tricks I could learn and use?
Thanks,
Erez.

[Mtik]

You just have to get a "feel" for DOF. Generally, if I want a shallow DOF I'll try to shoot wide open. However, lenses don't usually perform thier best wide open.

If I want a super crisp shot with a shallow DOF, I'll shoot 2 to 3 stops down.

The DOF preview button lets you see ( sorta ) what will be in focus at the chosen DOF. It's hard to see because it's pretty dark, but you can do it as long as your aperture is relatively large and you're taking a picture of a well lit subject.

You also have to take into consideration what you're shooting at. If I'm taking a landscape shot with almost no foreground, I don't need to stop way down ( everything in the picture will be at the same "plane" ). If I really want the foreground and background to be in focus, I'm forced to stop way down. However, just like shooting wide open, shooting too far stopped down will degrade IQ. It's all a game of give and take.

-Tim

[Gromguitar4]

One thing that I was told once is that the shallower the depth of field (Smaller the f# like 2.8) then it will be harder to catch moving subjects in focus. I just want to know everyone elses thoughts on that and I hope that helps you Erez

[henryscat]

With a shallow DOF you have more of a chance for a blurry photo due to the small margin of error that it allows. However if you are capturing a moving object then you will need a small aperture to get the shutter speed higher.

DOF is definitely a "feel" thing as stated above. Only with trial and error will you get to a 2nd nature stage.

As a rule, portraits and action shots should in general have a shallow DOF to throw the background out of focus and make your subject stand out.

[Nicole]

One thing that I was told once is that the shallower the depth of field (Smaller the f# like 2.8) then it will be harder to catch moving subjects in focus.

I guess that this makes sense in theory, but in reality, I've had quite good luck catching action at large apertures (low f/stops). I photographed some dancers at a Diwali festival, and shot the whole thing around f/2.2. I found that as long as I was tracking the person that was moving I was able to get most of them in focus aside from some lovely capture of movement.

[Fraggleroxer]

i think one thing that is offten overlooked is your focal range. if you are shooting at your longest focal range lets say 200 on a 70-200 lens, you will get less DOF then if you were shooting at the 70 end.

[AZ4Runner]

There are basically three primary things that affect DOF.

1. Aperture selection
2. Focal range
3. Distance to subject

Large apertures (1.8, 2.8, 4), plus long focal distances, and close targets will yield the shallowest DOF.

Small apertures, wide angle focal lengths, and distant targets will yield the greatest DOF.

Understanding which aperture you want to use is really more about what are you trying to show in your images? Are you trying to draw focus to a specific subject, are you trying to show that subject as a part of a group or part of its surrounding? Bryan Peterson's discussion on creatively correct exposures in his work entitled "Understanding Exposure" will give you some guidelines to follow when trying to decide "what aperture" do I want to use here.

Since this is the digital photography forums, I presume you're shooting digital. Which gives you the option of taking several frames at different settings to figure out which are best for you and what you're trying to accomplish with your image.