Saturday, January 28, 2012

Depth of Field

I thought it was time to revisit "The Wizard" for a little Depth of Field wisdom:

There are four major factors that affect depth of field: 1) Lens aperture (f stops); 2) focal length of the lens; 3) the distance from the subject to the camera; and 4) the distance from the subject to the background.

You'll see only the effect of three of the factors affecting depth of field, because I never changed the distance of the subjects to the background.

So! Here's my trusty 50mm 1.4 lens, Dorothy (no, Glinda! First, I wrote "Dorothy", but someone corrected me and of course, this is Glinda!), The Tin Man, The Scarecrow and the Lion. Glinda is the focal point. The background is a DVD case and the ugly base of a poinsetta (a pretty poinsetta, but not the foil around the pot), and some random yellow flowers.

f/2.8 50mm
In the photo above, you can see that a large aperture produces less depth of field. Remember, f values like 1.4, 2.8, etc., mean large aperatures relative to f values like 11, 16, 22, etc., which produce more depth of field. The greater the depth of field, the more of the background that is in focus. Including ugly, cluttered backgrounds.

f/5.6 50mm

f/11 50mm
The photo above has a smaller aperture, or opening, with an f value of 11, than the first photo with the f value of 2.8. And now Glinda has to share the spotlight more with her buddies, the Scarecrow, The Lion and the Tin Man. How annoying is that? Let's dump them with a large aperture again, and a lens with a longer focal length.  Larger aperture = shallower depth of field.

This next set of photos shown were taken using the 85 mm 1.8 lens. Obviously, 85 mm is a longer focal length than the 50 mm lens. Wide angle lenses have more depth of field than longer lenses. Compare this next photo, at f/2.8, with the first 50 mm photo above, also at f/2.8. Longer focal length = shallower depth of field.

Oh, that Glinda! She's just about completely ditched the Lion and Tin Man, and all that you can see of the Scarecrow now is a blur of his elbow. (The Scarecrow is missing primarily because of the much more narrow angle of the 85mm lens than that of the 50mm, but it's the shallow depth of field that booted his buddies.

f/2.8 85mm

f/5.6 85mm

And by f/11, the Tin Man and Lion are making more of an appearance again.
f/11 85mm

Now look at this next set of photos, using my 70-300mm lens, set at 200mm. I had to move the tripod further away from the subjects for these photos, in part because there was no way I could get the camera to focus on this subjects while staying as close to the figures as I was with the 50mm or 85mm lens.

And the 3rd factor affecting depth of field is distance from the subject to the camera, so these next two photos are introducing two variables: the long focal length of the lens (less depth of field), and greater distance from the subject (more depth of field).  The closer you are to the subject = shallower depth of field.

If I had been able to keep the distance the same as the f/5.6 50mm, and the f/5.6 85 mm above, you would have seen even more pronounced blurring of the background in this 200mm photo:
f/5.3 200mm

Even at f/11, with the 200mm lens, look how creamy the background continues to be. Now imagine the possibilities of shooting outside using a longer focal length, keeping your subject at least 10 feet from a background, and you being as close as you can to your subject.  The further the subject is from the background = greater blurring of background (which can be quite useful in isolating your subject as the focus of a photo).

(Personally, I'm not going outside until it's significantly warmer!)

f/11 200mm
And because we all know that the Wizard used smoke and mirrors, if you have any additional bits of information about depth of field that you'd like to add in the comments, please do so!
And here's a helpful DOF link:
PS (I wish I had Dorothy!)

And a link for a  DOF calculator

And a video tutorial


Nicki said...

Excellent illustration of DOF with different lenses.

Jill/Twipply Skwood said...

Very nice!

Anonymous said...

That's not Dorothy.

Angela2932 said...

OMG! You're right! Of course, it's Glinda!

pat said...

Brilliant! Love this--you've made good use of your time!

Stephanie said...

very good tutorial....but more important very entertaining!

Iowa Sunshine said...

thank you for sharing your time with this tutorial!!! the characters were a hoot :)

Tracie Gibbs said...

Good tutorial from one of my all time favorite movies!

Beth said...

Nicely done!