Photography - Depth of Field

I know you've heard this term, and it's referring to what is in focus in the photo. Think of a parallel "plane" to your camera lens. This "plane" is what is in focus and any area before it and any area behind it is out of focus. With a 50mm lens as wide open as it can go, you get that lovely creamy blurred background (bokeh) and your subject is nice and sharp and really stands out.

That's the theory anyway.

But, if you are anything like me, then most likely you have MORE out of focus than you'd like! It's a pain, and "fixing" it might mean being a LOT steadier than you think. It could also mean that if you focus then recompose, then the recomposition shifted the plane of focus just enough so that what you thought would be in focus is now out of focus.

ONLINE DEPTH OF FIELD CALCULATOR

Open that link in a separate window, so that you can refer to it and this post at the same time. :) I'm going to show you something that totally shocked me when I first saw it.

Select your camera type - for this experiment, I'm choosing the Canon 30D as that is what I shot with while on Vacation this past week. Then I'm going to select the 50mm lens (focal length is 50mm) as I shot with it quite a bit, especially in lower light conditions as I was able to open it up VERY wide allowing better chance of not using a flash indoors. If you are using a lens that states 18-55mm, then you will need to choose which focal length you are shooting at.

I'm selecting the f-stop of 1.8 as that is as wide open as I shot on vacation. Now, the tricky part? Select how far away the subject of what you are focusing on is from the camera.

If you are taking a close up photo of a child's face, you are probably 3-5 feet away. Select one of those. I chose 5 feet.

Off to the right there are near and far distances. That is the DEPTH of what is going to be in focus. In my case, it was 0.2 feet. Do you know how much that is? That's 2.4 inches. But, honestly, 5 feet away didn't fill the entire frame with the child's face, it was more a head and shoulders shot. Did the child wiggle when you took the photo? Did you focus and recompose? You only have a total of 2.4 inches of "wiggle" room to keep the child's eyes in focus!

Now, for filling the frame? Well, most likely I'm 3 feet or closer. How much room do I have at 3 feet away? 0.07 feet, or 0.84 inches. LESS THAN ONE INCH! You must be incredibly steady here to keep eyes in focus.

Now, lets see what happens if you have a 70-200mm lens and are shooting at f/4.0? Say we're 5feet away, 200mm focal length and f/4.0: YIKES, a 0.03 feet depth of field, that's really narrow (and you are REALLY close to a child to be using this focal length, the frame most likely only has a single eye in it! LOL)

With a 200mm lens at 4.0, I'm typically shooting across a baseball field, so let's say 25 feet away. This would give me .71 feet, or almost 12 inches! When shooting sports, that's not a whole lot, but the creamy dreamy background is worth it.

I recommend, if you are having trouble with parts of an image out of focus using a specific lens fully open, consult this online depth of field calculator...it might be that the area in focus is too narrow for the squirminess of your subject, your focus recompose, and your own steadiness.


This image was taken on the TTA, and Samuel was sitting across and diagonal from me so about 3-4 feet away. The info is ISO100 (bright sunny day), 50mm lens, f/3.5, and SS of 1/60 (shade area). I had 0.19 feet in focus - I focused on his eyes, and if you notice his nose and mouth are fully in focus as well. The ears are slightly out of focus (right click on it and open it up in another window to see it larger). the top front of his hair is in focus, the back is not. Notice his arm and the ride seat behind him are nice and blurred.


Now this one was shot indoors at the Living Seas with Nemo and Friends. ISO3200, 50mm lens again, f/1.8, shutter was 1/500 (yes I could have lowered the ISO or changed the aperture). I remember being about 4 feet away. Open in another window just the image - you will see that the black of the ears is not in focus, but that the back of the head is. It was not perfect, and were I doing this for a client's portrait I would have probably changed the aperture to 3.2 or 4.0 so ensure more of the head was in focus. I was more about not using flash, and this particular location has a well lit area.

I know many photographers who can successfully shoot sessions of children wide open on 1.4. I am not nearly steady enough for this, so I mostly shoot all my photos around 2.8-4.0. However, I'm aware of the DOF and how narrow my area of focus is if I want to do a particular shot that is in my head. Using a very narrow depth of field is useful in bringing attention to a particular subject (think of a child holding a sea shell, or a child holding a red envelope at Chinese New year, or what about a newly engaged couple and the ring, etc.). Where as, there is also a time for shooting with narrower apertures, of like f/11 or f/16. Think of the large family groups, or what if you wanted to have an entire sand castle creation in focus with the creator right beside it?