The Field is Pretty Deep

What is Depth of Field?

Depth of field is the distance in front of and beyond the subject that is in focus. The main influences on depth of field are camera type, aperture, and focusing distance. Depth of field is a gradual transition- things further from the focus point get more and more out of focus. To understand this transition from in-focus to out of focus, you have to understand the "circle of confusion". This term is used to define how much a point needs to be blurred to be perceived as out of focus. When the circle of confusion is perceptable to human eyes, the point is no longer "acceptably sharp." Larger apertures/smaller f-numbers give you a shallower depth of field, meaning a more select portion of the frame is in focus. The opposite is also true.


This picture has a fairly shallow depth of field, so only one pool ball is in focus.



This picture has a much larger depth of field, so almost everything in the frame is in sharp focus.


Besides changing aperture to change your depth of field, you can also use the hyperfocal distance to make your pictures sharper. The hyperfocal distance is the point where the image is sharp (anything in front of it is out of focus) when your aperture is set to infinity. To make up for this you can aim at the hyperfocal distance, which will make everything in front of the point sharp too.


This is an example of how to use hyperfocal distance to create a sharper image.

How Can I Control Depth of Field?

1. Adjusting The Aperture.
Like I mentioned, having a smaller f-number means you have a shallower depth of field- less of your photo will be in focus. Also, the larger the f-number you use, the greater depth of field, and the more of the image will be sharp. When stopping down, if you use too small of an f-number, you can lose quality, so make sure you only stop down as far as is necessary. Also, the smaller the aperture, the longer exposure you'll need, so a tripod is helpful for this type of shot.

These three pictures show the same photo with a wide aperture, a medium aperture, and a narrow aperture, resp.



2. Focal Length.
The longer the focal length of your lens is, the shallower depth of field you'll get. If you use a 30 mm lens, everything will probably be fairly sharp. If you were to use a zoom lens of 135 mm, your depth of field is cut, and the background will be much more out of focus. And if you use an even more powerful telephoto lens, say 300 mm, the background will be almost completely blurred. The longer the focal length of your lens, the more dramatically the background will be blurred.

Here is the same photo, taken with a 35 mm lens, a 135 mm lens, and a 300 mm lens, resp.

3. Focus Distance.
The easiest way to control depth of field-- where you are in relation to your subject. The closer you are to the subject, the narrower depth of field any lens or aperture will give you. This is especially dramatic when shooting macro, when subjects are greatly magnified and also very close to the lens. So if you want to get a sharp picture of a landscape, you'll have greater depth of field the further away you are. If you want to take a picture of someone's eye, blurring out everything else, your best bet will to get up close and personal with your model!


Here is the same image, focusing on the background, the middle ground, and the foreground, resp.

(4.) Camera Sensor Size
When you're choosing sensor size, your major choices are 35mm, medium format, and large format sensors. (Camera sensors, as we learned about earlier, are grids with millions of pixels that catch light to create an image.) As sensor size increases, depth of field for a givin aperture will decrease. This happens because larger sensors require you to get closer to your subject, or use a longer focal length (zoom in) to fill the frame. Because of this, you have to use smaller aperture sizes to maintain the same depth of field on a larger sensor.