Understanding Depth of Field

Understanding Depth of Field is important, this video by Dylan Bennett gives you a good overview of what it is, how it works and how to control it.

Example of Shallow Depth of Field. Photo by Stephen Heron
Example of Wide Depth of Field. Photo by John Bruckman

Depth of Field and The Circle of Confusion

depth of field
Depth of field is the distance in focus on either side of the focal point - by Ben Frantz Dale

Understanding Depth of Field, or DoF, is one of those topics in photography that may not be as intuitive as it may seem.

Most people grasp the concept that the wider your lenses aperture is open, which translates to a lower f-stop number, the less distance is in focus on either side of the focal point. The narrower your lens aperture, which is a higher f-stop value, the greater the distance in focus on either side of the focal point.

That’s the simple explanation, it gets more complicated from there. The reality is the focal distance on either side of the focal point is not a clarity cliff that stays sharp until you hit the edge and suddenly falls off. DoF is actually a continuum where the focus gradually falls off to the point it’s visible with the human eye. There’s no critical point in transition, until you can see it.

depth of field
The effect of a smaller aperture on depth of field, the smaller the aperture, the greater the DoF - by Chabacano

There’s even a term for that nebulous spot, caused by the light rays not coming into perfect focus, it’s called the “circle of confusion”, also known as the disk of confusion, and the blur spot.

The standard to determine an acceptably sharp circle of confusion is the distance a single point becomes so out of focus it’s noticeable on a standard 8×10 inch print viewed at a distance of 1 foot.

The circle of confusion changes not only at every f-stop, but it also changes with the lens focal length (how far it’s zoomed) as well. At smaller focal lengths, the DoF tends to increase, all other factors staying equal. Another factor is the distance to the focal point, how far away the subject is.

As you can see there’s a lot of subjective observation in that standard and, indeed, human eye perception is much finer than the standard lens manufacturers use. If that isn’t confusing enough, the circle of confusion is different for every print size and viewing distance. So take the DoF marks on your lens with a grain of salt and understand that near the outside edge, you likely see the difference.

To bring this around to some practical application, if you need depth of field, a good rule of thumb is to use the aperture priority mode on your camera and use at least f/8 or f/11. In most lenses the circle of confusion falls off quickly at f/5.6 or lower. If you’re shooting for bokeh, deliberately throwing the background out of focus, you’ll be shooting at f/5.6 or below.

Ironically filmmakers were drawn to fast lenses for the very capability of throwing the background out of focus! It’s not just still photography where the subject comes up.

DoF is another one of those subjects where it’s important to experiment on your own equipment and understand where your lenses fall in the circle of confusion. Don’t trust the factory marks, get out there and shoot some samples.

There’s no substitute for gaining an intuitive grasp of your lenses DoF and the only way you can do that is get out and practice.  Every lens will be different.  This should be a ritual the first time you get a new lens.

Bokeh Demystified

bokeh explained
A good example of bokeh - by Angel mat-eye

Bokeh is the Japanese word for “blur” and can lead to some common misconceptions about the effect. I’ve heard bokeh explained as, “Just a blurry background.” It’s tough to bite back the annoyance that arises at such a simplification. A Rembrandt is not just a pretty painting and bokeh is more than blur.

More specifically, bokeh is a highly stylized background created by selectively blurring parts of the picture in a way that highlights the subject. Not merely a blurred background, but one that pops with colors and patterns.  Good bokeh doesn’t always require a subject, sometimes just the pattern of lights without a subject is just as appealing.

You don’t need special equipment to achieve bokeh, but it helps to have a fast lens, like the Nikkor 50mm f/1.4 and a selection of ND (Neutral Density) filters. Those help achieve the lower f-stops you’ll need and they’re also handy for shooting video where you have less latitude in shutter speed selection. You don’t have to use ND filters, you can also experiment with your camera’s Aperture Priority mode (the “A” setting on Nikon, “Av” on Canon) and let the camera set the exposure, but I like the results with ND filters a little better and I can still lock a subject in motion.

For the inspirational bokeh, look for sunlight filtered through leaves and foliage or bright pinpoints of light in the background.

Get as much separation as you can between your subject and the background.

As far as I know there are few cameras with an “auto bokeh” setting, so you’ll want to use the widest aperture (lowest f-stop) your lens can achieve.

If you need fill flash, you’ll be limited to flash sync shutter speeds, which may or may not yield the desired f-stop. Times like these is when you may want your neutral density filters.

You can also cheat and get a similar effect in post-processing with Photoshop or GIMP, but I like getting the best possible results in the cameras and save the time in post.

Lytro cameras lets you focus after you have taken the photo

Lytro, a new camera start up, is trying to make the biggest change in the photography world since the 1800s. Instead of taking a traditional photo that just captures one plane of light their camera captures the entire light field in one shot, this allows you to adjust the focus after a photo is taken. The camera is built on research from the mid-1990s called light field technology, where 100 cameras were required in the same room to produce the same type of photo, Lytro is able to recreate that effect and fit it into your pocket.

The Lytro camera uses a microlens array sensor which captures more light data, from many different angles. Then that data if sent through powerful software that allows you to switch the focus point. In addition the camera is much faster than traditional cameras, there is no shutter lag or autofocusing device, this allows you to take photos faster.
(click the image to set your focus point)

The camera also gives you the feeling of 3D, by reorienting a photo after it is taken. You are also able to take photos in much lower light than regular cameras. When you take a traditional photo you have one opportunity to set the depth of field, while light field camera takes a lot of photos from different locations and angle which allows it to produce this type of image.

The company has raised $50 million to bring their new light field camera to the market. There is a big risk that this might be too much innovation and that consumers will not buy the camera if the price is too high. There is no word on how much the camera will sell for, but they say it will be priced for the “Consumer market” and should be out by the end of the year.

What do you think, is this just a neat feature, or the next innovation in cameras?

(Via NYT and TechCrunch)

Low light and shallow depth of field Canon S90 photos

Canon Powershot S90
The Powershot S90 from Canon is what we call a pro-digicam, its a compact point and shoot with full manual controls, and high end features like a wide f/2.0 aperture, and a large sensor great for high iso low light shooting.

Following are some photos that caught my eye, especially since they were taken with a tiny point and shoot rather than a big DSLR.

'Ghosts' by alexbrn, showing a pattern of light from stained glass
  • f/3.5
  • 28mm
  • 1/100s
  • 80 ISO

Ghosts by alexbrn. The color and light in this photo are really unique, nice eye to catch that.

'Heaven' by aurelien, concert photo
  • f/2.8
  • 35mm
  • 1/40s
  • 500 ISO

Heaven by aurélien. Concerts present a challenge because they’re so dark, but the lighting is also an opportunity for photos like this. The photographer took the shot at 1/40s (almost as slow as you’d want to go hand-held), risking blur, and even with a slow shutter speed like that needed to use a relatively wide aperture of f/2.8 and higher than normal ISO of 500 to get a good exposure.

'New Grassn' by koocbor, great example of shallow depth of field
  • f/2.0
  • 28mm
  • 1/320s
  • 80 ISO

New Grass by koocbor. Notice how only the grass in the front is in focus, and everything in the background is blurred. The photographer achieved this narrow depth of field using two techniques: a wide aperture of f/2.0 (only available on a few cameras), and by getting close to his subject while keeping the background distant.

'Escalator' by tetradtx, a low-light wide-angle photo
  • f/2.0
  • 28mm
  • 1/30s
  • 200 ISO

Escalator by tetradtx. The perspective in this photo really draws you in. Again, another low light shot, taken without a flash. The photographer used a wide aperture again of f/2.0, and a slow shutter speed of 1/30s to get a good exposure. The photo is very sharp, impressive if they didn’t use a tripod. The shot was taken at 28mm, which although isn’t as wide as some cameras is still fairly wide and is responsible for creating the wide-angle perspective you see.

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