Wednesday, January 27, 2010

An old school lesson on DOF and Hyperfocal Distance


I'm having a great time updating our Practical Approach Web site.
I can see I'll be adding to this for a quite a while — it's quite addicting. I'll keep you updated here as to when new entries are made as well as on Facebook.
Example of latest entry:

Focusing for depth of field in the 'old-days' wasn't just an option, it was the way we guaranteed success. If you needed three feet of focus, then that's what you did — you looked at your depth-of-field scale on your lens, adjusted your aperture correctly and simply 'dialed-in' three feet of focus distance. To check your focus area you pressed the depth-of-field preview button, made any adjustments necessary, and that was that. If your subjects were spread out further, you simply dialed-in what you needed (picked a smaller hole). And if you wanted max focus range (from a few feet to infinity) you simply figured out the hyperfocal distance, adjusted you lenses' focus-ring and shot accordingly. There was no trick to it, no secret spells cast and we didn't even use image stabilization to make sure our pictures were 'crisp' — not breathing and holding the camera steady seemed to work amazingly well for us back then. I guess the air is different today.

We did what was needed, because we knew it was needed. Depth-of-field control was an obvious necessity. We saw more than just subjects. We cared about more than just one thing. Today though things are different, these techniques have been lost and the words themselves belittled. After 25 years of auto focus people actually think they are shooting a picture of just one thing (always). They've become oblivious to the fact that depth of field can be controlled. The words and phrases listed above (depth of field, dialed-in, depth of field preview, scale, hyperfocal distance and even focus-ring) just don't click. The truth has been lost — apathy and ignorance have run amuck.

Many new photographers today sadly lean on smile recognition software, sensor types and editing programs. They listen to 'professional' digital photographers drone on and on about what camera and which lens work best. They lament the loss of image quality ... when they have no idea what the word 'quality' truly means.

Image 'quality' comes from the content of your message, not how many pixels your image is made of or what sensor is creating them. Remember, garbage is still garbage no matter how much of it you have or how 'clean' you can make it.

To see what's been lost and possibly find a reason to learn these terms and techniques, let's look at a few simple 'old-fashioned' lenses and how those 'old school' photographers saw the world and used those options, terms and techniques to guarantee success.

Reading an old-school depth of field scale

Lets begin by looking at the outside of a lens. This is one of my all time favorite lenses that is always with me. It's gotten some use as you can see but I can't imagine ever being without it. It's my 'go to' lens. It's a classic Nikon 28mm and it's as close to my heart as any piece of plastic with glass in it has ever been.

Near the bottom of the lens you can see some familiar numbers. The f/stops on this lens range from f/2 to f/22, although every conceivable aperture can be dialed-in by simply moving the aperture ring slightly between each number. This was an awesome feature on all lenses 'back in the day.'

Immediately above the f/numbers you'll see the depth of field scale (the multi-colored lines), as shown in the above image.

These lines are color coded as you can see. The colors on the scale match the various colors in which the apertures are painted.

In the center of the scale you'll see your current focus point, as represented by the single dot in the above image. This is the spot where you are currently focusing. You'll notice that it rests directly below the focus distance scale. This particular lens is currently focused at nearly two feet away.

As shown in the above image, the top line of the scale is in feet and the bottom is in meters. Don't get these mixed up.

To use the depth of field scale simple look at both vertical colored lines that represent the aperture you are using. The distance between the colored lines is your current depth of field. If you were to use the lens above at its current focus position, then at f/16 you would be able to get everything from 1.5 feet to nearly 3 feet in clear (acceptable) focus. Everything else will be usually be unacceptably blurry.

At f/22 our depth of field opens up a bit, allowing for more things to appear in focus.

Of course the 'appear in focus' is the key phrase here. At any given time, no matter which aperture, focal length or subject distance you've chosen — only one thing will be razor sharp (whatever you actually focused on.) Depth of Field is based on acceptable blur levels and that really is a personal thing. What you see with these guides is based on a shared human bias of acceptability. Your own version of 'acceptable blur' may (and probably will) vary from this scale. But at least it's a place to start.

Many newer lenses do not offer this seemingly important feature.

This above Nikon 'kit' lens does not have any depth of field information at all. It even lacks a focus distance scale. (It's called a 'kit' lens because it is one of the more popular lenses found when purchasing a camera and lens together ... in a camera 'kit.') As shown in the below images many other lenses have this scale, though it may appear different and may not offer as much information as you'd like.

Hyperfocal distance

If you were to set your focus point to infinity and have your aperture set to a smaller size (f22) you can see from the below lenses' distance scale that there is a considerable amount of focus distance beyond infinity. This focus depth (depth of field) is being wasted.

This is a pretty natural thing to do (to waste focus distance.) Since people shoot in auto focus and since their camera has to focus on something, then they are ALWAYS wasting focus depth. An artist though understands how to harness this power and use what lens designers termed hyperfocal distance. Notice on the distance scale above how the focus distance (depth of field) goes from about 5 feet to infinity and then beyond.

But what if we moved the focus point, as in the above photo. What if we simply refocused the lens without looking through it. What if we just moved the infinity marking to the outer edges of our depth of field scale. Now you are shooting at your hyperfocal distance. Your focus point is somewhere near five feet (as you can see on the above lens), and your minimum focus depth is now at two feet (the distance between the two orange lines associated with the dialed-in f/22 aperture). Meaning that everything from two feet to infinity is now in focus and NOTHING is being wasted.

This seems like a brilliant thing to do, but think of the problems for the auto-focus shooter. Since his camera has to focus on something, he has a problem. What if there is nothing at the five foot range. His camera can not auto-focus on air. That's impossible. However if you're manually focusing this is no problem, just look at your depth of field scale and move the focus ring where it needs to be (in this case five feet).

You don't even have look through the lens. It's easy if you have the courage. The problem is, of course, once you look through your viewfinder at this focus setting EVERYTHING WILL APPEAR OUT OF FOCUS. This is not a problem, it's just a fact of life. If you remember, since your camera employs an automated aperture system, you are looking through your lens with its largest aperture (in this case f/2) instead of f/22 (that you have dialed-in). Again, not a problem for the In Focus artist, he simply ignores this illusion and if he needs to ensure the acceptability of his focus, then he employs the depth of field preview button, disengages the automated aperture system and sees the world as he will capture it — with everything from two feet to infinity being in sharp focus.


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