So you shoot landscapes, right? And you want a scene like the one above to be sharp from the leaves in the foreground to the distant hills, right? Now, if you’ve been shooting landscapes seriously for a while, you’ve probably heard about this thing called hyperfocal distance and might have used it in the past. You might have a handy printed reference or one of those apps on your phone, where you enter your camera model, the focal length, and the aperture and it computes the hyperlocal distance for you.
So you set your wide-angle zoom to a focal length of 10mm, to enhance the perspective of the scene, and to an aperture of f/5.6, because you know that is the the sweet spot where your lens is sharpest. After all, you figure that, even at that relatively large aperture, depth of field will be sufficient to get everything in focus, from the first vines to the houses on the hills in the background, if you focus at the hyperlocal distance mark.
Since modern lenses don’t have a depth-of-field scale on the barrel anymore, you fire up an app on your smartphone to compute that distance. Turns out that, if you focus the lens at 0.89m (or about 3ft) everything from 0.65m to infinity will be in focus. Using the focusing distance scale in your viewfinder, you set it to a bit less than 1m and take a shot.
Not completely trusting math, you check the image on your LCD display to verify that everything is perfectly in focus and so it seems.
Once at home, you download the picture on your computer and start examining it for defects and it immediately occurs to you that the background is a bit soft, a softness that was not really apparent on the small LCD screen in the field. It’s not just that the background is out of focus, but focus progressively fades with the distance, starting from a point relatively close to the camera.
The softness is only visible when you zoom in, but it’s still disappointing, because you were thinking of printing this image really large. Most of all, you feel annoyed and betrayed. Wasn’t the hyperfocal distance meant to guarantee sharp focus from the near limit to infinity? Why is everything at infinity ever so slightly blurred in your image? Where was a mistake made?
Wanting to verify what you had learned, you do some research: you google the term “hyperfocal distance”, which leads you to the corresponding Wikipedia article, where you read:
hyperfocal distance is a distance beyond which all objects can be brought into an “acceptable” focus.
Fine. but what is deemed “acceptable”?
I won’t go into details here (you can find them on Wikipedia) but suffice to say that the limits of acceptability are established on the basis of conventional values for visual acuity, viewing distance and enlargement. What is acceptable for an 8×10 print on a wall might not be acceptable when pixel-peeping images at 100% on a monitor, or when printing large.
In any case, not everything inside the zone of acceptable focus is equally sharp. Sharpness is at a maximum at the focusing distance and decreases towards the limits. If the near limit is 0.65m, as in the example above, objects at 0.65m are still considered acceptably sharp and objects at 0.64m are not. But everything that is at 0.65m is only marginally sharper than everything that is at 0.64m. Sharpness decreases progressively, it does not stay constant within the DOF zone and then abruptly falls at the edges.
This is why distant objects are a bit blurry: because they are at the limit of acceptable sharpness. A bit farther away and they would be considered too soft.
What does this mean? Is hyperfocal distance useless, or of limited use? Should we limit ourselves to small prints, when we use it?
Well, not really, but to understand why, you will have to wait for the next article in this series.
UPDATE: Part 2 has been published here.