Understanding a Lens’s Depth-of-Field Markings

Photo of 25mm Zeiss lens made for "analog" (film) cameras. The depth-of-field scale on the lens barrel is marked for discussion.
This classic Zeiss 25mm lens made for the high-end Contax 35mm “analog” cameras of yesteryear, is hyper-focal focused at f/5.6, with adjustments for a more suitable standard of “acceptable sharpness”. Objects from about 6 feet, all the way to “infinity”, should look acceptably sharp.

The depth-of-field (DOF) markings on classic manual-focus lenses, like the illustrated Carl Zeiss 25mm lens, can lead to confusion. This is especially true when we adapt such lenses for use on modern digital cameras. Perhaps it’s because landscape shots are a particular interest of mine, or perhaps it’s because I had some great photography teachers, back when I was learning the basics, and read some good books before that, but I honestly don’t even remember not having at leastsomedegree of comfort with the depth-of-field markings on my lenses. Indeed, I’ve frequently pre-focused a lens, based on exact calculations of where I wanted my depth-of-field, then just used the viewfinder to frame the composition. But, to be fair to Annie Leibowitz, who confesses during her Masterclass course to still having some discomfort with depth-of-field indicators, it’s far simpler when it comes to the landscapes I was typically composing: in a landscape,everything must be sharp! This is a situation that lends itself well to the use of hyper-focal depth-of-field.

Screenshot from the Annie Leibowitz Photography Masterclass
Annie Leibowitz confesses to her students, during a “Masterclass” interview, that, when picking focus for a portrait, she “finds one thing and prays”.

Desirable depth-of-field can vary by the image

So I really can understand when a great portrait photographer, like Annie Leibowitz, says that she “prays” when it comes to depth-of-field. I sympathize… and often do the same when shooting portraits. Especially with the longer lenses we often use for portraiture, depth-of-field can be very shallow, indeed. What degree of sharpness and depth-of-field works for a portrait can vary from composition to composition and subject to subject. In most typical portraits, we probably want a soft background, while in other compositions, we may want at least some recognizably sharp elements in the background. But we still normally want to keep primary focus on the main subject, with the distant background much“softer” than the subject. That said, portraiture is also about artistic expression, and such rules are not always true, especially if the subject’s eyes are not visible. We may sometimes find that the best composition is one in which our primary subject falls partly (or even completely) out-of-focus, with sharper focus on other elements in the scene. But, except for some “figure in a landscape” -style shots, we would rarely aim to use a lens’s hyper-focal focus when shooting portraiture. If you’ve taken the time to get used to your lens’s focal properties, you’ll know what aperture provides enough depth-of-field to provide sufficient sharpness in all desired areas of your subject, with enough background softness to look good.

Most professional cameras allow for a broad range of “bracketing” options when taking a photo. With a landscape, as long as I know that I’m happy with a composition and that want everything to be sharp, I can use hyperfocal focusing rules to shoot everything in sharp focus in one shot, and maybe only bracket my exposure.

Classic manual-focus lenses made it easy to see what was going to be in focus before you took your shot. You didn’t need auto-focus if you knew that the closest and furthest elements in your composition were going to appear “acceptably sharp”. But, back when the official depth-of-field markings were made for this lens, it was uncommon to print an image much larger than 8″x10″, and it was expected that a viewer would stand back a bit to look at such a print. So the markings on most lenses made for 35mm film are marked with a depth-of-field scale that doesn’t measure up to modern standards for sharpness. That said, you may be happy with the results from such lenses, if you take the time to experiment and learn how to get the best from them. To be more certain of “acceptable sharpness” in all areas of your image, when using such lenses and attempting to use hyperfocal focusing, you should adjust by at least one f-stop. Here, the lens is set to f/5.6, but the infinity mark is turned inside the f/4 mark (to the right of the central focusing mark). The f/4 mark to the left of the central focusing mark is aligned with 2m—about 6 feet. This (about 6 feet to “infinity”) is the range in which we should expect to see “acceptable sharpness”.

What does this mean? It means that we can walk around, with a lens set in this fashion, and with the camera on a tripod set to a reasonable height, and just shoot nice landscape images based on composition, as long as the nearest element of interest is at least 6 feet away from the camera (or whatever our “close limit” is for the lens and aperture we’re using). This 25mm lens, despite its age, is perfect for landscapes; at f/5.6 or f/8, with the lens suitably hyperfocal focused, I can achieve beautiful foreground-to-background sharpness. Such a lens is also great for “figure-in-a-landscape” portraits, group shots, and (turned a bit further from the infinity end), portraits with a bit greater depth-of-field.

For most portraits and close subjects, you'll have to adjust focus much closer than the lens’s hyperfocal distance.
With a portrait, or other key subject matter closer to the camera, we should normally let “infinity” fall out of focus, and instead dial in a depth-of-field window that maintains acceptable focus on the foreground subject’s face and body.

Experiment to Find Your Real Hyper-focal Focus Points

I know from experience that, if I have my 25mm lens set to f/5.6, I should use the depth-of-field markings for f/4 to achieve a better standard of “acceptably sharp”. But that’s just for this lens and aperture. At f/11, with the same lens, I can align the “infinity” mark just inside the depth-of-field mark intended for f/8, and everything from about 3 feet to infinity will appear sharp.

Really, “knowing from experience” is better learned from methodic experimentation. I knew that old lenses were marked for depth-of-field based on producing a sharp 8″x10″ print. Today, we “pixel-peep” and we expect to be able to crop and still see “acceptable sharpness”. So, when using older lenses that still have sufficient resolution to work well with a modern sensor, we can experiment to understand how to adjust for the depth-of-field scale:

  • Lock down your camera movement by using a tripod and use a cable release or your camera’s timer function.
  • Use a shutter speed high enough that the image will not be affected by shutter or mirror movement.
  • Choose a suitable “test subject” with good detail in distant “infinity-focus” areas and use ISO low enough to ensure good rendering of that detail.
  • Set your lens to each f-stop for which you want to calculate an accurate hyper-focal distance, and shoot a series of test shots from actual infinity-focus down to infinity aligned with the working aperture’s DOF marking (what used to be considered “good enough”)

For each aperture, find the closest-focused shot you took that still provides true sharpness in distant “infinity” details. And take note of the exact focus setting, because that shot was taken at the proper hyper-focal focus point for that lens and aperture. If you can repeat that, in the field, you can maximize the depth-of-field available to you in a single exposure and save “bracketing” for exposure.

In addition, you might also want to extend your focus bracketing experiments to better shoot group portraits and candids, on-the-fly, with good background separation, but maximal foreground/mid-ground depth-of-field. Bear in mind that depth of field is split about 1/3 in front and 2/3 behind your focusing distance (except if the lens is hyper-focal focused. Also note that depth-of-field drops off dramatically as the focusing distance is reduced. In a macro shot, you may have a millimeter or less that appears “acceptably sharp” in front of your plane of focus. Whatever depth-of-field you have in front of the plane of focus, expect double that distance behind the plane of focus. So, in tightly framed portraits, you might have only one eye which is “acceptably sharp”, or the subject’s eyes may appear sharp, but not their nose or body. If you learn the limitations of your lenses, you‘ll know at what point you might start to expect issues with your depth-of-field. (And in those times, you’ll learn to pray, like Annie and I do… and you‘ll know when you need to stop down a bit more, or “bracket” your focusing, and shoot a whole lot to be sure you have something you can use.

“Focus Bracketing” and “Focus Stacking”

Focus bracketing (a set of shots with adjustments in the lens’s focus) is now supported by many professional cameras (and control software). Even if your camera doesn’t natively provide the feature, and even if you aren’t controlling your camera with special software that provides calculated focus bracketing, you can easily make a set of shots with slight changes in focus between each one. You may find you like the depth-of-field in one shot better than the others. Or you may want to maximize or control depth-of-field through the use of “focus stacking”. This technique will be covered in greater detail in coming articles, but if you’re not yet familiar with the concept, what we are talking about is simply merging the sharp areas from two or more exposures, in order to create a single image with greater apparent depth-of-field in the subject area, quite similar to how we might shoot multiple images to achieve greater dynamic range (i.e. when creating HDR photos to get better detail in highlight and shadow areas). And, indeed, the two techniques may sometimes be combined.

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