The following is not intended to be a thorough tutorial on depth-of-field and setting the hyperfocal distance on a lens to obtain the greatest depth-of-field. For this there are plenty of excellent guides on the internet – it is more of a get-you-started guide. But first a little preamble…
Sometimes photographer friends, especially those just starting out, are a little puzzled watching me wandering around taking ‘street’ shots with my manual camera and non-auto focus lens, “Aren’t you focussing?” sometimes they say. My usual answer is, “No, I’ve set the hyperfocal distance for the aperture I’m using.” “Eh? What’s hyperfocal?” Well…
The Depth-of-Field Scale
It might be hard to believe (just kidding) but once upon a time lenses and cameras didn’t auto-focus – some still don’t! Look at most manual-focus lenses (and some auto-focus) and as well as a distance scale marked in metres and feet, you are likely to see another scale engraved next to it, which does not move – the depth of field scale.
This is depth-of-field scale has a series of numbers coinciding with the apertures on the lens. Each number is printed twice, left and right of the centre position. For example, if a lens has apertures running from f2 through to f16, you will find a ‘2’ at the centre, and running out left and right each side ‘2.8’, ‘5.6’, ‘8’, ‘11’, ‘16’ corresponding the lens’ apertures. Obviously, these markings vary with the specification of the lens (its focal length and its apertures).
It is the depth-of-field scale that allows one to ascertain what will be in focus from what we have focussed upon, back towards the camera’s position, and also to a point from the point of focus to farther away to the far horizon (infinity – written and marked as: ∞).
These two points of focus are:
the near limit – the point nearest the camera that is in acceptable focus
the far limit – the point most distant from the camera that is in acceptable focus.
The depth-of-field is the zone in front of and behind the point of focus that is in acceptable focus: the depth-of-field scale shows us this for a given aperture of the lens we are using.
So, How Is It Done?
Look at fig. 1 above. You will note that the distance scale shows that the lens is focussed at about 5m (shown in dark green), and that the aperture ring (in red) is set at f8. With these settings the depth-of-field scale (in blue) shows that at f8 – the two blue coloured 8s – the zone of acceptable focus extends from about 2.75m at its near limit to almost infinity (∞) at its far limit.
What Happens When We Change The Aperture?
In simple terms the wider the aperture (the smaller the f-number, eg f2.8, f2, f1.4 etc) the less depth-of-field and the smaller the aperture (the larger the f-number, eg f8, f11, f16, f22 etc) the more depth-of-field. For example in fig. 1 with the lens focussed at about 5m at f4 you will see the zone of focus extends from about 4m to almost 10m. Stopping down to f16 and still focussed at about 5m the near limit increases to about 1.5m to all the way past infinity (∞). Since a lens cannot focus farther than infinity, this ‘extra’ depth-of-field is ‘wasted’ for want of using better words.
To gain this ‘extra’, usable depth-of-field when set at f16 turn the focus ring so that the infinity mark (∞) is aligns with the righthand ‘16’ on the depth-of-field scale (fig.2). The near and far zones of focus then are shown as 1.5m and infinity (∞). (See fig. 2 below)
So, back to the original question: “Aren’t you focussing?” In fig. 3 you can see for ‘street’ I set my lens to focus at about 3m. At f8 my depth-of-field extends from about 2m (near focus) to nearly 10m (far focus), which is plenty depth-of-field for most of the photographs I take. In essence, with a 35mm lens I treat my camera as a point-and shoot, concentrating on the scene before me rather than wasting time focussing.
Points To Remember
* Smaller apertures give a greater depth-of-field than larger apertures – find a suitable balance with the given shutter speed.
* Wide-angle lenses inherently have a greater depth-of-field than telephoto lenses when focussed at the same point and using the same aperture.
* Experiment – use the creative possibilities of limited and extended depth-of-field with the lens you are using.
* Look at the depth-of-field scale: what is it telling you? What are your near and far limits with your chosen aperture? How do these change with different apertures or a different point of focus? How will my photo look? Will the background be blurred or the foreground? Will my principal point of focus be sharp?
By becoming accustomed and proficient in the use of the depth-of-field scale, you can make full use of your lens’ capabilities, eg you could experiment in using the depth-of-field scale’s left-hand markers in setting the near point of focus rather the right-hand to infinity or another distance, in this way you can allow the background to become blurred depending on the aperture. It is all a matter of experimentation.
I hope the above is of use.