It’s here at last – the hyperfocal distance!!!
Ken Rockwell writes about all things photographic and I admire his brash, no-nonsense reviews of equipment and comments on techniques & software. If I’m thinking of buying some gear then I’ll usually look at his review of it before purchasing.
Recently I read a comment of his to the effect that “there is no such thing as depth of focus (DoF)” He went on to qualify this fairly controversial statement by explaining that DoF relies upon you accepting a certain level of softness in the image, which is correct in a way, but unlikely to be a problem in real life.
The definition of the Hyperfocal Distance is
“The hyperfocal distance is the closest distance at which a lens can be focused while keeping objects at infinity acceptably sharp. When the lens is focused at this distance, all objects at distances from half of the hyperfocal distance out to infinity will be acceptably sharp.”
From that is apparent that your possible depth of focus is very large indeed, but the crucial phrase is “acceptably sharp”.
All lenses, no matter the cost or make, obey certain rules relating to the science of optics. From those rules can be calculated the DoF for any lens, of any focal length, at any aperture and at any focus distance. The maths are (for me) complicated so I rely on a smartphone app which tells me that a 200mm lens at f2.8 focussed on a subject 20 feet away has a DoF of 1.2 ft ie anything from 39.4ft to 40.6ft will be acceptably sharp (there’s that phrase again!).
At 10ft focus distance the same lens has a DoF of 0.072ft or nothing, really. The rapidly diminishing DoF is one of the reasons that a lot of accidental photographers claim their new f2.8 lens “doesn’t focus properly” or “isn’t sharp”. The real reason is, quite often, that they have overlooked the limited DoF of their lens when wide-open and close to the action. At 10ft the same lens has a DoF of around 4” at f11, so the nose, and eyes in a portrait (human or animal) might both be just in focus.
The one thing I haven’t mentioned so far is that DoF is also dependent on the camera’s sensor due to the fact that different sensors have – wait for it – different “Circles of Confusion”. Now that really is a phrase to make you think twice about being a photographer! So what on earth is a Circle of Confusion? – if you’re really interested then please Google it because for now all that I will say is that it relates to the size of a point of light focussed on the sensor that is, or appears to be, sharp. It is a very, very small point of light.
So what has all this got to do with the Hyperfocal Distance? Well, the HD is a way of maximising your DoF – all the way to infinity.
Using the app on my phone (or you can use tables) I know that the HD for my 50mm lens at f11 is 40.5 ft. If I focus my lens carefully on an object 40.5 ft away then “anything from HALF THE HD (ie 20.25ft) to INFINITY will be acceptably sharp.
It works. Try it for yourself with a 50mm or wider lens. Calculate the HD distance for your set-up, focus your lens at that distance, switch auto focus off, and take some shots without refocussing the lens at all.
Now that you have convinced yourself as to the merits of the HD, you can combine it with the “sunny 16” rule and take photos all day without refocussing the lens or adjusting the aperture or shutter speed. Magic!
The downside is, of course, that you can’t blur the backgrounds and if the light changes then you might have to recalculate the settings, or alternatively set the ISO to Auto before you start off on your experiment.
Birds in flight and sports might be a bit difficult too, but the upside is that, if your camera is pre-set to the HD & sunny 16 then you will get a useable image should Martians land in front of you. Then you can adjust the camera setting for subsequent shots knowing that you’ve got one in the bag – you don’t even need to check the lcd/histogram.
Of course, the HD is really of little everyday use to most photographers. But knowing that your image might look out of focus simply because of a limited DoF at your chosen setting is very important!