Zone Focusing and Hyperfocal Distance
I was listening to an episode of the Martin Bailey Photography Podcast recently. Martin was talking about hyperfocal distance and how to calculate it. If you don’t already listen to Martin’s podcasts then I suggest you do, because they’re very good. Martin has an ability to explain complex tasks and concepts in a way that’s easy to understand.
While I was listening to the podcast I started thinking about zone focusing – a technique used by many street photographers when out making images. The image of the Melbourne Ambassadors (below) was made using zone focusing. (Fujifilm X100S at 1/200 sec, ƒ8, ISO1600).
So, what is zone focusing?
Zone focusing is simply a way to set the focus on your lens so that you don’t need to worry about focusing for each individual image. Once set, you can concentrate on composing and framing the image before exposing the frame.
Using zone focusing is actually quite easy, but it does require a little knowledge about your your camera and lens.
In simple terms, zone focusing requires that you manually focus your lens. You select an aperture and then focus on an object at about the distance you think you might be likely to shoot at, then leave the focus ring there. From that point on you simply frame and shoot knowing that your image will be acceptably sharp at the distance you focused, plus some distance closer and some distance further than the point of focus. Providing your subject is within that range, it will be in focus. What we are talking about here is the Depth of Field – the range of distance in front of the camera that will be acceptably sharp.
Using the photo of the Melbourne Ambassadors (above) and the Depth of Field calculator available at DOFMaster we can see what the depth of field was for this camera / lens combination. The Fujifilm X100S has an APS-C ‘crop’ sensor and a fixed lens with a focal length of 23mm.
From DOFMaster, for the Fujifilm X100S –
- Focal Length of lens 23mm
- Aperture ƒ8
- Focus Distance 2.5m
- Near focus limit 1.43m
- Far focus limit 9.97m
This tells us that providing our subject is between 1.43m and 9.97m from the camera it will be in focus. That gives us quite a large variation and margin for error when framing our subject. If we open the aperture to ƒ2 though (the largest aperture available on the Fujifilm X100S), the margin for error becomes much smaller –
- Aperture ƒ2
- Focus Distance 2.5m
- Near focus limit 2.11m
- Far focus limit 3.08m
You can see here that with an aperture of ƒ2 and pre-focused to a distance of 2.5m, the range of focus is only between 2.11m and 3.08m – so your subject must be between those distances from the camera in order to be in focus.
When using zone focusing while shooting street photos, it pays to use a smaller aperture to increase the depth of field. The image above of the traffic controller was also shot with the Fujifilm X100S using zone focusing – 1/100 sec, ƒ8 and ISO1600. The distance to subject was about five metres.
How does zone focusing work? Well, that’s a little complicated and varies depending on the focal length of your lens and something called the circle of confusion. Calculating the circle of confusion is not something most people would do and is not something I’m going to explain in this post. Luckily for us though, there are some average numbers we can use for the circle of confusion that are actually quite accurate in real-world uses.
Common values for circle of confusion include:
- 0.030 (full-frame sensor)
- 0.020 (APS-C 1.5 ‘crop’ sensor)
- 0.015 (m4/3 sensor)
Looking at the DOFMaster Depth of Field Calculator, you can see there is something listed on the calculation page called the Hyperfocal Distance. The hyperfocal distance is the closest distance at which the lens is focused that produces an image that is acceptably sharp from the point of focus right through to infinity. The part of the image in front of the hyperfocal distance, that is also acceptably sharp, is half the distance to the focus point.
Calculating the hyperfocal distance for any particular lens is actually quite a simple formula – the hyperfocal distance is equal to the focal length squared, divided by the lens aperture multiplied by the circle of confusion. The result of that calculation is added to the focal length of the lens. The result is the hyperfocal distance in millimetres. So, dividing the result by 1000 will give you the hyperfocal distance in metres.
For the Fujifilm X100S at ƒ8, the calculation would be –
Hyperfocal Distance = ((23 * 23) / (8 * 0.02)) + 23 = 3329mm = 3.329m
Near focus distance = 3.33m / 2 = 1.66m
With the camera focused at 3.33m and an aperture of ƒ8, everything between 1.66m and infinity will be in focus.
Here’s a quick chart of the hyperfocal distance for the X100S at different apertures –
Hyperfocal Distance and Zone Focusing in practice
Using the chart above, you can see that if using a Fujifilm X100S when out shooting street photography, you could choose an aperture in the ƒ4 – ƒ8 range and know that you could get sharp images without having to rely on the camera’s autofocus system every time. If shooting at ƒ4, providing your subject was at least 3.32m away from you, it will be in focus; similarly if you chose an aperture of ƒ8, providing your subject was at least 1.66m away from you, it would be sharp.
Of course you don’t have to focus at the hyperfocal distance. Focusing closer will simply mean the image will not be sharp all the way out to infinity. As we saw earlier focusing at 2.5m with an aperture of ƒ8 gave us an acceptably sharp focus range between 1.43m and 9.97m, which is still very useable.
This final image was also made with the Fujifilm X100S at 1/320 sec, ƒ8 and ISO1600 with a distance to subject of about two metres.
Give zone focusing a go… head over to DOFMaster and use their calculator to find the Hyperfocal Distance of your favourite camera / lens combination then go out and try it out!