hyperfocal distance - another effect of crop factor

Hyperfocal distances are interesting. No, really. I'll explain: The eye is relatively easy to confuse. I'll explain that later on.

There's something called the "circle of confusion" (coc) and this is essentially the smallest thing the eye can detect as being "sharp", i.e. not blurred. This is in reality generally around 0.2mm, but changes in Digital circles with the size of the sensor. Bottom line? For an APS-C camera (so a D7000, K5 and the like, but not µ4/3 or full frame) it's considered to be 0.02mm. More here but to be honest, we just need the 0.02. This is another reason why it's nice to know the size of your sensor

Hyperfocal distances use this coc to their advantage. If you focus a lens at a specific distance then everything between half that point and infinity will be in focus. The distance varies for the focal length of the lens used - so a 28mm has a greater hyperfocal distance than a 10mm - and the aperture used. That should start to explain why wide lenses have such a greater depth of field than a long telephoto.

There's a rather good wikipedia article on the subject of hyperfocal distances, and it includes the following formula:

focal squared / f x 0.02

that's it. It's not complex.

Example: 28mm lens, f8.

28 x 28 = 784
8 x 0.02 = 0.16
784 / 0.16 = 4900

Therefore: set focus to 5m and f8 on that 28mm SMC-M and leave it; everything between 2.5m and infinity will be in focus.

I've been testing this at work for video footage and it functions pretty well. Everything really is reasonably in focus, too, and that to infinity.

To make it really easy and to give some reference points, here a quick table, working in mm at both f8 and f16. You can do the rest of the maths yourselves.

Set focus to these distances and everything from within half of the distance to infinity will be acceptably in focus.

mm....f...distance
10....8....625
12....8....900
14....8....1225
15....8....1406.25
16....8....1600
18....8....2025
20....8....2500
24....8....3600
28....8....4900
30....8....5625
40....8....10000


10....16....312.5
12....16....450
14....16....612.5
15....16....703.13
16....16....800
18....16....1012.5
20....16....1250
24....16....1800
28....16....2450
30....16....2812.5
40....16....5000

 - Bret