Thursday, January 19, 2012

Tech Talk: Hyperfocal Distance

Greetings, volks. Welcome to Hohenfels Volks, THE place for our place! Today we’re going to learn about hyperfocal distance.

What is hyperfocal distance? It’s the distance you focus your lens for to have a maximum DOF. When you focus at this distance, everything from about half that distance to infinity is in acceptably sharp focus. To accomplish this and to define acceptably sharp focus you need to know your circle of confusion (COC.) COC is the largest size that a point or spot can be without appearing out of focus. For an APS-C size sensor, which most of us have, that number is .019. The smaller your COC, the greater your sharpness. Although, for different sensors and films that number is different. For 6cmx9cm film, it’s generally accepted to be .07, and for 35mm or full frame sensors, it’s about .03.

Things get mathematical here, so you may want your calculator. You can calculate the hyperfocal distance for a given lens and aperture using this method. Take the focal length of your lens and square it to get variable a, next take your aperture or f/stop and multiply it by the COC to get variable b. Divide a by b, and there you have your hyperfocal distance. Here’s how it looks in mathematical terms

H =F²/(f x C)

In the equation above
H = hyperfocal distance
F = focal length
f = f/stop

As an example, your lens is 50mm, you wish to focus on something 10 meters away, use f/11, and you’re using an APS-C sensor. 50x50/(11x.019). This gives us 2500/(11x.019) or 2500/.209, and finally approximately 11.9 meters. If you focus at infinity on your lens, your DOF will run from 11.9 meters to infinity. If you focus at 11.9 meters, your DOF will run about 6 meters to infinity. By focusing at your hyperfocal distance, you can maximize your DOF in an image and get that winning shot. By using this calculation on a variety of focal lengths and f/stops, you can see why smaller apertures (bigger f-numbers) give you greater DOF.

There are 2 other ways to figure it out. Both are much easier, if you are using a higher end lens with a scale on it, you set the infinity symbol on your lens to line up on your f/stop at the far scale, then everything from the matching f/stop on the near scale to infinity will be acceptably sharp. That allows for Maximum DOF and zone focusing. The other easier way is to look it online. There are so many sites that you can find on Google just searching for hyperfocal distance, that you’ll never be at a loss. I prefer using DOF Master, as they have some great stuff there and it’s too easy. You just enter your info and away you go!

I hope this gives you some idea of how to use your focus for maximum DOF and how to get that extra bit of oomph to make your image stand out. Next time we’ll be calculating DOF, more math so keep that calculator handy!

Don’t forget to post any of your images you’d like to see here at the Hohenfels Volks Facebook page. Of course, commenting on both Facebook and here is always appreciated, too!

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