hyperfocal distance or focusing x number of feet ahead

[sbakewell1101]

hi, i am readying bryan petersons book understand exposure, and he talks about prefocusing for maximum depth of field (pg 50) and "focusing 3 feet ahead of him (pg 51) i did some searching and this led me to hyperfocal focusing... can someone explain this to me a bit? i really dont "get it" i use single point focus when i do portraits but i am looking to just learn more about distance and such... thanks for you help!

[Aegea]

The hyperfocal distance is where you focus so that the far end of your DOF is at infinity, i.e. infinity is just in focus. The near end of the DOF is then ... well, wherever it falls for that aperture, focal length, and sensor. The wider the aperture or the bigger the focal length, the further the hyperfocal distance will be, all else being equal.

[RichardTaylor]

You may find this website very helpful.

Online Depth of Field Calculator

[SwissJon]

Hyperfocal distance is great.. I use it most of the time with my Landscape photography to figure out what aperture to set the camera to get everything in the frame in focus. When you're in the field, online DoF calculators are next to useless, either print out a chart, or get an app for your phone (I use "Simple DoF")

Basically, at F/2, the depth of field is MUCH smaller than the depth of field at F/22, and that depth of field changes for each point in between. Also, the depth of field at 18mm is much larger than the DoF at 180mm. At some point, when you twist your focus ring, you will come to a point where infinity is in focus. That point ISN'T infinity, it's some point in front of infinity, and every point between that "some point" and infinity, and also everything half way between you and that "some point" is also in focus. This is the hyperfocal point. It's the first reading on your focus scale that allows infinity to be in focus.

Now it's not quite that simple, because as I said above, the aperture and the focal length also effect the Depth of Field. So by zooming in on something, you may throw the background out of focus, or zooming out you may throw it into focus. Additionally, by altering the aperture, you may throw the background into and out of focus.

Ok, so knowing all this, we can set the camera up.. Zoom the lens to the point where we have the composition we like. Then we decide at what distance we want the focus to start.. Let's say we have set the lens to 18mm and there are some flowers one metre from the lens that we'd like in focus, so we set the lens to f/9, (a nice sharp f/stop on most lenses) and the Hyperfocal distance chart tells me that the hyperfocal distance is 1.8m. Ok, so I set my focus on my lens to 1.8m and the flowers, because they're more than half way between 1.8m and me, will also be in focus.

Ok, so another example.. I've zoomed into a patch of grass poppies 30m away at 55mm (taking the other end of a kit lens) in a field at sunset over a mountainrange.. I'd like the sunset in focus because of the mountains, but nearby, about 10m away, there's a thick patch of nettles. We decide they're ugly, but the colour is nice. By setting our lens to f/3.5, the hyperfocal distance is 44m. The front focal point is therefore 22m, and the poppies will be in focus and the nettles will blur and you will be left with their colour only. (Ok, this example may not be one you want to try, but you get the idea) Notice here that I did not set my camera to focus ON the poppies, I set it to focus BEHIND the poppies.. If I had set the lens to focus at 30m, then the front focal point would be 17m (still enough to blur the nettles) but the rear focal point would no longer be infinity, it would be at 95m, and the mountainrange would look blurry, not at all the effect I wanted to achieve. Remember, I focused here BEHIND the poppies, at the hyperfocal point, to get the right effect

So by calculating the hyperfocal distance, we can choose the kind of effect we want to achieve.. Initially that is likely to only be trying to get everything you want in focus, but as you get the hang of it, you can use it to ensure that certain things are not in focus too. It's a very very useful thing to learn, and I really suggest you make your life easy and get an app for your phone, rather than trying to do everything via a chart, or worse, figuring it out before you leave the house.