I am a sucker for those landscape photos which have a prominent object in the foreground with beautiful scenery stretching away into the far background. And both the near object and the far background are in focus. Here’s some examples of what I mean, from a couple of photographers whose work I admire: Anne McKinnell and Matt Kloskowski:
What springs to my mind when I see these is the question, “Where did the photographer set the focus point to get everything looking sharp?”
There’s the hard way: take two photos, one with a near focus and one with a far focus, layer them in Elements or Photoshop, and use masking to carefully blend the two sharper parts. Or we can look to this information poster and try to figure out what settings we can experiment with:
Researching the question, however, throws up the term “hyperfocal distance” which is defined as the focal point distance, H, from the camera so that everything from H/2 to infinity is in acceptable focus. So, for example, if there’s a rock in the foreground, say 3 meters away, if I make my focal point 6 meters away, does that mean that everything from 3 meters to infinity will be in focus? Well, not quite. It’s a little more, but only a little more, complicated than that.
There is a simplified formula one can use for most DSLR cameras to get a rough value for the hyperfocal distance H (in meters), so long as one isn’t using it for macro photography (see below for a comment):
H = (FL x FL)/(30 x f)
where FL is the focal length of your lens (when the scene is set up) and f is the f-stop.
So, let’s go back to the example numbers. Suppose that, using my 28-300 mm zoom lens, when the scene is composed to my liking I’ve got the lens set at a focal length of 72 mm. Normally, I would think that I’d probably want to set the f-stop at f/22 so I get good depth of field. Let’s see what happens if I did:
H = (72 x 72)/(30 x 22) = 7.85 meters
Oops. That says that everything from half that distance (about 3.9 meters) all the way to the background would be in focus. But my rock is 3 meters away, so it would not be in acceptable focus. What can I do? I could adjust the f/stop or move my camera back about a meter. Let’s see what would happen if I set the f/stop at 28:
H = (72 x 72)/(30 x 28) = 6.17 meters
Closer – everything from about 3 m 9 cm away from the camera to the far background would be in acceptable focus. Unfortunately, my rock, 3 m away, would still be fuzzy.
At this point I’d could slide my tripod back about a meter and recompose the scene. Or, I could look at adjusting the focal length a little bit. Let me move my zoom setting to 70 mm and make sure the scene still looks good (I am making the composition just a little bit wider and taller, so I want to make sure I am not including more of the closer foreground). Now when I do the calculation I get:
H = (70 x 70)/(30 x 28) = 5.8 meters
So, if I focus on a point which is 5.8 meters away from the camera, then everything from 2.9 meters (including my rock) to infinity will now be in focus and I can take the photo (either using Aperture Priority and letting the camera figure out the exposure, or using Manual, setting the f-stop to 28 and selecting the correct exposure).
How do you set the focus to 5.8 meters? Most lenses have a scale on their focal ring enabling you to set the focus at a particular distance. If you have to estimate where the 5.8 meter position on the focal ring is, it might be a good idea to manually bracket where you think it may be i.e take two additional photos, moving the focus ring marker to either side of your chosen position.
You’re probably thinking, “I don’t want to have to carry a calculator with me!” You don’t have to if you’ve got a smart phone. As might be expected, there is an app for all of this. For example, if you’re carrying an iPhone or an iPad for gps use, you can download and install Simple DoF, an app which will do all the calculations for you.
In order to be modern I’ve used meters throughout the above examples. But I have to confess that I would mentally estimate 5.8 meters in feet (about 18) before I understood where I should be focusing. To make it somewhat easier by having H come out in feet, I could have used the simplified formula:
H = (FL x FL x .109)/ f
That would have given, respectively, 25.7 ft, 20.2 ft and 19.08 ft. Our rock is 3 m away (just under 10 feet) so anything less than 20 ft for the hyperfocal distance H works.
I stated above that the formula we’re using is simplified. That’s because I’ve dropped one term from it. The correct formula is:
H = (FL x FL)/(30 x f) + f/1000
For most purposes, f/1000 is miniscule (in our examples above we should add 22mm or 28 mm to our distance). But, if you are doing macro photography, the omitted term may be important.
You might also think that a focal length of 72 mm is awfully long for a landscape photo. And you’re probably correct. So let’s run quickly through the example above, but this time we’ll assume a focal length of 30 mm. We’ll still want to make sure that our rock at 3 meters distance is in focus, as is everything from there to infinity (although it might not matter all that much if those hills that are 3 km away are a tad fuzzy). And, another wee problem raises its head – we’ve heard from a sage photographer that we should be trying for an aperture of between f/8 and f/13 because the optics of most lens are designed to be at their best within that range. So, what problems are we going to face as a result of these new conditions?
Let’s look at the near “in focus” distance – half the so-called hyperfocal distance H. If we were to put 30mm in for FL and 6 meters in for H (because we want H/2 to be 3 meters), our formula would become:
6 = (30 x 30)/(30 x f)
or 6 = 30/f
so f = 30/6 0r 5
So, if we select f/5, and focus at 6 meters, we will end up with our rock in focus and the background also in focus. And what turns out to be a bonus is that if we change our aperture to f/11, and keep our focus point at 6 meters, then our near “focus distance” actually shrinks to less than 2 meters (try it by plugging in 30 for FL and 11 for f in the simplified formula). In other words, going to wider angles (shorter focal lengths) actually makes it easier to find the focus point which will meet all our conditions.
Finally, to be complete, I need to point out that the number 30 in the formula is derived from two things: converting the answer to meters (dividing by 1000) and your camera’s “circle of confusion” which is .030 for most DSLR’s (you can find the correct value for your camera at http://www.dofmaster.com/digital_coc.html).
I do hope that your personal “circle of confusion” hasn’t grown wider because of my use of equations!