Where To Focus? Hyperfocal Distance Explained

Posted by: In: Apps, In-Camera, Software, Techniques 07 Feb 2011 Comments: 0 Tags: , , , , , ,

In this article I want to talk about hyperfocal distance.

What is Hyperfocal Distance?

Do not let your eyes glaze over, it’s really interesting and can improve your landscape photography over night. I promise. Or your money back?

We’ll also review some cool apps for your iPhone that will help! (I only own an iPhone, and nothing else, but I’m sure these apps are available on other smartphones!). We’ll take a look at some online calculators too.

Before we begin though, I’m assuming you know something about depth of field. This is the term used to describe the bits of a photo that are in focus, and is closely related to the Aperture of a lens. If you have no clue what I’m on about, please consider buying Bryan Peterson’s “Understanding Exposure” which is an amazing resource on understanding how the camera deals with light. In terms of sharpness though, if you imagine refilling your wine bottle with leftover wine (stay with me…) without using a funnel (a wide aperture of say f1.8), you end up with wine everywhere. Mostly over the bottle, the carpet, your hands… If you use a narrow aperture (f22), then all the wine goes in the bottle and nothing is spilled.

Now imagine wine as light, and you can see that with a narrow aperture, we have all the wine where we want it – in focus. Using a wide aperture, we only have a tiny amount in focus, and lots splattered everywhere else (out of focus, known also as Bokeh).

That’s the simple view.

But there is a way to measure how much of the front-back area of an image will be sharp in relation to where you are focussing. By understanding this relationship, and being able to calculate it, you can very roughly know how much of your image will be in focus.

Let’s explain further. The below image shows our cat – Oscar, as a playful kitten (rather than the miserable lazy curmudgeon he is now)

Cat demonstrating depth of field

As you can see, his eyes are nice and sharp, but his front paws and the carpet at the back of the image are blurred. If you’ve been photographing a while, you’d expect this. What I can tell you from a mathematical point, is that if I assume his nose (my point of focus – it’s an old photo and should have been his eyes) were half a meter away from the lens… I have 39mm (millimetres!) of focus beyond the nose, and 33mm of focus in front of it. So his nose, whiskers and eyes are in focus, the rest is blurred.

Had I used f1.8 instead of f4, I would have just a 30mm of sharp focus and the eyes would probably be out of focus… Conversely if I’d have used f11, I would have 79mm in front of the focal point, and a massive 131mm beyond.

So you can see that from a creative standpoint as well as a technical one, knowing the rough hyperfocal distance gives you an idea of where to focus. In terms of portraiture and sports, it’s not something everyone has the time to calculate. Also, some people are limited by available light. Aperture after all is a key component in getting light onto the sensor, and in dark lighting, a wider aperture often is neccessary.

However for landscapes, the term Hyperfocal Distance is used to represent the distance at which you need to focus in order to ensure everything beyond that point (out to infinity) and half that distance back towards the camera is in sharp focus.

So, let’s look at this scene.

An example of hyperfocal distance

Where would you focus in this image? Before I learned about proper focussing techniques I would have aimed for the tree on the left. Maybe the “middle” of the picture.

Let’s look at the setup. This was taken at f14 with a focal length of 35mm. That tree is about 80m away from me. My Hyperfocal distance extends from about 5m in front of me, off to infinity. So those reeds in the bottom right hand corner are only a few meters away, but they would be blurred and out of focus.

So where do I focus?

I focus at the Hyperfocal Distance. I know, that if I focus there, everything beyond it, and everything (roughly) halfway between me and it will be sharp. I also know that that is the best place to focus for maximum sharpness through the depth of field. With the settings above (35mm, f14, 70m to my main subject), I can focus at 4.6m and still get everything sharp. So instead of 5m to infinity, I now have 2.3m to infinity. Sounds ridiculous doesn’t it? But it’s true.

Imagine these distances multiplied by kilometres as you focus on that big mountain in the distance, and you’ll begin to understand what I mean.

How Do I Calculate Hyperfocal Distance?

You don’t. You let something else do it for you. This is where the iPod, iPad, iPhone (and other smartphones) come into their own. They are portable, and handy for little applications such as this. There are many online free hyperfocal distance calculators, but out in the field, you tend not to have a computer to hand. So these apps are very useful.

And they’re cheap!

A Paid Hyperfocal Distance Calculator

Hyperfocal distance calculators are common. It’s a mathematical equation, so there are many free apps out there. However the ones I tried had little niggles that left me wanting more. But I couldn’t complain – they were free! So I plumbed for a paid app, and PhotoBuddy was the one I went for. Not only did it have the Hyperfocal distance calculator with a handy visual guide (that you can drag with your finger), but it has a host of other little functions too. Sunset/Rise times, phases of the moon, a bulb timer for your long exposures, WB lists etc etc. The list goes on… Just click the link and read “More”…

Other paid apps just didn’t have the functionality and/or useability of this app, (to be honest, all the little extras did it for me) and since downloading it, it’s been worth every penny.

A free App…

I haven’t reviewed all the free apps out there, but if it’s not costing you anything, what harm is there in downloading them all and trying them for yourself. Of the ones I tested, I found iDof Calc to be the best. It has a simple, fast, easy to use interface that does exactly what is says on the tin. No adware, and smooth functionality.

So next time you’re out taking landscapes, have a think about your hyperfocal distance, and focus on something a bit closer than the mountain in the distance. It’s surprising (at middle aperture ranges like f11) how close you can focus and still retain front-back sharpness.

Online…

You may be determined to look online, in which case I can recommend the excellent DOFMaster website for further reading and interest as well as an online calculator. As an aside, they also have an iPhone app – cunningly titled DOFMaster.

-Sc

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