Awkward focus

How do you focus a camera that doesn’t tell you when it’s in focus? That’s really awkward.

If you can learn how to do this trick, there are loads of interesting old cameras that you could use. They can be reasonably cheap too, as people do prefer things you can focus. And yet, you may have heard the pundits talking about magical solutions like zone focussing or hyperfocal distances. What’s a poor boy to do when you thought zones were something to do with exposure and hyperfocals were what old people went to opticians to get?

Focusing a lens means moving it nearer or closer to the film or sensor, so that the light from your chosen subject is brought to the least fuzzy point. There was some stuff about it here. Many lenses have a built-in screw thread so that turning them moves them in and out, without letting light leak past. Other arrangements are possible, but they mostly all do the in and out thing.

Now, our eyes are not perfect and there is a lower limit to the size of things we can see. As you get older, that might be grandchildren. Grant me though, that we can’t see atoms, or even molecules. So when an image is projected onto the film or sensor by a lens, there will be a range of distances where everything appears sharp. If you could look closer, perhaps with a microscope, you could see that that amount that was truly sharp was less than it appeared to the eye. This is why small prints or pictures often look sharper than they are when you make them bigger.

But for practical purposes, there is a range of distances in front of the camera between which stuff looks sharp. This is the depth of field. Where this zone falls and how deep it is depends on several things. Let’s assume for now though that these things are outside your fine control: you can make a basic choice like the camera you are using, but you can’t change the lens on it. Let’s also assume that your camera might have one of the two forms of focusing: controlled and guess, where guess includes fixed and not adjustable. If your camera provides accurate and adjustable focusing and that is what you want, then move along – there is nothing to see here. But there can be good reasons why you might want to use your adjustable camera as though it was not. The main one is often speed of use. Focusing takes time.

So, how do you make best use of either what you are stuck with or what you choose to adopt? According to type is the answer. Guessed focusing comes in three forms: fixed, zone and scale.

Fixed is where there is no adjustment possible. It’s not autofocus – it means the focus of the lens is fixed and you do your best to put the subject in the sharp zone. If you are lucky you may be able to find out from the manual or t’interweb where the focus distance is, or what the depth of field is. I have a fixed-focus camera, and the manual lists the range of sharp(ish) distances for each aperture setting. Without this information you may have to find out, or just live with it. It’s a fair assumption that a fixed-focus camera will be set to somewhere around the distance where you can get an adult in the frame, around mid-length. My own fixed-focus camera is set for about 8 feet. You could leave it at that and just work with it, or use a bit of film in testing. What you need is a long fence or railings that you can shot at an oblique angle so that your picture shows it from close to far. Before you shoot, pace out some distances and mark them with chalk or a stone. Then examine the developed image to see where it is sharp and how far away that is. Then get someone to stand that far away and look at them using the camera, to get an idea of what that distance looks like. Or make a simple version of the card rangefinder. Then shoot everything at the sharp distance.

Fence

Next up is zone focusing. This is where the lens offers a set of symbols for where it will focus. These are usually head and shoulders, group, mountains. Again, you can work with it or do the fence test to get an idea of what each setting does.

Zone focus

In the case of my camera, head and shoulders works out around 1.5 metres or a bit less than 5 feet. Groups fall at around 5 metres/ 15 feet.

Cameras like this can be very quick to use – pick the type of picture you are making, set the symbol for focus and go. Providing the aperture is around f8, you are likely to have enough depth of field to not have to worry.

Scale focusing is like using the symbols, but without the symbols. This is where the lens is marked with real distances, but you have to guess or measure the distance of your subject and adjust the lens accordingly. The lens on the camera above has both a distance scale and symbols. It sounds dreadful – how will you ever be able to estimate the distance acccurately? Use some basic rules:

  • A head and shoulders is around 5 feet, or a bit less.
  • An adult, shot vertical on 35mm with a 50mm lens, just about fills the frame at 10 feet (3m).
  • A group will be around 15 feet, or 5m.

Then use a reasonably small aperture like f8 and it will mostly work. If you are picky or nervous, make yourself a card rangefinder. It will easily fit in the camera case or your wallet.

You can even use a ‘proper’ camera with scale focusing. The street photographers do this for speed. You need to have a lens that has depth of field marking on it.

DoF

If I set this lens to f8, then everything between 2.5 and about 5m will be sharp. If that’s the most likely distance for stuff I want to take pictures of, I can set the lens and aperture and use the camera like a point and shoot. It would let me do slightly wide head and shoulders shots through to slightly tight groups without having to adjust a thing. This is what news photographers used to do, to give them the reaction time they might need to get the decisive moment (as legend would have it).

Then we come to the secret weapon of landscape photographers: the hyperfocal distance. Given a particular aperture, the hyperfocal distance is the point you focus the lens at that gives a depth of field spanning from half that distance out to infinity. It sounds like magic, and the actual point you need to focus on varies with the film or sensor size, the lens and the aperture. You don’t have enough fingers and toes to do the maths. So you either use an online resource or an app to calculate it for you, or use the depth of field markings that the lens maker gave you.

Say I’m using the lens in the above photo and I want both a group of people and the mountains in the background to be sharp. So I want a depth of field from say 4m out to infinity. I twist the lens to find a pair of aperture markings that put infinity on one side and my closest distance at the other. Then set the aperture to match the marks – the point of focus is already set correctly. Job done.

Hyper

In this case I need f11 and my closest sharp distance is perhaps 3.5m. The actual point of focus of the lens is 6m, but I don’t care.

This also works well if you are taking pictures of things that occur a bit further away, but variable. Some sports or activities, for example. Set the depth of field to cover the area of the action and concentrate on taking pictures.

So there you are – sharpness made simples, and a way to make use of the cheap end of the camera market.

Author: fupduckphoto

Still wishing I knew what was going on.

One thought on “Awkward focus”

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