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iStockphoto Photography Standards: Focus

In our first article on Lighting, we talked about properly exposing an image, bringing the right amount of light into our camera, giving either the film or digital sensor inside the correct information it needs in order to reproduce what we see. Now the next step is to get it all in focus.

Usually when we reject images for focus, it is because of one of three main problems:

  • The image is out of focus in general — it appears soft or even blurry.
  • The camera moved during the exposure.
  • There is focus, but it's on the wrong place in the image.
We've created some examples of each of these situations. While our examples represent pretty much the worst of the worst case scenarios, the general principles hold up across the board. Your own images may be rejected for much less than what we've shown here, but hopefully seeing these will give you a sense of what we mean.

In this case, absolutely nothing is in focus. Either you had the wrong shutter speed for your exposure, your subject moved slightly, or your hands were just too shaky. Whatever the cause, this is too blurry to be useful for anything.



There are sharp areas of the image, but they are wrong for the composition, limiting its usefulness. In this case, the tips of the wings are in focus but the face is too soft.


You attempted an artistic blur, or played with the depth of field for compositional reasons, and it just didn't work.

In this case, the 'experiment' is a failure. It doesn't look good, and doesn't communicate anything other than 'out of focus'.

Focal Length & Correct Exposure

The rule of thumb is: your exposure time should be 1/XX for the focal length XX for any given aperture.

So in practice, if you're shooting with an 80 mm lens, your longest exposure time for a hand-held shot would be 1/80th of a second.

This rule applies to full-frame cameras. For digital cameras with sensors smaller than 24 x 36 mm (aps-c for example, with 1.6 crop), you need to multiply your focal length by the difference (1.6 in this case) and adjust your exposure time accordingly.

Note: this is a general guide and is dependent on many other factors. Image stabilizing (IR/VR) lenses will allow shooting at much slower shutter speeds, as will good posture and shutter pressing technique. Too much coffee or a rapid pulse will cause you to shake more and a faster shutter speed may be required.

Wrong shutter speed for light conditions
Very soft, no point of focus


Steadiness

Some people can hold their hands and body very, very still, allowing them to shoot longer exposure times hand-held. Many people cannot. To compensate for any shaking, you can either adjust your exposure to bring in more light, by bumping up your ISO or opening your lens more, or do something to brace your body and camera. Lean on a wall, a tree, use a monopod, a tripod, rest your lens on something solid: anything to keep your camera steady. Especially in less than ideal lighting situations, the steadier your camera, the sharper your focus will be.

The longer your focal length, the steadier you'll have to be. That's why a 24 mm lens doesn't need any image stabilization, and your favorite 300 mm tele lens probably has it built-in.

Extreme camera-shake example
Get a tripod!

Composition

What is the most interesting part of the image that you have in mind? Where do you want the viewer's eye to be drawn when they see it? This is your primary focal point and it needs to be in focus. Often an image is sharp in places, but will be rejected for focus reasons because some essential part of the composition is too soft.

Don't rely too much on your camera's autofocus. There are times when autofocus thinks on its own and picks a different focal point than you may have in mind, locking onto a completely different part of the frame, thereby missing all the action and your primary subject. You can end up with a really unfortunate shot, especially if you're working with a small depth of field.


Sharp in the wrong place
Soft where it matters most


Each new generation of modern digital cameras now comes with bigger and bigger maximum output files. At a certain size, as long as the overall image is sharp, a minor focus misalignment, where the primary focal point may not be in the ideal place for the composition, can be tolerated. However, if the overall focus is soft and the main focal point is away from the ideal compositional spot, the shot won't work. It's all about overall context.

In this example, we can see the obvious difficulties with small depth of field. The auto focus has locked on to the grass surrounding our subject, leaving the face out of focus, which sadly renders the image useless on so many levels.


Sharp in the wrong place
Soft where it matters most


In the case of flat textures, the entire field must be tack-sharp for it to be useful. If you've spotted a rusty metal wall that would make a great background, focus is going to be the most important consideration, as any kind of softness will leave it unsuitable for the kind of use people will want it for.

Too soft for a texture
Too soft to be much of anything

Motion & Deliberate Blurs, or "I Did That On Purpose"

Of course, there are always tricks, and what makes an image really work might not always be 'correct'. Intentionally unfocused images, under the right circumstances, are acceptable. Again, it's all about overall context and execution.

Does it look good? Does it make good use of the frame? Is it an attractive abstract, or a jagged, confused jumble? Does it look attractive, or just incorrect? If there isn't a particular 'in focus' area, is the eye instead given a compelling direction to lead it through the image? These are the questions you need to ask yourself when attempting to move beyond conventional focus. Be tough on yourself.

Unsuccessful motion blur
Unsuccessful DOF experiment
Confused & Jumbled
Too soft, too ugly to be useful


Panned images would be one of these occasions. That means following your subject in action across the frame with a longer exposure time (usually horizontally), giving it an extra feel of motion, leaving everything but your subject, or part of it, in focus. Camera focus IQ in servo mode is your best friend here and it's rather easy to master.

Another nice trick with these long(er) exposure shots is to use a flash with its second curtain sync, meaning the flash will shoot just before the exposure time ends, freezing the action and leaving you with the last moments in focus.

You've probably seen lots of great long-exposure shots of streaming water of all kinds (rivers, sea waves, usually with a focus on some rock or fixed object somewhere in the frame), motion blur shots of large group of people walking and doing their everyday stuff — rush hour crowds, underground stations with blurred trains, traffic, cycle races — anything that holds a message of motion, action and so on works as long as the technical side of it covers all the bases.

Parfocal lenses

Some of your zoom lenses might be what’s called ‘parfocal’. This means that they stay in focus when the lens is zoomed in or out. If you are shooting at the wider end of your lens, try zooming into the longest focal length the lens offers. Focus and while holding the shutter release half way down zoom back to wide and take the shot. It could be a lot sharper than just taking the image at the wide end.




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