Aperture-priority mode is the favoured auto-exposure mode of many photographers

because of the control it gives, from people shooting vast landscapes to those

photographing the smallest of insects. It's considered by many to be the mode that

maps most closely onto how certain kinds of photographs demand photographers think

about how they're shooting. Getting yourself out of green auto and into shooting a mode

forces you to think about and lets you control certain important aspects of your shot.

Note: This is a quick-and-dirty primer; for even more gory technical details, head over to How to Choose a Lens Aperture (F Stop), which

covers a lot of things skimmed over or ignored in this article.

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Edit Steps

1. 1

Set your camera to aperture priority mode. This differs from maker to maker (read

your manual), but here are some hints for a few common types of digital camera:

Most Nikon digital SLRs: You have a mode dial. Turn this to "A". Once you've done

this, spinning your front control dial (on your right-hand grip, very close to the power

button) will adjust your aperture. (If you have a camera without a front control dial, then

your rear control dial will adjust your aperture instead.)

High-end Nikon digital SLRs: Hold down the "MODE" dial while turning the rear

control dial until you see "A" in your top LCD. Your front control dial will then adjust your

aperture.

Nearly all Canon SLRs (and some Canon point-and-shoots): Turn your mode dial to

"Av". Your main control dial (next to the shutter button) will then adjust your aperture.

Many point-and-shoot digital cameras do have an aperture-priority mode, but you may

have to work through menus to activate and adjust it. This is just a simple way to tell

the computer and parts already present to work together, which shouldn't cost much

extra, but shows the manufacturer has taken care to help you make the most of even an

inexpensive camera.

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2. 2

Memorise some basic terminology. You'll need it to make sense of the rest of this

article:

f/ numbers are your apertures. This is represented as a fraction of your

lens' focallength. A smaller aperture is a larger f/number; f/32 is a much smaller

aperture than f/5.6.

Stopping down means to use a smaller aperture than your lens' largest (smallest f/

number).

Wide open is the opposite of being stopped down.

Depth of field is, formally, "the range of object distances within which objects are

imaged with acceptable sharpness". There is only one distance at which objects will be

in perfect focus; the depth of field covers the subject-matter that is outside your

intended area of perfect focus, but that are still close enough to being in focus so that to

the viewer, all that gets captured within the depth of field appears deliberately within

focus.

3. 3

Test your lens. All lenses are different and are better shot at different apertures for

optimal performance. Get out and shoot something with lots of fine texture at different

apertures and compare the shots to figure out how your lens behaves at various

apertures. Here are some hints as to what to look for:

Nearly all lenses have lower contrast and are less sharp at their widest aperture,

especially towards the corners of your image. This is especially true on 35mm and

digital camera lenses. On sharpness, this is a totally separate issue from depth of field;

this will happen even with a flat subject. Consequently, if you're going to have detail in

the corners of your pictures that you want to keep sharp, then you'll want to use a

smaller aperture. For flat subjects, f/8 is typically the sharpest aperture.

Most lenses will have some noticeable amount of light fall-off wide open.Light

falloff is where the edges of the picture are slightly darker than the centre of the picture.

This can be a good thing for many photographs, especially portraits; it draws attention

towards the centre of the photograph, which is why many peopleadd falloff in post

production. But it's still good to know what you're getting. Falloff is usually invisible after

about f/8.

All lenses will be softer across the frame if you stop down far enough.[1] This is an

inherent physical limitation of camera lenses; forcing light through a smaller hole

causes light rays to interfere with each other.

Zoom lenses can vary depending on how far in or out they are zoomed. Test for the

above things at a few different zoom settings.

4. 4

Get out and shoot.

5. 5

Control your depth of field. It's as simple as this: a smaller aperture means more

depth of field, a larger aperture means less. A larger aperture also means more

background blur (which is a related, but not identical, issue to depth of field[2] ). Here are

some examples:

Use a small aperture to force more depth of field.

Remember that depth of field becomes shallower the closer you get. If you're doing

macro photography, for example, you might want to stop down far more than you would

for a landscape. Insect photographers often go way down to f/16 or smaller, and have to

nuke their subjects with lots of artificial lighting.

Large apertures force backgrounds to be thrown out of focus; this is great for portraits, as in this shot made at f/2.

Use a large aperture to force a shallow depth of field. This is great

for portraits (much better than the silly automatic portrait scene modes), for example;

use the largest aperture you have, lock your focus on the eyes, recompose and you'll

find the background is thrown out of focus and is, consequently, made less distracting.

Remember that opening the aperture like this will cause faster shutter speeds to be

chosen. In bright daylight, make sure you aren't causing your camera to max out its

fastest shutter speed (typically 1/4000 on digital SLRs). Keep your ISO low to avoid this.

Remember that you won't see any of this through your viewfinder (or on your

screen as you're composing. Modern cameras meter with the lens at its widest

aperture, and only stop down the lens to its selected aperture at the moment of

exposure. What's more, viewfinders on modern digital SLRs don't even show the true

depth of field even if you're shooting the lens wide-open with faster lenses (meaning

ones with a larger maximum aperture).

Many SLRs have a depth-of-field preview button on the front of the camera. If you've

ever hit a button on your camera and then wondered why your viewfinder went dark,

that's the one. Unfortunately, because it darkens the viewfinder, it's very difficult to

gauge your depth of field this way (though it might give you some indication of how far

out-of-focus distant backgrounds are, which is not the same thing). A better option

on digital cameras is to simply take the picture, then play it back and zoom in on your

LCD to see if the background is adequately sharp (or blurred) enough.

6. 6

Control your shutter speeds. Using a larger aperture means that you can use faster

shutter speeds (or a lower ISO with the same shutter speed); conversely, a smaller

aperture will force a longer shutter speed, or require you to kick up your ISO to grab the

same one. This has several practical applications:

Grab the fastest shutter speed you can. If, for example, you're hand-holding your

camera or trying to freeze motion in poor light, set your aperture to the largest one your

lens has. Crank up the ISO as far as you dare, too (exactly how high is tolerably noisy is

something with which you'll have to experiment for yourself). The camera will then grab

the fastest shutter speed you can use.

Grab the slowest shutter speed you can. This is great if, for example, you want

to blur motion (think of those dreamy flowing water pictures). Set your ISO to its lowest

setting, stop down to f/16 (or smaller, if you're willing to defy the laws of physics, or at

least if you're fine with diffraction kicking in). The camera will then grab the longest

shutter speed that the situation permits (though typically modern cameras won't time out

exposures longer than 30 seconds).

7.

7Shoot for sharpness. As mentioned earlier, nearly all lenses are sharpest stopped

down a little. If you've made your own tests as suggested, then use this aperture for any

shot for which you think it'll give you an adequate depth of field and shutter speeds. For

those of you shooting stills from a tripod, then use this aperture all the time.

If you're too lazy to have made your own tests (and really, shooting test subjects like

walls isboring), then there's plenty of wisdom embodied in the old saying: f/8 and be

there. f/8 typically gives sufficient depth of field for most still subjects and it's where

35mm and digital SLR lenses are typically at their sharpest (or close to it).Ad

Edit Tips

When not actively using your camera keep it ready for whatever may present itself by

leaving it in fully-automated program mode, or perhaps in aperture-priority mode with a

reasonable default aperture such as f/8.

Don't worry too much about the results of your tests. Those tests will tell you how to

get the sharpest results on a flat subject in ideal, tripod-mounted situations, not about

the shot that real-world conditions will necessarily permit. In particular:

o If you really need a lot of depth of field, don't worry about using smaller apertures,

even those at which diffraction is obvious. The defocus caused by part of your

subject being out of the depth of field is a very, complex thing that's impossible to

correct; it's an extraordinarily complex phenomenon that differs from lens to lens, and

even on the same lens depending on aperture, subject distance and focal length.

Diffraction, on the other hand, is a relatively simple phenomenon. A simple "unsharp

mask" in your favourite photo editor will often work fine.

A simple "unsharp mask" in your favourite photo editor might be sufficient to plaster over the effects of diffraction, as done here; the difference between the f/8 and f/32 shot is now invisible. If you need the small apertures, use them.

o Don't hesitate to shoot your lens wide-open if you need it. For example, if you're

hand-holding and can't stop down a little without getting camera shake, or you want to

freeze motion, then shoot wide open; a little visible fuzziness in the corners is a lot less

ugly than the effects of camera shake or a blurry moving subject. The lower contrast is

trivial to correct in software, too.z