Annoying problems at common aperture settings (and how to solve them)

jmeyer | Photography Tutorials | Tutorials | 10/08/2012 02:00am0 Comments

12 3 4 Next » One of the most important steps in learning about photography is understanding how to use aperture, because controlling your lens’ aperture settings enables you to take control over depth of field and dictate the size of the sharp area around the focus point in an image.

If you want a lot of the image to be sharp, for example, you need to select a small aperture setting such as f/22 and if you want to restrict the depth of field to isolate a subject from the background, you need a nice wide aperture setting such as f/2.8 or f/2.0.

Whatever aperture setting you use, you need to select an appropriate shutter speed to ensure that the image is correctly exposed.

If you shoot in aperture priority mode (often signified by A or AV on the mode dial), you set the aperture setting that you want while the camera takes care of the shutter speed.

Most cameras allow you to adjust aperture in 1/3-stop or EV steps. In this article we’re going to take a look at some of the common problems with using wide, middle and small aperture settings and explain how to overcome them.

Problems with wide aperture settings

SUBJECT IS SOFTBecause depth of field is very restricted at very wide apertures it’s absolutely vital that you focus at exactly the right point – especially if you are shooting a very close subject with a long lens as depth of field decreases as focal length increases and subject distance decreases.

SolutionMake sure that the active AF point is over the most important part of the subject. In some cases you may find you are better off focusing manually. If possible, magnify the live view image on your camera’s LCD screen to get a really good view of the the target area and make sure it is razor-sharp.

BACKGROUND TOO SOFTShooting with a very wide aperture helps separate your subject from its surroundings by blurring the background, but sometimes the surroundings can be too soft and unrecognisable.

SolutionIf you want to retain a little context try closing down the aperture a little even just one stop can make a huge difference.

IMAGE IS SOFTEven if the focusing is spot-on, many lenses produce slightly soft results when they are fully open.SolutionClose down a little and you’ll find the point of focus is significantly sharper.

IMAGE IS OVEREXPOSEDOpening the aperture right up means lots of light can reach the sensor so only a very short exposure is used. In very bright conditions it may not be possible to set a fast enough shutter speed and this will cause your images to be overexposed.SolutionIf you encounter this problem, the first thing to check is your camera’s sensitivity setting, you need to set the lowest value possible.If the image is still overexposed use a neutral density (ND) filter on your lens to reduce the amount of light that enters your camera. ND filters are grey filters that cut out light and don’t produce any colourcast.

Problems with middle aperture settings

SUBJECT NOT ISOLATED FROM BACKGROUNDMid-range aperture settings such as f/8 and f/11 are often a great choice because they usually get the best

out of a lens, producing sharper results than shooting wide open and avoiding problematic diffraction associated with very small apertures.However, depth of field is greater than when using larger aperture settings and this can mean that the subject is not sufficiently isolated from the background.

SolutionDepth of field generally extends twice as far behind the point of focus as it does in front, so try to make the most of the depth of field that a mid-range aperture setting gives you and focus towards the front of the subject.If you are photographing a group of people, for example, don’t focus on the back row, focus on the front row – or a row near the front.

NOT ENOUGH DEPTH OF FIELDAlthough using a middle aperture setting ensures the focal point of your image is nice and sharp, there may not be sufficient depth of field to get it all sharp. This a particular problem when shooting close-up and macro subjects, but it can also be an issue with landscapes.SolutionA relatively simple solution with static subjects is to take a series of images, each one with the focus set to a different distance into the scene.Take the first shot with the nearest part of the scene in focus, then refocus just a little further into the scene and take the second shot before focusing further in again.

Repeat this until you have shot with the focus on the furthest part of the scene.

Now all the shots can be combined to create one image that is sharp throughout. This can be done manually using any image editing software that supports layers – Photoshop Elements is fine.

But it can also be done automatically using Combine ZM, which is free to download and use, or using Photoshop’s Photo Merge function.

For more on controlling depth, see our guide to Depth of Field: what you need to know for successful images.

Problems with using small aperture settings

BLURRED MOVEMENTUsing a smaller aperture means that less light can pass through the lens and a longer exposure is required. This can introduce blur if the subject moves during the exposure.SolutionIf there’s not enough light you can create some by turning on a lamp, using a studio light, turning on your flashgun or activating your camera’s pop-up flash.Alternatively, use a higher sensitivity (ISO) setting. Some photographers worry that using high sensitivity settings will mean that they produce noisy images, but modern digital cameras produce remarkably clean images at settings we would have only dreamed about a few years ago.

CAMERA SHAKEAny involuntary movement of the camera during an exposure will introduce blur and the longer the exposure the more likely you are to move the camera when it is handheld.SolutionAlthough you can use a higher sensitivity setting to allow a faster shutter speed if your subject in stationary you don’t need a short exposure to freeze its movement and a better solution that enables you to produce the highest quality result is to support the camera on a tripod so it is rock-steady.For the best results you should use a remote release or the camera’s self timer to avoid introducing any wobble by pressing the shutter release.

In addition, SLR users should consider using the mirror lock-up facility. This turns shooting into a two step process.

The first press of the remote shutter release triggers the mirror to lift (the viewfinder will go black), while the second, which is made after you are sure any vibrations caused by the the mirror lifting have died, trips the shutter.

As compact system cameras (CSCs) don’t have a mirror, CSC users don’t need to worry about mirror lock-up!

FOREGROUND SOFTAlthough using a small aperture ensures that there’s lots of depth of field, if you don’t use it properly you can still wind up with a soft foreground.

SolutionAs depth of field extends twice as far behind the focus point as it does in front, if you focus on the horizon or towards the farthest point of the scene, much of the depth of field is wasted.Instead you need to focus towards the front of the scene so that more of it is within the sharp zone created by the lens’ depth of field.

Hyperfocal distance focusing is usually mentioned at this point, but using it requires using tables or a lens depth of field scale.

Rather than getting bogged down with this, a far better rule of thumb is to focus about one third of the way into the scene.

SOFT IMAGESAlthough using a small aperture setting results in lots of depth of field, another rule of physics means that the sharpest part of the image isn’t as sharp as in an image taken using a slightly wider aperture.This is because of something called diffraction, the impact of which becomes more noticeable as the aperture is closed down. Put simply, diffraction is the bending of light rays as they pass by the edge of the aperture.

Using a smaller aperture means that a greater proportion of the light waves are bent and as a result the image is softened more significantly.SolutionThe only way to avoid diffraction from spoiling your images is to use a larger aperture, even one stop may be enough.So next time you are shooting a landscape, don’t set the smallest aperture possible, open up a stop or so.

And for the best results, use a mid-range aperture setting and focus stack as described earlier.