Often it’s difficult to understand why this is the case when we believe we’ve done everything as we should, but the fact is that this could be down to a number of reasons, from issues with equipment and technique to the subject and even environmental factors.
Here are six tips make sure you always stand the best chance of capturing images with clearly defined details.
1. Insure your shots with a minimum shutter speed
Many modern cameras allow you to set a minimum shutter speed, and this is an effective way to ensure images always stand a chance of being captured sharply – particularly when using lenses or cameras without any kind of image stabilisation.
When shooting in the Shutter Priority or Manual exposure modes you will probably already be using an appropriate shutter speed for your scene, although in the Aperture Priority mode it’s easy for shutter speeds to occasionally dip below what’s recommended for that particular focal length.
So how do you set this to the right speed? For general-purpose use, a good idea is to set this to the reciprocal of the focal length of your lens, taking into account any crop factor applied by your camera’s sensor.
So, a speed of 1/50sec would suit a 50mm lens used on a full-frame body, or alternatively 1/80sec or so if using a camera with an APS-C sensor.
If you’re using a camera with a particularly high-megapixel sensor (24MP or 36MP, for example), you may want to set this slightly higher to be on the safe side. On your camera this may be offered in same setting where you can adjust ISO (sensitivity) to an Auto option.
If your subject is moving, consider setting this to a speed that you know will render it sharply in relation to how fast or erratically it moves.
For posed images of people this does not need to be much higher than 1/100sec or so, although for those moving around a speed of 1/160sec or even 1/250sec would be more appropriate. Obviously in these situations you may also wish to employ continuous AF too.
2. Know when not to use focus-and-recompose
The focus-and-recompose technique is a popular way of achieving focus in an image when, for whatever reason, there isn’t an AF point covering the subject.
What typically happens here that that the photographer will use the central or another key AF point to focus on the subject, before recomposing the shot to the desired composition. This usually works well with distant subjects but can cause softness with closer ones.
So why is this? Depth of field increases with subject distance, so when you’re focusing particularly closely to a subject, any shifts in subject or camera position after focus has been confirmed can leave the subject slightly out of focus.
This is particularly problematic with wider apertures where depth of field is shallow, so be aware of this if you do choose to employ this technique here.
f/8
Wide-aperture lenses are great in low light and when trying to achieve very shallow depth of field, but most don’t give their optimum performance at their widest aperture. In fact, they tend produce sharper images when they are used at a smaller one, such as f/5.6 or f/8.
The main reason for this is because of an image-softening effect known as spherical aberration, which is particularly problematic at wide apertures.
It’s certainly the case that some optics are surprisingly sharp at the widest f-stop, but closing down the aperture – even slightly, thus maintaining the kind of shutter speed and effect you want in your image – can often help details be better defined.
Of course, that doesn’t mean you should always stay away from wide apertures. In fact, you may prefer a slight softness when shooting portraits or when images aren’t likely to be viewed at 100%, and the advantages of a having a very shallow depth of field may outweigh minor losses to sharpness.
4. … but don’t always use the smallest either
Although it’s possible to achieve expansive depth of field at very small apertures, push this too far and you may see sharpness compromised.
The reason for this is down to an effect known as diffraction, which concerns what happens with light as it passes around an obstacle of some kind, which in the case of lenses would be the aperture blades.
Most lenses can be stopped down to f/16 or f/22 but if can get the depth of field you need in an image at a slightly wider aperture such as f/11 or f/13, or if you use hyperfocal focusing, you may find this serves your images better.
5. Activate Face detection
When capturing people, one mistake many photographers make is focusing on the bridge between a person’s eyes rather than on the eyes themselves.
In some cases this isn’t too great an issue if the aperture is small enough to ensure depth of field renders both in focus, although when shooting close to the subject with a wide apertures – as you may well be doing with portraits – this can mean that the eyes are a little soft.
Obviously the best course of action is to always focus directly on the subject’s eyes, although when shooting multiple images in different compositions, it’s all too easy to slip on the occasional shot.
Activating Face Detection is a good way to ensure that the camera knows what it’s focusing on, and often these systems will try to ensure that the eyes are as sharp as possible.
6. Change your technique when using a tripod
Using a tripod can be an effective means of improving sharpness in your images, although even when using one it’s possible to compromise the result in many ways. The key thing to ensure is that the camera remains as static as possible during the exposure, which you can make sure of in a number of ways.
Using a remote release of some kind is a good way to ensure the camera is not touched at the point of exposure, although if you don’t have one, the self-timer option can be used successfully in its place.
Your camera may also have a mirror lock-up mode that allows the mirror to be raised independently of the shutter opening to capture the exposure (also a potential cause of blur), and you may be able to use this in conjunction with a remote release.
Make sure to turn off your image stabilisation system when using a tripod too, as this can create vibrations that work against the very thing the system is trying to prevent.
Your camera or lens may automatically sense then they are being used on a tripod and deactivate image stabilisation of their own accord, so check to see whether this is the case to save you the effort.
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