FIXED FOCAL LENGTH LENS IT IS well known that fixed-focal-length lenses generally produce sharper results than zoom optics. However, b...
FIXED FOCAL LENGTH LENS
IT IS well known that fixed-focal-length lenses generally produce sharper results than zoom optics. However, buying a range of such lenses is costly, so instead use image library software, such as the Organizer in Adobe Photoshop Elements, Lightroom, Adobe Bridge or Apple Aperture, to find out which focal lengths you use most. Using the search filters, find all images taken using a particular zoom lens and then search by focal length. I found that out of 5,062 images I took with an 18-200 mm super zoom lens, 2,450 were taken between 18 mm and 24 mm – a fixed 18 mm or 20 mm lens would therefore be ideal and certainly a lot sharper than the optic I used. Fixed-focal-length lenses do not have to be expensive. Both Canon and Nikon offer 50 mm f/1.8 optics at less than £200, and older, used AF versions can be found for around £100. And don’t forget that old manual focus lenses are also available for many camera systems. If your photography isn’t reliant on fast focusing speeds, these can be extremely sharp and good value for money. One of the sharpest lenses I own is a 55mm f/3.5 Micro Nikkon lens from 1963, which cost me just £45.
CHOICE OF FOCAL LENGTH
THERE is no escaping the fact that some lenses are sharper than others. This doesn't mean that you need to abandon all your optics and spend thousands of pounds on new ones, but it may help if you learn which of them are sharper than others, and at what settings. Take the kit zoom and super zoom lenses of the 18-200 mm variety. These are never going to be the sharpest lenses you can buy, but there are ways to maximise their performance. For instance, a zoom lens will usually perform the worst at its extremes, so before you zoom all the way in, think about taking a few steps forward and using a focal length nearer to the middle of the zoom range. This slight adjustment can make a significant difference. It is similar story at the minimum focal length where a zoom will also show distortion. Here, you should zoom in slightly and take a few steps backwards. Finding the focal length at which a zoom lens is sharpest is straightforward. Use a tripod to keep the camera steady and then simply photograph the same subject at different focal lengths, keeping the subject the same size in each frame. Now see which focal length produces the sharpest result. Of course, the more you pay for a zoom lens, the better the image quality should be and, as lenses hold their value far better than cameras and can always be used when you upgrade, it is always worth buying the best you can afford.
MANUAL FOCUS AND LIVE VIEW
IF YOUR camera is mounted on a tripod, take advantage of this by using live view to magnify the image on the rear of the camera. You can then manually focus the lens with real precision, making sure the desired area is precisely in focus – for example, the subject’s pupil rather than the end of their eyelashes.
APERTURE plays a vital role in the sharpness of an image. The rule of thumb is that a lens is at its sharpest when stopped down 2 stops from its widest aperture. Therefore, an f/2.8 lens should start to reach its sharpest at f/5.6. When used with an aperture set to its maximum, lenses are more prone to suffering from distortions, chromatic aberrations, flare and coma, all of which have an adverse effect on sharpness. Conversely, diffraction starts to occur as an aperture becomes smaller. When the aperture is very small, the light tends to bend as it exits the hole. These divergent rays have to travel further to reach the focus plane, which means they end up being slightly out of phase, resulting in a slight blurring. So while the effects of diffraction are often only slight, they can cause noticeable loss of detail. To test which aperture is the sharpest on any given lens, aim the optic at a particularly detailed subject and lock the focus to this point. Now, in aperture priority mode, take the same image at every given aperture. By examining the results at 100%, you will see exactly which aperture settings produce the sharpest image – these are usually between f/5.6 and f/11, depending on the lens. It is worth considering this information when shooting landscapes, when generally you’ll want to get as much of the image in focus as possible. While a small aperture of f/22 will increase the depth of field, it will also increase diffraction, which will reduce the image sharpness. Instead, use hyperfocal focusing, where the aperture and point of focus are calculated, to maximise the depth of field and sharpness across as much of the image as possible.
MANY DSLR cameras now come with a feature that allows the autofocus to be fi ne-tuned, even allowing it to be adjusted for individual lenses. It can be the case that lenses display a slight front- or back-focus effect. Most of the time this will barely be noticeable, but for absolute precision it is worth checking your individual lenses. There are commercially available focus-checker devices that can help you to check and adjust the AF of your camera. However, a quick search online will also present a variety of free charts that you can download and make yourself. The basic premise is to focus on the focusing chart and look at how sharp the point of focus is. If your lens is perfect, the focus should be on the exact point that you have focused on. However, if the lens is slightly out, the
point of focus may be just in front, or just behind, the intended target. Using the camera’s AF fi ne-tune facility, it is possible to tweak the AF performance of the lens by a tiny fraction to accommodate any flaw in the focus of the lens. Most cameras then have the option to save this setting so that it is automatically applied whenever this lens is used. By going through and adjusting each of your lenses, you can make sure that you get the best performance from them every time.
THE CAMERA’S shutter is a tool for freezing motion, be it the movement of the photographer or the subject. If you are photographing a moving subject, remember to use a shutter speed that is fast enough to freeze its motion. While 1/125sec may be appropriate for someone walking leisurely, it won’t be fast enough to perfectly freeze the motion of someone sprinting or leaping over a hurdle. If the speed is too slow, the motion won’t be frozen and the subject will appear blurred. Similarly, any movement the photographer is making will also have an effect. If you are shooting handheld, the rule is that you should always use a shutter speed at least as fast as the 35mm focal length. Therefore, if you are using a 300mm lens on a full-frame DSLR, you should use a shutter speed of 1/300sec or faster. If you are using a 300mm lens on a camera with an APS-C-sized sensor, then you should be using a shutter speed of at least 1/450sec (which takes the crop factor into account). Although image stabilisation will obviously help to reduce the effects of camera shake, for best results try and adhere to this rule as much as possible.
THERE are a few things that are hard to avoid when you press a camera’s shutter button. One is that you will inevitably move the camera slightly. The other is that the movement of the camera’s mirror springing upwards will cause tiny vibrations. One of the ways to avoid these movements is to use mirror lock-up mode. When available, this moves the mirror up when the shutter is pressed, with the shutter being released after a short delay or when the shutter is next pressed. This delay allows any vibrations or movements to settle. In taking these slight movements out of the equation, the resulting image should be slightly sharper.
ANOTHER habit of most photographers is to use the centre AF spot to focus and then, with the focus locked and shutter button half pressed, reframe the shot. This technique works if you have a large depth of field, but with a shallow depth of field the otherwise fractional shift in AF distance can slightly soften focus. It is far better to shift to a more appropriate AF point positioned over the subject. Another option is to use a single AF point and continuous tracking; it is then possible to use the centre spot focus and reframe technique as the focus tracking will adjust for the slight movement.
ALTHOUGH the level of sharpening and noise reduction can be set to varying levels in-camera, it is always best to shoot raw images. When an image is saved as a JPEG fi le, it is compressed to save space, but this can cause a loss of detail sharpness. Capturing images as raw fi les and then using raw-conversion software to process them offers far more control over how sharpening and noise reduction are applied.
AS WITH luminance noise reduction, you should remove any default settings and start sharpening from scratch. In this way you will have complete control. I find that sharpening can usually be applied a little more strongly than the default settings allow, but it is dependent on the subject.
Most sharpening tools use an Unsharp Mask technique, which increases edge contrast to make them appear sharper. To successfully sharpen an image to its full potential, it is important to understand what each of the changes you make does. Adobe Camera Raw has four different sliders for sharpening, each performing a different task. While they may have slightly different names in other software packages, the basic functions are the same. The Amount slider controls the strength of the sharpening, basically adjusting the low contrast of edges to increase or decrease the effect. The Radius slider determines the number of pixels from an edge that are affected by the sharpening. Using a small number will only affect the area around very distinct edges; a larger number will apply the sharpening effect to a greater distance away from the edge, causing a stronger contrast effect. It can, however, create a halo effect around these edges, so it is best to keep the Radius fairly low, usually between around 0.5 and 2 pixels. Holding down the Alt key while moving the Radius slider shows a preview of which edges will be affected, highlighted in white. Grey areas remain unaffected. Look out for haloed edges and reduce the setting accordingly. The Detail slider is quite straightforward: it controls the degree to which details are sharpened. The higher the setting, the more fi ne edges are sharpened. When at a low setting, only the major outline edges will be affected, and not the smaller surface texture details. Again, holding the Alt key while moving the slider shows exactly which detailed edges will be affected. Perhaps the most useful of the sharpening tools is the Masking slider. This masks those areas of the image that you don’t want sharpened. When set to 0, no masking is applied, but when at 100 sharpening will only be applied to major edges. Where the masking slider is particularly useful is in actually making sure that any luminance noise in skies isn’t made worse by the sharpening process. Hold down Alt and use the Masking slider to ensure that you only sharpen those edges that need it.
MOST raw-conversion software will apply default sharpening and noise reduction based on the ISO sensitivity of the image. However, these aren’t always the best settings to use. When it comes to noise reduction, it is luminance noise reduction that is the most destructive. It works by blending neighbouring pixels together to remove the speckled luminance noise. In doing so, the process often blurs texture detail, creating images that look blurred or smudged, but with sharp edges.
When applying luminance noise reduction, start with no reduction applied and then gradually increase the level until the edge has been taken off any speckling, but before any signs of smudging or loss of surface detail emerge. It is better to leave a hint of speckled luminance noise in the image than cause a loss of detail and sharpness from too much noise reduction. Colour (chroma) noise reduction usually has no effect on the sharpness of an image, so it is generally acceptable to apply as much as is necessary to reduce any coloured noise.
YOU MAY not think so, but ISO sensitivity has some effect on sharpness because as the sensitivity increases so does luminance and chroma noise. These reduce detail, but not as much as noise reduction, which blurs and smoothes image noise causing a loss of image sharpness in fine detailed areas. Wherever possible, try to shoot at your camera’s native ISO sensitivity, which is usually ISO 100 or 200. Doing so will mean the sensor and image processor will not have to amplify any analogue or digital signals – an action that can itself create image noise. Similarly, avoid ‘Lo’ ISO settings. These generally just use the camera’s native ISO sensitivity and then underexpose the image accordingly, before boosting the signal to produce a correct exposure. Generally, any image noise produced is very slight, but there can be less detail in highlight areas compared to using the camera’s native ISO sensitivity.
WHETHER it is optical- or sensor-based image stabilisation, if you are shooting handheld you should always switch it on if available. Even if you are using a fast shutter speed, the extra stabilisation can make a difference. However, image stabilisation should not be considered a substitute for a proper camera support. Although it makes it possible to shoot images handheld at far slower shutter speeds than would normally be possible, for critical sharpness a fast shutter speed or an appropriate support should always be used.
DEPTH OF FIELD
THE APERTURE of a lens is, of course, used to set the depth of field. It may seem obvious to say that the subject must fall within the given depth of field, but pay real attention to how the depth of field may affect sharpness. If you are shooting a portrait image at a very wide aperture of, say, f/2.8, and either you or the subject moves forward or back by just an inch or two when taking the picture, it may be enough to throw the subject slightly out of focus. The eyes, for example, may now be not as sharp as they should and the focus point may be nearer the front of the subject’s nose. Increasing the aperture by just 1 stop will increase the depth of field enough to help reduce the effects of this movement.
IF YOUR camera doesn’t have a mirror lock-up function, the self-timer function can be just as useful. By setting the self-timer to fi re a few seconds after you have pressed the shutter button, any force you may have applied to the camera when pressing the button will have subsided before the image is taken. A self-timer becomes even more useful when combined with mirror lock-up. This means that the mirror can spring up and then, when you press the camera’s shutter button a second time, it will be a further few seconds before the shutter automatically opens. Once again, this means that the camera should be perfectly still and free from even the slightest shake.
TRIPODS AND SUPPORTS
A TRIPOD is perhaps the best tool for making sure that an image is pin-sharp. While it can sometimes be a pain to carry around, the benefits of using one are huge. With the camera mounted on a sturdy tripod and head, there should be no camera movement during the exposure and virtually no excuse for the image to not be sharp. However, it isn’t just tripods that can help steady your camera – monopods also offer a great deal of support. Although they are not as stable as a tripod, monopods can make a significant difference to the sharpness of your images. Some professional portrait photographers even use monopods when shooting in a controlled and well-lit studio environment, as they offer support but with a degree of flexibility not found with a tripod.
CORRECT AUTOFOCUS MODE
SOMETHING that is often overlooked is the correct autofocus mode. On a basic level you have a choice between single and continuous AF. If you are shooting a still object, such as a still life or a landscape image, then single AF mode is the most sensible choice, while continuous AF is the obvious choice if your subject is moving. However, if you are handholding the camera and shooting something like a portrait image, where the depth of field maybe shallow, it may be worth using continuous AF. As previously explained, if you or the subject lean forward or back slightly, continuous AF should help maintain sharp focus on the subject.
FOR ABSOLUTE precision, a remote release is key. Using a remote release means that a camera’s shutter button doesn’t have to be pressed at all. As a result, the camera won’t be subject to any movements created when you press the button. Once again, when combined with a mirror lock-up and a tripod, a remote release should allow for pin-sharp pictures.