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Focus issues

Correct focus is vital for the serious photographer and we’ve all been frustrated when an otherwise great image is let down by a lack of sharpness. Soft images can be caused by a multitude of different issues, some that indicate a fault in the camera or lens, others that may require a change of technique or settings.

We’ve outlined some of the most common causes of sharpness problems below. If you have been through all these points, taken corrective actions and are still experiencing issues, it may be that your kit is at fault; in which case get in touch and our repair technicians will be happy to take a look.

Are my lenses and accessories good enough?

Unfortunately, there is no getting away from the fact that the quality of the lens you are using has a significant impact on its ability to resolve detail. This can mean a higher price tag, but there is no doubt that it is worth investing in the best quality glass you can afford. This is particularly important if using one of the top-end DSLR sensors where resolution is sufficiently high to render the tiniest of detail. Unfortunately, this also means they can also capture the smallest of movements in the equipment, so if you have recently upgraded your camera you may need to get accustomed to shooting with a tripod or at a faster shutter speed than previously to eradicate any blur.

Most photographers are aware that use of a teleconverter will impair sharpness, but may be surprised by the difference a filter can make. Again, it is worth investing in a good one to minimise any negative effect. Whatever lens or filter you are using, don’t forget to keep them clean! A layer of dust, smears or fingerprints on the outer optics will not be conducive to optimum image clarity!

Am I using the right AF settings for the conditions or subject?

It is not only sensors that have become more sophisticated; autofocus technology has too. Cameras are now equipped with a vast array of focus options and areas, but this doesn’t mean they are capable of predicting your intention, so you will need to ensure you choose the best settings for the situation. Select the most appropriate AF point for the area you want to focus on and don’t confuse the camera by using multiple focus points or a predictive AF setting for stationary subjects; save this for when you need to track moving subjects. If you think you are experiencing sharpness problems, make sure you test it on single-point focus.

Is my shutter speed high enough?

We are sure most of you don’t need reminding, but if your shutter speed is not fast enough when shooting handheld, the resulting images will suffer from the effects of camera shake. When this occurs, there will be all-over blur with no sharp areas in the image. As a general rule, the speed you use should be at least as fast as the focal length (or effective focal length) of the lens. So, if you are hand-holding a lens with an effective or actual focal length of 200mm, you will need to employ a shutter speed of at least 1/250sec to avoid blur. A lens with VR or IS should enable you to achieve good results with speeds 2-3 stops slower. However, if this does not appear to be the case your lens may require attention from our service department.

Am I selecting the right aperture?

The sharpness of any lens will not be constant, it will change with the aperture, focal length and subject distance in use. Using smaller apertures can create diffraction blur and larger ones defocus blur. Every lens will have a “sweet spot” – one particular aperture setting that will produce maximum resolution of the in-focus area and this is usually a few stops down from wide open. Many users expect the widest aperture to be the sharpest and sadly this is not the case – if sharpness is more important that the depth of field, try finding the sweet spot of your lens and always bear this in mind to get the best balance for your needs.

Should I apply sharpening to my images?

Don’t make the mistake of believing that sharpening is a correction tool – it isn’t. In fact it is way of enhancing the edges within an image by increasing the contrast and thereby increasing definition and revealing detail. Don’t overdo it, but we would recommend applying some in-camera or in post-production, or your images will lack bite and appear soft.

Do my lenses need to be ‘matched’ or calibrated to my camera body?

This can sometimes be the case, but it is rare. At the time of production, there will be a range of acceptable tolerance for the focus set-up of the camera and lenses. In most cases, any slight difference within that scale will be unnoticed, but if the body is at one end of the tolerance scale and the lens at the other, you may find that the two together produce a slight back or front focus; the actual point of focus is slightly behind or in front of the intended subject. Your camera may have an AF Fine-Tune or Micro-adjustment feature that will enable you register the AF position for an individual lens, from which the camera will compensate every time that lens is attached.

It should be noted that this facility should not be necessary for most lenses and is not intended to be a substitute for attention in a service department where fundamental optical problems are concerned.

I have ruled out the above; what next?

If you have eliminated user issues, our Service Department is here to help remedy any fault with your Nikon or Canon body or lens; but there may still be some investigation required to identify the cause of the problem. Sample images can often help us in this respect, but they must be RAW or unedited JPEGs. This way, we can view the shooting data and even the focus area that was in use at the time of shooting. Your images may help us to identify the problem, or at least to reproduce the conditions in which it is exhibited. It will also help if you can identify which item is giving you the problem; are your images soft with numerous lenses, indicating a possible fault with the body, or is a single lens the culprit?

The problem seems to be with the camera body; what could it be?

For focusing to be accurate, the camera’s body dimensions/depth – or the measurements from lens mount to the plane of focus – must be correct to within a fraction of a millimetre. Correcting any anomalies with the dimensions could require a realignment or calibration of the mirrors or sensor, but if there is damage/distortion to the bayonet or internal frame of the camera, the affected parts will need to be replaced.

My lens no longer focuses correctly; what could be the cause?

You may not always be aware of it happening, but lenses do get knocked and some internal parts may also be subject to wear, including those keeping the lens elements in place. This will affect optical alignment, meaning image sharpness/resolution will suffer. The Fixation technicians will replace any worn or damaged parts, ensure all the optics are properly centred and perform the set-up/calibration process to return your kit to the manufacturer’s specification.

Why do my lenses continually hunt for focus?

There can be many reasons why equipment fails to find focus at all, ranging from dust on the camera’s AF sensor to misplaced optics in the lens. Before concluding there is a fault, however, it’s worth checking a couple of things. For example, is there sufficient light or contrast for the equipment to focus? And what is the minimum focus distance of the lens in use? If your subject is too close for that particular lens, it will not find focus.

My images are in focus, but why do they look blurred through the viewfinder?

In a separate process to the actual focusing, the prism in the top of the camera will reflect the image into the viewfinder to assist you with composition. Because manufacturers know that users’ eyesight will vary, most modern DSLRs have a built-in dioptre that can be adjusted to improve the clarity of the viewfinder for the individual. This adjustment is usually done via a dial or slider at the side of the viewfinder. Try moving this until the LED info or grid lines displayed in the viewfinder are as sharp as possible to your eyes. If the adjustment is ineffective, the viewfinder optics may need attention from our technicians.

Why is the AF not activated when I press the shutter-release button?

Failure to activate the AF is likely to mean that a trip to the service centre is unavoidable, but it still may be worth a quick check of the basics. Some lenses will have a switch for AF or MF and the camera also needs to be set to one of the AF modes, rather than to manual focus. If your camera has an ‘AF-ON’ button on the rear, top or right side of the camera, it is worth checking to see if this activates the AF instead. If it does, the issue may be solely with the shutter-release button, rather than a more major AF problem. Better still, it may be that you have unwittingly selected a custom setting that has activated this button for AF, rather than your shutter release. If you don’t know where to find this option, a quick reset of your settings should rectify it.

Why does focus change if I focus at one focal length and then zoom to a different one?

Most AF zoom lenses designed for DSLR stills photography are varifocal, rather than parfocal. This means they are not designed to retain focus throughout the zoom range and there is likely to be some shift of focus when zooming, which is perfectly normal. Designing them as parfocal would mean big compromises in terms of size and price, and generally users of such lenses do not require it because they use the AF function, so the focus shift is of no consequence.

Where parfocal lenses may be needed is in video production/cinematography and we would recommend lenses designed specifically for this purpose.

Why does my lens focus past the infinity point?

Again, we are back to the varifocal nature of most lenses, which means that infinity focus will shift with different focal lengths. In addition, lens components will expand and contract with temperature changes, which will also affect the focus position. Plus, a hard stop at the point of infinity is likely to damage – or reduce the life of – the strong motors required to move focusing elements speedily, so all things considered, it’s probably no bad thing.