In Part I we covered blur induced by the subject as well as by the camera system. Now we’ll talk about other contributors to image sharpness.
Poor contrast can be the result of severe convection in the air, particulates in the air such as water droplets (fog), smoke, or dust, flare from light entering the lens at extreme angles, very dark scene (low key), very bright scene (high key), or from poor lens optics.
Although long lenses are very nice for shooting over long distances, they cannot overcome the poor optical quality of the air in between the camera and the subject. Even the best lens will only be able to capture what it has to “see” through. Beware of cool air over land that is heating up. As the heat rises (low density) it will try to mix with the cooler air (higher density) above and density has a huge effect on light (it bends it), and will tend to blur the edges in your scene, thereby reducing the contrast. Just moving to a different location where you are not shooting over the warm ground may be all that is necessary. In many cases though, you have no choice but to accept the poor quality or come back another time.
Inadequate depth of focus can greatly reduce image quality, especially if you are near your illumination limit and are restricted to using your lens wide open. If you can afford to stop down at least a little, you can get more of your subject in proper focus and help to correct for other focus inadequacies. Don’t be afraid to let your ISO creep up a little, especially if you are using good noise reduction software in your processing. I have some fine images taken with a cropped sensor camera at an ISO of 12800! Moving away from your subject, while keeping the focal length the same, can also increase your depth of focus as can switching to a cropped sensor camera.
Improper focus can be tough to tackle. Although auto focus has made amazing advances in recent years, it does not know what part of the image you want in focus. You may have to make minor manual adjustments, something I almost always do anyway. Poor vision or the use of glasses, multi-focal especially, may hinder your ability to achieve proper focus. I prefer to wear my contact lenses rather than my progressive glasses when I shoot, for this reason. Also, you may have a technical issue with your camera or lens that prevents them from achieving focus within specifications. All of these issues can work together to further degrade an image.
Poor or dirty optics can further reduce image quality. You’ve probably heard that it’s best to put your money into your lenses rather than your camera bodies and this is still quite true. The best camera out there can’t do much but capture the image that is coming through poor optics. Teleconverters are a common source of poor image quality. You want to get the very best teleconverter you can afford to put behind your expensive glass. The same holds true for filters. Personally, I don’t use any filters for wildlife photography. While some people swear by a UV or clear filter for protection, I use my lens hood for that. It also does a great job of reducing lens flare from unwanted sources of light.
Make sure you keep your lenses as clean as possible. Fingerprints, smudges, rain, condensation, splashes, etc. can all add up to reducing your contrast and sharpness and therefore reducing image quality. It is useful to carry basic lens cleaning supplies with you. And speaking of condensation, when shooting in warm, humid areas, be mindful of trying to use a cold camera when you step out of an air conditioned car. You could easily spend the next ten minutes waiting for your lens and camera to warm up enough to drive off the moisture. It takes extra long when using large aperture lenses.
Next we’ll talk about the camera sensor itself and some software resources.
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