Image Sharpness – Part I

All photographers want their images to be as sharp as possible. There are several factors that can contribute to unsharp images. Blur from subject movement, blur from camera movement, lack of contrast, inadequate depth of focus, inaccurate focus, poor or dirty optics, and low signal-to-noise ratio all contribute to degradation of an image. I’ll take each of these issues and describe what they are, how you can avoid them, and what you can do about them during processing.

First a little primer. Image sharpness is a factor of a number of things but visually, we see things as being sharp when we can easily discern edges. Proper focus definitely helps but even a perfectly focused image can appear out of focus or blurry if the contrast is low enough that edges are hard to detect. Try reading in dim light for a real-world example. One of the first steps in some image detection and recognition systems is to detect the edges. Much of the work I did in my professional career was that of improving image brightness, contrast, and sharpness, all of which play together to create an optimal image.

Good sharpness but excessive motion blur

Good sharpness but excessive motion blur from a one half second exposure

Blur from the motion of your subject is sometimes hard to control, especially if your shutter speed is already limited by the amount of light, aperture, and usable ISO values you have at your disposal. Always try to keep your shutter speed as high as possible in order to minimize motion in your subject.

Obviously, having the fastest lens and the camera body with the best high-ISO performance is a help but it can also be expensive. Although some inexpensive zoom lenses are very handy, investing in something like the very popular Canon 100-400mm f4.5-5.6 or the Canon 400mm/f5.6 prime lens may be worthwhile. In addition to being a little faster, the optics are guaranteed to be better too.

Blur from camera movement can come from several sources. Hand holding, using an inadequate tripod, having the camera or tripod resting on a moving object, motion from the camera’s mirror, or motion caused by shakey hands or improper shutter release.

Hand holding is fine as long as you follow the rule of thumb that says you want the shutter speed to be as fast as the reciprocal of the focal length. So if you’re using a 400mm lens, you want your shutter speed to be at least as fast as 1/400s. You can certainly get away with shower shutter speeds but when you are getting close to or below this threshold, consider holding your breath, resting against a tree or a solid object, resting your elbows against your chest, and locking the camera against your body as tightly as possible.

I used to avoid using tripods and I’m still not fond of them but after seeing the results I can get by using them, I am rarely seen without one. In fact I finally broke down and paid big money for one that will probably outlive me. But the quality and stiffness of this system is now so much better than anything I ever had before. And with the big supertelephoto lenses I use today, I was way overdue for such a steady support. Most affordable tripods will be made out of aluminum but the better ones are made out of carbon. They are a little lighter than their aluminum counterparts but they are so much stiffer which is important when using heavier cameras and lenses. Also the higher quality ball heads and gimbals are usually well worth the money spent. The used market often offers some good deals.

Using a high dollar tripod doesn’t guarantee great results. You also need to consider the surface you are on and whether or not there is wind hampering your stability. Be careful when shooting on piers or walkways, especially if joggers are frequent. You can sometimes feel every footstep of people who are several hundred feet away and if you can feel it, your camera can too.

And just when you think you have the most stable platform available, your hands can introduce vibrations as well. Consider a wireless shutter remote or at least using the timer which is built into most cameras. Wireless remotes can be had for very little money and are wonderful for reducing shake with long lenses and they can work while in your pocket, making cold weather days more tolerable.

In the next part we’ll talk about some of the optical degradations to image sharpness.

Featured image: Reconstruction of George Washington’s birthplace in Westmoreland County, Virginia. Canon 1Dx with Canon 16-35mm/f2.8 lens. Five exposures bracketed by 2/3 stop and tonemapped (HDR) with Photomatix Pro. Handheld.

Interested in getting better pictures? Consider one of my private or semi-private clinics.

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