Monday, February 17, 2014

Understanding and Achieving Image Focus and Sharpness: Part IV

Nikon 51 point Autofocus System layout in the Nikon D4 DSLR, photo courtesy of Nikon CorporationImage sharpness depends on multiple factors including focus.
While it's true an image can't be sharp unless the subject is in focus, the converse is not necessarily true, that an image which is in focus, will necessarily be sharp. Image sharpness is fundamentally controlled by focus, but there are other important factors which enable in-focus images to be sharp.

In Part I we looked at how modern digital cameras autofocus (AF), and what factors influence AF systems' ability to focus quickly and accurately.

In Part II, we discussed choosing the best focus mode for a particular subject, manual or autofocus, or using them together, as well as single versus continuous focus, all to achieve a solid focus for a variety of situations common to travel photographers.

In Part III, we got to the nitty-gritty of using autofocus and manual focus, including looking at the different AF area and tracking modes, and focus locking methods.

In Part IV, below, we discuss photographer focus technique, and other factors which enable photographers to make sharp images.

Most photos are made while photographers are handholding their cameras, as opposed to using a tripod or monopod. You can't focus a camera well if your camera is shaking, even when using autofocus. If you're in focus, and whether you're shooting a moving subject, or a static one, camera “shake” or involuntary camera movement will cause your images to be unsharp, blurry.

Good handholding technique is therefore essential, whether photographing a static or moving subject, unless using a device to assist you holding your camera/lens. Keep your feet comfortably spread under your body. Hold the camera/lens with one hand on the left side of the camera for short lenses, or under the lens for longer lenses, for good balance, and other hand on the right side of the camera so your fingers can use the camera's controls and press the shutter release. Use your face/forehead to steady the camera/lens by pressing the camera to your face/forehead when using the viewfinder. Keep your elbows in and against your body to give your camera/lens further support.
If you can, lean against a wall or lampost, etc., to help you steady yourself and camera/lens.
If you're using the monitor on the back of your camera to frame and focus, the most important physical thing you can do to hold the camera steady is to not hold the camera/lens out, far in front of your body, but closer, so you can keep your elbows against your body to give the camera/lens at least limited support. When photographers hold the camera/lens using the monitor on the camera's back with outstretched arms they substantially reduce their ability to get a sharp image, despite vibration reduction (optical stabilization) and a fast shutter speed.

Even with good handholding technique, it's hard to hold the camera steady if you “stab” your shutter release. Marksmen are taught to squeeze their triggers, so the act of triggering their shot doesn't move the gun away from their target. It's no different with a camera. Instead of “stabbing” the shutter release, place your finger atop the button, and gently press it down in a rolling motion.

It's also important to understand that sometimes the camera can't achieve autofocus when you press down the shutter release in one quick motion. If you can, to achieve focus, press your shutter release halfway down to activate autofocus, then after focus is achieved, press the shutter release the rest of the way to make your photo.

When using a tripod, many believe you immediately achieve the ultimate in holding your camera/lens steady. Unfortunately, it's not true. Many tripods aren't up to the task, according to your camera/lens weight, and the focal length of the lens. There are three main techniques one can use keep your camera/lens steady when held with a tripod, but first, don't waste your budget on a tripod not capable of holding your camera/lens well.
  1. Use a remote shutter release to eliminate any movement of your camera/lens due to even “gently” pressing the shutter release button directly.
  2. For cameras which use a mechanical shutter mechanism, when using a long telephoto lens which by its magnification accentuates any movement or vibration, place your hand gently on top of the lens to dampen vibration of it.
  3. For cameras which have a mechanical shutter mechanism with moveable mirror, such as an SLR or DSLR, lock the mirror up, if your camera has that feature, after you frame your image and focus, to eliminate mirror mechanism vibration.
Sometimes, achieving a sharp focus with autofocus is impossible because the quality of the subject doesn't meet the needs of the autofocus system. As explained in Part I, a plain subject with little contrast or with a great deal of nearby foreground clutter is extremely hard to focus upon. Therefore, learning the ability of your camera to autofocus is imperative, so you know when to use manual focus, or when to start with autofocus to get close, and finish with manual focus.

Don't forget to use “depth of field” (DOF) well to achieve focus and sharpness. Have enough DOF to ensure the main subject of your image is in focus. DOF can make up for small errors in focus. Consider setting the DOF so that part of your image may not be in focus, to set up a contrast of sorts in the image, which can focus the eye on your main subject, and help increase the appearance of sharpness in that main subject.

It's also important to recognize what makes the human eye see sharpness in photographic images. Of course, the images must be in focus, but that doesn't guarantee sharpness.

Detail, image detail, makes images look sharp to our eyes. A wide swath of formless, monotone in your subject will not help your image look sharp, but differences in contrast, lines, and well defined specific shapes in your images will. How you frame your subject, what you include in it, and what you leave out will all influence the sharpness of your image.

Use your subject, use the whole scene, which you photograph, to produce a sharp image.

1 comment:

Jon - Warranton said...

Great finish to a great series Ned. Thanks.

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