Learn how to take tack sharp photos!

One of the most common questions I receive in the comments and via email concerns sharpness. Readers are not satisfied with the quality of their pictures and seek advice. It is not surprising, considering that blurry photographs are nearly impossible to salvage and can ruin an otherwise exceptional shot.

In this article series, we will investigate the most common causes of blurred pictures:

• Camera Shake: Caused by long exposure times. Image stabilization can only do so much; learn what you can do to avoid it.
• Motion Blur: Fast moving subjects can cause blur. Learn what to do about it.
• Wrong Focus: What are the focus techniques that will give you sharp pictures?
• Depth of Field: What you need to know about it to get sharp shots.
• Wide-angle Lens Focus: Some points you should know if you decide to go wide.
• Telephoto Lens Focus: And the other way around.
• Camera Issues: Many blame their tools for poor artistry. Sometimes the gear really is to blame; find out how to test your camera.

Camera Shake

This problem alone keeps Manfrotto in the business of providing world-class tripods.

Factors like available light, aperture (size of lens opening), and sensor sensitivity (ISO) determine the time you need to expose your sensor to light. During that time, the picture the camera sees must not change. Therefore, the camera cannot move.

If the exposure time is short, all things are well. Our involuntary hand movements are slow by comparison. If the exposure time is longer, we cannot hold the camera steady long enough anymore.

Image stabilization promises to remedy the situation, but it also gives a false sense of security. Just like the electronic stability systems of your car ultimately succumb to physics, the image stabilization of your lens or camera can only extend the useful range. You still need to understand how to deal with camera shake.

When do you need to worry about camera shake?

Unfortunately, this depends on the focal length of your lens. When you hold very strong binoculars to your eyes, the picture looks very shaky. The large optical magnification amplifies the small movement of your hands.

By contrast, looking through a magnifying glass does not have the same affect.

The longer the lens focal length (binoculars), the shorter your exposure time needs to be to make the shaking invisible to your camera. When the picture the sensor sees moves less than one pixel in distance, the movement is invisible.

Avoid camera shake without using math:

If you dislike math, you can use this method to determine if you need a tripod:

• Set your camera to Auto ISO.
• Check your camera manual for the Auto ISO range. Usually, the maximum ISO level for Auto is not the maximum level the camera is capable of utilizing. The Canon Rebel 450D, for example, can go to ISO 800 in auto mode.
• Shoot in automatic mode or aperture priority mode and always check the ISO setting in your viewfinder.
• If the camera ever hits the maximum, vary the aperture (smaller f-number) until the ISO drops down. If it does not, you probably need a tripod.

Avoid camera shake using math:

Math can do a better job predicting camera shake. Skip over this section if it overwhelms you!

For 35mm film cameras, the rule was that exposure time should be shorter than 1/(focal length). If you had your lens set to 100mm, an exposure of 1/125s would allow you to shoot handheld.

Many digital SLRs have sensors that are smaller than the 35mm film used to be. The reduction in size translates into an "equivalent focal length" that is different from the markings on your camera. You can look up the crop factor (focal length multiplier) for your camera and calculate the equivalent focal length as:

Equivalent focal length = crop factor * focal length

The Canon Rebel series, xxD series, and Canon 7D cameras all have a crop factor of 1.6. This means, with the lens set to 100mm the equivalent focal length is 160mm and the exposure time should be 1/160s or shorter.

Image Stabilization

Image stabilization adds about 2 to 3 stops to your exposure time. For each stop, multiply the exposure time by 2.

For the 100mm example above, we then get:

1/125s * 2 * 2 ~ 1/30 s

If you try to expose longer, you will get blur, despite the image stabilization. I found that no Canon Camera I have used factors image stabilization into the calculation when you set it to Auto ISO.

How camera shake looks like

When you have a blurry picture due to camera shake, all parts of the image will show the same blurriness. The foreground and the background have the same level of blurriness.

Come back to read about Motion Blur in my next article of this series or subscribe to my feed to get it delivered to your reader for free.