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NOTE: This is the third of a series of articles about understanding and controlling shutter speed, especially handheld. In my last article I listed each factor  which I will cover in depth in upcoming articles. Please see the list of all the articles in this series  to understand how you can use slower shutter speeds in your photography. See the first article in this series for an example of a sharp photo taken handheld at 1/2 second.

The zoom setting or the focal length of your fixed lens affects the minimum shutter speed you can use to get sharp pictures when handholding a camera. Telephoto lenses require a much faster shutter speed than a wide angle, for example, or a blurred image may occur. Why is this so? The telephoto lens magnifies the image but it also magnifies camera shake.

RULES OF THUMB

In the film days the following rule of thumb was true and still is a good starting point when making test shots. However, I am suggesting that with practice and with my tips in future articles, you should be able to shoot while handholding at about 4 stops slower than the old rule.

In the following list, lens are listed in their 35mm camera equivalent focal lengths.

Wide Angle Lens (28mm, 35mm equivalent):
Old rule = 1/30 second minimum
Digital = 1/2 second possible with practice

Normal Lens (50mm, 35mm equivalent):
Old rule = 1/60 second minimum
Digital = 1/4 second possible with practice

Moderate Telephoto (100mm, 35mm equivalent)
Old rule = 1/125 second minimum
Digital = 1/8 second possible with practice

Normal Telephoto (200mm, 35mm equivalent)
Old rule = 1/250 second minimum
Digital = 1/15 second possible with practice

Extreme Telephoto (500mm, 35mm equivalent)
Old rule = 1/500 second minimum
Digital = 1/30 second possible with practice

A FORMULA FOR SHUTTER SPEED/FOCAL LENGTH

For those of you who are mathematically minded, here is the old rule of thumb set out as a formula:
The shutter speed should be the reciprocal of the lens focal length (35mm equivalent) rounded off to the next higher shutter speed --- for example a 50mm lens needs a 1/50 shutter speed -- which rounded off would be 1/60.

HOW TO FIGURE THE 35MM EQUIVALENT FOCAL LENGTH FOR YOUR DIGITAL CAMERA

If you want to know the 35mm equivalent of your digital camera zoom setting or your fixed lens, here's how to figure it out:
#1. Get the specifications (spec sheet) for your particular camera from a website such as:
http://www.dpreview.com
which often lists the specs after a review of the camera.
#2. Get the size of the digital sensor from the spec sheet such as: 1/2.5" (7.18mm) sensor
#3. If using a zoom lens, take a series of shots from wide to telephoto and then read the EXIF data for the focal length setting for each shot.
#4. Go to the following calculation site:
http://www.digified.net/focallength
and type in:
== the sensor size
== the focal length
THEN press the calculate button
and voila: you will see the 35mm equivalent focal length

BTW the above site will give you the Lens Multiplication Factor for your lens so that in the future you only need to multiply the EXIF recorded focal length by that factor rather than having to go to the website to make the calculation.

For example: in the test photo I shot for the first article in this series the EXIF data told me that:

• the focal length setting for the zoom was: 14.52
• my sensor had a Lens Multiplication Factor of 6
• Therefore: my 35mm equivalent focal length for that zoom setting was:
• 14.52 X 6 = 87 mm (rounded off) or a moderate telephoto setting

For more about these techniques see my book: Experimental Digital Photography.

CONCLUSION:
Nevertheless, I need to emphasize that the shutter speed you can use successfully is quite personal. Use the general rules in this set of articles as starting points only. You should make a series of tests to determine what your lowest shutter speed can be with a given focal length for you as an individual. I will cover in detail how to conduct such tests in a future article.

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