When holding your camera, if you use too slow of a shutter speed, you may get camera shake.
Your photograph may appear to be out-of-focus.
The photograph may be streaky, and objects may have doubled edges.
The slowest shutter speed you can safely use depends on the focal length of your lens.
If you're at 200mm (telephoto), you need a faster shutter speed than when at 18mm (wide-angle).
Here's a rule of thumb
Whatever the focal length of the lens is, that's the slowest shutter speed you can use when hand holding your camera.
Do the following when using slow shutter speeds without a tripod.
• A heavier camera is more stable.
• Lean against something, or rest your elbows on something.
• Press the camera against something, such as a lamp post.
• Rest the camera on a surface, and use the self-timer or a remote shutter release, to trip the shutter.
• Press the shutter release gently, or use a remote shutter release.
• Press the shutter release at the bottom of your exhale.
Your body is more stable then, and not when you're holding your breath.
Your camera or lens may have image stabilization.
This technology allows you to use slower shutter speeds.
Often, you can use shutter speeds that are two-stops slower.
For example, let's say you were able to avoid camera shake with a 300mm lens by using a shutter speed of 1/500th of a second.
With image stabilization, you may be able to use 1/125th successfully.