This simple calculation shows how slow you can shoot and still hand hold your lens
There are some simple calculations you can make to determine the optimal length of time you can hand hold a lens for.
This is important information to know because managing a 70-200mm lens at 70mm is very different to managing it at 200mm. Increasing the zoom reduces the length of time you can handhold the lens because any movement in the lens will be exaggerated at full zoom.
The rule of thumb for calculating the length of time to handhold a lens is to take the inverse of the focal length. So, with a 70-200mm lens at full zoom the calculation gives you a handhold time of 1/200 sec, at 70mm it is 1/70 sec.
For a 70-300mm lens at full zoom, your limit is around 1/300 sec.
You can improve these times with Image Stabilization or anti shake features if they are built into your lens or camera but these values give you a rough guide to help you avoid capturing blurry photos.