Lens wobbles

QI have bought my first telephoto lens, but I just can’t seem to get anything sharp using it down at my local nature reserve. Is the lens faulty? Brad Masterson

AIt’s possible the lens is faulty – but before you contact the seller, do a few simple tests yourself with the camera and lens combination on a tripod, using autofocus to lock onto a static subject. You could even use a brick wall – just something to let you check whether the autofocus is working correctly.

If it is, my guess is you are using too slow a shutter speed for the length of the lens, and the lack of sharpness is just camera movement. This catches a lot of people out. The guideline is that your handheld shutter speed should be at least the same as the focal length; so for your 400mm lens, the minimum shutter speed would be 1/400 sec, but preferably a bit faster.