Lenses are one of the most important components of your camera in terms of getting crisp and clear images. The lens does all the focusing, so the better the lens, the better the photograph (especially when making enlargements). However, there are other elements responsible for the sharpness of your images. Before you blame an unsharp photograph on the lens, there a few other crucial things to consider. In fact I hate to say this but the vast majority of unsharp shots are the result of photographer error not a lemon lens.
Shutter speeds that are too slow for some shots such as moving targets, will not produce the sharpness you are looking for if you are looking to ‘freeze’ the action. Moving targets require faster shutter speeds. Generally though, for objects that are not moving, the rule of thumb is 1/focal length of the lens as the slowest shutter speed to use while hand holding a camera. This means that if you have a 200mm lens the SLOWEST handheld‚ shutter speed you need on any subject is 1/200. Choosing a speed slower than that introduces the photographer’s own movement into the image and sharpness is sacrificed. Generally following this rule will give you favorable results. Practicing at different shutter speeds will give you a good grasp on things; so practice, practice, practice. While you’re practicing, slap the lens on a tripod and shoot some text on a newspaper pasted to your wall at different apertures. Use a cable release. Now you can gauge the sharpness of that lens you were questioning!
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