There are many reasons why your picture may not be as sharp as you would expect. The important thing to keep in mind is that it is probably NOT the lens fault! Most softness issues are caused by the camera operator, not the gear.

Lets see what could go wrong.

Shutter speed is too slow

Do you know the golden rule of shutter speed related to focal length? It should be at least 1/focal length, rounding down. So if you are shooting with a 100mm lens, your shutter speed has to be 1/125 or faster. Shooting slower, will put you at risk of camera shake. The solution to camera shake is to either use a tripod/monopod or use a lens with some sort of image stabilization.

Camera shake is not the only issue caused by a slow shutter speed. The other one is related to subject movement speed. It is often overlooked but if the shutter is too slow, a small movement of the subject can result in a soft image. This issue happen most often when using the AV mode and the picture is exposed based on the brightest part of the frame and there is some movement in the darker areas.

here are a few guidelines:

  • kids & fast moving subjects: 1/250 sec
  • subject in an ‘official’ photo shoot: 1/125 sec
  • sport: 1/1000 sec

Aperture is too wide

While shooting at wide aperture produces incredible bokeh, people often forget how narrow the depth of field actually is. Long lenses with wide aperture (85L, 135L, etc.) when set wide open can have a plane of sharpness that is only a few millimeters deep. This make it near impossible to have the target point in focus when the subject is moving. Actually, even a subject who is trying to stay still can move in/out of focus by simply breathing! The solution? Stop down the lens.

Stopping down the lens will also improve the overall sharpness of the image. It is a fact: lenses get sharper as they reduce their aperture, up to a certain point. While this point is generally around 5.6-8, you dont have to go that far to benefit from improved sharpness. Even a single full stop will yield a significant improvement. Try it, you will see!

Lost focus

If you have not separated the focus button from the shutter button, it is quite possible the camera tried to refocus while you where pressing the trigger. This is a hard to catch issue because everything happens quickly but it does happen. The solution? Separate them.

You tried to recompose

Off all the causes, this one is probably the most under estimated and requires a few illustration so it will deserve its own article (coming soon). Until then, do not recompose your shots unless the aperture is a few stop smaller than what is required.

Conclusion

While there are a few more reasons, these three are the most common from my experience. We will review the others and also the technical ones in an upcoming post.

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