Focus in Photography

Having got your exposure correct, it is time to think about focus.

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The human eye is instinctively drawn to things that are in focus, and so it is normal that the most important part of the shot is in focus and any parts that are irrelevant or distracting in a scene are out of focus. We’ll talk more about Depth of Field in the next post, but you might want to refresh your memories with this post.

If your images are not sharp here are some of the possible reasons for this, and some solutions;

Shooter

1 You (or your camera) are not focussing properly. If you focus manually, check that your eyesight is true and that the dioptre in the viewfinder is set correctly. For autofocus, make sure that the camera is focussing in the area you want – cameras these days have multiple focus points and it’s possible that the wrong point is being selected as the focal point of the image. You might also want to check the calibration of your lens/ camera combination which you can do with a calibration chart. I’ll be covering this in more detail in a later post.

2 You are getting camera shake when you take a picture. More common at telephoto length as the tiniest movement is magnified greatly. You can improve this by one or more of the following – increase your shutter speed, use a tripod (turn off image stabilisation if you do), make sure your stance is firm and the camera is held as close to you as possible (not way out in front), don’t shoot if you’re out of breath.

3 Your subject is moving. This can be improved by – increasing your shutter speed, asking your subject not to move (i.e. for people), pan the camera at the same speed as the subject (i.e. for moving cars, planes etc.)

10 Reds

4 You are too close to the subject. Camera lenses have a minimum focusing distance, for some lenses it might be 30cm for others it might be 90cm. If you are closer than the lens minimum then it will not focus properly.

5 The camera can’t find enough contrast in the scene to latch on to. Autofocus systems in cameras work by looking for areas of contrast in an image. Focussing on a white wall is difficult as there is no contrast, but focussing on a nail stuck in that wall is fine because the nail provides an area of dark contrast against the wall. If you have a low contrast scene look for an area with some difference in tone that you can focus on.

Minimalist Sweden

6 It is dark. As mentioned above, your camera needs to see contrast to focus. If the scene is very dark it may not be able to recognise contrast. Most cameras have a focus assist beam – a red beam of light that fires when it’s dark, this helps the camera focus. The light then goes off before the shot is taken. You may have to go into your menu system to enable this assist beam.

7 Your lens is smeary. Hopefully you would have noticed this, but maybe there is a greasy fingerprint on the lens that is causing the image to blur.

 

Many of the above solutions involve choosing a faster shutter speed. As a general rule if you are shooting hand-held, your shutter speed should be equal to or faster than 1/ focal length – so on a 100mm lens, you should be at 1/100th of a second or faster. For a 300mm lens this speeds up to 1/300th of a second.

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Be careful at wider apertures though – if you’re shooting with a 14mm wide angle lens 1/14th of a second will more than likely be too slow and you’ll introduce blur just by your natural tiny movement. Anything longer than about 1/50th of a second is going to be a struggle for most people shooting hand-held.

Having explained how to get sharp focus, what if you want part of the image to be out of focus? We’ll cover that in the next post on Depth of Field.

 

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2 responses to “Focus in Photography

  1. Pingback: Technical analysis of a photograph | paul j chapman photography·

  2. Pingback: Techniques for analysing and judging photos | paul j chapman photography·

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