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Why does an unfocused lens still give a focused view with a longer exposure? For example, I took an out-of-focus photo with a ¹⁄₁₀th second exposure (at f/7.1), but when I change to 10 seconds (at f/22), it seems to be in focus.

Why is this?

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    The only thing I can think of is the camera choosing a smaller aperture when you reduce the shutter speed. A smaller aperture (larger f number) leads to a larger depth of field; with a small enough aperture it may be that the whole scene fits inside the DOF and focus doesn't really matter. – JohannesD Jun 16 '14 at 13:55
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    Whilst I understand that English may not be your first language, are you able please to expand on your question? Give an example (an example photo) with the settings used to take it. As it stands, your question makes little sense. – Mike Jun 16 '14 at 14:06
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    And what aperture where both photos taken at? – Philip Kendall Jun 16 '14 at 14:18
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    f/22 10secs and f/7.1 1/10sec – Kapil M Jun 16 '14 at 14:20
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    Well then, there's your answer. You changed aperture as well as shutter speed, so you've got a different depth of field. – Philip Kendall Jun 16 '14 at 14:32
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You used a smaller aperture (larger f number) which results in a greater depth of field, thus the image was less far out of focus. It has nothing to do with the longer exposure. If you had added a bunch more light so that you could take it at f/22 with a 1/10 second exposure, you would get the same amount in focus as you did with the 10 second exposure at f/22.

  • Thank you for the answer. and i will be trying this when I get time! – Kapil M Jun 17 '14 at 13:24

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