Accurately comparing FF vs APS-C sensor performance? An open discussion.

Started Apr 8, 2013 | Discussions thread
Allan Olesen
Senior MemberPosts: 1,721
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Look at effective lens diameter, and it all makes sense
In reply to VirtualMirage, Apr 9, 2013

You went a long way to discover something which can be explained much easier if you just look at the effective lens diameter (for example you have an effective lens diameter of 25 mm if you shoot with focal length 100mm and f/4):

  1. At the same shooting distance and same field of view, you will get the same DOF with the same effective lens diameter, even with different sensor size.
  2. At the same shooting distance and same field of view, you will capture the same total amount of light per second with the same effective lens diameter, even with different sensor size.
  3. At the same total amount of light you will get the same amount of noise on cameras with comparable sensor technology, even with different sensor size.

1+2+3: Same DOF = same noise, even with different sensor size.

Some explanation to item 1 which may not be obvious at first:

Shallow DOF is caused by different parts of the lens looking at the subject from different angles and thus seeing slightly different parts of the background aligned with a point in the foreground. At the same shooting distance and the same effective lens diameter these angles will be the same, no matter what focal length and sensor size you have behind the lens.

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