Saturday, November 2, 2019

Depth of field is affected by image size.

As an image gets larger, out of focus areas become more apparent.
Depth of field is a cardinal concept in photography.  The main aspects of controlling depth of field include focal length, aperture, and point of focus.  An often overlooked aspect relates to the size that the image is to be viewed at. 

Consider this scenario.  You are photographing something and check the image on your rear LCD display to make sure it looks good.  Yes, everything seems great, including the focus.  All the stuff you wanted to be in focus seems to be.  You take the image home and view your creation on the computer.  The now much larger image wasn't what you expected.  There are blurry areas before and after the subject.  Zoom in a bit and it gets even worse!  How could you have missed that?

It happened because depth of field is based on a number of criteria, including size of the final image.  As the photograph gets larger areas that originally appeared in focus become progressively more blurry.  This seems like an enormous problem, but only counts based on another factor; proximity of viewer.

Have a look at the images above.  The top one seems fine with everything nicely in focus.  It would have looked fine on the camera's LCD screen.  As you view following enlargements it becomes apparent that the focus wasn't quite what it could have been.  However, an important consideration has been overlooked. 

Move further away from your viewing surface, whether it is laptop, desktop monitor, cellphone, or tablet.  As you get farther away the enlarged components of the photo see less blurry than they were.  This is why you can enlarge a photo to fit a highway billboard sign and it seem all in focus.  Chances are that, as you get closer to it, parts of it may start to look a little fuzzy.

Enlargement size and viewing distance go hand in hand.  It turns out the real factor affecting whether something is in focus or not is based upon the image falling upon your retina.  By managing the amount of enlargement, including cropping, and the viewing distance, you can alter depth of field to some extent.  It is not the main method of course, but it is something to consider.

Thanks for reading.   www.ericspix.com

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