Friday, March 04, 2011

Understanding Depth of Field in Photography

I think I was fairly incoherent in discussing depth of field yesterday so I m going to refer everyone to the illustrations in this article Understanding Depth of Field in Photography. there are way too many words in this article but the images are helpful. first scroll down to the three images of a statute. if you look carefully you can see that in the first example more of the faces are in focus than the next and the last one has the least amount of information in focus before and after the statue. look at the label. it says f8' f5.6 and f2.8. these are referring to the size of the aperture or opening in the lens. the smaller number is actually the bigger opening. I think this is because like some speed settings these are fractions, so 1/8 is smaller than 1/2.8. I never have to think this through when I shoot. it's automatic and so it's always hard for me to explain. back to the article, scroll back up to the image of the light going through the lens with some of it converging on the film/sensor and some of it converging before or after the sensor. this basically illustrates focus. now zip on down to the bottom of the page where there are two purple images of differing depth of field as a result of a larger or smaller aperture. this shows why the different size results in a longer or shorter depth of field. so I often combine the effects of different apertures with the soft focus on the perimeter of the lens baby lens. to maintain a good exposure I change the speed of the opening to counter an extreme aperture. if the camera is wide open then I need the lens to open and close fast. so then I have a short depth of field and most of the image will be soft. but I can't record change over time. when i want to do that i use a small aperture and a long speed. so that while more of the subject will be in focus, the movement of me, or the subject or the camera is recorded as swirls or zig zags etc. i'm sure this is still a bit unclear as I have the flu, but I'll be back Sunday.

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