The Importance of Depth of Field

Depth of field is defined as, “that area around the subject that is in acceptably clear focus”.   

I chanced upon a copy of a local magazine and took the time to look through its pages. I always go through magazines by first glancing at all the pictures then go back and review select articles. This particular magazine interested me because some articles were accompanied by photographs that were not in focus.  At first, I put it to poor printing, but this particular issue had a cover and several photographs in it by a friend of mine and they were sharp.

So why were some images “soft” and others as good as those we regularly get from the lab when we take our memory cards in for printing?  Modern cameras do the focusing for us and it is fairly difficult to get several images of stationary subjects that aren’t sharp.

Now I’ll go back to why I opened this column with the definition of depth of field; and why I think there are lots of photographers that are either spending time adding sharpness using PhotoShop or printing images that lack that overall sharpness. 

The problem I see happening all too much is that many photographers forget that basic concept of how depth of field works with a given lens and think “a wider aperture gives me more light therefore I can shoot with a faster shutter speed” and therefore, “I don’t need a flash or a tripod”.  Well, they are right to a point and (I’m not going to discuss at this time why I think most photos of people benefit from camera flash.) I think that photographers need to be reminded that limited depth of field comes with problems.

When I looked at those images in the magazine I thought about depth of field and how, although the lens may have been very capable of producing sharp images at F2.8, it couldn’t overcome the basic rules of depth of field.  I found there were sharp elements in the pictures, but so much was just out of the “limited area of focus” around the subject that the “softness” affected how the entire image was viewed. 

If one reads the internet forums or asks photographers what lens would be their favourite, of course they would come up with many different choices of focal length, but more often than not they would also indicate they wanted an aperture of F2.8.  The reasons given for that small aperture are either so that the photographer can “shoot in low light or so they can soften the background”.  That’s good, however, one of the purposes of the aperture is to control depth of field. The smaller the aperture the wider is that in-focus area around the subject, and the larger the aperture the narrower that in-focus area around the subject is.  Remember that means that a smaller aperture has a higher number like F16, and a larger aperture has a lower number like F4.   

I think it is a good idea for photographers to have equipment that allows different perspective. I own lenses that have apertures of F2.8 and larger, but I do not take them for granted. I select lenses and use their different apertures to create the effect on my subjects that I want. My advice? One should think about the picture about to be taken and select an aperture that works for and not against the subject.

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