Depth of Field (DOF)

An analysis on Depth of Field (DOF) where large aperture gives maximum frame blurry and narrow aperture gives maximum sharpness. DOF is a keyword of acceptable zone of sharpness. Click pictures with same subject, same frame and analyze it whether the subject is in focus or not. Consider a Dx or Fx format DSLR with prime or zoom lens but the distance should be same for all clicks.

Often we hear that the narrow aperture gives more DOF which means more sharpness or razor sharp images. A subject with blurry background or foreground creates a shallow depth. Photo artists creates such shallow depth of field for more attention on the subject and the out of focus areas create some beautiful bokeh.

If there is intense light and the subject is fully focused or sharp, photo artists must uses small or narrow aperture. We can find sharp pictures in a landscape, street, group photos and so on. Here narrow aperture means f/8, f/11, f/16 etc. However, for portrait or removing busy background, photo artists uses larger aperture like f/4, f/2.8, f/1/4 etc.

Now the question arises why narrow aperture creates sharp image along with background and foreground? We have God gifted lenses in our eyes. It focus so fast and accurate that we think all are sharp in nature with foreground and background.

But the fact is not true. Let’s go for an experiment. Put your finger from eyes in such a distance that it gives you sharp image. Concentrate on that finger and your brain says that background is in out of focus. In general, we move our eye balls so fast to focus from one object to another that we believe all are in focus. Scientifically, when we focus on a subject, both the lines from A to A1 ends in a point in our eye ball lens.

Circle of Confusion – 1

So, we think that image is sharp. Similarly same thing happens in our camera lens and we get a sharp image.

If the two lines does not end in a point, image turns into out of focus or blurred in some portion of the subject, that means if both the lines intersect each other before the lens of camera and two lines hit the lens instead of one is known as Circle of Confusion.

If the Circle of Confusion is large enough then it produces more out of focus pictures. For example:

Circle of Confusion – 2

Here you can easily find out that it focus the total side face of a human being. So, a particular area is in focus and the other place will be in out of focus, Lens can focus in a particularly place but circle of confusion concentrate various places. As a result viewer finds so many unfocused areas and analyze it as an unfocused picture.

In contrary when the circle of confusion is less, image turns into more sharper than the previous one.

Circle of Confusion – 3

Here we can see that circle of confusion is smaller enough and the top and bottom lines touches the human face. So, here the face is in tends to focus concentrating on a single point of the face, say, the eye.

The circle of confusion is so small that we think human face is focused and the small circle of confusion only happen when photo artists uses narrow aperture and the light beam passes lesser than the previous one. This is the overall story of narrow aperture with more sharp image along with foreground and background.

Thank you for your patience to read till the end of the article.

Happy clicking, happy sharing.