posted by flosse_r on Explained!

1 comment

There was a large number of requests to actually explain Aperture and depth of field instead of just the Aperture function and f-stop . Well I can understand this because as I looked at the actual definition of Aperture and searched for a human understandable explanation, I realized there are very few real explanations.  Well this is now changed .

Basically the aperture controls how much light gets through the lens in a stream size. The wider the aperture, the wider the light stream and the shallower the depth of field. As you make the light stream smaller, the depth of field increases. This is because the circle of confusion, basically everything outside a certain visual circle, stays the same within a sensor format (see FullFrame vs. Crop explanation for more on Sensor sizes). It’s like your peripheral vision, everything outside our normal peripheral vision is outside the circle of confusion. So e established that the circle of confusion stays the same and that everything INSIDE this circle is recorded.

While this makes sense once you wrap your head around it, I think in order to quicker understand how Aperture works an illustration is in order:

As you can see a the Aperture gets smaller the sharp area becomes bigger. Focus is not taken into consideration as of yet in this example. Focus and zoom distance basically moves that crosspoint of the two aperture edges and in doing so affects the depth of field in front and behind the subject.  Now this explanation might be simple for the advanced and professionals but this is exactly what is happening with the Aperture. Still hard to get your head wrapped around? Well check this out. In Macro Photography the depth of field is amazingly thin because you focus so close to the sensor.  The lens elements move to accommodate the very close focus point and in doing so they create a VERY, VERY shallow depth of field. We are talking millimeters here at life size Macro Shots (1:1). You can see the folioing photos to make the point. They are shot in f4.8, f8 and f22. This is a 67mm lens cap from my lens and as you can see on close focus even at f4.8 the depth of field is not even as wide as the letter N and even at f22 you BARELY get your field of view in focus.

I hope this helped you out in actually understanding depth of field and Aperture more. Yes, it is a bit simplified but it brings the point across so that everyone can understand it.

Tags: aperture, depth of field, dof, lens, lenses, macro, photography, sensor