Aperture

As the title says, I will focus on Depth of Field (simply called DoF) and the relationship between aperture and shutter speed values. Depth of Field = the area of a photograph where the subject(s) is in clear focus. Playing with Depth of Field values makes a lot o sense when you what to isolate your subject from distracting areas of the background or foreground, thus making it a great thing to play, but not restricted to portraiture, commercial and macro photography.

The amount of Depth of Field in a photograph is given by 3 factors. First, and most important, the aperture value. Aperture is the opening of your lens when you press down the shutter button. Inside every lens you’ll find set of circular blades that move together to control the amount of light entering your camera. DoF values on your camera are represented as “f” followed by a number. That “f” comes from “f-stop” or light stop.

The bigger the f number, say f22 or f32, the less light enters your camera and DoF values of final picture are greater (more field is in focus). In the same way, for smaller apertures (f1.2 / f1.4 / f2.0) more light enters your camera and the DoF is very shallow or narrow (less field is in focus). To conclude:smaller f values => lens aperture is wide open (more light) => shallow DoF (less in focus), and the opposite,bigger f values => lens aperture is smaller (less light) => greater DoF values (more in focus).

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Buying a macro lens can be expensive (especially a real macro lens such as MP-E 65 for EF Canon EOS bodies). Fortunately there’s the cheap alternative: macro extension tubes. With 100 EUR you can actually have 3 of different sizes which can work independently or together. That’s the case with Kenko Automatic Extension Tube Set DG:

Fig. 1: From left to right: 1 – 12mm tube; 2 – 20mm tube; 3 – 36mm tube.

Extension tubes are to be mounted between your camera body and the lens. What they actually do is to physically modify your minimal focal distance, thus allowing you to get closer to your subject by moving the lens away from your camera, resulting in a magnified frame.

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