Aperture, when do you adjust it and why?

Definition.

The aperture is an adjustable opening in the lens that allows light through to the recording media. The size of the opening is referred to as the f-stop.

Understanding it.

When setting the f-stop keep in mind that the smaller the number the larger the opening. Therefore an f-stop of f/4 gives you an opening larger in diameter than an f-stop of f/22.

As a result a lens set at f/4 will let in more light than a lens set at f/22.

Lets take a closer look. The “f” in f-stop stands for focal length with “stop” referring to the action of restricting the size of an opening. This opening then is a fraction composed of these two values.

A=f value/stop value.

For example a lens with a focal length of 100mm and an f-stop of f/4 will have an opening diameter of 25mm, (100/4). With the same lens 100mm and an f-stop of f/22 the opening would be 4.5mm, (100/22).

Now you see why the larger f-stop means a smaller opening and therefore less light reaching the sensor.

Here is a simple diagram to emphasize this point.

An important aspect is in getting the exposure correct. This is where aperture and shutter speed go hand in hand.

When you increase the f-stop this closes the opening, which means you will need to slow the shutter speed in order to maintain a correct exposure.

If the opening is too small and the shutter speed too fast not enough light will reach the sensor and the photo will be too dark.

If the opening is too large and the shutter speed to slow too much light will reach the sensor and the photo will be too bright.

You need the perfect balance between the two in order to achieve the correct exposure and have a photo worthy of printing and framing.

If you don’t want to worry about manually setting the shutter speed use the aperture priority mode (AP). Sometimes referred to as aperture value (AV).

In this mode you set the aperture and the camera automatically chooses the shutter speed, wonderful.

Setting the depth of field (DOF).

You will also need to change the f-stop when setting the depth of field.

If you whish to set a shallow DOF, you need to choose a smaller f-stop. This will allow more light through the opening so make sure the shutter speed is adjusted accordingly.

By choosing a higher f-stop you will increase the DOF but decrease the amount of light reaching the sensor. Again make sure the shutter speed is adjusted correctly.

Keep in mind you can always use the semi-automatic modes to help you out.

Pay attention to the shutter speed though, you may have to use a tripod if the speed chosen gets too slow for a hand held shot.

Summary.

You may be required to change the f-stop in order to maintain a proper exposure.

You may chose to change it in order to obtain a desired effect.

No matter which it is, aperture and shutter speed go hand in hand. If you change one you will need to change the other.

Keeping the two in balance will ensure a proper exposure and give you the desired effect.

Pay attention to the settings and use a tripod whenever necessary.

Actually it would be better to use a tripod whenever and wherever feasible. After all the sharpest photo possible is your goal.

But remember these are not hard fast rules. They are guidelines to help you understand the basic operations.

Make sure you break the rules. Take some under exposed shots and some over exposed. You may discover some pleasing effects.

Enjoy your photography and remember keep shooting.

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