Aperture Priority Mode in Photography: When and How to Use It (Part II)

Read part ONE

EXERCISES

Location: The suggested values in these exercises are based on my experience from an average classroom environment, which is not too dark or too bright. I assume your living room has similar light conditions. You can do the exercises anywhere, but that could mean a significant change in the suggested values for them to work well.

Select your subject: The goal of the exercises is not to produce breathtaking photographs but to understand how the camera settings work. In that sense, any subject will do. A more significant factor for the exercises to go well is the subject’s background. It should be simple, with plain light conditions, not a window or other intense light source.

Please refer to your camera manual for the following:

How to select aperture priority mode

How to set f-number

How to set ISO value

Where in the viewfinder or camera display you can monitor the actual f-number and shutter speed

How to select the appropriate ISO value for the exercises:

Select aperture priority mode (A/Av).

Set f/8.

Point the camera at your subject and check the shutter speed. Some cameras in this mode do not continuously display the shutter speed. If it disappears, press the shutter button halfway down and let it go again. The shutter speed should reappear in the camera display and/or viewfinder.

Adjust the ISO value until the shutter speed is around 1/160. That is the correct ISO value for all the exercises.

Note: On some cameras, like Nikon, you have to turn off automatic ISO in a specific section of the camera menu in order to enable its manual setting. Otherwise, it will remain automatic even when you set the value manually. (Refer to your camera manual for specific instructions.)

If you don’t manage to set the ISO value manually, you could set it to automatic.

EXERCISE 1: Learn to set an f-number on your camera

Select aperture priority mode (A/Av).

Set f/14 (on some camera models with non-interchangeable lenses, the maximum is f/8 or a similar value).

What did you achieve by doing this?

The choice of f/14 (a reasonably high f-number) will create a large depth of field in your photograph - the foreground and background will appear sharp. This is the right choice if you are shooting a landscape, group portrait, or similar subjects where a large depth of field is necessary. The camera will automatically adjust the shutter speed to secure the correct exposure. Notice that the camera’s exposure choice can be right or wrong.

EXERCISE 2: Understand the implications of the f-number choice

Select aperture priority mode (A/Av).

Set f/8.

What did you achieve by doing this?

What is the difference compared to f/14?

In this photograph, the depth of field will be slightly shallower than in the previous exercise because the f-number is lower (the aperture is bigger). If you retake the same photograph, the foreground will be equally sharp, but the background will appear somewhat less sharp.* Notice that as long as the photograph is taken in the same light conditions, the exposure will remain unaltered because the camera measures the very same light, resulting in the same exposure choice.

* If you continued to take photographs, both with f/14 and f/8, but did not notice any difference in the depth of field, I will give the full explanation of depth of field in one of the following posts. In the meantime, take my word for it: a lower f-number creates a shallower depth of field and vice versa.

EXERCISE 3: Simplicity of a semiautomatic exposure mode

Select aperture priority mode (A/Av).

Set f/5.6.

What did you achieve by doing this?

What is the difference from the f-numbers in the previous exercises (f/8 and f/14)?

Take a simple photograph of your subject.

With a low f-number, such as f/5.6, you can achieve a shallow depth of field; the foreground is sharp, and the background is blurry (or vice versa). That is the only difference from the two previous exercises. The exposure will remain the same, as you are still photographing in the same light conditions.

If you take a photograph, it should be sharp and properly exposed. At this point, you can call such a photograph a success. That demonstrates the simplicity of this semiautomatic exposure mode. You can gain control of your camera with little experience as the camera does half of the work: you set an f-number for the desired depth of field, and the camera takes care of the exposure by automatically adjusting the shutter speed.

If your photograph is not sharp and properly exposed, the possible causes could be:

Your room is too dark

Exposure compensation is not reset to zero

Metering is set wrongly

Complex light conditions around your subject

Focus issues

EXERCISE 4: Understand how the camera operates in aperture priority mode

Select aperture priority mode (A/Av).

Set f/5.6.

Find the f-number and shutter speed in the camera display. If the shutter speed

is not displayed, press the shutter button halfway down and let it go. It should reappear.

Point the camera to your subject and keep it that way.

Change the f-number gradually from 5.6 to 22 and monitor the shutter speed simultaneously. Notice: every time you change the f-number, the camera automatically adjusts the shutter speed. Why?

Because the camera compensates to maintain its “correct” exposure. When you point the camera at the subject, the camera measures the light through the lens to determine the correct exposure, or at least the exposure the camera believes is correct. Once the camera picks a particular exposure, it will not “change its mind” as long as light conditions remain unchanged.

You started the exercise by pointing the camera toward the subject. The camera measured the light and automatically adjusted the shutter speed to obtain the correct exposure. As you gradually reduced the aperture size, light was lost.

The camera extended the shutter speed to regain the same amount of light in order to maintain the “correct” exposure. For example, if the shutter speed was 1/100 at f/5.6, when you decreased the aperture to f/8 (one stop less light), the camera compensated by a one-stop longer shutter speed of 1/50 (one stop more light).

There are two more lessons to be learned from this exercise. Firstly, if you select a small aperture size, meaning a high f-number like f/22, there is a substantial risk that you will force the camera to prolong the shutter speed to such an extent that handheld photography becomes impossible (for example, 1/2). Secondly, you need to realize that changing the f-number in aperture priority mode will not modify the photograph’s exposure.

EXERCISE 5: Understand how the camera operates in the aperture priority mode

Select aperture priority mode (A/Av).

Set f/5.6.

Find the f-number and shutter speed in the camera display. If the shutter speed is not displayed, press the shutter button halfway down and let it go. It should reappear.

Point the camera at various brighter and darker objects around you and monitor the f-number and shutter speed.

Notice: The f-number remains constant as you are in charge, but the camera continuously adjusts the shutter speed. Why?

In the semiautomatic exposure mode aperture priority, the camera determines the exposure. During the exercise, you direct it toward subjects of various brightnesses. The camera works hard to expose all of them properly. As the aperture size remains unaltered, the camera’s only option to produce the right amount of light for the correct exposure of all the subjects is shorter and longer shutter speeds. For brighter subjects, the camera will need less exposure time - a faster shutter speed will be selected. The camera will need more time for darker subjects to do the same, so the shutter speed will be automatically extended.

It is worth noting that on occasions when you aim your camera at a very dark subject, it may select a shutter speed that is too-long for handheld photography.