Here is what you need to know
There are many photography articles that explain the different shooting modes of your camera. However, many of them do not explain the relationship between shooting modes, exposure, and metering.
If you want to understand how your cameras exposure modes work, then you must learn about exposure values or EV’s as there known. Once you understand this, then choosing and using your cameras different shooting modes easy.
Most photographers will have come across the exposure triangle.
However, the exposure triangle, misses the most important concept in photography, Exposure values (EV)!
Why is that important? Because for every given exposure value, there is a predetermined combination of aperture and shutter speed that can be used to ensure that whatever you are photographing is correctly exposed.
Exposure values are a set range of brightness values ranging from -6 (starlight night) to 16 (sunlight day). Exposure values can be higher, but in terms of photography these are the most quoted values.
So how do these values apply to photography? Simple, when you use your cameras internal light-meter, it measures the brightness of a scene or subject and sets an exposure value, this exposure value is translated into a shutter speed and F-Stop.
For example, at ISO 200 and with a metered scene brightness equivalent to EV 12, you can use the following combination of aperture and shutter speeds.
How does that relate to your cameras shooting modes? Your camera shooting modes range from fully automatic through to full manual control.
Camera modes simply provide a way for you to take some control or full control over your exposure settings.
And because there is a correlation between EV (scene brightness) and the use of ISO, Aperture and Shutter speed, making a change to one or more of these settings in a semi-automatic modes means that the camera will adjust the other parameters to ensure the exposure is identical.
Staying with our example, this means that at an ISO of 200 at a brightness value of EV12, our exposure would be F/8 @ 1/125s. So, in full auto mode, the camera will set an aperture of F/8 @ 1/125s.
In aperture priority mode – If you set the Aperture to F/8, the camera will set the shutter speed to 1/125s.
In shutter priority mode – If you set the shutter speed to 1,125s, the camera will set the aperture to F/8.
In programme mode – The camera will set the aperture to F/8 and the shutter speed to 1/125s.
This shows that each of these modes do parallel things by making one of the variables constant, and then changing the other one to give a correct exposure. Which means that, if you understand how they work, it will not not matter which semi-automatic mode you choose.
The only reason to choose either aperture priority (AP) or shutter priority (SP) mode is when you need to be absolutely sure that either your aperture remains constant (AP mode) or your shutter speed remains constant (SP mode).
Or you want to be more creative with your use of aperture or shutter speeds. In either of these modes you can vary one of the constants and arrive at a shutter or aperture speed of your choosing. In other words
Varying your aperture in AP mode changes your shutter speed. So, you can vary your aperture to arrive at a desired shutter speed.
Varying your shutter speed in SP mode changes your aperture. So, you can alter your shutter speed to arrive at a desired aperture.
I might almost argue that the only three modes you need on a camera these days are:
Intelligent Auto mode – camera looks after all settings.
Programme mode – with programme shift for fluctuating combinations of aperture and shutter speed.
Manual mode – to have full control over aperture and shutter speed combinations, and for varying exposure without using exposure compensation dials or buttons.
Whatever camera mode you use, your goal is to use your camera’s setting to give you the optimum exposure for the scene being photographed, and to use your aperture and shutter speed combinations creatively.
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