Today's most of the consumer level DSLRs have dedicated scene modes like close-up, portrait, sports etc which sets exposure automatically when you dial into the mode. Besides these pre-programmed modes, it also comes with few other exposure modes (A, S, P and M) to allow you control over camera’s default settings. When you dial into those pre-configured mode, portrait mode for example, you really do not have a control over exposure. If you want to manually set the exposure, you have to use one of the four modes (Aperture Priority, Shutter Priority, Program Mode and Manual Exposure) available in your camera.

Out of these four modes, three of them are semi-automated modes and one is fully manual mode. When you want to change from one mode into another, you would have to rotate the Mode Dial and select the mode you want to change into. These settings are not specific to any particular camera model but different companies may use different alphabets to denote these modes. For example, Nikon’s shutter priority mode is denoted by letter S whereas Canon’s is T but the idea behind it’s functionality is the same. But in this blog, I will be taking Nikon DSLR as a reference camera when I explain these different modes. Now, let’s get into our first exposure mode which is an Aperture Priority (A) exposure mode.

1. Aperture Priority

In an Aperture Priority (A) mode, you set the lens’ aperture value or give priority to the aperture value and your camera sets the shutter speed to control the overall exposure of the image. This mode is probably best when you want to control the opening or the closing of your lens to gain shallow or deep depth of field. You would have to use the smaller F-stop (f/stop) value to get the shallower depth of field (famous for portrait or close up shots) and you might want to use the larger f/stop value to get everything in focus (widely used in landscape photography).

This mode is best if you want to lock the aperture at fixed value and want your camera to set the shutter speed according to the aperture value you set. If your current aperture value and the shutter speed doesn't match to give you optimal exposure for the subject, you will get Lo or HI indicator in the camera viewfinder telling you that subject is too dark or too bright resulting into underexposed or overexposed photograph. If you get the indicator on, you might want to consider adjusting your settings.

2. Shutter Priority

Our second exposure mode is the Shutter Priority (S) mode which is just an opposite of the Aperture Priority mode. In this mode, you set the shutter speed and your camera will adjust the aperture value for the corresponding shutter speed to give you the balanced exposure. You might want to use this mode when you want to shoot fast moving subjects to freeze the motion (shooting sports events for example). This mode is also famous for landscape photography specially if your frame contains moving subjects like water falls or vehicles where you can control the speed of shutter to produce long exposure effects.

3. Program Mode

Third exposure mode is the Program Mode (P) which is almost like an Auto mode but it will let you override some of the settings on the camera. Nikon uses sophisticated algorithm to determine the best exposure by using the combination of aperture and shutter speed. The algorithm takes the present lighting conditions and other variables into account and program the camera setting to the best of it’s ability. When you frame your photograph and the correct exposure can't be achieved using pre-set value, Lo or Hi indicator in the camera viewfinder warns you about the underexposed or overexposed image. If you get the warning, you can adjust ISO setting to change the light sensitivity and see if that makes any difference.

Unlike Auto mode, Program mode allows you to change the camera parameters such as Exposure Compensation, Metering, ISO, White Balance etc. If you want to change the shutter speed and the aperture value, use the main command dial (also called rear command dial) and it will give you the different combinations of aperture value and shutter speed with the same exposure. When you do that, the letter P (for the Program Mode) changes into (P*) into LCD screen which Nikon calls the "Flexible Program". If you want to go back to the default settings of P mode, you just have to rotate the command dial to the left or the right until P* changes into P.

4. Manual Exposure

Our fourth and final exposure type is Manual Exposure (M) mode. If you want the complete control of your camera, Manual Exposure mode is what you need to dial into. Most of the experience photographers and the professionals use this mode very often because they know how their camera metering system is going to react under certain shooting environment. In the Manual Exposure mode, you can set the shutter speed and the aperture value in whichever combination you like. When you are in Manual mode, rotate the main command dial to change the shutter speed and the sub-command dial (also called front command dial) to change the aperture value. In this mode, you can set everything manually including ISO, White Balance, File Type etc.

Personally, my favorite for the landscape or the cityscape photography is an Aperture Priority (A) mode where I can set the lens aperture to certain value and let the camera decide the shutter speed. If the lighting situation is tricky, I use the Manual mode and control both the Aperture value and the Shutter speed individually.