Control of shutter speed and aperture of the Nikon D3100 camera is available in modes M, P, S and A. Moreover, you can achieve the same exposure with different combinations of aperture and shutter speed values. Fast shutter speeds and large apertures soften background details and freeze the subject, while slow shutter speeds and small apertures bring out background details and blur moving objects.
Shutter-priority auto (S)
In this mode, the camera allows you to manually set the shutter speed, and then automatically adjusts the aperture value for optimal exposure. A fast shutter speed should be used to freeze the movement of objects, and a slow shutter speed should be used to blur it with wiring or to capture illuminated night landscapes. To do this, set the mode dial to S and select a shutter speed by rotating the command dial. The shutter speed will be displayed in the information display and viewfinder. Then you can focus and take a picture.
Aperture-Priority Auto (A)
In aperture priority mode, the user selects the value, and the camera sets the optimal shutter speed for the given conditions. A larger aperture and lower f-number will help blur objects in front of and behind the subject in focus. These settings are best used when shooting portraits and for blurring the background. Small apertures and large f-numbers sharpen background and foreground details, ideal for landscape photography.
In order to start shooting in this mode, you need to turn the Nikon B3100 mode dial to position A. Then the camera prompts you to select the aperture, its value is displayed on the information screen. Rotate the command dial to select the desired aperture, then focus and shoot.
Manual mode M
In this mode, the shutter speed and aperture are set by the photographer. The mode dial should be rotated to the M position, and then the exposure indicator should be checked. In the event that the lens is equipped with a built-in microprocessor, and the selected shutter speed differs from the automatic parameters, the exposure indicator will indicate whether the picture will be over- or underexposed. If the limits of the exposure meter's measuring system are exceeded, the indicator starts blinking. It can be seen on the information screen of the camera as well as in the viewfinder.
In manual mode, you yourself choose the shutter speed values in the range from 30 to 1/4000 seconds, you can also set the parameter "bulb exposure", then the shutter will be open for a long time while its release button is held down. The diaphragm is set by pressing the button with its image and rotating the control dial. Aperture and shutter speed values are displayed in the information display and in the camera's viewfinder.
