Although the Nikon D5100 does not provide completely manual control of exposure when shooting video, there is a way to preset both its aperture and shutter speed in advance. Using this technique, you preset the camera's minimum and maximum ISO range, and take advantage of its auto-ISO feature to select the correct exposure for each shot.
In the ISO Sensitivity Settings sub-menu:
Auto ISO Sensitivity Control: ON
ISO Sensitivity: 100 (set to lowest ISO you want the camera to use)
Maximum Sensitivity: 3200 (set to max ISO you want the camera to use)
Minimum Shutter Speed: 1/60 (preset to your desired shutter speed)
The twist here is that you use Minimum Shutter Speed to manually preset the video shutter speed you want the camera to use. Since I always shoot video at 1/60 second, I've only needed to set this once. The camera then uses its light meter to automatically set exposure with an ISO between the (minimum) ISO Sensitivity and Maximum Sensitivity presets. However, if the required ISO for a scene lies outside your preset ISO range, the camera will override your Minimum Shutter Speed preset. In lighting conditions where the shutter speed drops too low, I use the Exposure Compensation button to lower exposure until the shutter speed is boosted back up to my preset speed. Once all settings look good, I use the Exposure Lock button to keep the exposure fixed while filming.
While this may sound convoluted, it gives you more convenient control over exposure than Manual mode would. Here's how you use it in practice:
1. Set your desired aperture in Aperture Priority mode.
2. If you prefer, adjust focus in the viewfinder.
3. Enter Live View mode and confirm focus.
4. If needed, use Exposure Compensation to set desired shutter speed.
5. Press Exposure Lock button.
6. Press Video Record button to start filming.
In the ISO Sensitivity Settings sub-menu:
Auto ISO Sensitivity Control: ON
ISO Sensitivity: 100 (set to lowest ISO you want the camera to use)
Maximum Sensitivity: 3200 (set to max ISO you want the camera to use)
Minimum Shutter Speed: 1/60 (preset to your desired shutter speed)
The twist here is that you use Minimum Shutter Speed to manually preset the video shutter speed you want the camera to use. Since I always shoot video at 1/60 second, I've only needed to set this once. The camera then uses its light meter to automatically set exposure with an ISO between the (minimum) ISO Sensitivity and Maximum Sensitivity presets. However, if the required ISO for a scene lies outside your preset ISO range, the camera will override your Minimum Shutter Speed preset. In lighting conditions where the shutter speed drops too low, I use the Exposure Compensation button to lower exposure until the shutter speed is boosted back up to my preset speed. Once all settings look good, I use the Exposure Lock button to keep the exposure fixed while filming.
While this may sound convoluted, it gives you more convenient control over exposure than Manual mode would. Here's how you use it in practice:
1. Set your desired aperture in Aperture Priority mode.
2. If you prefer, adjust focus in the viewfinder.
3. Enter Live View mode and confirm focus.
4. If needed, use Exposure Compensation to set desired shutter speed.
5. Press Exposure Lock button.
6. Press Video Record button to start filming.