I have just purchased a new D3100 and when I snap a picture, only a small portion of the picture on the bottom appears, the rest of the screen is black. Am I doing something wrong or is the camera at default? Thanks for any help on this a I am new to DSLR cameras
Keep in mind that the image is projected on to the sensor upside down.
The OP said that it was the bottom portion of the picture that was appearing, and the top part just black.
If the mirror was only moving enough to partially uncover the sensor, it is the bottom part of the sensor that would be exposed, which would be receiving the top part of the image. That's opposite of what the OP reports.