I use a Nikon D610 and whenever I take a picture, I get a black bar at the bottom covering half of the photo. How do I fix this? Is my shutter speed off? It isn't very fast, but no matter what I do I can't figure out a way to fix it. The camera is 3 months old even without flash I get the black bar in my photos.
The D610's maximum sync speed is 1/200s. If you have set your shutter speed higher than this, and you are not using Auto-FP (high-speed sync) or you're using a flash that cannot do high-speed sync, you get dark bars at the top and/or bottom of the frame.
Essentially, the shutter speed on a camera is controlled by the gap between the 1st and 2nd curtains. The larger the gap, the longer the shutter speed. As your shutter speed increases, this gap gets smaller, and at your maximum sync speed, is just large enough that your entire sensor is uncovered when the exposure is made.
Any faster, and the gap becomes smaller than your sensor, and since the flash burst is much faster than your shutter speed, parts of your sensor are covered by the curtains during the flash burst.
FP (focal plane) or high-speed sync mode requires that the camera and flash communicate with each other timing-wise, so that the flash can pulse light in sync with the gap sweeping across the sensor for the duration of the exposure, thereby getting the flash's illumination to the entire frame. But this will reduce the light from the flash a great deal (about two stops), and does require a flash and camera body combination that can perform HSS. E.g., a D3100 or a Yongnuo YN-560 cannot do HSS.
Edit: Didn't see that this is happening even without flash--in that case, you probably have a faulty shutter and need to get the camera serviced.