what is the best focusing mode for 50mm prime lens. Manual mode or Auto mode to get crisp results ?
There are special situations where MF will be more reliable, but most of the time AF is better:
- Lenses that are designed for AF are usually difficult to focus manually with great precision. The internal focusing mechanism is designed for AF speed, which means that small movement of the focusing ring makes relatively large difference in the focus plane. The focusing rings usually do not have the right amount of mechanical precision, damping and smoothness needed for precise focus
- MF focusing requires that the optical path through the viewfinder is precisely assembled and ideally adjustable, and this is not always the case with lower end DSLR cameras
- Smaller DSLR cameras usually do not have very good viewfinder (dim and small)
- Lower end cameras usually have fixed focusing screens that aren't great for manual focusing with fast lenses and they do not have any focusing aids like old cameras used to have
- AF is able to acquire focus very quickly, so it is easier for the photographer to follow moving subjects and be ready in the decisive moment
There's no definitive answer to this. It depends on what your subject is and what the situation allows. If you're shooting still life or landscape from a tripod, you can switch to Live View, zoom in and use manual focus. If you're shooting sports or live music, there will be a lot of movement involved, so it won't be easy without continuous focus (AF-C).
Strictly, to get "crisp results" they are both exactly equal and capable. Autofocus and manual focus both do the same thing -- bring the image into focus -- and by moving the glass they both do this the same way.
It's really about the user, the camera, the conditions. Try using manual focus by simply racking back and forth and you'll get nowhere. Try using autofocus in a busy scene to focus on a small detail and you'll get nowhere. Understanding the camera and its capabilities, and how to achieve the photo you want is how you can determine what's best to use.