Phase Detection and Contrast

maiMelissa

I am listening to this online course on photography by ImprovePhotography and today they discussed two types of focus, Phase Detection and Contrast. I am not sure I understand the meaning of the two. I think he said if you are in Live View, then it's Contrast and you only use it where there is a big contrast on your subject and the surroundings. I hope I got it right. Can someone please clarify to me what those two things are and when to use or not use them? I have never taken pictures in Live View, I always use Viewfinder

PBked

Hi Melissa,
You don't half ask them do you? There are many sites on the web which will explain phase detection for you. If you have degrees in electrical and mechanical engineering you may even understand what they are saying.
All DSLR's use phase detection autofocus. It is fast, fairly efficient and expensive. The circuits and sensors that make up this system send information to your lens which tell it what movements to make to the internal lenses in order to produce a focussed image.
All compact cameras with a rear LCD and DSLRs with live view use contrast detect which balances contrasts across your view to give a focused image. The circuitry for contrast detect takes up less space in the camera, costs less to produce, and is fairly efficient for the majority of views (try using contrast detect to photograph a white cat on snow and you will get a blinding headache).
As to your question, you do not really choose to use them. Phase detect occurs when in DSLR mode, and occurs contrast when you are in Live View. However, it is possible on your camera to choose phase detect when in Live View, but let's not go there.
Regards

maiMelissa

Thanks PBked for your explanation. I think I will let this one rest and just continue with other lessons. I'm doing online lessons to improve my photography.