Back button focusing is taking focusing away from the shutter button and assigns it to one of the buttons on the back of the DSLR. Focusing using the back button of the DSLR is a very useful feature. It can be used to shoot moving subjects as well as still subjects. With the shutter button half pressed in AI Servo mode, it will refocus each time as the camera tracks the moving subject and this results in a lot of wasted out of focus images and one will need to switch from “One Shot” mode to “AI Servo” and vice versa (Canon cameras) when subject stops and starts moving randomly. There is no point in the camera having a high frame rate if it simply cannot lock focus using the shutter button and this reason is enough to use the back button to lock focus.
Most cameras normally come with exposure mode automatically set. This allows you to just go ahead with photography as your camera is already set to select settings for you. This helps especially when one is a beginner but as you progress in photography, you will desire to have some clear and crispy images which might not be possible to attain with the preset exposure modes. Moving on to semi automatic modes provides you with more room to explore and with proper practice you will be able to effectively master how you can set the exposure triangle effectively to be able to realize the desired images. Mastering the exposure means understanding the amount of light allowed to hit the sensor of the digital camera when you press the shutter button, which is very important.