The pros to using Magic Lantern Rack Focus is that it’s free and you can get very precise focus points. No more overshooting your focus points and having to backtrack. I believe you can also achieve absolutely no camera shake by using a remote (instead of pushing the play button on the camera body) to trigger the focus point switching. However, the lens’s motor is very loud when it is autofocusing between focus points. It might just be my lens, and this can be remedied by using an external microphone. Also with this Magic Lantern rack focus method, you can’t adjust the speed or the length of time to get from focus point a to focus point b. The only other pitfall I can see is that this method will drain your battery more than just manually pulling focus. But if you have time to set up your shots and want precise focus pulling, using Magic Lantern is great choice.
Video Preview & Directions:
Step by Step Directions for Magic Lantern on Canon T3i:
Set your lens to automatic focus.
Focus on the end point
In the Magic Lantern menu (press the trash can button). Scroll to “Focus End Point.” Click on the set button twice to get back to live view.
Use the arrow keys to focus on the next area of interest.
Hit the trash can button (magic lantern).
Press the play button to pull focus.