This digital video tutorial explains why your exposure changes when you zoom: cheaper lenses have variable f-stops. Watch more at http://www.lynda.com/course-tutorials/DSLR-Video-Tips-Rich-Harrington/103707-....
This specific tutorial is from the DSLR Video Tips series presented by lynda.com authors Rich Harrington and Robbie Carman. The complete DSLR Video Tips course is presented as a weekly lynda.com series and covers the most common questions videographers encounter when shooting and editing with DSLR (digital single-lens reflex) cameras, from choosing a frame size and frame rate to understanding moiré.
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