As I mentioned in my recent post, the shutter speed you use may change depending on the camera you select. Motion issues are related to the field of view coverage. No adjustments to shutter speed are needed with full frame sensor cameras. Smaller sensor cameras need to add in the ‘crop factor’ so the ‘focal length equivalent’ is used for determining the shutter speed. Crop sensor Canon cameras may have a 1.6x or 1.7x crop factor, while Nikon DSLR crop sensors are typically 1.5 x. The camera crop factor will be listed in the manual.
So, if a zoom is set to 40 mm focal length on a Nikon camera with a 1.5x crop factor, the full frame focal length equivalent at the 40 mm zoom setting is 40 x 1.5 = 60 mm (full frame equivalent focal length for the crop sensor field of view). So the shutter speed needed to stop action for subtle motion photos is now 1/60 sec. Adding 1, 2, or 3 stops for faster motion scenarios takes it from 1/60, to 1/125 (+1 stop), 1/250 (+2 stops), and 1/500 (+3 stops).
It’s important to practice any photo concepts until they make sense, and then become intuitive. If the math is overwhelming, take it slow, and experiment at home in a comfortable chair. The first consideration is always the actual composition. Look through the camera (lcd or viewfinder) and adjust the zoom to the composition you’d like. Next, look at the lens and assess what focal length the zoom is set to for that composition. Use that focal length number as the denominator for the shutter speed. (If zoomed to 100 mm, the slowest shutter speed to stop subtle motion would be 1/100 sec. (full frame) – 1/150 sec. if using a 1.5x crop sensor camera –1/160 sec if using a 1.6x crop sensor – or 1/200 if working with a 2x crop 4/3 camera). Shutter speed is the most important setting for a motion shot. Set the shutter speed, then select an effective aperture and ISO setting to create a proper exposure. My next post will cover creative uses of motion blur using slower shutter speeds.