You might wonder why this post about photographing birds in flight is filed in the “Flash” category. Take a look at a closeup of that bird. See the catchlights in the eye and beak? See the shadow from the speedlight underneath the beak?
We sometimes forget that in many of our flash shots, the flash itself can act like a fast shutter (about 1/1000 of a second), and can have a sharpening effect on pretty much anything we shoot. This is real sharpening: Not the pretend sharpening that photo editing programs use. The degree to which flash sharpens an image depends partly on the brightness of the ambient lighting vs the brightness of the flash. As the ambient dims, the role of flash increases, and with it the sharpness of the image because of the flash.
This bird was probably about twenty or thirty feet away. When shooting fast-moving subjects like birds I usually turn off auto-focus and manually focus on something at about the range I’m expecting. When I’m throwing bread for these outings, I’ll throw a piece and set my focus on the spot where it landed. It’s important to be sure that your camera is capturing the largest possible size (pixels wide x pixels high), because often you’ll be cropping down to something other than the middle of the frame.