What does “tack sharp” mean?
It means everything in the image that should be sharply in focus is sharply in focus. You know it when you see it. It’s one of the first components of a photograph your eye instinctively recognizes. If the element of the photograph you want to convey isn’t “tack sharp”, your viewer’s eye will wander through the image looking for the focus point. No matter what other positive elements the photograph contains, an out-of-focus photograph should be immediately deleted.
Never show bad photographs!
“Tack sharp” results from blending mechanical set up with artistic skills.
Set up your camera with the lowest ISO possible. (You may have to use a higher ISO if your subject moves so the shutter speed is fast enough to avoid blurring). Stabilize your camera by using your tripod. Trip the shutter without introducing movement by using a cable release, a self timer, or the mirror lockup. Select an image quality setting like JPEG-fine/Large which yields high resolution images. A fill flash will illuminate areas so they’ll be sharper.
Choosing the aperture gives the photographer the most artistic control. A small aperture (f/16) gives a deeper range of sharp focus while a large aperture (f/4) allows the subject to be in sharp focus while the rest of the image is muted. This tends to concentrate the viewer’s attention on the area in focus. Focus on the eyes. People instinctively look at your subject’s eyes. If the eye is in focus, other components will be secondary and accepted. Thank technology for digital camera LCD review screens! Simply take a test shot and then zoom in to verify its “tack sharp”.