I think you're using a good rule-of-thumb - but maybe for the wrong reason!
If a person walks at about 3mph, that's 4.4 ft/second. His foot is
stationary for half each step and moving at double that (on average) for the
swing - lets say at peak 10ft/sec.
So in your 1/250th of a second, the foot moves 10ft x 12 inches-to-a-foot /
250 = a half-inch. A half-inch blur on a foot-long foot is probably just
about tolerable to be considered a sharp rendition of the foot.
But none of the above has any consideration for the lens focal length or the
amount of magnification for the print. For sure on a 4x6print of a
full-sized body the tiny blur on the foot is not going to be seen. But if
you zoomed on just the foot it would be another story.
I think we end up with having to define what is an acceptable
circle-of-confusion or some such stuff.
I find it all much easier to do the simple math for how fast an object is
moving and setting the shutter speed for the amount of blur I want.
Concerning camera shake, now we're talking more complex math and I like the
"1/focal-length rule of thumb for 35mm format".
Jez
On Tue, Jul 29, 2008 at 4:33 PM, Chuck Norcutt <
chucknorcutt@xxxxxxxxxxxxxxxx> wrote:
> I beg to differ. It very greatly affects angular velocity across the
> image plane... in other words, subject motion from the camera's
> perspective.
>
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