Well... now I am back where I started... with two opposing replies! I
think the best thing to do is as another poster stated, and just do
some tests to see for SURE!
Thanks all,
Steve Parrott
On Aug 22, 2007, at 8:20 AM, Don Weiss wrote:
Steve Parrott wrote:
I know someone here can answer this for me. I will try to explain
as clear as I can.
I know the "rule" is your shutter speed should be at least the
reciprocal of your focal length to avoid blur, (assuming no form of
image stabilization).
I want to use a lens with a max zoom rating of 250 on a digital SLR
with a crop factor of 1.6, so the 35mm equivalent would be 400mm.
When zoomed all the way out, should I be sure my shutter speed is
at least 250.... (the lens rating), or 400.... (the 35mm
equivalent)?
Bob Wise replied:
Use 1/250 for your rule of thumb. The cropping isn't image
magnification.
I remark:
Use 1/400. Camera shake is based angular displacement. Your hold
produces a (presumably) given amount of angular shake. Cropping down
a given focal length produces more image displacement, as a fraction
of image dimension, for a given amount of angular displacement (i.e.,
camera shake). The 'crop factor' corrects for this.
Ergo, if the minimum speed for a 250mm to avoid shake is 1/250 second
for full frame, then it is 1/250 * 1/1.6 = 1/400 sec. for a 1.6 crop.
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