JW writes:
<<Could you plug in some numbers maybe? An example would help me. Are
you
<<proving the old rule that a "safe" shutter speed is 1/f, refining it,
or
<<disproving it?
Yes, relevant today chasing Flutterbys. Might have 15min tomorrow for
one more try.
The thread is related to refining the 1/f rule of thumb for macro.
Looking at review of IS lenses with the IS off, it is remarkable that
on most tests 40-60%
of shots are sharp or have mild blur at 1/f shutter speed. Depends on
the lens and operator of course.
With macro many think magnification is the main relevant variable and
that was my untested view until recently. The geometry and math
would argue that focal length remains important. It is a gross
simplification but likely good enough to multiply the 1/f by (1+M)**2
where M is the magnification. So at 1:1 with a 100mm macro lens one
would require about 4 times faster shutter speed or 1/400 to get a 50%
chance of a sharp or mild blur shot. Lateral shake is almost irrelevant
for low mag but imp't for
higher mag thus the advantage of the 5 axis IBIS in Oly bodies or the
hybrid system in the Canyon 100 macro. Tripods even better of course
but not always feasible.
CN writes:
>>But your wording below gives me some pause to ask: What is the
nature
>>of the motion being measured?
I just chose a simple motion to model. Angulating the cam up or down
(yaw?) will do--which was the type of camera shake to which I was
referring but many others apply
equally well. It is easy to see how mag affects blur as at any angular
velocity of shake the image moves over more pixels on the sensor/film
proportional to the magnification. More shake =higher angular
velocity=more blur. Assuming I interpret the math correctly focal
length doesn't have a thing to do with how many pixels the blur affects
or the angular velocity per se. However the image linear velocity is
higher on the sensor thus more blur proportional to the focal length.
I would have to think a bit more about the easiest/best experimental
design to demonstrate that but Chuck can probable come up with that
anyway.
Standing on terra firma but quicksand can not be excluded yet, Mike
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