I've still got a Garrard 301 turntable ( which I don't use of course)
which has three sets of strobe markings on it for setting the correct
speed, either at 331/3, 45, or 78 rpm. Under a normal incandescent
globe these marks appear to stop when the speed of rotation is correct
-----Original Message-----
From:
On Behalf Of Deane P. Lewis
Sent: Tuesday, July 22, 2008 12:20 PM
To:
Subject: Re: Seeing things
Hi Tony, when you look through your Non-SLR camera's viewfinder, you are
looking at a miniature LCD screen. I think what you are seeing with the
rotor blades has to do with their rotation rate being a near multiple of
LCD screen's refresh rate, creating this illusion.
At the risk of revealing too much regarding my age, back when I serviced
studio turntables, I used to check their speed with a special disk that
had radial bars on it, designed to work under the 50Hz lighting we have
in Australia. The disk sat on the rotating turntable in place of the
record, and if the speed was correct, the bars on the disk appeared to
stand still.
The other phenomenon you mention - having an image look sharp in the
viewfinder, but blurry when reviewed, is likely motion blur caused by
using a shutter speed that is not fast enough.
Regards,
Deane Lewis - http://dl.id.au
-----Original Message-----
From:
On Behalf Of Tony Ashton
Sent: Tuesday, 22 July 2008 11:02 AM
To:
Subject: Re: Seeing things
Gidday all,
Puzzle for people found with binoculars or cameras glued to their eyes.
Tyto Wetlands is next door to Ingham airstrip. Medium-big helicopter
took off as I was watching Black Kites. Casually looked through 10x32
Gerbers (as you
do) as chopper sped across sky. Main rotor blades stood out sharply, in
rotation. Focussed digital Panasonic FZ30 camera (not DSLR, no live
preview; lens set at 700mm=) on chopper, and the blades came almost to
halt. Back to
binos: blades turning. Back to camera: blades near halt. Seems sighting
through camera viewfinder accentuated stroboscopic effect. Perhaps mono
v stereo vision? Would this apply if viewing through a scope? If what
you see isn't what you get, it might explain why seeming pin-sharp
images seen during autofocussing hold no magic on review. Imagine a
hummingbird photographer seeing stable images and getting blurred
results. On the other hand, imagine stalling wing movement to assist
identification of, say, flying waders. Comment?
FYI: Immature Red-Capped Robin gone after seven weeks here, northeast of
range, but immature Rufous Songlark, also outside range, still about.
Plus rare showings here and further north of 100+ Sulphur-crested
Cockatoo flocks.
Cheers, Tony Ashton
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