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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