Wants me to log in. Not a Facebook user, so no can do. John Coyle Brisbane, Australia
-----Original Message----- From: [email protected] [mailto:[email protected]] On Behalf Of Peter Loveday Sent: Friday, 24 December 2010 1:58 PM To: Pentax-Discuss Mail List Subject: Re: The Physics of Photographing Moving Subjects I'm sure someone will have a more scientific answer, but I'm going to take a guess and say those lines represent the overlap between the blurs of adjacent spokes. - Peter -----Original Message----- From: Doug Franklin Sent: Friday, December 24, 2010 2:09 PM To: Pentax-Discuss Mail List Subject: The Physics of Photographing Moving Subjects OK, I know there are some folks around the list that know a lot more about the physics, optics, and other science surrounding our hobby than I do. And I'm asking their help in understanding something. In the following photo, take a specific look at the way that the wheels and in particular the spokes are rendered. It's a digital capture, but I've seen the same effect in film captures. http://www.facebook.com/photo.php?fbid=119672688098162&set=a.114665221932242 .11964.100001662949948 Specifically, notice that the spokes, especially on the rear wheel, appear mostly as blurs of grey. But also notice that there are specific highlights that look like slightly blurry spokes themselves. The number of these artifacts in the photo is identical to the actual number of spokes on each wheel. I specifically checked after having noticed this effect in previous shots. But I don't understand how they get there. I'm suspecting is some sort of "temporal moire" thing going on, but I can't envision the mechanism. And that's the help I'm asking. I'm hoping one of you can explain the physical mechanism that's leading to those blurry spokes in the wheel instead of just showing a less "peaked", more uniform grey blur. The shutter speed was 1/250, which is intentionally slow enough to give the wheels and background a blur while giving me a chance to get a sharp shot of the body while panning (I shoot almost all of the moving car shots on the track at 1/250, if you can see the wheels in the shot; 1/125 if it's a slow corner). The car was going about 100 miles an hour and accelerating as the shot was taken. -- Thanks, DougF (KG4LMZ) -- PDML Pentax-Discuss Mail List [email protected] http://pdml.net/mailman/listinfo/pdml_pdml.net to UNSUBSCRIBE from the PDML, please visit the link directly above and follow the directions. -- PDML Pentax-Discuss Mail List [email protected] http://pdml.net/mailman/listinfo/pdml_pdml.net to UNSUBSCRIBE from the PDML, please visit the link directly above and follow the directions. -- PDML Pentax-Discuss Mail List [email protected] http://pdml.net/mailman/listinfo/pdml_pdml.net to UNSUBSCRIBE from the PDML, please visit the link directly above and follow the directions.
