Comments on: Actual Cherries, and Long (Daytime) Exposures http://regex.info/blog/2007-05-29/475 Not a photo blog, but sometimes I play one on TV Tue, 02 Dec 2008 21:06:09 +0000 http://wordpress.org/?v=2.0.12-alpha by: Thomas http://regex.info/blog/2007-05-29/475#comment-4828 Wed, 30 May 2007 08:56:20 +0000 http://regex.info/blog/2007-05-29/475#comment-4828 <p>Your post about the traffic light brought me back to a phenomen which I would like to report.</p> <p> I have been in Korea and went along the rails ( I am working for a subway project in Incheon). I had to make a report about the rails, the points and the signals. To prove my report I decided to take some pictures. For the rails and the points no problem at all, but for me and my customers big surprise the signals 'refused' to be taken in a picture:-))</p> <p> The signals are LED type and one aspect was shown at the time of the picture. I took my digital camera (PANASONIC LUMIX FZ-1) and while looking to the display and waiting for the focussing of the cam, the strange thing happened. At the beginning of the shot, the red aspect of the signal was clearly to see in the display, but while focussing it slowly disappears and at the moment of the shot itself it was completely gone! The picture shows a dark signal! Which was of course not dark at all in real!</p> <p> Finally I focussed the cam manually to the stand of the signal, moved the cam to the signal itself and took the picture very quick. It worked out, the picture shows a red aspect signal. But strang, isn't it?!</p> <div class='jfriedl'><p>Thomas, I'd guess it's because LEDs flash. They flash too quickly to notice normally, but if you swing your gaze very quickly past them, you should be able to see the flashing. When you took the photo, it was probably during a moment between flashes.</p><p> As for it slowly disappearing, you were looking at the preview display on the camera, right? I'm guessing that the update frequency of the camera was close to (but not exactly) an even multiple of the update frequency of the LEDs, and that it would slowly come back if you looked longer.</p><p>Now, if you'd like to see a really freaky effect, look at this <a href='http://forums.dpreview.com/forums/readflat.asp?forum=1002&message=23120838&changemode=1' rel="nofollow">thread about a propeller</a>. —Jeffrey</p></div> Your post about the traffic light brought me back to a phenomen which I would like to report.

I have been in Korea and went along the rails ( I am working for a subway project in Incheon). I had to make a report about the rails, the points and the signals. To prove my report I decided to take some pictures. For the rails and the points no problem at all, but for me and my customers big surprise the signals ‘refused’ to be taken in a picture:-))

The signals are LED type and one aspect was shown at the time of the picture. I took my digital camera (PANASONIC LUMIX FZ-1) and while looking to the display and waiting for the focussing of the cam, the strange thing happened. At the beginning of the shot, the red aspect of the signal was clearly to see in the display, but while focussing it slowly disappears and at the moment of the shot itself it was completely gone! The picture shows a dark signal! Which was of course not dark at all in real!

Finally I focussed the cam manually to the stand of the signal, moved the cam to the signal itself and took the picture very quick. It worked out, the picture shows a red aspect signal.
But strang, isn’t it?!

Thomas, I’d guess it’s because LEDs flash. They flash too quickly to notice normally, but if you swing your gaze very quickly past them, you should be able to see the flashing. When you took the photo, it was probably during a moment between flashes.

As for it slowly disappearing, you were looking at the preview display on the camera, right? I’m guessing that the update frequency of the camera was close to (but not exactly) an even multiple of the update frequency of the LEDs, and that it would slowly come back if you looked longer.

Now, if you’d like to see a really freaky effect, look at this thread about a propeller. —Jeffrey

]]>