Archived posting to the Leica Users Group, 2000/10/06
[Author Prev] [Author Next] [Thread Prev] [Thread Next] [Author Index] [Topic Index] [Home] [Search]Roy- You happen to be talking in my neighborhood!! TVs, at least the NTSC standard here have a vertical sweep frequency of about 15K, painting an interlaced pattern of odd and even lines on the screen based on the AC current frequency of 60Hrz- so that the screen is swept 60 times a second, or thirty frames a second- each being scanned twice- once for the even lines and once for the odd numbered lines- So, a shutter speed of 1/30 of a second or slower will prevent the 'dark bars' from appearing. IF you are where they use the PAL system, you need to figured the Frames persecond to adjust your exposure. and if there is any variation in your shutter speed, then test to see if it might be off at 1/30- but a 10% variation should not be a problem. Computer monitors on the other hand, are set to scan at various rates depending on their resolution and have adjustable scan rates, but if you are worried about regular TV, andy speed of 1/30 or slower will eliminate the bars. The exposure too, is somewhere betweenthat of tungsten and daylight, depending on the screen phosphors- a test is always a good idea!!! Dan ( Been there, done that!) POst - ----- Original Message ----- From: "Roy Zartarian" <royzart@connix.com> To: <leica-users@mejac.palo-alto.ca.us> Sent: Thursday, October 05, 2000 9:26 PM Subject: [Leica] Photographing a video monitor > LUGs, > > I'll be doing some shots where a video monitor is a significant part > of the image. Because noise must be kept to a minimum, I'll use > an M body. > > What's the fastest shutter speed I can use with the focal plane > shutter to prevent bands from appearing across the screen? I recall > reading somewhere that 1/8th sec or slower is necessary but can't > locate the information among my resources. > > Thanks > Roy > >