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Tonight when I took a photo, I found that a horizontal line going upwards in live view while auto focusing. What would cause this?

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  • Auto focusing in live view is generally a pain. It is slow as it can't rely on the usual methods. Other than in a few cases, not using it is a better idea. (Comment, add as I know this doesn't answer your question)
    – Holloway
    Mar 21, 2015 at 20:10
  • Does this line look like an indicator of some sort, or does it appear to be a weird artifact from the scene?
    – mattdm
    Mar 21, 2015 at 21:06
  • Were you using natural or artificial light? If artificial, was it fluorescent?
    – Darkhausen
    Mar 21, 2015 at 23:36
  • As @Darkhausen suggests, metal halide, mercury vapor and other discharge lamps, as well as fluorescent, flicker at twice the mains frequency; there may be an anti-flicker setting to change update frequency.
    – DrMoishe Pippik
    Mar 22, 2015 at 3:19
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    I was taking photos under street light
    – Bhargav Padia
    Mar 22, 2015 at 5:33

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As you were taking pictures using artificial light the most likely cause of your horizontal line is a small frequency difference between your live view sensor refresh rate and the local power-line frequency.

As you were using street lighting there would be a brief period, imperceptible to us, where the scene isn't illuminated - this would cause the band. As the street lighting isn't synchronised with your sensor, this band could appear at any point within your live view image - if it was synchronised the band would occur when the sensor refreshed and so would not be visible. Working on the assumption your sensor updates at 60Hz (a very precise 60Hz), if your local mains power-line frequency was off-spec at say 59.5Hz (which frequently happens as it's not referenced by a quartz crystal oscillator, unlike your camera) this would result in movement of the band.

A similar phenomenon can occasionally be seen in some film and TV programs where there is a CRT display in the scene with a slowly moving horizontal band. This is caused by the same things, a lack of synchronisation, and a minor frequency difference between the mains-powered CRT in the scene and the observing video camera.

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  • thanks for your answer darkhausen. so technically there is no problem in my camera like I was worrying about.
    – Bhargav Padia
    Mar 22, 2015 at 12:05
  • I suspect your camera is probably fine. Have you tried using live view under tungsten lighting? I expect you won't have any banding issues with tungsten but it's worth confirming. It's also worth checking DrMoishe Pippik's note about flicker reduction. Apparently on setup menu 2 you will find the option for flicker reduction during live view under fluorescent or mercury vapour lighting, with the option to set it to either 50Hz or 60Hz depending on your region. Hopefully this will help reduce your banding...
    – Darkhausen
    Mar 22, 2015 at 14:36
  • Will try it soon.
    – Bhargav Padia
    Mar 22, 2015 at 14:45
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    Hi darkhausen, I tried your suggestion and it worked. I set flicker reduction to 50hz from 60hz. Thanks
    – Bhargav Padia
    Mar 22, 2015 at 20:01

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