Why is this happening?

[Karinia]

Hello,

I was shooting a wedding and then my camera started to do this black line through my photos. Its random, shows up both mostly horizontal, but have seen a few vertical ones. Sometimes it will happen and sometimes it will be fine. Anyone seen this before? I cannot figure it out for the life of me. Do you think there is something wrong with my shutter?

My camera hardly has as much use on it. I use my camera around once a year. I am severly upset.

I have a Canon 6D. I also was using 3 different lenses. 

[Karinia]

The lights were dimmed and they are also using a special type of lights that are creating an even worse flicker effect. As a result its messing with my shutter release and timing. So sometimes light gets in one shutter blade in sense, while not another. Also why I would get some picture and some pictures were okay. I will actually have to slow down my shutter to fix it. This is what the Canon rep said, as well as everyone else here. They seem to be right since outside of the venue, with the flash, everything is working fine.

[TCampbell]

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@isidroco wrote:

Can't be the lights of the venue, because it wouldn't have rotated the dark line when you rotated the camera, it's a flash obstruction issue (or maybe mirror didn't rise fully within the camera obstructing some of the light). Sorry for the caps, didn't mean to be rude.

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The camera has a "rolling" shutter and in two ways.

If shooting stills, the shutter "opens" from top to bottom.  Once nuance is that the lens projects the image flipped upside down onto the sensor.  So a shutter door physically opening at the "top" of the sensor first, means it's actually what we think of as the "bottom" which get the initial exposure to light.  

To make sure each pixel gets exposed for the same amount of time, the a second door closes behind the first door.  Again... top to bottom physical (which records as bottom to top on the image because the image is inverted inside the camera).

If the shutter speed using any setting faster than the camera's fastest flash-sync speed (in the case of hte 6D I think that's 1/160th) then the second door actually starts closing before the first door is completely open.  You get the effect of a gap which sweeps across the sensor from top to bottom.

When shooting video it's a bit different because the shutter opens and remains open while in video mode.  But it has the same effect (but even more pronounced) because in this mode it uses a "rolling electronic shutter".  That means it cannot read all rows of data simultaneously... it has to read them in row by row (a sensor that can read in all rows at the same time is called a "global shutter").

It basically reads in the first row of pixels, then the next, and the next, and so on.  The banding can be caused by the state of the lighting at the time that particular row was being read off the sensor.  Since the rolling shutter reads the rows in the same order regardless of orientation, the banding will still be in the "long" direction of the sensor (so when held vertically they look like columns instead of rows)

If it helps, here's a video using extreme high-speed with slow mostion to illustrate what happens inside the camera and how it works... and the effects of a "global" vs. "rolling" shutter.

[isidroco]

Thanks Tim Campbell for your detail explanation, so using a slower shutter or another light source could fix the problem.