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Thread started 27 Oct 2010 (Wednesday) 08:48
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7d exposure consistancy?

 
sWampy
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Oct 27, 2010 08:48 |  #1

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What could be causing these shots to look so different? I was trying to get used to/figure out auto iso. I had the 7d in full manual, 50mm 1.4 set to 2.5, auto iso, 1/500th. I took like 9 shots in a row, no flash, no changing in lighting, and got the results of the image at the link below, plus the next 8 images. They exposure keeps changing, it reminds me of using a flash with the wrong shutter speed, but no flash. All these shots were back to back standing in the same spot, with no changes to anything.

http://picasaweb.googl​e.com …62010#553258866​5937096226 (external link)
http://picasaweb.googl​e.com …62010#553258868​3586709810 (external link)
http://picasaweb.googl​e.com …62010#553258870​1400644402 (external link)
http://picasaweb.googl​e.com …62010#553258871​6912543298 (external link)

Others taken with auto-iso turned off look fine.

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wrussi
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Oct 27, 2010 08:56 |  #2

well the people that you were taking a picture of were moving therefore causing a change in metering on the camera, specially since these people are wearing black. i say the changes in exposure are normal

why were you doing auto ISO if you had the camera in manual?

try redoing your "test" with some non moving objects and see if you get results like this.


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TheBrick3
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Oct 27, 2010 08:56 |  #3

I'm not a 100% sure which issue you're referring to. If it's the motion blur, then 1/500th probably was not fast enough and the inconsistency comes from variable amounts of motion. If it's the white balance, that could be caused by other camera's flashes.


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Cesium
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Oct 27, 2010 09:33 |  #4

Turn off auto white balance.




  
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Jim_T
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Oct 27, 2010 09:34 |  #5

Looks like fluorescent light flicker...

Fluorescent light isn't constant. It varies in brightness. It happens so fast that our eyes can't see it, but the faster camera lens is capturing the changing illumination levels.




  
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apersson850
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Oct 27, 2010 09:34 as a reply to  @ TheBrick3's post |  #6

It's the light.
You can see the fluorescent tubes in the ceiling. They flicker too fast for humans to notice, but the camera will.
You'll often get inconsistent results with all sorts of metering and automatic exposure. That's because metering is done a fraction of a second before exposure, and during this fraction, the light changes. Depending upon how these lights are supplied, you may get light and/or color changes even in fully manual modes.

OK, I was beaten by Canada by a few seconds!


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sWampy
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Oct 27, 2010 09:34 as a reply to  @ TheBrick3's post |  #7

No flashes anywhere in the room, not that much movement, one image yellow tint on right, next middle, next left, almost random though. Just doesn't seem like exposure/white balance/??? should bounce around this much, and only half the image seems to be effected often.


IMAGE: http://lh6.ggpht.com/_GxSAe6agPJo/TMg37X7UMiI/AAAAAAAA8A8/E35_U9xNIMs/s800/10-26-2010.jpg

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Eric
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Oct 27, 2010 09:37 |  #8

stop using auto ISO. Looks more like inconsistency in white balance to me.


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apersson850
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Oct 27, 2010 09:40 as a reply to  @ Eric's post |  #9

That comes with the flickering. They change both in intensity and color.


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Jim_T
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Oct 27, 2010 09:40 |  #10

http://photo.stackexch​ange.com …ighting-and-shutter-speed (external link)




  
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Eric
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Oct 27, 2010 09:41 |  #11

notice the WB only changes with your framing. Seems consistent when the same framing is used. Its when you throw in 4100 kelvin florescent tube into the mix compared to that light bouncing off the wood floor which would change the color temperature.


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sWampy
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Oct 27, 2010 09:41 |  #12

apersson850 wrote in post #11174168 (external link)
It's the light.
You can see the fluorescent tubes in the ceiling. They flicker too fast for humans to notice, but the camera will.
You'll often get inconsistent results with all sorts of metering and automatic exposure. That's because metering is done a fraction of a second before exposure, and during this fraction, the light changes. Depending upon how these lights are supplied, you may get light and/or color changes even in fully manual modes.

OK, I was beaten by Canada by a few seconds!

Seems weird it would only do it with auto iso, and none of the images showing iso levels changing at all 3200.


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paparios
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Oct 27, 2010 09:44 |  #13

sWampy wrote in post #11174169 (external link)
No flashes anywhere in the room, not that much movement, one image yellow tint on right, next middle, next left, almost random though.

As others have explained, this is a problem related to the frequency of the electric power (which is 60 Hertz or 1/60 sec) producing the light which the camera meters.
If you are shooting at 1/500 sec, it means that sometimes, as the electric power is passing through a value of 0 volts or nearby, your metering will see a darker scene and try to compensate, while on other times, when the electric power is passing near a value of 110 volts, the metering will indicate a brighter scene and also try to compensate.

Miguel


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Eric
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Oct 27, 2010 09:45 |  #14

Must be the old magnetic ballast in the lights. Tell them to upgrade to electronic ballast T8's.....

Or just set your WB manually to florescent or correct in post.


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JackProton
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Oct 27, 2010 09:47 |  #15

Its part of the nature of fluorescent lights. Fluorescent lights flicker at a rate of 120 times per second. This was quite noticeable to the naked eye with older fluorescents. The intensity and color temperature of the light can shift during that 1/120th second cylce so when you use a short shutter speed, you can actually catch the light at a point in time where its very different from what the camera expected.

http://blog.tommyimage​s.com …r-fluorescent-lights.html (external link)
http://en.wikipedia.or​g …ent_lamp#Flicke​r_problems (external link)




  
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7d exposure consistancy?
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