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Thread started 08 Nov 2013 (Friday) 12:59
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Exposure settings in Auto v's TV

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Nov 08, 2013 12:59 |  #1


I was wondering if something could please explain something to me either I just don't understand how my Canon 50d works or there is something wrong with it

In fairly low light conditions i.e dark outside with living room light on if I set my 50d to full auto mode it will take a perfectly exposed image with the following settings 1/60, f4.0, ISO400.

If I then my camera to TV mode and set the shutter speed to 1/60 with ISO400 the camera will auto select apperature of f4.0. When I look through the view finder f4.0 will be flashing which I thought it only did to indicate over or under exposure? The needle is in the middle of the exposure comp bar. I'm confused? If I take the picture the picture is exposed fine, why is the f4.0 flashing?

Any help greatly appreciated:-)

John ­ from ­ PA
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Nov 08, 2013 13:52 |  #2

Can you post two representative images with EXIF info intact? Also what lens are you doing during this comparison?

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Nov 08, 2013 17:54 |  #3
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Sounds like it want to open up the aperture, and it was already wide open. Next time that happens, use slower shutter speed or higher ISO. That should fix it. Oh, that is normal for Canon cameras.

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Nov 08, 2013 18:45 |  #4

When you say 'full auto', do you mean Green Box mode, or do you mean P?

It does seem odd that [ISO400, 1/60 f/4] results in blinking aperture in TV mode, but no blinkies in Green Box/P mode....with the identical settings! if it wanted a faster aperture, and the lens could not do that, blinkies are normal -- but not at the same indicated settings as other modes.

Running a quick test on my camera...

  • If I put my camera (40d) into Tv mode and point it to a dimly lit area at 1/60, because my lens cannot open wider than f/2.8, the f/2.8 starts to blink
  • If camera in Green Box mode, it pops up the built in flash, switches to 1/60 and chooses f/3.5, no blinkies
  • If camera in P mode, it leaves aperture at preset value, and slows the shutter suitably (to 0"3) no blinkies.

lukefildes wrote:
The needle is in the middle of the exposure comp bar. I'm confused? If I take the picture the picture is exposed fine, why is the f4.0 flashing?

The location of the EC needle does NOT alter the amount of exposure needed to render a 'proper exposure' simply biases the meter to shift what it thinks is 'proper exposure', when the needle is not centered. If 1/60 f/4 was 'just enough', cranking in EC +1 might then cause the aperture to blink (if f/4 is wide open for that lens) because in Tv mode it simply cannot get more light thru the lens, due to the aperture.

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Nov 08, 2013 18:48 |  #5

What lens and focal length are you using? Did you change your focal length for the second shot?

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Nov 08, 2013 19:30 as a reply to  @ Snydremark's post |  #6

Was f/4 the maximum aperture for that lens (and focal length if a zoom)?

If so, it could simply be that the scene was slightly different and there was a little more darker tone in the shot when you were in Tv. If the full auto shot was shooting wide open, then locking the ISO and setting shutter speed with Tv could result in the camera wanting more aperture if you pointed the camera at a part of the room where there was perhaps a bit less light wall and a bit more dark furniture, the meter would read the scene differently and want to increase exposure a bit to compensate for the darker tones it is now seeing. Did you happen to look at the exposure meter and notice if it was showing slight underexposure? It would probably only be one notch, a third of a stop or so, if the images are both near identical, but that would be enough to start the aperture number blinking.

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Nov 08, 2013 21:31 |  #7

You probably just had a another metering mode besides evaluative in Tv.

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Exposure settings in Auto v's TV
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