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05-06-2012, 07:45 PM   #1
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Exposure fluctuations

Hi all.

I was hoping some one might be able enlighten me as to what has happened here?

Correct



Incorrect



I was attempting a time lapse video of the stars over my town under a full moon, about 500 shots in I started to get the odd photo with a different colour cast to it. a good quater of the last 200 photos have this problem.

Pentax K5
Settings:
Focal Length - 30mm
Shutter speed - 15sec
Aperture - F6.3
Manual mode
Metering mode - Multi-segment
White balance - Tungsten
ISO - 1000
Manual focus
6m JPG
Interval settings - 20sec
755 frames over 4 hours
Battery was fully charged and still showed half charge when I stopped the interval shooting.

One other thing of significance, the 755 photos were split into two folders. Every other time I have tried this all the photos will be in one folder.


Last edited by DoubleD; 05-06-2012 at 08:20 PM.
05-06-2012, 08:21 PM   #2
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Why set white balance to tungsten? Why not daylight?
Not really answering the question, but I think you can still fix the white balance on jpegs using Pentax Digital Camera Utility.
05-06-2012, 08:41 PM   #3
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Just a personal preference for tungsten when doing time lapse videos. I normally set it to daylight when I do star trails to get more colour into the stars.
05-06-2012, 09:03 PM   #4
dms
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Given night time city lights I would/do also use tungsten.

05-06-2012, 09:19 PM   #5
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What was the starting and ending times of your set? You are likely getting a lot of pre-dawn sunlight coming up over the horizon. Notice how the lower half of the sky is significantly brighter in the second shot?

You'd expect to see that very blue sky when you have sunlight and Tungsten WB, even long before sunrise, and long after sunset.

Also, notice how the light on the ridge to the right looks the same in both shots? That tells me that the difference in light/color in the sky is indeed from sunlight.
05-06-2012, 10:08 PM   #6
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Start time was 7.45pm, finish was 11.47pm. unfortunately those two shots were consecutive shots at 10.49pm so the daylight was long gone.
Also it only started happening intermittently in the last 200 or so shots out of the 775 shots taken.
05-07-2012, 06:00 AM   #7
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Is the setting 10. WB Adjustable Range (in Custom Settings 2 menu) set to Fixed? If not then the camera can slightly adjust (automatically "fine-tune") white balance even if you set wb to specific light source (e.g. tungsten, daylight, etc). See page 209 and 91 of the manual.

Probably some light source fouled the cam and it "fine-tuned" white balance of those shots.
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