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10-29-2012, 08:14 AM   #1
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Differences in brightness between consecutive shots in manual mode (K-5)

Hello everyone,

I was wondering if anyone could provide an explanation as to why I get such big differences in luminosity between two consecutive shots. I set out to make a time lapse video of the sunrise last week. The setting of my camera, a K-5, were as follow:

- Manual mode & focus
- ISO 200
- F6.3
- 1/60s
- Jpeg, 2M, ****
- Interval: 1s

My camera seemed unable to take two consecutive shots with the same luminosity. It's worth noting that this only happened during low light conditions, once the sun was up, the differences between photos stopped (except for the slow increase in luminosity as the sun rose of course). Anyway, 2/3 of the photos taken before sunrise are useless, which is very frustrating. I hope someone here can tell me what went wrong or what I did wrong. Could this be because I left the white balance on auto?

Here are two consecutive shots, taken 1 second apart, at the beginning of the shooting. You can see that one is much brighter than the other (look at the sky).

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10-29-2012, 09:38 AM   #2
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What setting do you have in the Custom settings menu for Auto EV compensation?
10-29-2012, 09:45 AM   #3
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Auto EV compensation: 1 (Off)
10-29-2012, 09:47 AM   #4
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It could also have to do with highlight or shadow adjustment. Also, the sun rising actually does have a huge effect on the amount of light, even in seconds. Its entirely possible that long exposures taken one after the other would have very different brightness.

10-29-2012, 09:47 AM   #5
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well...

one other thought; light coming in through the viewfinder could mess with the meter (not a big issue in manual mode) but could possibly leak and change the image a smidge.
10-29-2012, 09:55 AM   #6
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Were the differences gradually increasing or some lighter some darker? At sunrise the light does change very rapidly, particularly if there are moving clouds. Your eyes adjust so it does not seem so at the time, but the camera just records what is there.
10-29-2012, 10:06 AM   #7
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QuoteOriginally posted by Na Horuk Quote
It could also have to do with highlight or shadow adjustment. Also, the sun rising actually does have a huge effect on the amount of light, even in seconds. Its entirely possible that long exposures taken one after the other would have very different brightness.
Highlight/shadow adjustment are both off. The exposure time are rather short in this case, 1/60th of a second. I don't think it played a role here.
The natural increase in sun light cannot explain why every other picture is dark/bright. It's like this: photos # 4271, 4273, 4275, 4277, 4279 are darker, while # 4270, 4272, 4274, 4276, 4278, 4280 are brighter. For a time-lapse video this is very annoying, it appears like I photographed a strobe light!
10-29-2012, 10:08 AM   #8
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QuoteOriginally posted by jatrax Quote
Were the differences gradually increasing or some lighter some darker? At sunrise the light does change very rapidly, particularly if there are moving clouds. Your eyes adjust so it does not seem so at the time, but the camera just records what is there.
Some darker some lighter like I just explained above, it's not a gradual increase.

10-29-2012, 10:55 AM   #9
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I think Auto White Balance could be a factor. If I open up a RAW file and move the WB slider up and down, I get brightness changes. Does your software show the color temperature applied to each image?

Any other Auto setting could be a suspect, but it doesn't sound like there were any.

If you have a screwmount lens or a mirror lens, you could have complete control over the lens aperture. Or I guess shoot wide open with anything else. Normal K-mount lenses are fully open on the camera and stopped down to shoot for every shot. If the aperture isn't that precise, you might get slight variations in each shot. But since you have more consistency when the sun is up, that's probably not the issue.

There are a few other threads about brightness changing in time-lapse shots, not all of them resolving the issue.
10-29-2012, 11:08 AM   #10
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I had the same problem with a set of shots on saturday - manual exposure but significant differences in the brightness of each RAW. All corrections off. I was using my da70 and can only assume at 7fps the iris can stick sometimes and not shut down fully to the set aperture.
10-29-2012, 12:51 PM   #11
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QuoteOriginally posted by Just1MoreDave Quote
I think Auto White Balance could be a factor. If I open up a RAW file and move the WB slider up and down, I get brightness changes. Does your software show the color temperature applied to each image?
Knowing the color temperature would indeed be very useful. But in a jpeg file it doesn't seem possible to read the color temperature that was applied by the camera. If that information is stored, it's probably recorded in the proprietary part of the file. At least that's what I understood after doing a quick internet search. Maybe the people at Pentax can extract that information.
10-29-2012, 12:59 PM   #12
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AWB should be off for a time-lapse -- leave it on a fixed setting.

Of course, the lens aperture could just be at fault -- what is the lens?
10-29-2012, 01:09 PM   #13
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QuoteOriginally posted by vonBaloney Quote
what is the lens?
The lens is a Sigma 18-50 F2.8 EX DC Macro But I don't think the lens had anything to do with it since I only have those differences in brightness in low light conditions, the images I took when the sun was up are all ok. I'm beginning to think that the WB was at fault, I should have chosen a fixed color temperature.
10-29-2012, 01:14 PM   #14
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QuoteOriginally posted by vzbx Quote
The lens is a Sigma 18-50 F2.8 EX DC Macro But I don't think the lens had anything to do with it since I only have those differences in brightness in low light conditions, the images I took when the sun was up are all ok. I'm beginning to think that the WB was at fault, I should have chosen a fixed color temperature.
That would explain it -- the color temp is changing rapidly at sunup/sundown, and with a time-lapse you probably want to actually see those color changes rather than have them all corrected out...
10-29-2012, 01:56 PM   #15
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QuoteOriginally posted by vonBaloney Quote
the color temp is changing rapidly at sunup/sundown, and with a time-lapse you probably want to actually see those color changes rather than have them all corrected out
Yes... and no I think. Maybe someone with a better knowledge of how WB works can correct me if I'm wrong, but AWB still allows you to see the colors changing, it's just that the camera proprely balances them so that you picture doesn't appear yellowish, or blueish etc.
I think in this case what happened is that with little ambient light, such as in the pictures above, the camera had trouble finding the right WB and was applying a different one with almost every shot. Sunlight reflection on the clouds could also have played a part as someone mentioned before. So far that's the only logical explanation that I can come up with.
But in the end you're right, I was careless, I should have locked the WB. Oh well, nevermind, live and learn... Thank you all for the help
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