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10-21-2011, 06:31 PM   #1
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Video lighting flux

I just watched some video from our vacation. I usually use a camcorder but my new Sony camcorder just stopped working the second day of vacation so I was forced to use the movie mode on the K-5. Anyway, when viewing the files a number of the clips show a lot of fluxation in the lighting going from lighter to darker. The camera was on a tripod aimed in one direction so it should not be showing such lighting changes. Has anyone experienced that with the movie clips from the K-5? I'm not sure how to post video on this site otherwise I would have included that.

10-21-2011, 06:37 PM   #2
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QuoteOriginally posted by Jool Quote
Anyway, when viewing the files a number of the clips show a lot of fluxation in the lighting going from lighter to darker
Use exposure lock (AEL) when shooting video with your pentax bodies - just remember to re-meter if there is a big change in the lighting conditions.

QuoteOriginally posted by Jool Quote
The camera was on a tripod aimed in one direction so it should not be showing such lighting changes.
The slightest change of any lighting in the shooting environment will change the exposure (clouds moving in, etc).

To explain what is happening, or to give you some insight on why it is happening, imagine you taking a photo with your K5 in AV mode then pivoting your camera to the left still shooting the same subject but the lighting changes a small bit, a little less light changes your shutter speed thus changing the exposure - this is what is happening, using AEL will solve the fluctuation. For consistency, you should use a light panel if doing a lot of video work...



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Last edited by joe.penn; 10-21-2011 at 06:45 PM.
10-21-2011, 11:48 PM   #3
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Is it a faster frequency variation, rather than the slower adjustment of automatic exposure changes? Does it look like it's kind of moving up or down the screen, instead of just a global change? Where you shooting a scene primarily lit by fluorescent lights? Were you in Vegas? Sounds to me like it might have been a Mhz issue. Fluorescent lights pulse, at 60hz in this country, and at 50hz in others. That's why some countries shoot at 30fps, and some countries shoot at 25fps. When you match the frequencies, the pulsing goes away. You can somewhat reduce it's effect by adjusting the shutter speed, but it's hard to get rid of it entirely. You could also drop down to 720p/30.

Or, something was causing the camera to think it should be altering the exposure, like difference color/luminosity items moving in and out of the scene.
10-22-2011, 06:30 AM   #4
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Also be sure to not use spot metering as any small change in the middle of the screen will affect the entire picture.

10-22-2011, 08:13 AM   #5
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The scence was outdoors swimming in Lake Superior. It was very overcast and stormy so the sun was not coming in and out. I did not use spot metering. Yes, I was viewing the files in Sony Vegas Pro 11. I would like to attach a clip but the file size limit for .avi (which the K-5 shoots in) is only 3Mb. I don't know that I could get even a small part of the clip to be that small.
10-22-2011, 10:13 AM   #6
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QuoteOriginally posted by Jool Quote
The scence was outdoors swimming in Lake Superior. It was very overcast and stormy so the sun was not coming in and out. I did not use spot metering. Yes, I was viewing the files in Sony Vegas Pro 11. I would like to attach a clip but the file size limit for .avi (which the K-5 shoots in) is only 3Mb. I don't know that I could get even a small part of the clip to be that small.
Honestly you don't need to attach a clip (at least I don't need to see one) as I know what the problem is - next time use AEL and you are set.

BTW: This is a very well documented issue for video on pentax bodies:




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10-22-2011, 11:28 AM   #7
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This was the first time I took video using a DSLR so I know there are problably a lot of settings on the camera that would make it better. I always use a camcorder for video but being on vacation and having my camcorder nonfunctional I didn't have a choice but to use the K-5. I will try the AE lock next time if I ever have to use the movie function again. Even though the lighting didn't really change I know a DSLR does not function the way a camcorder works. I will try to fix the video I already took in my editor. If you have any other tips or settings for shooting video with the K-5 please post it. Thanks for the info about the exposure lock.
10-22-2011, 12:43 PM   #8
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QuoteOriginally posted by Jool Quote
This was the first time I took video using a DSLR so I know there are problably a lot of settings on the camera that would make it better
That is the whole issue with video on Pentax bodies, there really are no real workable/good settings, Pentax flutters greatly in video - we RULE in APS-C imaging and totally suck in video (suck as in not bad, but wayyyyyyyyyy behind the others)



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