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Old Sep 18, 2004, 9:05 PM   #1
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I recently purchased a digital rebel in hopes of using it as a portable time-lapse camera. It isn't well suited for this purpose.

With the camera locked on a tripod, the aperature, shutter and focus in manual, the "density" from frame to frame is unpredictable. I can knock off 200 frames and the density in everyframe is a little different. The effect played back at 30fps is a lot of fluttering and flickering. Looks like at an old movie.

Now I have shot tons of timelapse work with a 35mm motion picture cameras and video cameras and this is not normal. The sensor is obviously processing the highlights above and beyond the aperature and shutter.

Has anyone encountered this issue. Is there a way around it. Or do you know of a digital camera/sensor that doesn't respond in this disconcerting manner?
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Old Sep 18, 2004, 9:43 PM   #2
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Ok -- you've got my curiousity up.

What do you mean by "knock off 200 frames"? How, at what intervals, and what other camera settings (resolution, JPEG Quality, etc.).

You do have very limited dynamic range with a Digital Camera compared to film. So, exposure needs to be more precise. In other words, you probably can't just pick an aperture/shutter speed combination and expect the frames to look the same (unless they are taken very close together, and the light is very steady).

What is your subject (is the scene changing)? JPEG Compression could also come into play.

Let us know more information about what you are doing, camera settings, etc.


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Old Sep 18, 2004, 11:25 PM   #3
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Shooting at different times of day. Usually clouds and sun in the shot. 5 seconds between each shot. Now I could go out and shoot this with a mo pic camera or video camera for that matter: same scenario, use one shot every 5 seconds, and I will not get this same flickering in the density from shot to shot. There is something definately going on with the CMOS sensors. Not an issue if you are just working with stills. But if you are going to string the images together as an animation you need a little consistency from image to image.

It is not just that the sun is peeking out from behind clouds . . . the sun, and the entire image brightens and darkens. I have shot the sun coming from behind the clouds before. The entire image doesn't dramatically change. Yes, the sun gets brighter, but it doesn't have a overwhelming effect on the entire frame.

Maybe Nikon with their older, more mature CCD sensors will be more predictable. I wish I knew for sure.
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Old Sep 18, 2004, 11:47 PM   #4
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My suspicion would be that the light is simply changing that much. The human eye may not notice a small change, but the camera probably will.You don't have as much exposure latitude with Digital as you do with film. I doubt that there is muchdifference in dynamic range betweenthe CMOS sensor used in the Canon Digital Rebel, as compared to the Sony CCD sensorused in the Nikon D70.

I'd probably try going autoexposure (or at least aperture priority) with it instead of manual. Then, the camera would compensate for changes in EV between frames.
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Old Sep 18, 2004, 11:56 PM   #5
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Here's the movie. My point is that it already looks like the camera is compensating for exposure...which is exactely what I don't want it to do. The sun brigtens, and the camera looks as if it is compensating by closing the iris. This is not what is needed. The sky is not changing that dramatically. What is changing is the way the sensor is responding to the increased brightness of the sun.

Download the file from this link.

http://f2.pg.briefcase.yahoo.com/bc/...case.yahoo.com
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Old Sep 19, 2004, 4:07 AM   #6
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Hi,



Try setting your cameras white balance to a manual setting. If night shooting set it to fluorescent light. If day, set to sun, cloud or shade. I do a lot of panoramas and mosaics. If I dont manually set the white balance, the camera sets a very slightly different one for each shot, therefore when played in a movie, it will flicker. I have done with with time lapse, and it came out just fine. Mine went from day to night with clouds shooting over a mountain, and then showed the movement of the stars. I started with 5 secs delay with the camera on AV mode, so it set the shutter speed, and as it got darker the shutter went down to 30 secs, therefore I took a lot of pics over about 5 hours...sad I know but it looks good and I had just got the 10d!!!



Good luck!




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Old Sep 19, 2004, 5:32 AM   #7
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try shooting in RAW not JPEG because RAW files are not processed there is less chance of this "flickering"
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Old Sep 19, 2004, 5:57 AM   #8
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I agree, shoot raw. You can select a average WB and apply it to all the frames.
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Old Sep 19, 2004, 9:30 AM   #9
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stats79 wrote:
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Here's the movie. My point is that it already looks like the camera is compensating for exposure...which is exactely what I don't want it to do. The sun brigtens, and the camera looks as if it is compensating by closing the iris. This is not what is needed. The sky is not changing that dramatically. What is changing is the way the sensor is responding to the increased brightness of the sun.

Download the file from this link.
Your movie looks exactly the I would expect it to with a camera locked to a fixed aperture, shutter speed and ISO speed. The lighting is changing and the camera is not.

The scene is getting gradually darker as the sun goes down, and the flickering appears to be caused by the traffic, combined with the changes in the reflections in the water.

As I mentioned in my previous post, if you want the camera compensate for the changes in lighting, then you will need to go with a mode like Autoexposure or Aperture Priority (if you want the frames to look close to the same brightness, which it sound like you do).

Given the darkness of the scene with the sun going down, I'd go with Aperture Priority (Av Mode) with a fixed White Balance (as suggested by Freefly)

Personally, Iwould consider using a littlebrighter exposure, too, since the metering is underexposing the scene as a whole with your current settings,because you're shooting into the sun. You can use Exposure Compensation (set to a + EV value)to do this (although be careful not to use too much, or you'll cause blown highlights).

As others have suggested, you can also shoot in RAW, and you'll have more control over the images later. This will also give you more exposure latitude, given the amount of contrast in this type of scene (with both the bright sun and the darker areas in shadows).

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Old Sep 19, 2004, 11:43 AM   #10
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I don't know if you took a look at the other movie. That piece of animation was shot with locked aperature and shutter. The sun periodically peeks out from behind the clouds, adding a great deal of ambient light to the scene and yet...you don't see the same annoying flutter in the image.

Say what you will, but there is definately an issue with the Canon sensor. It overreacts to slight increases in highlights in the scene.

Shooting with variable shutter or aperature will only increase the amount of flickering in the image.
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