Wavy Background at DVinfo.net

Joe Piechura · November 27th, 2012, 02:22 PM

Hi. I've been using this camera in 24fps with a shutter speed of 50 and I've noticed that occasionally the background to one of my shots will be all wavy (probably the whole image, but you only notice it on the solid background). The first few times I used the camera, I had a few very wavy images because I'd accidentally set the shutter speed to 60 and I was wondering if it might be something to do with the shutter speed not being exactly double the frame rate. Maybe it does it on every shot, but it's only noticeable on certain solid colour backgrounds, but I don't think so. It's not so bad that it ruins the shot (like with the shutter speed of 60) but it is visible. This is my first film with the camera, so maybe I'm doing something wrong? Using mainly the Lumix 20mm if that's relevant.

William Hohauser · November 27th, 2012, 04:29 PM

Fluorescent lights being used?

Joe Piechura · November 28th, 2012, 01:46 AM

Yeah. So I'll get this with any fluorescent lights?

Guy Smith · November 29th, 2012, 08:27 AM

How ironic - right after reading this yesterday I shot a scene and saw wavy lines. Fluorescent lights!

Interestingly I shoot under fluorescent lights all the time - 4' and 8' tubes, mostly - and rarely see this issue. On this occasion the room was lit by CFL Flood Light Bulbs similar to this: http://imagethumbnails.milo.com/003/...86_trimmed.jpg

I vaguely remember this happening once before and if memory serves I mitigated the issue by selecting a different shutter speed. The light level was very low yesterday so I added a 250 photo flood incandescent light and even with the fluorescent lights on the wavy lines were gone.

Bruce Foreman · November 29th, 2012, 06:39 PM

CFL's can be very bad offenders in this area. Be sure your shutter speed either matches or is a multiple of the power line frequency. In the US this should be 1/60th second (or multiple), in countries where the line frequency is 50Hz shutter should be 1/50th.

I got it bad once with CFL's and I had the shutter set to 1/50th (line frequency was 60Hz) trying to stay close to 1/48th for motion blur.

William Hohauser · November 30th, 2012, 07:12 AM

The problem is that fluorescent tubes blink with the frequency of the AC electrical system. 60 or 50 times a second depending on the country. Having shutter speeds that are not at the same rate can cause strobe patterns in the image, especially if the tube is the only source of light. Even if you are at the right shutter, the intervals might not coincide between the camera's rolling shutter and the tube and you still get dark banding. CFLs are supposed to be direct current like a neon tube and not blink, but while I haven't experienced this, apparently there are CFLs that behave like the AC driven tubes. Professional CFL lights (and tubes) never blink unless the bulb is defective or very, very old.

November 27th, 2012, 02:22 PM	#1
Joe Piechura Regular Crew Join Date: Jul 2012 Location: Ho Chi Minh City, Vietnam Posts: 57	Wavy Background Hi. I've been using this camera in 24fps with a shutter speed of 50 and I've noticed that occasionally the background to one of my shots will be all wavy (probably the whole image, but you only notice it on the solid background). The first few times I used the camera, I had a few very wavy images because I'd accidentally set the shutter speed to 60 and I was wondering if it might be something to do with the shutter speed not being exactly double the frame rate. Maybe it does it on every shot, but it's only noticeable on certain solid colour backgrounds, but I don't think so. It's not so bad that it ruins the shot (like with the shutter speed of 60) but it is visible. This is my first film with the camera, so maybe I'm doing something wrong? Using mainly the Lumix 20mm if that's relevant.

November 27th, 2012, 04:29 PM	#2
William Hohauser Inner Circle Join Date: Dec 2005 Location: New York City Posts: 2,650	Re: Wavy Background Fluorescent lights being used? __________________ William Hohauser - New York City Producer/Edit/Camera/Animation

November 28th, 2012, 01:46 AM	#3
Joe Piechura Regular Crew Join Date: Jul 2012 Location: Ho Chi Minh City, Vietnam Posts: 57	Re: Wavy Background Yeah. So I'll get this with any fluorescent lights?

November 29th, 2012, 08:27 AM	#4
Guy Smith Regular Crew Join Date: Dec 2011 Location: San Diego, CA Posts: 48	Re: Wavy Background How ironic - right after reading this yesterday I shot a scene and saw wavy lines. Fluorescent lights! Interestingly I shoot under fluorescent lights all the time - 4' and 8' tubes, mostly - and rarely see this issue. On this occasion the room was lit by CFL Flood Light Bulbs similar to this: http://imagethumbnails.milo.com/003/...86_trimmed.jpg I vaguely remember this happening once before and if memory serves I mitigated the issue by selecting a different shutter speed. The light level was very low yesterday so I added a 250 photo flood incandescent light and even with the fluorescent lights on the wavy lines were gone.

November 29th, 2012, 06:39 PM	#5
Bruce Foreman Trustee Join Date: Nov 2006 Location: San Angelo Texas Posts: 1,518	Re: Wavy Background CFL's can be very bad offenders in this area. Be sure your shutter speed either matches or is a multiple of the power line frequency. In the US this should be 1/60th second (or multiple), in countries where the line frequency is 50Hz shutter should be 1/50th. I got it bad once with CFL's and I had the shutter set to 1/50th (line frequency was 60Hz) trying to stay close to 1/48th for motion blur.

November 30th, 2012, 07:12 AM	#6
William Hohauser Inner Circle Join Date: Dec 2005 Location: New York City Posts: 2,650	Re: Wavy Background The problem is that fluorescent tubes blink with the frequency of the AC electrical system. 60 or 50 times a second depending on the country. Having shutter speeds that are not at the same rate can cause strobe patterns in the image, especially if the tube is the only source of light. Even if you are at the right shutter, the intervals might not coincide between the camera's rolling shutter and the tube and you still get dark banding. CFLs are supposed to be direct current like a neon tube and not blink, but while I haven't experienced this, apparently there are CFLs that behave like the AC driven tubes. Professional CFL lights (and tubes) never blink unless the bulb is defective or very, very old. __________________ William Hohauser - New York City Producer/Edit/Camera/Animation