For the first time I needed to use the 720P 50 frame slow motion on my Canon 7D for a doctor's reception shot being for a TVC. Unfortunately I had some fluro light issues that were causing some camera flickering. I therefore tried to adjust my shutter speed only to find that in that mode it doesn't go below 60. Yet when I use the 1080p mode I can go down to 30. This is on the manual setting. Has anyone else encountered this problem? As I wasn't able to fix this flicker, I had to turn off the fluros and bring in my own lighting kit.
To anyone interested, I'm shooting my first feature film and I'll be posting up some of my experiences using the Canon 7D. Would love to hear about yours too. It's a real learning curve. Hope to see you there, become a follower: http://sixloversmovie.blogspot.com/
Fluro lighting is driven by alternating current. In the USA this is 60khz, in UK and other PAL countries its 50khz. To sync your camera you need to shoot at frame rates or shutter speeds to match this.
So if you are in the US you should shoot 720 60p. It's okay to shoot at 30p too, as this is exactly equivalent to 2 cycles.
You can't shoot at shutter speeds that are slower than your frame rate. Think about it, if your are using a frame rate of 60p you haven't got time for a 1/30th shutter exposure on each frame, as its twice as long as your frame rate.
1080p has maximum frame rate of 30p on the Canon cameras, this is why you can use a slower shutter speed of 1/30th second.
I've run into this issue with my T2i as well. What I've found: if the fluorescent, neon, or other cycling light has a bad ballast, it doesn't matter what shutter speed you shoot at, it will give the wavy lines. We have a couple fixes: 1) use DC only lighting (LEDs, DC fluorescents, tungsten bulbs), 2) replace the faulty ballast(s), 3) use different lights. I'm no lighting expert, but when ballasts go bad, they get louder and they cycle funny which can cause wavy lines like a moire pattern. When we shoot with brand new lights, we get no waves.
We were shooting at a bar with much neon. We loved the low light on the T2i and wanted to try some moody lighting. It looked absolutely great everywhere except by one neon light whose ballast was getting pretty old and pretty obviously highlighting our actor with a halo of blue, wavy lines. We replaced the light out of frame with a couple LED strips with bits of blue and red gels taped to them and it worked great. I've heard good things about car lighting LED strips, cathode tubes, and DC neon and fluorescent, but I've not tried them.