Why 2x fps?

T

testdasi

New member
I have read from various places that it's best to set shutter speed to 2 times the fps (i.e. 1/50s for 25fps). I have 2 questions regarding this:
1. Why?
Why is it not exactly 1/25s? Why not 3x, 4x? Why 2x?

2. What shutter speed to set for 24fps and 60fps?
The GH1 does not allow me to set shutter speed at 1/48s and 1/120s. Around 1/48, it only allows 1/40 or 1/50. Around 1/120s, it only allows 1/100s or 1/125s. I have been setting it at 1/50 and 1/125 respectively but it's still bugging me if I'm doing right.

My apology if it sounds too noobie. I'm good with still but still entry-level in term of motion pics.

Many thanks.
 
Take a look at this.
http://blog.tylerginter.com/?p=385

Ultimately it's all up to you. If your shots don't have much motion most of the time you can get away with 1/25 on 24fps footage and not a soul will be able to tell whether or not you followed 180 rule. So his advice about night shooting is really more like "use at your own risk".
 
1) It gives the best balance between motion blur and stuttery images. Faster shutter speeds cause moving objects to jump from frame to frame rather than move smoothly through it. Slower than 1/50 (or 2x the frame rate) and moving objects become too blurry and lose detail.

2) Because the GH1 is primarily a still camera it doesn't include proper shutter speeds for video. But the truth is that 1/50th and 1/125th are close enough. You could cary your shutter speed slightly from the 2x rule and nobody will be able to tell the difference, as long as you keep it in the same ballpark. In fact many film cameras do not have perfect 180 degree (where the 2x rule comes from) shutters. They often vary by several degrees.
 
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