Off topic / Extreme action/I love 50i at DVinfo.net

Jonas Nystrom · April 15th, 2006, 06:56 PM

I think you get a little bit of topic in the thread "xtreme sport type shots with lots of motion". So here in this thread, a new question:

I tried out som action shots, and here is deal: I would like to shoot fast action @ 25f (living in the PAL world). My choice is a fast shutter, @ 2000 or something. In the picture, my daughter throw a stone, background is blue skies, and if I could freeze the whole sequense, the motion of the stone would end up in a dotted line!

And here comes the maybe stupid silly question: Is thera any work around? Could shout at fast shutter/25f without retain the "dotted stone line". Or is this a artifact created by the compression (HDV)? Or is it like my impression, fast action with high speed shutter is better in interlaced?

Bob Grant · April 16th, 2006, 05:50 AM

The answer is fairly simple. You're taking 25 frames per second but each frame only records 1/2000th of a second. So the first frame records 0.5mSecs of the stones motion, then nothing is recorded of its motion for 39.5mSecs and then another 0.5mSecs of its motion etc.
Result, a dotted line.
That's why ideally the shutter speed is as low as possible, around 1/40th at 25fps for video or 1/60th (I think, for film, the camera needs time to move the film).

Even at 50i you'll still get a dotted line, less so than at 25p though.

Of course at the lower shutter speeds you get motion blur, the object moves with the frame. That creates a problem for slo mo which is why sports stuff is shot with a faster shutter speeds but it makes the action look stroby. The ideal is to use a very fast frame rate but such cameras get expensive.

April 15th, 2006, 06:56 PM	#1
Jonas Nystrom Major Player Join Date: Jan 2006 Location: Göteborg, Sweden Posts: 306	Off topic / Extreme action/I love 50i I think you get a little bit of topic in the thread "xtreme sport type shots with lots of motion". So here in this thread, a new question: I tried out som action shots, and here is deal: I would like to shoot fast action @ 25f (living in the PAL world). My choice is a fast shutter, @ 2000 or something. In the picture, my daughter throw a stone, background is blue skies, and if I could freeze the whole sequense, the motion of the stone would end up in a dotted line! And here comes the maybe stupid silly question: Is thera any work around? Could shout at fast shutter/25f without retain the "dotted stone line". Or is this a artifact created by the compression (HDV)? Or is it like my impression, fast action with high speed shutter is better in interlaced? __________________ Jonas Nyström, DoP :: HOT SHOT® SWEDEN :: www.hotshot.nu :: RED #1567, RED 18-50mm T3 :: XL A1, Letus Extreme :: XL H1, 20X & 6X lens (for sale) :: www.vimeo.com/nystrom

April 16th, 2006, 05:50 AM	#2
Bob Grant Trustee Join Date: Nov 2005 Location: Sydney Australia Posts: 1,570	The answer is fairly simple. You're taking 25 frames per second but each frame only records 1/2000th of a second. So the first frame records 0.5mSecs of the stones motion, then nothing is recorded of its motion for 39.5mSecs and then another 0.5mSecs of its motion etc. Result, a dotted line. That's why ideally the shutter speed is as low as possible, around 1/40th at 25fps for video or 1/60th (I think, for film, the camera needs time to move the film). Even at 50i you'll still get a dotted line, less so than at 25p though. Of course at the lower shutter speeds you get motion blur, the object moves with the frame. That creates a problem for slo mo which is why sports stuff is shot with a faster shutter speeds but it makes the action look stroby. The ideal is to use a very fast frame rate but such cameras get expensive.