25p from 50p PAL TM700 Shutter Setting

[Mysticalguides]

I am considering purchasing a PAL TM700 to use as a first person camera in a feature. I have read that the 25p mode is of lesser quality than the 50p mode on vertical and horizontal resolution.

My question involves the shutter when shooting at 50p mode for a 25p finish.

In order to have a 180 degree shutter when shooting 25p you set the shutter to 1/50 sec; to have a 180 degree shutter when shooting 50p you set the shutter to 1/100 sec.

Now if you wanted to shoot 50p all the time but extract a 25p signal (with an 180 degree shutter) then it seems logical that you would set the shutter to 1/50 sec for the 50p mode.

Has anyone tried to do this with the TM700? Can it be done and what is the image like? Does the 25p motion look correct? What is the blur like if you convert the 50p to slow motion played at 25p considering that the shutter is always on?

Any feedback, links to discusssions or TM700 footage shot with this shutter setting would be greatly appreciated!

Thanks!

Stelios.

 

[hazydave]

I am considering purchasing a PAL TM700 to use as a first person camera in a feature. I have read that the 25p mode is of lesser quality than the 50p mode on vertical and horizontal resolution.

Not really.

Not really. Tthe camera can record 1080/50p at 28Mb/s, or 1080/25 at 17Mb/s. So per frame, you have 0.56Mb/s per frame for 50p, 0.68Mb/s per frame for 25p. And of course, for every I-Frame at 25p, you need two at 50p, all things being equal. On the other hand, frame to frame motion at 50p is always half of that at 25p, so the AVC algorithms are more efficient, even given the smaller bit-budget.

My advice: shoot what you're going to use. If I need 1080/24p (I'm in NTSC-land), I'll shoot at 1080/24p. There are other occasions that suggest 1080/60i or 60p is the right answer... for example, maybe I don't have my target media definined. Or I want 1080/60i for DVD, but something progressive for the web.

My question involves the shutter when shooting at 50p mode for a 25p finish.

In order to have a 180 degree shutter when shooting 25p you set the shutter to 1/50 sec; to have a 180 degree shutter when shooting 50p you set the shutter to 1/100 sec.

Now if you wanted to shoot 50p all the time but extract a 25p signal (with an 180 degree shutter) then it seems logical that you would set the shutter to 1/50 sec for the 50p mode.

You have two choices. If you're shooting 50p for 25p, you can shoot at 1/50th second, then drop every other frame to convert to 25p, and maintain your 180 degree shutter. Or, shoot the 50p at 1/100th second, and blend frames in the conversion to 25p, which will also give you an effective 180 degree shutter effect.