24hz and 25hz

bfrench

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Hi,
Most people here seem to use 50 or 75hz for PAL
material and 48, 60 or 72hz for NTSC. Is there any
reason why I should not use 25hz for PAL and 24hz
for NTSC? Quite often Reclock advises a multiple of
these and as flicker isn't a problem (DLP pj) I should
be able to use them shouldn't I?
Are there any advantages/disadvantages that I should
be aware of?

Barry
 
I've just realised that I can't get 24hz but I
can get 25hz (SIM2 domino 20H)

Why would 50 or 75 be any better?


Barry
 
The main reason people use multiples of 25 is that some types of display, especially digital panels, don't support such low refresh rates a 24 and 25.

If your display handles them then 24, 25 and 30 are optimal as multiples of them cause frames to be doubled and the guy who calibrated my system, when I asked him about this, told me that some people can acutally see the tripling of frames you get if you use 75 for PAL or 72 for NTSC..

25 is always right for PAL, 30 is for NTSC derived from video and 24 for NTSC derived from film .. I have to admit not knowing why but experience shows it's the case. :)
 
25 frames per second and 24 frames per second are only of use for film sourced material. If you watch something recorded on video camera's interlaced at 50Hz or 60Hz it's likely to look a mess at those refresh rates.

Gordon
 
Ooops, I meant 50 is always right for PAL even though it doubles the frame-rate for film material.

Tell me Gordon, something I've never figured .. AIUI all movies are shot at 24fps, when converted to PAL how is the frame-rate converted? Or is the famous 4% PAL speed-up?
 
Yes movies are shot at 24fps and then sped up by 4% when converting to PAL or slowed to 23.976 and have 3:2 pulldown applied to take up to 29.97 for NTSC (59.94Hz).

Rob.
 

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