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Thread: 1080/50 or 1080/25

  1. #1

    Default 1080/50 or 1080/25

    Should I record 1080/50 given that compression in Premier is only 1080/25 (or of course 720/50) - advantages/ disadvantages?

  2. #2
    Join Date
    Feb 2006
    Surrey, UK
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    Let's get one thing clear. teh /50 or /25 is nothing to do with compression. This is how many fields per second are captured. And, to avoid further misunderstandings, this is nothing to do with shutter speed (although frames/fields per second should be taken into consideration when setting shutter speed)

    Now, whay amd I saying "fields" per second and not "frames" per second?

    This depends on whether you are shooting interlaced or progressive footage.

    NB The following uses the PAL standard as adopted by the UK as camlover is using 25/50 which are the PAL (and SECAM) rates. For the US and other parts of the wortld which use NTSC the figures are 30/60.

    Progressive footage means a whole image is shot every 1/25th or 1/50th second (like a "flickbook"). Simples as the Meerkats would say.
    Interlaces footage harks back to the times when TVs were made of wood and the cathode ray tubes produced images by zapping dots onto the screen in a series of horizonntal lines. Creating an image that way took a long time and by the time the zapper had got to the bottom of the screen, if the subject was moving, it would have shifted a bit and everything would look a bit skewed. Engineers overcame this problem by scanning alternate lines of the image. That way, instead of having a skewed image that took 1/25th sec to complete, they would have one less skewed image that took 1/50th sec plus a secodn image taken 1/50th second later. The odd lines would be from the first image, the even lines from the second. (It is for this reason that if you do not correctly "de-interlace" iterlaced footage on a PC, you will see the "comb" like effect on the vertical edges of horizontally moving objects.

    However, technology has advanced, and it is now commonplace to be able to capture and display complete images (ie not just the odd lines or the even lines) every 1/50th second.

    1080/50p means 50 complete images per second (P is for "progressive)
    1080/25p means 25 complete images per second
    1080/50i means 25 comlete images per second, comprising 25 "odd" fields and 25 "even" fields.

    The standard in the UK is for TVs to play back 25 frames (whether that equates to 25 complete frames or 2 x 25 odd + even fields) per second.

    There IS a difference in look between 25p and 50i. 50i is arguably better for fast moving subjects. 25p, being very close to film (which is shot as complete images at 24 frames per second) is favoured by those after a "film look". As a complete image is taken each time it also results in better stills taken from it.

    So why use 50p if the target playback willonly play back 25p? As I understand it the only real benefit is if you want to slow down the footage. Obviously if you shoot at 50P and halve the playbacjk speed you are going to have one captured frame for each resulting frame. No doftware interpolation required. I'm not aware of any other reason unless you will be playing back on different devices taht are genuinely capable of displaying 50 frames per second.

    This is NOT an expert opinion. Merely my understanding so please wait for others to respond confirming or correcting me!

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