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Re: 24 F.P.S. and PAL



>Hi, I'm going to be shooting something, that is going to be edited in Spain
>(PAL).
>Probably on an AVID. My question is this, If I shoot it at 24 F.P.S. will
>there be a problem Telecine-ing it onto Pal Format?
>Also, does that cause a problem in conforming for Matchback to finish on
>film?
>
>Thanks
>Steven Gladstone


Steven,

Your concern is well considered.  I put a document together some time ago for the use of my clients, as well as an aid to myself.  There are several scenarios, each with a unique treatment, most of which I tried to summarize below.  Whenever I have to answer these questions I use this to refresh memory.  I may have missed something, and the scope could perhaps be broadened, so I hope the group will add further insights.




Film Production For A 50hz Broadcast System (PAL)
						          In A 60hz Environment

A chief complication to this method of production is the possibility of encountering an objectionable visual flicker.  Two conditions which can produce this flicker are:
1. Camera speeds of other than 24fps in the presence of 60Hz HMI's or florescents, and/or
2. Transfer rates of other than 25.00fps in the PAL standard.  These varispeed transfer rates produce a video pulldown ratio which may produce pulldown flicker and/or jitter effect (usually seen on very slow pans).

Note:  any pulldown produces a mixing of two frames and a possible flicker effect.  In the NTSC environment this is commonplace (the 3:2 pulldown method of stretching 24fps film into 29.97 NTSC video) but is largely unnoticed by reason of osmosis.  To the PAL viewer accustomed to a much cleaner marriage of film rates to video rates the pulldown effect can be objectionable.  Incidentally, pulldown also occurs in standards conversions as well.

To sidestep both the flicker and the pulldown problem, select method #3, in the chart below.  This method incurs a 4% speed up of the film.  Audio must similarly be sped up by 4% to retain sync (speed up of the audio does produce a change in pitch, but this is typically and effectively addressed with a Lexicon pitch corrector).  In nearly all cases this is an attractive solution, but this must be considered on a case by case basis.

Below is a chart which illustrates five potential production/post-production scenarios, each with their respective pros and cons:

Note: this chart must be viewed using a mono-spaced font such as Courier or Monaco so that it's layout can be viewed correctly.




Methods of Production/Post Production


Parameters             1              2              3              4              5


Transfer to           PAL            PAL            PAL            PAL            NTSC
 (video format)

Film                                                                         (A) 24.00fps
Production         24.00fps       24.00fps       25.00fps       30.00fps           or
Speed                                                                        (B) 23.98fps

Film
Transfer           24.00fps       25.00fps       25.00fps       30.00fps       23.98fps
Speed

Audio T/                      (A) 30.00fps                                  (A) 30.00fps
Production         25.00fps         or           25.00fps       30.00fps           or
Rate                           (B) 25.00fps                                  (B) 29.97fps

Audio T/C                      (A) 31.20fps
Transfer           25.00fps         or           25.00fps       30.00fps       29.97fps
Rate                           (A) 26.04fps


Pros & Cons

   Method #1
     Pros:
      1. Nearly no flicker (see Cons)
      2. No speed up
      3. Retain TLC control of audio element & production of audio T/C data
     Cons:
      1. Potential pulldown problem (*12:25 pulldown ratio may produce pulldown flicker
         and/or jitter effect)
         * Ratio = Film frames : Video fields


   Method #2
     Pros:
      1. No flicker
      2. No potential pulldown problem
     Cons:
      1. 4% speed up of film & audio (although audio can be pitch corrected)
      2. Sacrifice TLC control of audio element & production of T/C data


   Method #3
     Pros:
      1. Nearly no flicker (see Cons)
      2. No speed up
      3. Retain TLC control of audio element & production of audio T/C data
     Cons:
      1. Potential flicker for productions shot in the presence of 60hz HMI's, or florescents


   Method #4
     Pros:
      1. Nearly no flicker (see Cons)
      2. No speed up
      3. Retain TLC control of audio element & production of audio T/C data
     Cons:
      1. Potential pulldown problem (*5:12 pulldown ratio may produce pulldown flicker
         and/or jitter effect)
         * Ratio = Film frames : Video fields
      2. 20% increase in film usage


   Method #5
     Pros:
      1. Nearly no flicker (see Cons)
      2. No speed up
      3. Retain TLC control of audio element & production of audio T/C data
     Cons:
      1. Potential pulldown problem (*4:10 pulldown ratio may produce pulldown flicker
         and/or jitter effect)
         * Ratio = Film frames : Video fields
      2. Standards conversion to PAL (may produce additional pulldown flicker and/or jitter
         effect, as well as other conversion artifacts such as slight softening of the image)



Sadly, each scenario offers at least one compromise.  The nature of the end product and production considerations will influence your decision.

Hope this helps!

Tim Bond



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