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The cinematography.com entrance exam


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#1 Guustaaf Damave

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Posted 17 June 2012 - 03:43 PM

In order to sign up for this forum you need to figure out what "ST US TV FPS" stands for and then give the correct answer with second decimal accuracy. 30 is not close enough. So I guess it is tech geeks only here. WTF?
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#2 Adrian Sierkowski

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Posted 17 June 2012 - 04:39 PM

29.97
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#3 Brian Dzyak

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Posted 17 June 2012 - 04:39 PM

In order to sign up for this forum you need to figure out what "ST US TV FPS" stands for and then give the correct answer with second decimal accuracy. 30 is not close enough. So I guess it is tech geeks only here. WTF?



????

29.976 is the answer, but those acronyms are not standard either. WTF is ST supposed to mean without figuring out the rest of the puzzle? I don't get it.
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#4 Adrian Sierkowski

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Posted 17 June 2012 - 04:44 PM

I think that ST would be "standard," US? Or maybe it's a typo for SD?
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#5 Jock Blakley

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Posted 17 June 2012 - 08:07 PM

"STD" rather than "ST" would probably be a little bit less ambiguous - then Google it and the third result is a thread here with the answer :P

Of course there is an additional challenge for people who don't have English as a first language and so would instinctively answer as 29,97 rather than 29.97.
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#6 Saul Rodgar

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Posted 17 June 2012 - 08:40 PM

for real?
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#7 Keith Walters

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Posted 17 June 2012 - 10:45 PM

In order to sign up for this forum you need to figure out what "ST US TV FPS" stands for and then give the correct answer with second decimal accuracy. 30 is not close enough. So I guess it is tech geeks only here. WTF?

Actually the correct answer is: 4500000 ÷ 286 ÷ 525 which to 100 decimal places comes to

29.970029970029970029970029970029970029970029970029970029970029970029970029970029970029970029970029973 :P

And Jim Jannard said I know nothing :D
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#8 Brian Drysdale

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Posted 18 June 2012 - 02:40 AM

In order to sign up for this forum you need to figure out what "ST US TV FPS" stands for and then give the correct answer with second decimal accuracy. 30 is not close enough. So I guess it is tech geeks only here. WTF?


It's of little concern if you work in Europe and only shoot at 25 fps. However, in the US you can get caught out by the slight difference by not having the second decimal accuracy. Fortunately other things get discussed other than US television frame rates.
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#9 Sean Elder

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Posted 17 July 2012 - 02:10 PM

Does it matter if the answer is 29.97 or 29.976? Also, in Europe would you shoot 24.97 or 48.97? or am I over thinking again?

Edited by Sean Elder, 17 July 2012 - 02:12 PM.

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#10 Stuart Brereton

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Posted 17 July 2012 - 02:50 PM

Also, in Europe would you shoot 24.97 or 48.97? or am I over thinking again?



You're over thinking it. In Europe we shoot 25fps. The decimal points in the American frame rate arise from a quirk in the NTSC system, which I'm sure someone else can explain better than me.
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#11 Gregg MacPherson

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Posted 17 July 2012 - 03:13 PM

Does it matter if the answer is 29.97 or 29.976?


Cinematographers may have a special math dispensation. For everyone else 29.976 rounds up to 29.98.
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#12 luminous

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Posted 18 July 2012 - 01:09 AM

In order to sign up for this forum you need to figure out what "ST US TV FPS" stands for and then give the correct answer with second decimal accuracy. 30 is not close enough. So I guess it is tech geeks only here. WTF?

standard united states telivision frames per secone 29.97
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#13 Brian Drysdale

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Posted 18 July 2012 - 02:13 AM

standard united states telivision frames per secone 29.97


Luminous you need to use your real name, it's one of the forum rules.
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#14 Keith Walters

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Posted 18 July 2012 - 08:06 AM

You're over thinking it. In Europe we shoot 25fps. The decimal points in the American frame rate arise from a quirk in the NTSC system, which I'm sure someone else can explain better than me.

The original monochrome NTSC system had a line frequency of 15.75kHz which is what you get when you multiply 30 pictures/sec by 525 lines. It had to be 30 pictures/sec to avoid interference from stray magnetic fields from the 60 cycle AC power mains, particularly with 1930s design TV receivers.

When they added colour in 1954, they had to minimize interference between the new colour subcarrier and the existing monochrome signal and vice versa. This can be achieved by making the subcarrier frequency so-much-and-a half times the line frequency. The figure they settled on was 227.5 times the line frequency.
However there was a further problem that the colour subcarrier was also subject to interference from the 4.5MHz FM sound carrier. This can similarly be minimized by making the sound carrier an exact multiple of the line frequency, since that will give it the same "half-cycle offset".
The problem was that 4,500,000 is nowhere near an exact multiple of 15750. The closest is 286 times, which comes out to 4,504,500. Because NTSC uses only narrow deviation FM, the 4.5kHz error would result in severe sound distortion.
However, since all TV sets of that era had horizontal hold controls, a more practical solution was to leave the sound carrier frequency alone, and make the line frequency equal to 4,500,000 divided by 286, which to 27 decimal places comes to
15734.265734265734265734265734266Hz
Dividing that by 262.5 gives (to 100 decimal places)
29.970029970029970029970029970029970029970029970029970029970029970029970029970029970029970029970029973 frames per second.

Although this theoretically then made the TV receivers more susceptible to stray magnetic fields from the AC power mains, by then receiver technology had improved enormously, and sets were far less affected by this. Also, by that time, networking using trans-continental microwave links was rapidly proliferating, making local power-line synchronization impractical anyway.

With film originated material, in an NTSC 3:2 pulldown telecine, the film has to run slightly slower than the cinema rate 24fps
You can calculate it this way:

15734.265734265734265734265734266 divided by 15,750 which comes to
0.99900099900099900099900099900102

24 multiplied by 0.99900099900099900099900099900102 gives you
23.976023976023976023976023976024fps

When all TV Post-Production was done on film, using identical equipment to that used for cinema release movies, the sound track was simply part of the film print, so it didn't matter at all what frame rate was used in the telecine for the final transfer to videotape, the sound had no choice but to remain in sync with the picture. In fact, in PAL countries the film was simply sped up 4% to 25 frames per second, which produces a noticeable pitch change, but few people seemed to notice.

The Post Production problem, that many people still do not really understand, started when people began editing film-derived material on editing machines that were only ever designed for use with NTSC video cameras, where the sound and video are normally recorded on the same tape.

With film-derived material, the first necessary step is to marry up the film images with the sound recorded on a separate crystal-sync tape recorder, usually a Nagra. This was usually done by the old fashioned but perfectly adequate clapper board technique.

The problem is this: If you simultaneously shoot say, 100 seconds of crystal-synced sound and 100 seconds (2,400 frames) of film, and then try to match them up using an NTSC telecine and an existing studio crystal-sync tape playback unit, the sound clip will still take exactly 100 seconds to play back, but the 2,400 frames of film will take 100.1 seconds, because it's running at only 23.976 fps!

If you're matching up a take that's more than a minute long, the sound starts to get noticeably out of sync with the picture. What's worse, the sound also tends to get ahead of the picture so for example, you will hear an actor speak before he opens his mouth. This is far more irritating than the other way round, because we are used to "sound-follows-action" in the real world, but never "action follows sound".

The usual workaround was to effectively "jerk" the film forward by one frame every now and again, to get them back into sync, the so-called "drop-frame" technique.

You might ask why they didn't just slow the sound playback down by the same amount, and certainly that is what is done with modern PC-based editors, but it wasn't quite so easy "back in the day". It could only be done by physically modifying the audio tape playback machine, which was both costly and inconvenient. Drop-frame was the cheaper option and was almost universally used!

With the much more technically advanced CCIR PAL system, (not those weird-ass South American mutations :rolleyes: ) the 15,625Hz line frequency is already an exact sub-multiple of the various sound carriers used (5.5MHz, 6MHz, 6,5MHz etc) so none of the above steps are necessary. :P
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#15 Keith Walters

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Posted 18 July 2012 - 06:39 PM

Does it matter if the answer is 29.97 or 29.976? Also, in Europe would you shoot 24.97 or 48.97? or am I over thinking again?

Since the answer is actually just 29.97, it probably does matter :lol:
You're confusing it with 23.976, the frame rate for running 24fps film through a 3:2 pulldown telecine. (See above).
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#16 Tim Tyler

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Posted 27 July 2012 - 09:35 AM

In order to sign up for this forum you need to figure out what "ST US TV FPS"


The exact question is: Std US TV FPS
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#17 Tom Jensen

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Posted 27 July 2012 - 09:45 AM

And...everyone should be required to take the grip clip test.
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#18 Keith Walters

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Posted 28 July 2012 - 02:38 AM

The exact question is: Std US TV FPS



And the correct answer is derived by dividing the NTSC TV sound carrier frequency (4.5MHz) by 286, and then by 525
4500000 ÷ 286 ÷ 525, which to 100 decimal places comes to
29.970029970029970029970029970029970029970029970029970029970029970029970029970029970029970029970029973
You can look that up In Donald Fink's 1956 edition of the Television Engineering Handbook if you don't believe me :rolleyes:

29.976 seems to be frequently quoted, but that is actually incorrect, apparently confused with 23.976 fps film.
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