"Mat Overton" wrote in message
...
Why is cinema film shot at 24
frames/sec rather than 20, 25 or 30, given that 50Hz (halved to derive
25
Hz) and 60Hz (halved to derive 30 Hz) are the standard mains
frequencies?

The rates for film have absolutely nowt to do with mains power. And like
most of the other answers given here have more to do with practicality.
Silent film was run at anything from 8 up to around 20 fps, eventually
18fps
was standardised upon as the ideal rate to give smooth motion without
jerkiness (When each frame was show twice, giving an effective frame rate
of
36fps). With film costs of the time, anymore would have been too
expensive.
Most film was also 70mm, but was cut in half by film makers (to give twice
the length) who couldn't afford the cost. When sound came along 18fps
wasn't
enough length to squeeze in good enough optical or magnetic sound quality,
and the best quality / cost compromise was 24fps (Again each frame is
still
shown twice). Film being mechanical could easily be any speed regardless
of
the mains voltage or cycle. (Indeed some modern projectors require
3-phase).
25fps only came later when interlaced electrical television was invented
as
the easiest way to work with the 50 / 60Hz cycle of modern power.

So someone consciously decided to standardise on values of 18 (rather than
20) and 24 (rather than 25). I can't understand the reasoning behind that.
People in days gone by seem to have shunned multiples of 5 and 10, don't
they? Of course everything in computing is based on powers of 2 or 16, but
at least there's a very logical explanation for that.

I hadn't realised that early film was 70 mm rather than 35 mm. I'd assumed
that 35 mm double-sprocket came first, then this was halved to 16 mm
double-sprocket which could be sliced lengthways to give two lengths of
Standard 8 single-sprocket, and that 70 mm was developed about the time that
widescreen formats were devised in the 50s as being twice the width of 35
mm.

By the way (going further off-topic) what was the format for still
photography that gave a frame size slightly larger than the 24x36 of 35 mm?
I have some slides from the early 60s (when my parents first got married)
which are fractionally larger than normal 35 mm and have only a couple of
sprocket holes per frame, and only on one side of the film. The frame is
about 38.5 x 26.5, still mounted in the standard 50 mm x 50m cardboard
mount.

How is the speed of a projector governed: I'd always assumed that in the old
days the motor was locked to the mains frequency like in an electric clock
and that now it's controlled by quartz crystal. What a shame that the world
didn't standardise on a single worldwide frequency and voltage in those
early days of mains power - preferably 48 Hz to sync with existing film
standards! What frame rate was the original EMI 240-line TV system (the
rival to Baird's system). Was that 25 Hz. Was there any equivalent
pre-cursor to the 525/30 American system.

Interesting that all the standards for the dimensions of film (apart from
the overall length of cine film) are measured in mm, given that the first
cine film was shot in Leeds and presumably a lot of the development would
have been in the UK and America.

Martin Underwood wrote:
[snip]

The weirdest one is the spec for high-definition TV which uses 1080
lines - neither 2xPAL (1250) nor 2xNTSC (1050) lines, so *both*
standards will have to be interpolated using weird conversion factors
(leading to loss of sharpness) when showing old low-definition
material on high-definition.

Aaah - you are confusing active with total number of scanning lines there
Martin.

The 1080 HD standard refers to the number of active lines (not the total
number of scanning lines), and so compares with 480 active (or 488) for 525
and 576 active (or 575) for 625 lines, which if line doubled would give 960
active (1050 total) or 1152 active (1250 total) assuming the blanking stayed
in the same proportions. Given that transmission systems no longer need to
transmit the non-active lines, and non-scanning displays (non-CRT devices
like LCDs, Plasmas, DLPs etc) don't either, the active line structures are
more important than the total number of lines (including vertical blanking
etc.)

HOWEVER I believe that the 1080 standard is actually closest to the
Japanese 1125 total system (which most HD kit on sale in the 80s and 90s was
built for - apart from the odd bit of bespoke 1050/1250 stuff) which had
1030 or 1050 active lines (can't remember which) and someone must have taken
the pragmatic approach partially. In fact I believe that quite a lot of
stuff still has 50 or 30 lines missing ??

The 1080 number in square pixel terms makes loads of sense - 1920x1080 is
16:9 with square pixels - though 1080 is not completely divisible by 16 (so
1088 is often used in MPEG transmission terms?), 1920 is, and is a nice
number!

Using a common image scannning structure irrespective of frame rate also
means that many frame rate conversions will require no re-sampling of the
image area (and thus no interpolation) at all, and also allows cameras to
work on multiple standards using the same image sensors (It is common for HD
cameras to be able to run at 24,25 and 30p or 50 or 60i). If 1080/24p is
used (as it increasingly is) as the production format, it can be converted
to 1080/25p or 1080/50i by a slight frame rate conversion (i.e. speeding up
by 4%), and it can be converted to 1080/60i by using a 3:2 pulldown, neither
of these requiring any significant interpolation.

Your argument for downconversion is understandable - but given that the
frame rate conversions are more difficult than basic image scaling the loss
of quality when going from 1080 rather than 1152 or 960 to 576 or 480 is
pretty negligible - as in the case of NTSC/480 regions you are starting off
with a sharper image, and in PAL/576 regions only 72 fewer lines (and given
that you are throwing between 505 and 600 away in the downconversion that
probably doesn't matter massively)

Basically the choice of a common 1920x1080 (or two standards if you include
1280x720 - though 720p stuff in 50Hz regions is pretty unheard of I think)
scanning structure for all frame rate flavours of HD is more significant
than the choice of one that is linked to a legacy resolution based on 525 or
625 analogue scanning standards.

Steve

wrote in message
...
On Sun, 29 Feb 2004 15:03:03 GMT, as the pitiful wreck that had once
been "Martin Underwood" was cut from the mess that
had once been his life, he managed to utter:

I hadn't realised that early film was 70 mm rather than 35 mm. I'd
assumed
that 35 mm double-sprocket came first, then this was halved to 16 mm
double-sprocket which could be sliced lengthways to give two lengths of
Standard 8 single-sprocket, and that 70 mm was developed about the time
that
widescreen formats were devised in the 50s as being twice the width of 35
mm.

Are you perhaps forgetting 9.5mm centre sprocket film?

I was drawing a veil over this oddity. Putting the sprockets in the centre
of the film seems a very strange decision because you have to space the
frames further apart to avoid them encroaching into the frames. Mind you, I
suppose each of those frames can then go right up to the edges of the film,
rather than losing a "sprocket strip" down one side. Perhaps it wasn't such
a bad idea after all...

In article m,
says...

wrote in message
...
On Sun, 29 Feb 2004 15:03:03 GMT, as the pitiful wreck that had once
been "Martin Underwood" was cut from the mess that
had once been his life, he managed to utter:

I hadn't realised that early film was 70 mm rather than 35 mm. I'd
assumed
that 35 mm double-sprocket came first, then this was halved to 16 mm
double-sprocket which could be sliced lengthways to give two lengths of
Standard 8 single-sprocket, and that 70 mm was developed about the time
that
widescreen formats were devised in the 50s as being twice the width of 35
mm.

Are you perhaps forgetting 9.5mm centre sprocket film?

I was drawing a veil over this oddity. Putting the sprockets in the centre
of the film seems a very strange decision because you have to space the
frames further apart to avoid them encroaching into the frames. Mind you, I
suppose each of those frames can then go right up to the edges of the film,
rather than losing a "sprocket strip" down one side. Perhaps it wasn't such
a bad idea after all...




Not a good idea when the sprocket slips!

Ashley

In article , Ashley Booth wrote:
Are you perhaps forgetting 9.5mm centre sprocket film?

I was drawing a veil over this oddity. Putting the sprockets in the centre
of the film seems a very strange decision because you have to space the
frames further apart to avoid them encroaching into the frames. Mind you, I
suppose each of those frames can then go right up to the edges of the film,
rather than losing a "sprocket strip" down one side. Perhaps it wasn't such
a bad idea after all...




Not a good idea when the sprocket slips!

Not really. Actually, all the 9.5mm projectors and cameras I remember used a
claw, not a sprocket, and it could make quite a mess if it missed the holes.
What they used to do was have much longer holes, almost frame height, for the
first few inches of film in the cartridge so that the claw would have a greater
chance of going through one of them instead of punching extra holes. The
leading edges of the long holes had the same spacing as the proper ones, so
after the camera had been run for a few seconds, everything lined up. Lacing a
projector properly took a bit of care, but you could see the film so it was
relatively easy. You don't have this problem with a sprocket mechanism as in
35mm of course, because the pins are permanently engaged with the holes.

9.5mm was technically quite a good idea, as the force pulling the film through
the gate was balanced with no sideways component tending to make it jam as in
16mm or 8mm, and the picture area was nearly the same as 16mm, even for sound
film which had a slightly smaller frame to accommodate the sound track.
Technically good, just different from the rest of the world, but that's the
French for you.

Rod.

In Roderick Stewart writes:

In article , Mat Overton
wrote:
Film being mechanical could easily be any speed regardless of
the mains voltage or cycle. (Indeed some modern projectors require 3-phase).
25fps only came later when interlaced electrical television was invented as
the easiest way to work with the 50 / 60Hz cycle of modern power.

It's nothing to do with interlace. Television frame rates were chosen to be
the same as local mains frequency to minimise the effect of inadequate
smoothing of power supplies, which would cause hum bars on the screen.

There was also the problem of magnetic interference. Parts of Los
Angeles were still 50Hz in the late 30's, early 40's. RCA made a special
50Hz version of the pre-war TRK-12 television receiver that had shielding
around the kinescope, for use in LA.

I'm told that many cinema projectors are actually run at 25fps, though whether
this is just in Europe or America as well, I don't know.

For PAL film-to-tape transfers the film is run at 25fps, even though
it was shot at 24fps. The slight speed-up is preferable to the bizarre
pulldown you'd have with 24/25.

--
Tim Mullen
------------------------------------------------------------------
Am I in your basement? Looking for antique televisions, fans, etc.
------ finger this account or call anytime: (212)-463-0552 -------

On 1/3/04 10:48 pm, in article , "Tim Mullen"
wrote:

[snip]


I'm told that many cinema projectors are actually run at 25fps, though
whether
this is just in Europe or America as well, I don't know.

For PAL film-to-tape transfers the film is run at 25fps, even though
it was shot at 24fps. The slight speed-up is preferable to the bizarre
pulldown you'd have with 24/25.

Yep - though film for European TV is often shot at 25fps to remove the need
for speed up (though presumably is more expensive to shoot, as it requires
an extra frame of stock and processing every second...)

Similarly HD stuff shot for the European market is often shot using 25p and
slowed down to 24p for the US (where it may then be converted to 60i using
3:2 pulldown)

Steve

In article ,
writes
On Sun, 29 Feb 2004 15:03:03 GMT, as the pitiful wreck that had once
been "Martin Underwood" was cut from the mess that
had once been his life, he managed to utter:

I hadn't realised that early film was 70 mm rather than 35 mm. I'd assumed
that 35 mm double-sprocket came first, then this was halved to 16 mm
double-sprocket which could be sliced lengthways to give two lengths of
Standard 8 single-sprocket, and that 70 mm was developed about the time that
widescreen formats were devised in the 50s as being twice the width of 35
mm.

Are you perhaps forgetting 9.5mm centre sprocket film?

And 17.5mm stock, which really is 35mm cut in two. And they all have
umteen variations of singel perf, double perf and differnt shapes of
perf. hole too (neg, pos, interneg, etc.).

By the way, 70mm is only ever a release format (and then like hens'
teeth, save for Imax), as the camera stock (even Imax's, if memory
serves) is 65mm.

The extra 5mm is 2.5mm each side, outside the perforations, origianlly
for four of the mag audio tracks of the original (two more twixt perfs
and pictures), and presumably now some sort of digital format (adapted
Dolby digital possibly).

It's so long since I've seen a non-Imax 70mm print in the cinema, I've
no idea if they've successfully adopted an optical audio format for 70mm
or not, digital or otherwise.


Regards,

Simonm.

--
simonm|at|muircom|dot|demon|.|c|oh|dot|u|kay
SIMON MUIR, UK INDEPENDENCE PARTY, BRISTOL www.ukip.org
EUROPEANS AGAINST THE EU www.members.aol.com/eurofaq
GT250A'76 R80/RT'86 110CSW TD'88 www.kc3ltd.co.uk/profile/eurofollie/

In article m, Martin
Underwood writes
Putting the sprockets in the centre
of the film seems a very strange decision because you have to space the
frames further apart to avoid them encroaching into the frames.

They *do* encroach into the frames. It makes the pulldown smooth though,
as there are no twisting forces, and, as you say, the frame area is much
bigger than 8mm. 9.5mm still has a rather anoracky following, and you
can still get the stock. The later cameras are supposed to give very
good results.

The other oddity of 9.5mm is the ability to freeze frames for a finite
time, for titles, etc., following notches cut in the edge of the film.
Sounds like the origin of those hackneyed shots of the film catching
fire to me, but I've got a few old reels (cartoons, I think) with the
notches. Not every projector could do it though, the rest just ploughed
on regardless, I assume.

Regards,

Simonm.

--
simonm|at|muircom|dot|demon|.|c|oh|dot|u|kay
SIMON MUIR, UK INDEPENDENCE PARTY, BRISTOL www.ukip.org
EUROPEANS AGAINST THE EU www.members.aol.com/eurofaq
GT250A'76 R80/RT'86 110CSW TD'88 www.kc3ltd.co.uk/profile/eurofollie/

It's so long since I've seen a non-Imax 70mm print in the cinema, I've
no idea if they've successfully adopted an optical audio format for 70mm
or not, digital or otherwise.

Apart from DTS timecode no. Although Dolby did patent it's sprocket hole
spaces, but then they did the same for the opposite side of 35mm film, but
that was just to protect their interests.
Mind you who needs it - When you've seen a brand new mag striped print of
2001 on the Cinerama screen in Bradford you wonder what they'd bother with
anything else. (Apart from the envoronmental issues of mag striping, the
wearing out of the track, the degrading over time, the-...... etc, etc.!)