[GreenKeys] Secret DC Basement in NYC - Great History

Wed May 13 12:15:35 EDT 2015

      Frame rate for silent pictures is 16 frames per second. Theater 
projectors had three bladed shutters so the flicker rate was 48 
applications per second.  Sound films are at 24 FPS and most theaters 
have two bladed shutters so again the flicker rate is 48 per second.   
The flicker rate limits brightness since the sensitivity of the eye 
varies with brightness.  The visibility of flicker diminishes as the 
rate becomes higher and is nearly gone at about 60 FPS.  American 
television has a flicker rate of about 60FPS although some parts of a 
color TV image may be less.  British TV runs with a flicker rate of 50 
per second so those used to 60 frame TV will see it as flickering 
slightly especially in the highlights.
      A note:  very often TV transfers silent movies at sound speed. 
They claim the old time theaters sped up the movies to get more people 
through the theater.  This may sometimes have been true in the very 
early days of motion pictures but certainly was not by the time the 
industry reached some maturity.  Its just more trouble to transfer them 
at the correct speed plus many are just plain ignorant of the history of 
the motion picture.  It is very obvious when a film is run at the wrong 
speed.   Showing a silent movie at sound speed is like playing a 33-1/3 
RPM record at 45 RPM.  No one would tolerate it for a second but we are 
used to seeing the jerky motion of wrong speed movies so don't know any 
better.  To me it diminishes or destroys much of the dramatic value.

On 5/13/2015 8:02 AM, Roy Morgan wrote:
> On May 13, 2015, at 10:45 AM, Doug Alderdice <ka2wft at arrl.net> wrote:
>
>> I don't have a video but can maybe describe it.  It's strange, because at least for me when I look directly at an incandescent lamp operating on 25 Hz I don't see the flicker, it's something I am more aware of in my peripheral vision.
> As I understand it the center portion of the retina is less sensitive to changes in image with time but more sensitive to detail.  I, too have noticed the flicker in peripheral images when I see none in a centered image.  Perhaps our sight system evolved this way to favor increased detection of motion (perhaps of a predator, or prey) at the peripheral of our vision.  I think you can test this out easily with modern LED traffic lights, especially if you move your eyes to create a moving image on the retina.
>
>>   Movie frame rates are anywhere from 16 to 20-some per second, so it's comparable to 25 Hz AC lighting a lamp.
> Wikipedia tells something of this: silent films were shown at 22 to 26 frames per second (I think with single shutters, that is - each frame is shown only once).  Further:
> “...the rate of 24 FPS became standard for 35 mm sound film. At 24 FPS the film travels through the projector at a rate of 456 millimetres (18.0 in) per second. This allowed for simple two-blade shutters to give a projected series of images at 48 per second, satisfying Edison's recommendation….”
>
> It goes on to say that modern 35 mm films are shown at a rate of three per frame.
>
> I am pretty sure that the 16 mm systems are also run at 24 frames per second.  This is out of synch very slightly with television frame rates so that in transferring film to video, you need to drop a frame every once in a while to keep things in synch (sound and picture tracks, for instance).  If  I remember correctly, this got done at moments when a slight gap in the sound would not be noticed.
>
> I worked in film sound engineering, but it was a *long* time ago.
>
>   
> Roy
>
>
> Roy Morgan
> k1lky68 at gmail.com
> K1LKY Since 1958
>
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-- 
Richard Knoppow
1oldlens1 at ix.netcom.com
WB6KBL