[GreenKeys] Secret DC Basement in NYC - Great History

[Roy Morgan]

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