(Len Over 21)erroneously wrote in message ...
In article , (N2EY),
writes:

In article ,
(Len Over 21) writes:

In article ,
(N2EY)
writes:

Visual blending depends on the individual, but is around 20 flashes (dits)
per second.

The correct term is "persistence of vision." :-)

A term which is actually a misnomer:

Oh goodie, an "optical expert" you are now? :-)

I don't claim to be an expert at motiuon picture projection, Len. But
I do know some facts on the subject that you don't know. Apparently
that bothers you a great deal.

When were you ever an "expert" in optics in addition to doing your
"electrical engineering" thing?

One does not have to be an expert to know more than you do, Len ;-)

Just curious since I was directly
involved in a rather large DoD contract at Rockwell on an
interferometer.

Did the interferometer project motion pictures?

Had to work with lots of high-level optical
physicist types.

So? That doesn't correct your error.

Methinks you have a terrible "persistence of righteousness" about
your output in here. :-)

No, it's your "persistence of error" that causes you to insult the
messenger.

http://www.grand-illusions.com/percept.htm

There's the facts. But there are none so blind as those who will not
bother to look.

The actual persistence threshold varies with individuals and can
go down to 15 "flashes" per second. That seems to be a combined
function of the retinal cells and cerebral visual cortex.

Motion picture speed is 24 frames per second, but to eliminate flicker ecah
frame is flashed on the screen twice by means of a rotating shutter.

Not quite.

How "not quite"?

Modern standard sound motion pictures run at 24 frames per second. But each
frame is flashed on the screen twice, so there are 48 images per second on
the screen. A two-bladed rotary shutter is usually used in the projector.

Back when I actually RAN a projector in a cinema, the film rate was
24 frames per second.

That's what I wrote, at least twice, above. 24 frames per second is
the rate film goes through the projector. But it is not the rate at
which images are flashed on the screen.

Back when I was actually running a 16mm
projector, the film rate was 24 frames per second.

That's what I wrote, at least twice, above. 24 frames per second is
the rate film goes through the projector. But it is not the rate at
which images are flashed on the screen.

Once, when I rented
an 8mm projector to see some home movies of family, the film rate
was 24 frames per second.

That's what I wrote, at least twice, above. 24 frames per second is
the rate film goes through the projector. But it is not the rate at
which images are flashed on the screen.

While I never got a Masters in Optics,

I don't think you have an accredited degree in anything, Len ;-)

I can't ever recall any projectors that flashed on an image twice or any
other multiples.

Forgetful, huh? Here's a hint: Except for some museum pieces, they all
do it. T

All the mechanisms I've seen had the simple pawl
and shutter arrangement to blank the projected image during the
frame pull-down time.

Then you haven't seen any projectors newer than the 1920s or so.

The eye sees 24 frames per second and the eye-brain combination
perceives motion on a frame-to-frame basis.

24 frames per second. 48 images per second. Each frame is projected
twice. At 24 images per second, many people see objectionable flicker.
Which is where the term "flicks" came from.

It doesn't make any
difference if the SAME frame is flashed on twice, thrice, or quadruple
times.

Yes, it does. See the references.

What you and everyone else sees is those 24 frames per
second.

24 frames per second. 48 images per second. Each frame is projected
twice. At 24 images per second, many people see objectionable flicker.

The rate doesn't vary more than allowed by the internal
projector rate controls.

Feel free to post your American Cinematographer's association card
membership number.

Don't need one. Anybody who knows how projectors work knows I'm right
and you're wrong.

In the early silent film era, a speed of 16 frames per second was common, and
a
three-bladed shutter was usually used in the projector. Again, 48 images per
second.

The last time I saw any "silent films" was at the Rosenwald Museum
of Science and Industry in Chicago some time around 1950.

So?

The shutter is there to blank the "pull-down" time when
the geneva mechanism and pawl yank down the next frame.

That's not the only thing the shutter does. It also blanks the screen halfway
between pulldown intervals so that each frame is flashed on the screen twice.

...and you can send morse code in between the dits and dahs of
your solid-state break-in T/R switch.

Nope. I never claimed that. You are mistaken.

Of course you can. You SAY so therefore you are absolutely correct.

Nope. I never claimed that. You are mistaken.

What I CAN do when operating QSK/break-in CW/Morse is HEAR the receive
frequency between dits and dahs. Which is one of the big advantages of
CW/Morse over other modes. The first setup I used with that feature
was a homebrew station I designed and built about 1973. It used a
highspeed keying relay and a vacuum-tube TR switch.

Like it or not, I know far more about the subject of QSK/break-in
Morse/CW than you do, Len.

The
intermittent movement requires a free loop of film before and after
the shutter mechanism so that the supply and take-up reels can
move at an approximate constant rate. Note: A geneva wheel may
not be used in cheaper projectors but was standard in cinema
projectors for decades; there are other, simpler pull-downs.

Irrelevant to the discussion.

So is the subject of motion picture projection and your "48 per second"
frame rate.

24 frames per second. 48 images per second. Each frame is projected
twice. At 24 images per second, many people see objectionable flicker.

Motion picture frame rate standards are still 24 per second and that
is what nearly everyone sees. That's a comporomise between the
maintenance of persistence of vision and length of film needed for a
given time.

48 images per second. See:

http://www.bbctv-ap.freeserve.co.uk/supfr3.htm

or any reliable reference on motion picture projection.

Go for it...DEMAND to be recognized now also as an optical
expert.

I don't demand a thing, Len old boy.

As far as I'm concerned, the acquaintences I have in the motion
picture industry don't agree with you.

You don't understand how projectors work, Len.

For nearly all film projectors and editors, it is still 24 per second.

Incorrect.

:-) Check with the motion picture standards folks. Since before WW2
the motion picture frame rate has been 24 images per second.

24 frames per second. 48 images per second. Each frame is projected
twice. At 24 images per second, many people see objectionable flicker.

The frame rate and the image rate are not the same.

You're simply wrong on this, Len. 24 frames per second, 48 images per second.

Be a big boy and admit it.

What is a "big boy?"

Somebody mature enough to admit a mistake and learn something new.
Which leaves you out, Len.