Stopped down focus

Alan Browne wrote:

Ultrasound yes. IR no. You would need sub nanosecond timing for
accurate enough focus using IR. (speed of light is about 1 foot per
nanosecond).

I don't see the problem.

Computers do a couple of GHz nowadays. So you can get a stable
tact rate in these frequencies without trouble.

1 Hz = cycle 1s
1 kHz = cycle 1 millisecond
1 MHz = cycle 1 microsecond
1 GHz = cycle 1 nanosecond

No problem even for consumer electronics.

Even waaay back (1990 or earlier) my Dad had a video camera that
would measure distances by IR light. No, no patterns there, and
it didn't focus correctly when filming through a glass window.
(OK, focussing requirements are lower for moving images on small
chips with low resolution.)

-Wolfgang

wrote:

Wolfgang Weisselberg wrote:
1 Hz = cycle 1s
1 kHz = cycle 1 millisecond
1 MHz = cycle 1 microsecond
1 GHz = cycle 1 nanosecond

No problem even for consumer electronics.

But the return trip for an object 1m away would be less than 7ns, ie 7
cycles. I suppose it is possible to emit a signal and measure the
number of cycles until something is received, but I imagine that 15
years ago this was not feasible.

Sorry, having seen that with consumer VHS video cameras back
then, I disagree.

Also, I suppose you'd need to do some
processing to work out if the thing you received really is the signal
you wanted,

Send many signals and average over time (the focus motor has
a finite speed, thus doing averaging itself), and use either a
specific frequency or a specific pattern (patterns are no problems
either, how do you think IR remote controls work? And they have
been around a _long_ time.

and I don't know if this is possible in such short times
(since you must be ready to restart if it's the wrong signal).

No problem. Throw away signals detected a spurious, continue
sending pulses as before.

And did compact cameras in 1990 have 1GHz oscillators in them?

Oscillators are not _that_ new an invention.

Again, I don't
know; it seems hard to believe, but somehow they autofocused.

Hey, the Mercury capsule worked. Without any computers.

-Wolfgang

Wolfgang Weisselberg wrote:
No problem even for consumer electronics.

But the return trip for an object 1m away would be less than 7ns, ie 7
cycles. I suppose it is possible to emit a signal and measure the
number of cycles until something is received, but I imagine that 15
years ago this was not feasible.

Sorry, having seen that with consumer VHS video cameras back
then, I disagree.

But did they measure distance by measuring the time between emission
and reception? I don't know, I am asking.


Also, I suppose you'd need to do some
processing to work out if the thing you received really is the signal
you wanted,

Send many signals and average over time (the focus motor has
a finite speed, thus doing averaging itself), and use either a
specific frequency or a specific pattern (patterns are no problems
either, how do you think IR remote controls work? And they have
been around a _long_ time.

What do you mean? If your distance measuring is done by detecting the
time elapsed between emission and reception, then you have to emit,
wait until you receive the signal, and then divide that time by the
speed of light to get the distance, and only then activate the focus
motor to focus properly. Furthermore, changing the focus has absolutely
no effect on the signal received by the IR sensor; so I fail to see how
the speed of the motor enters into the discussion. Basically, I don't
understand what you're saying.

As for IR remotes, I don't know how quickly the TV (say) reacts, but I
suppose there is some time lapse between reception and reaction, since
you have to react differently according to the signal so some
processing is needed.



and I don't know if this is possible in such short times
(since you must be ready to restart if it's the wrong signal).

No problem. Throw away signals detected a spurious, continue
sending pulses as before.

What I was trying to say is this: You emit a signal, start a stopwatch
and wait; when its reflection is detected, you stop the stopwatch, and
may calculate the distance. However, to do that, you have to make sure
that the received signal is the reflection of whatever you emitted, so
you need to do some processing to check. If you process and find that
it is, then all is fine; but if it's not, then you have to wait some
more. The problem is that while you're processing the spurious signal,
the real one might have arrived. What do you do? I don't know if you
can process a signal while managing a queue of incoming candidates so
quickly (of the order of nanoseconds).


And did compact cameras in 1990 have 1GHz oscillators in them?

Oscillators are not _that_ new an invention.

No, but I was questioning whether 1GHz oscillators were built into VHS
cameras. As I said, I don't know, it's a question (although it sounds
too high-frequency, to be honest)

I think I am misunderstanding you. Could you please specify whether you
are talking about a system that measures the elapsed time between
emission and reception (as opposed to the angle of reception, a
completely different method)? If so, could you explain how the speed of
the focus motor has anything to do with the feasibility of doing this?

Thanks.

Wolfgang Weisselberg wrote:

wrote:

Wolfgang Weisselberg wrote:
1 Hz = cycle 1s
1 kHz = cycle 1 millisecond
1 MHz = cycle 1 microsecond
1 GHz = cycle 1 nanosecond

No problem even for consumer electronics.

But the return trip for an object 1m away would be less than 7ns, ie 7
cycles. I suppose it is possible to emit a signal and measure the
number of cycles until something is received, but I imagine that 15
years ago this was not feasible.

Sorry, having seen that with consumer VHS video cameras back
then, I disagree.

Also, I suppose you'd need to do some
processing to work out if the thing you received really is the signal
you wanted,

Send many signals and average over time (the focus motor has
a finite speed, thus doing averaging itself), and use either a
specific frequency or a specific pattern (patterns are no problems
either, how do you think IR remote controls work? And they have
been around a _long_ time.

and I don't know if this is possible in such short times
(since you must be ready to restart if it's the wrong signal).

No problem. Throw away signals detected a spurious, continue
sending pulses as before.

And did compact cameras in 1990 have 1GHz oscillators in them?

Oscillators are not _that_ new an invention.

Oscillators aren't, but inexpensive electronic devices that can operate at
gigahertz frequencies are.

If you know of any cameras that use the timing of a reflected light signal
for distance measurement please name them.

Again, I don't
know; it seems hard to believe, but somehow they autofocused.

Hey, the Mercury capsule worked. Without any computers.

-Wolfgang

--
--John
to email, dial "usenet" and validate
(was jclarke at eye bee em dot net)

wrote:
Wolfgang Weisselberg wrote:
No problem even for consumer electronics.

But the return trip for an object 1m away would be less than 7ns, ie 7
cycles. I suppose it is possible to emit a signal and measure the
number of cycles until something is received, but I imagine that 15
years ago this was not feasible.

Sorry, having seen that with consumer VHS video cameras back
then, I disagree.

But did they measure distance by measuring the time between emission
and reception? I don't know, I am asking.

Yes. To the best of my knowledge and memory. They would be
mis-focussing on windows, they were not hunting, the light
was not visible.

Also, I suppose you'd need to do some
processing to work out if the thing you received really is the signal
you wanted,

Send many signals and average over time (the focus motor has
a finite speed, thus doing averaging itself), and use either a
specific frequency or a specific pattern (patterns are no problems
either, how do you think IR remote controls work? And they have
been around a _long_ time.

What do you mean? If your distance measuring is done by detecting the
time elapsed between emission and reception, then you have to emit,
wait until you receive the signal, and then divide that time by the
speed of light to get the distance, and only then activate the focus
motor to focus properly.

The maximum stated range was 10 meters. So the maximum time to
wait would be 20m / c ~= 6.7 * 10^-8 seconds. If you allowed just
1/1000s before activating the focus, you'd be able to do more thas
10.000 measurements. (Not that you'd want to, it'd be draining
the NiCd battery (yep, that old), but you can cram in a few ...)

Furthermore, changing the focus has absolutely
no effect on the signal received by the IR sensor; so I fail to see how
the speed of the motor enters into the discussion.

The focus motor was not _very_ fast. So what would happen if
you had the following pattern of distance results (probably
a few dozen per seconds):

4m focus to 4m
4m still focussing
4m still focussing
....
.... arrived at focus
....
4m
4m still at focus
0.3m start focussing motor, now at 4.0m
0.3m still focussing (now at 3.95m)
4m reverse focus motor (now at 3.85m) (inertial mass!)
4m still reversing (now at 3.9m)
4m arrived at focus
....


The fact that the focus motor is slow DOES mean you average
out spurious signals. Think about this sequence. The whole
sequence probably takes half a second or less:

4.0m at 4.0
4.1m at 4.0 starting for 4.1
3.9m at 4.05 starting for 3.9
4.0m at 4.0 stop motor
3.9m at 4.0 starting for 3.9
4.1m at 3.95 starting for 4.1
4.1m at 4.0
4.0m at 4.1 starting for 4.0

You see, even with a fairly fast motor and slow updates, the
speed of the motor evens out a lot.

As for IR remotes, I don't know how quickly the TV (say) reacts, but I
suppose there is some time lapse between reception and reaction, since
you have to react differently according to the signal so some
processing is needed.

First patent for remotes: 1893, Nicola Tesla, US Patent 613809.
First remote controlled model airplane: 1932.
First remote controlled SAM missile "Wasserfall", WWII.
First wireless TV remote control "Flashmatic" 1955 (visible light)
First ultrasound TV remote control "Zenith Space Command",
1956. (4 buttons, 4 frequencies, no batteries needed!, and
6 extra tubes in the TV)
Many-Button remotes, prototypes at 1977-78.
IR-remote controls from the early 1980s.
Learing remote controls from mid 1980s.

Remember that the whole unmanned space exploration (and a
good part of the manned one as well) are using remote

Of course some lapse occurs because you have to decode the
whole signal, and probably wait for more pulses to come, but
the pauses are not that long.

and I don't know if this is possible in such short times
(since you must be ready to restart if it's the wrong signal).

No problem. Throw away signals detected a spurious, continue
sending pulses as before.

What I was trying to say is this: You emit a signal, start a stopwatch
and wait; when its reflection is detected, you stop the stopwatch, and
may calculate the distance.

Exactly. All you need is a 'counter' which can cope with a GHz
pulse and some start, stop and readout electronics. If you want
to do that digitally.

You can probably get by by discharging a capacitor over a resistor
while the light is going there and back again, and measuring the
rest voltage. And since the voltage is dropping fast at first,
you get increased accuracy with close targets. (Accumulate
by discharging over multiple bounce cycles.)

However, to do that, you have to make sure
that the received signal is the reflection of whatever you emitted, so
you need to do some processing to check.

Nope. It would be nice if you had. You can average over 10 or
100 or so measurements. You can use a well-defined frequency.
And you can say 'I don't care, it's consumer electronics anyway'.

If you process and find that
it is, then all is fine; but if it's not, then you have to wait some
more.

We are talking about times like .000000067 seconds per measurement
for the light to travel. Ok, take 1.000 times that time to
handle the stuff. We still talk about .00067 seconds. Negible.
About 1/2000s lagtime, even with generous handling time.

The problem is that while you're processing the spurious signal,
the real one might have arrived. What do you do?

You switch off or ignore the receiver once you get the first
signal. After all, you _will_ often get scatter from the
background, after the target has reflected.

I don't know if you
can process a signal while managing a queue of incoming candidates so
quickly (of the order of nanoseconds).

You are thinking digital. Try thinking analog.

I think I am misunderstanding you. Could you please specify whether you
are talking about a system that measures the elapsed time between
emission and reception (as opposed to the angle of reception, a
completely different method)?

Elapsed time.

If so, could you explain how the speed of
the focus motor has anything to do with the feasibility of doing this?

As I said, if you get a few spurious data (we are talking about
that VIDEOcamera), the focus speed can average them out.

For a photo camera you'd probably average measurements electrically.

-Wolfgang

IR has been used very extensively in Point and Shoot camera's

Ben, Why did you snip the part where I said:

"IR assist shines a pattern on the subject to get contrast lines for the
AF to focus on. AF assist is sometimes body mounted and more often
accessory flash mounted. "

Because in the 'IR assist' mode it is only used as a light source with
a pattern build in. Although light is neccesary for the focus system
the 'IR assist' is not an essential part of the workings of the focus
system.

The method I described uses IR as an integral part of the focussing.
The IR was triangulated, killing the IR beam would disable the
focussing system of those camera's.



That is what IR AF assist does. It does NOT do ranging as Colin first
implied (accidently or otherwise). That's what I was clearing up.



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-- [SI] gallery & rulz: http://www.pbase.com/shootin
-- e-meil: Remove FreeLunch.

wrote in message
oups.com...

Alan Browne wrote:
Ben Brugman wrote:
Ultrasound yes. IR no. You would need sub nanosecond timing for
accurate
enough focus using IR. (speed of light is about 1 foot per
nanosecond).


IR has been used very extensively in Point and Shoot camera's

Ben, Why did you snip the part where I said:

"IR assist shines a pattern on the subject to get contrast lines for the
AF to focus on. AF assist is sometimes body mounted and more often
accessory flash mounted. "

That is what IR AF assist does. It does NOT do ranging as Colin first
implied (accidently or otherwise). That's what I was clearing up.

Actually, you could also measure distance with IR easily:

1) two sensors, one emits, the other detects; given the reception
angle, you know the distance

It's not easily. Most sensors are not capable of detecting an angle.
Although triangulation is done, this is not done by sensors which
detect an angle, but with a row of sensors, where the detection is
done by registring on which of the sensors the centre of the beam
falls and working out the angle.
Or on older camera's the beam of the camera sweeps, the sweeping
mechanism is connected to the focus mechanism. The sweep
is stopped when the sensor detects the beam.


2) make the incoming reflected beam interfere with one directly from
the IR source; you could then deduce the elapsed time, hence the
distance (however, only modulo one wavelength, ie of the order of
600nm; that is, 10m and 10m plus any integer multiple of 600nm (eg 6m)
would be the same to this system; so please ignore this method...).
600 nm is not 6m.
A nanometer 10-9 meter, or 0.000000001 meter

Detection of this scale is difficult, and not usefull for AF.

Ben




I have no clue if method 1 is actually used, though I suspect it's what
was used in 35mm compacts; never having owned a film compact, however,
I don't know.

wrote in message
ups.com...
Wolfgang Weisselberg wrote:

Yes. To the best of my knowledge and memory. They would be
mis-focussing on windows, they were not hunting, the light
was not visible.


That proves it's IR radiation; it could be by triangulation, not by
measuring the time for the signal to come back.

It was done by triangulation. There are no cheap commercial
detectors available which receive enough light to detect a signal
with an accuracy of only nanoseconds. The sensors are just not
sensitive enough to detect light in such a short time.
At the time there where no cheap commercial electronics to work
fast enough to do the timing. So the method described of timing
light was (and still is) not feasable for consumer products.
Look at the price of a laser gun ten years ago to get an estimate
of how much that technologie would cost.
(The lasergun emits so much laserlight (not just ir) that this
technologie would not be good for the health of the persons
being taken pictures of, if this technologie would be used).

ben



Send many signals and average over time (the focus motor has
a finite speed, thus doing averaging itself), and use either a
specific frequency or a specific pattern (patterns are no problems
either, how do you think IR remote controls work? And they have
been around a _long_ time.

What do you mean? If your distance measuring is done by detecting the
time elapsed between emission and reception, then you have to emit,
wait until you receive the signal, and then divide that time by the
speed of light to get the distance, and only then activate the focus
motor to focus properly.

The maximum stated range was 10 meters. So the maximum time to
wait would be 20m / c ~= 6.7 * 10^-8 seconds. If you allowed just
1/1000s before activating the focus, you'd be able to do more thas
10.000 measurements. (Not that you'd want to, it'd be draining
the NiCd battery (yep, that old), but you can cram in a few ...)


But my point wasn't that the time interval is too long; it's that it's
too short.

Furthermore, changing the focus has absolutely
no effect on the signal received by the IR sensor; so I fail to see how
the speed of the motor enters into the discussion.

The focus motor was not _very_ fast. So what would happen if
you had the following pattern of distance results (probably
a few dozen per seconds):


You see, even with a fairly fast motor and slow updates, the
speed of the motor evens out a lot.


OK I see what you mean: you measure many times, the errors have little
effect. Well I don't think this is what cameras did/do. Feel free to
disagree.

As for IR remotes, I don't know how quickly the TV (say) reacts, but I
suppose there is some time lapse between reception and reaction, since
you have to react differently according to the signal so some
processing is needed.

First patent for remotes: 1893, Nicola Tesla, US Patent 613809.
First remote controlled model airplane: 1932.
First remote controlled SAM missile "Wasserfall", WWII.
First wireless TV remote control "Flashmatic" 1955 (visible light)
First ultrasound TV remote control "Zenith Space Command",
1956. (4 buttons, 4 frequencies, no batteries needed!, and
6 extra tubes in the TV)
Many-Button remotes, prototypes at 1977-78.
IR-remote controls from the early 1980s.
Learing remote controls from mid 1980s.

Remember that the whole unmanned space exploration (and a
good part of the manned one as well) are using remote

Of course some lapse occurs because you have to decode the
whole signal, and probably wait for more pulses to come, but
the pauses are not that long.


What do these dates have to do with anything? And "not that long"?
We're talking about reactions that must occur in nanoseconds.

What I was trying to say is this: You emit a signal, start a stopwatch
and wait; when its reflection is detected, you stop the stopwatch, and
may calculate the distance.

Exactly. All you need is a 'counter' which can cope with a GHz
pulse and some start, stop and readout electronics. If you want
to do that digitally.

All you need is a gigahertz oscillator? OK, I never paid any attention
to circuits etc, but it doesn't sound trivial to me. OK, maybe I am
wrong, but I'd be rather surprised if it's easy to build an accurate
gigahertz oscillator with cheap components. As I said, I may be wrong.


You can probably get by by discharging a capacitor over a resistor
while the light is going there and back again, and measuring the
rest voltage. And since the voltage is dropping fast at first,
you get increased accuracy with close targets. (Accumulate
by discharging over multiple bounce cycles.)


However, to do that, you have to make sure
that the received signal is the reflection of whatever you emitted, so
you need to do some processing to check.

Nope. It would be nice if you had. You can average over 10 or
100 or so measurements. You can use a well-defined frequency.
And you can say 'I don't care, it's consumer electronics anyway'.

If you process and find that
it is, then all is fine; but if it's not, then you have to wait some
more.

We are talking about times like .000000067 seconds per measurement
for the light to travel. Ok, take 1.000 times that time to
handle the stuff. We still talk about .00067 seconds. Negible.
About 1/2000s lagtime, even with generous handling time.


Did you bother to read what I wrote? I am arguing exactly the opposite
of what you're answering to.

The problem is that while you're processing the spurious signal,
the real one might have arrived. What do you do?

You switch off or ignore the receiver once you get the first
signal. After all, you _will_ often get scatter from the
background, after the target has reflected.

And what if the signal is spurious? You measure many times, would
probably be your answer. OK. I don't think anything works this way.

I don't know if you
can process a signal while managing a queue of incoming candidates so
quickly (of the order of nanoseconds).

You are thinking digital. Try thinking analog.

I think I am misunderstanding you. Could you please specify whether you
are talking about a system that measures the elapsed time between
emission and reception (as opposed to the angle of reception, a
completely different method)?

Elapsed time.

If so, could you explain how the speed of
the focus motor has anything to do with the feasibility of doing this?

As I said, if you get a few spurious data (we are talking about
that VIDEOcamera), the focus speed can average them out.



OK, I can see this will become long and tedious. I give up. Frankly, I
don't know how it works, so maybe you're right. I don't think so, but
maybe you are.

If you know of any cameras that use the timing of a reflected light signal
for distance measurement please name them.

Speedometercamera's with lasergun technologie use that technologie.

ben brugman wrote:
wrote in message
ups.com...
Wolfgang Weisselberg wrote:

Yes. To the best of my knowledge and memory. They would be
mis-focussing on windows, they were not hunting, the light
was not visible.


That proves it's IR radiation; it could be by triangulation, not by
measuring the time for the signal to come back.

It was done by triangulation. There are no cheap commercial
detectors available which receive enough light to detect a signal
with an accuracy of only nanoseconds. The sensors are just not
sensitive enough to detect light in such a short time.
At the time there where no cheap commercial electronics to work
fast enough to do the timing. So the method described of timing
light was (and still is) not feasable for consumer products.

Ben,
Thanks. I thought so.

Look at the price of a laser gun ten years ago to get an estimate
of how much that technologie would cost.
(The lasergun emits so much laserlight (not just ir) that this
technologie would not be good for the health of the persons
being taken pictures of, if this technologie would be used).

But does a police laser gun work like this? I'd have thought it would
use the doppler shift to measure speed (actually I'm sure). On the
other hand, I know that there are laser guns that measure distance
(used eg by the artillery), so these presumably do work by measuring
the elapsed time. Do you know if this is so?