A1 Simultaneous Zoom & Focus bombshell at DVinfo.net

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Canon XH Series HDV Camcorders
Canon XH G1S / G1 (with SDI), Canon XH A1S / A1 (without SDI).


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Old October 25th, 2008, 02:30 PM   #1
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A1 Simultaneous Zoom & Focus bombshell

Afraid this isn't going to be very elegant as I can't get a handle on these quote things, especially between forums, but here goes............

This from the "Support Your Favourite Camera" forum:

http://www.dvinfo.net/conf/remote-le...n-xh-a1-6.html


(** I should own up to the fact that earlier on in the thread I had spouted the percieved wisdom that zoom & focus could NOT be done at the same time, came back to bite me that one...........)

"Chris

Thanks for the info re one servo. I’ll have to search out the posts you refer to.

That said what I’ve written above re the differences between using the 2 controllers is true. At least with my gear.

The cam’s push auto focus is disabled when the ZR2000 is plugged in. With the ZR1000, I’m able to zoom with the lanc, and focus at the same time with the push auto focus on the camera.. I’ve checked the focus using the peak and magnfying functions and compared the distance readout between this and manual focus. I’m not talking about a last second focus when I release the zoom. I offer no explanation. I just know what I see. It works.


Jase Tanner




October 21st, 2008, 06:25 PM #78
Chris Soucy
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Well, stuff me...................

--------------------------------------------------------------------------------

If I hadn't seen it with my own eye's, I would never have believed it!

I am now having to re - evaluate everything I thought I knew about the A1, ZR1000 and Zoom and Focus.

So certain was I, that I hoiked out the A1 and tripod and tested it for myself.

It bloody well WORKS!!! (What's that saying about old dogs and new tricks?)

I don't know HOW it works, but it does.

It's easy to test this for yourself, set the ZR1000 zoom speed to slowest, rack the lens as out of focus as you can, hit the (Lanc) zoom rocker and then press the "Push AF" button on the camera, anytime you like.

The picture will swim into focus in very short order without the zoom counter missing a beat.

Even more amazing, as long as you have the "Push AF" button on the camera depressed, it tracks the focus perfectly all through the zoom.

Now, what's REALLY interesting, is that if you stop the zoom, having achieved focus, and barely touch the zoom rocker to zoom the other way, it snaps out of focus even faster than it snapped into focus in the first place!!!

Confused? You bet your sweet bippy I am.

Not tested (as yet) but needs to be: Does this behaviour show up with camera zoom controls, as well as Lanc?

I'm sure that once people have taken this on board and seriously played, all sorts of other little gems will crawl out of the woodwork.

My question to you Jase, is this:

When you mentioned the ZR2000 disables the cams "Push AF" button, were you saying/ implying that it transfers this ability (focus whilst zooming) to the Lanc "Push AF" or it is lost entirely?

Anybody got any suggestions as to how this is possible?

I got really excited there for a while as I thought this might well be a way out of the impasse I've been in with the A1 for over a year now with this damn Lanc focusing.

At the end of the day, sadly not, as my subjects never (or very rarely) lend themselves to "Push AF/ Auto" focusing, so I'm still in a hole.

Exceedingly interesting developement, nevertheless.

Jase, thanks for teaching this old dog at least one new trick!


CS"


End of extremely ragged import.


So, anyway, anyone got any ideas?

This has me completely flumoxed.

How can a single servo lens apparently zoom AND focus at the same time?

For those who think this is all malarky, do try this test in the comfort of your own home (assuming you own a ZR1000).

It really DOES work.

How?

Dunno!

Extremely confused.


CS

Last edited by Chris Soucy; October 25th, 2008 at 06:35 PM. Reason: **+
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Old October 25th, 2008, 02:36 PM   #2
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I thought when in auto focus mode the camera just switched rapidly between zooming and focusing. Depending on what you are focusing on this either worked or it would display a little bit of pulsing. I noticed the pulsing the most with my A1 when it was aimed at light sources such as signs. I am sure others will be able to chime in more about this though :)
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Old October 25th, 2008, 09:14 PM   #3
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I just tried this with the om-camera zoom and also with a Manfrotto 522 LANC controller.

The results for zoom and focussing are the same in both cases, when I start the zoom and then press Push Auto, there is a pulsing, shimmering effect while the camera tries to focus. When it achieves focus this effect is still there, but not as frequent, presumably because it only has to make small focus adjustments while zooming in after the initial focus finding.

I can also confirm that the focus goes right off when the zoom is reversed, but only with the LANC controller. This doesn't happen at all with the on-camera zoom controls. Very strange.

Richard
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Old October 25th, 2008, 10:40 PM   #4
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Theory Number #1

Based on zero knowedge of internal workings of the XH series camera's, but hey, gotta start somewhere.............

OK, first assumption:

The lens servo is actually capable of switching from Zoom to Focus functions so fast it can appear to give the impression of doing both simultaneously ie. multiplexing.

Theory, as far as it goes:

The lens rings and on camera zoom and focus controls are all daisy chained up on what I will call "the control bus".

Once a control has this bus, nothing else gets a look in.

Hence why using the on - camera controls does not allow this observed behaviour to work.

Now, let's assume the decoded Lanc signal by - passes this Control bus and actually feeds the simultaneous Zoom data to the servo control chip along with the Control Bus focus data.

As long as this chip is programmed to take data from each port in sequence (or take other commands at it's sole input in what must be a multiplexed environment), the servo gets alternative Zoom and Focus commands, which it then acts on.

Hence the Focus whilst Zooming effect seen, and why the "into focus" isn't light speed quick.

If this theory is correct, it would tend to imply that Lanc commands do not (in the main) use the Control Bus, and thus other Lanc enabled functions may by - pass it as well.

I suppose the question is - can anybody find any other Lanc commands that multiplex with usually incompatible camera commands.

The most obvious is the Lanc focus buttons and the on camera zoom, for example.

Anyone think of any others?

None of which explains the "zap out of focus" if the zoom rocker is hit the other way tho'.

If I wasn't so darn bus with this pesky G & T, I'd go have a play right now.

Of course, the above may be a complete load of hogwash, wish someone had the real answer.

Any other theories?


CS
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Old October 25th, 2008, 10:53 PM   #5
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Hi Chris. Don't know about control bus, it could just be one device having to do several tasks at the same time and so is multiplexing between them.

And as I said, I get the same response using the camera controls and the LANC controller, apart from the crazy defocus behaviour at the end. So it seems the same control mechanism is always used, regardless of which control buttons you press.

Richard
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Old October 26th, 2008, 06:47 PM   #6
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Quote:
How can a single servo lens apparently zoom AND focus at the same time?
Is is likely NOT a single servo. The auto lenses in past Canon Camcorder lines including the XL1, GL1, A1 Digital, and L2 had separate servo motors for zoom and focus. I would be very surprised if that was not the case with the XH series.
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Old October 26th, 2008, 08:03 PM   #7
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Further tests and interesting results...........

OK, a nice sunny day here, so time for some further tests of this interesting phenomina.

First off: the bizarre de - focus issue.

Test format: Focus switch = manual; Lanc zoom control = 1 (slowest). Lens hand zoomed to Z99 on object 6.6 metres away, lens focus set to 1 metre.

Press Lanc "Zoom Wide" rocker and instantly after, press and hold the IAF button on camera.

Within a second or two picture is in focus. Continue zoom to Z76 - ish, releasing the Press IAF button just before the end of the zoom. Tap the Lanc "Zoom Tele" rocker. Lens instantly de - focuses. Check focus distance set on lens, reads .8 metres (closest possible at Z76 - ish)

Crank the lens back to Z99 and touch focus ring, focus distance reads 1 metre!

The lens/ camera has "remembered" the initial focus set on the lens (when the Push AF button was pressed) and returns there if the zoom is reversed.

Conclusion:

If the "Push AF" button is depressed then released (in the process re - focusing the lens) whilst the Lanc is sending Zoom commands, the new focus setting of the lens is not written into some sort of buffer, leaving the initial focus setting instead.

If a reverse zoom is attempted, the initial focus setting is used to instantly re - focus the lens to where it was - somewhat akin to the Zoom Position Preset.

If the "Push AF" button is held down till after the Zoom rocker is released, the new lens position is memorised instead.

Second test: any other controls show similar symptoms?

Nope. The ZR1000 focus buttons do diddly squat if the lens is zoomed using the on camera zoom rocker.

Third test: What about setting Focus mode from "Manual" to "IAF"?

To cut a long story......Switching from M to IAF AFTER the Lanc zoom rocker is depressed produces the same "focus whilst zooming" as before, with the benefit of updating the current lens position the moment the zoom rocker is let go.

Switching from M to IAF before the zoom rocker is depressed behaves exactly the same, the lens will and does focus whilst zooming, and some pretty wild back and forth lens swinging was needed to confirm this was so.

In all cases the "perfect focus aquired" took longer (not much, but a bit) than if the lens was not being zoomed, confirming my suspicion that the lens operation is indeed multiplexing the commands somehow.

Don,

I'm not in a position to categorically say one way or the other about one or two servos, tho' I do recall Canon and others making much ado of the new "Dual Servo" lens accompanying the latest X series release.

If the XH A1 lens IS dual servo, it seems odd in the extreme that both cannot function at once - somewhat negateing the point of having two.

Every informed source I've ever read has said "ONE" only.

However, every other informed source I've read has said "can't zoom and focus at once", which, using the on camera controls, is true.

My point is, that using off camera controls appears to allows the A1/ G1 to behave like a twin servo lensed camera, despite (probably) only having one.

I doubt this news is going to cause the end of civilisation as we know it, but it may just be a help to indie, hand holders or fast action shooters to know this is possible.


CS
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Old October 26th, 2008, 09:16 PM   #8
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Quote:
Originally Posted by Chris Soucy View Post

However, every other informed source I've read has said "can't zoom and focus at once", which, using the on camera controls, is true.

My point is, that using off camera controls appears to allows the A1/ G1 to behave like a twin servo lensed camera, despite (probably) only having one.
Hi Chris. I get the same behaviour with and without the LANC controller. The camera does focus while zooming, only with a pulsing effect that is not desirable. People have been mentioning this for years. Wonder why you are seeing something different?

Richard
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Old October 26th, 2008, 09:47 PM   #9
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Hi Richard................

Guess I've never seen it as I've never used the camera with "IAF" switched on.

As I think I may have mentioned in my first post, practically none of my subjects lend themselves to the use of auto focus.

Many, if not all of my shots are done at the far end of the zoom range where I'm trying to pick out a mid ground critter against what can be a very far off background indeed.

AF in those circumstances is all over the place like a dogs dinner.

Even when I'm doing landscape shots, I leave the camera in Manual, zoom in, focus, zoom out to frame and shoot - AF never gets a look in.

I'll occasionally use the "Push AF" to see if it can better second guess me if I'm shooting closer than about 10 metres, but that's pretty rare.

Guess I only picked up on this as Jase seemed to highlight a rebuttel of the " A1 can't zoom and focus" mantra so often read on DVinfo.

Well, seems in fact it can.

Still haven't worked out a scenario where it's of any use to me, but that's another matter entirely.


CS
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Old October 28th, 2008, 05:42 AM   #10
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My information with respect the the XL1, GL1, A1Digital, and L2. is based on content of the Canon service manuals.

Given that autofocus it typically evaluated by image contrast, the act of zooming can cause image changes that may mislead the sensors, especially rapid zooming.

How the camera behaves when receiving multiple instruction at the same time is a mater of how the internal programming arbitrates between the the commands it is receiving and which commands receive priority if their is potential for interaction or conflict. LANC is a serial data protocol, at a relatively slow speed (9600 bps) and 8-bytes per data packet. Further as I recall, it often requires a repeat of a command before it executes the command.

Documenting and sharing camera behaviors is helpful to users.
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Old October 28th, 2008, 10:22 AM   #11
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Chris

I've been doing some more testing. My results are essentially the same as I first reported. Using the zoom rocker on the ZR1000 on the push auto on the XHA1 allows me to zoom and focus at the same time. I engage them simultaneously. Of course I realize that one or the other is in reality being activated first and that no doubt changes.

I've not noticed the defocus you refer to when hitting the zoom after the refocus is finished.
I did once, and only once, however see it pulse as someone has referred to above.

I've yet to experiment with any differences in zoom speed or how using instant AF vs normal AF may affect things. And just to be clear, the only AF I ever use is the push button, I never have AF turned on all the time.
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Old October 28th, 2008, 07:27 PM   #12
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Originally Posted by Jase Tanner View Post
Chris

I've been doing some more testing. My results are essentially the same as I first reported. Using the zoom rocker on the ZR1000 on the push auto on the XHA1 allows me to zoom and focus at the same time. I engage them simultaneously. Of course I realize that one or the other is in reality being activated first and that no doubt changes.

I've not noticed the defocus you refer to when hitting the zoom after the refocus is finished.
I did once, and only once, however see it pulse as someone has referred to above.

I've yet to experiment with any differences in zoom speed or how using instant AF vs normal AF may affect things. And just to be clear, the only AF I ever use is the push button, I never have AF turned on all the time.
Hi Jase. Can you just check something for me please? If you remove the ZR1000 and use the camera zoom rocker while you press the IAF button, do see see any different behaviour? I see the same thing with or without the LANC controller. So far no sign of a bombshell.

Richard
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Old October 29th, 2008, 01:40 AM   #13
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Hi Richard

If I focus and zoom at the same time using only the camera's push AF and its zoom, it works just fine. Is that what you're finding?
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Old October 29th, 2008, 02:02 AM   #14
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Yes Jase, that's what I see as well, thanks for confirming it.

The point about the XH-A1 being unable to focus and zoom at the same time is that the focus ring doesn't work while you are zooming. As far as I know, the auto focus and press to autofocus button have always worked, albeit with the pulsing effect that most people find nasty.

Does the ZR1000 have focus in/out buttons? The focus buttons on my Manfrotto controller do not work while zooming either.

Richard
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Old October 29th, 2008, 10:52 AM   #15
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Yes, it does and they seem to work fine but I never use them.
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