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usb remote quick response

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Offline ozcar

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usb remote quick response
« on: 09 / May / 2015, 04:43:44 »
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I am trying to use usb remote to capture images of various creatures that wander around at night in our garden. Since it is dark, CHDK motion detection seems to be ruled out so I have been using an IR beam as a trigger.

All I have done so far is set the usb remote control mode to "quick" hoping to get well, quick response, but the camera (PS A530) takes 4 to 5 seconds to respond, by which time the creature is usually long gone. I set the camera focus to manual, but that did not seem to make it any quicker.

I thought of sending "half press" to the camera before the sensor is triggered, but from what I have read the camera will only stay in half press state for a short time, while I need it to remain ready, perhaps for several days.

I'm sure others must have tried to do this, but I could not find anything useful, so I'm obviously not searching for the right words. All I could find was a discussion about quick response in order to synchronise more than one camera, but I don't know how to apply that to what I am trying to do with a single camera.

Suggestions?

Thanks.

Re: usb remote quick response
« Reply #1 on: 09 / May / 2015, 07:42:10 »
It should be possible to take a shot almost instantaneously when the USB remote is triggered.

Setting manual focus is a good idea to reduce shot time.   Are you doing this with the Canon controls on the A560 or CHDK?  (Note that SD override functionality via CHDK menus does not work well on some cameras.  However, the A560 should be okay.)

The other part of your delay is probably coming from the time it takes the camera to set exposure.  In a dark scene outdoors at night,  the camera will struggle to figure out what exposure to use.   The obvious answer to that is manually override the exposure with either the CHDK menu setting or a small script.

Are you using the camera's flash?  (Either by itself or to trigger a larger slave unit).  Or trying to take a longer exposure?

If using a script,  the set_aelock( ) function might also be useful.



Ported :   A1200    SD940   G10    Powershot N    G16

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Offline reyalp

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Re: usb remote quick response
« Reply #2 on: 09 / May / 2015, 16:22:02 »
All I have done so far is set the usb remote control mode to "quick" hoping to get well, quick response, but the camera (PS A530) takes 4 to 5 seconds to respond, by which time the creature is usually long gone. I set the camera focus to manual, but that did not seem to make it any quicker.
I don't know of any specific limit, it's certainly more than a few second.

It won't sit waiting for a synchronized remote for more than that, but sitting in half press for a long time should be fine, this is what the fast MD scripts do. You could always make it let up and re-press half press every few minutes/hours/days if you need to.

From half press to shoot should only be tens of ms, you shouldn't need synced remote level precision.

edit:
To clarify, the usb remote "one push" mode does have a time out for half press, but you could write a script that just sits in half press and waits for the remote signal to do a full press.
« Last Edit: 09 / May / 2015, 16:28:41 by reyalp »
Don't forget what the H stands for.

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Offline ozcar

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Re: usb remote quick response
« Reply #3 on: 09 / May / 2015, 19:45:42 »
To clarify, I was using the normal Canon manual focus, not CHDK (would it make a difference?). I am using the camera's flash (interestingly, most of the creatures do not seem to be greatly alarmed by this). I did not think to try setting the exposure, I was perhaps thinking that in the dark with the flash the exposure was somehow determined at the instant of the flash.

I will investigate setting the exposure, and also look at how to keep it in half-press mode with a script.

Thanks.


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Offline ozcar

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Re: usb remote quick response
« Reply #4 on: 13 / May / 2015, 20:35:15 »
Just an update with my (lack of) progress:

I tried manually setting the exposure. I thought that I could start with just copying what the camera had been setting automatically, but I could not do that, because for some reason the ISO setting and flash output are not displayed by the camera (and are not embedded in downloaded images). So I just messed around to get a reasonable exposure.

The camera did seem to be quicker to take a picture than when I only had manual focus set, but not super fast, certainly not in the millisecond range. After two days like that, I found the triggering was not working, but it definitely was working when I had been trying to get the exposure right!?

I don't know if this is due to me changing some other setting, but what I now have is:
When there is a trigger, there is a reaction from the camera - the auto focus assist light on the camera comes on briefly twice, and each time the light comes on there is a slight mechanical sound from the camera, like it is making some tiny change to the aperture or focus, but the flash does not go off, and no picture is taken.

Now that is with the rotary dial on the camera set to "M" which I did to set the exposure manually. The strange part is that if I put the rotary dial to "P", where I had it initially, or to "AUTO", then the camera does take a picture (on triggering, there is a tiny beep from the camera, the auto focus assist light comes on for a longer time, then the flash goes off and a picture is taken.

So, camera on "M" - no picture, but Camera on "P" or "AUTO" and I do get a picture, and at this stage I'm definitely not changing anything else in between.

CHDK Settings, Remote Parameters, Enable Remote [.], Switch Type [OnePush], Control Mode [Quick].

The USB remote trigger is a 100 millisecond pulse.

I tried changing the USB remote Switch Type to TwoPush - did not seem to make a difference, then tried Control Mode [Normal] which causes the auto focus assist light to come on only once, rather than twice, but still no picture. This was all with the same 100 millisecond trigger pulse (something I can also change, but it takes a bit more work).

I will continue with my tinkering, but if anybody has any idea what is going on, please do tell.

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Offline reyalp

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Re: usb remote quick response
« Reply #5 on: 13 / May / 2015, 21:46:41 »
Quote
The camera did seem to be quicker to take a picture than when I only had manual focus set, but not super fast, certainly not in the millisecond range.
If you want that kind of response, you will need to have the camera waiting in half press and just use the remote to trigger the full press. This will require scripting.

Quote
So, camera on "M" - no picture, but Camera on "P" or "AUTO" and I do get a picture, and at this stage I'm definitely not changing anything else in between.
This is strange. I've seen cameras refuse to shoot if it isn't able to focus while in auto modes, but I don't think I've noticed that in manual.

One thing to watch out for is that flash settings are usually per mode. So if you are in P and set the flash to auto, and then switch to M, the flash will be in whatever mode you last set it to for M, not what you just set. I don't know if there's any combination of flash settings that will make the camera not shoot though.

Don't forget what the H stands for.

Re: usb remote quick response
« Reply #6 on: 13 / May / 2015, 22:42:37 »
Let me know if you'd like to try a script and are not sure how to write one.
Ported :   A1200    SD940   G10    Powershot N    G16

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Offline ozcar

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Re: usb remote quick response
« Reply #7 on: 13 / May / 2015, 23:08:02 »
Millisecond response would be good, but I probably don't really need that.

Truth is, I don't have a good handle on the response I am getting. When I originally tested things, back at my desk, I had the camera set for  auto focus and exposure, and the response seemed promising, but I did not actually measure it. At a guess, it might have been around a second, or perhaps a little longer.

However, with the camera "on location" it was failing to catch the action (I have a video camera there as well). So, I tried setting manual focus, but it was still not fast enough. What I now think is happening, is that immediately after turning the camera on and setting it up, the response is reasonable, but after the camera has been on for a long time the response gets real bad. On one occasion, by counting the video frames, I saw it take nearly five seconds before the flash was visible as it took the picture (which showed the tip of a tail and hind foot of a passing cat). I have now retrieved the camera and am doing an experiment to see if the response really does increase after some time.

I'm no further in figuring out why it now fails to trigger when set on "M". I tried increasing the USB remote trigger pulse from 100 ms to 750 ms but that made no difference. I believe that with my aperture, shutter speed, ISO and flash settings, it does take a picture if I manually press the shutter button, but I will double check that when I have finished the testing I mentioned above.

I may end up trying to do something with a script, but right now I'm just trying to make some sense of what I have been seeing.

Thanks for your comments.

Edit:
Testing done this afternoon with the camera set to "P" (with manual focus, but automatic exposure).

The time the camera takes to respond does appear to depend on how long it has been "on standby", waiting for the trigger.

Immediately after setting up the camera, I took several shots, and the response was around one second. I then left it waiting for the trigger for 90 minutes, and it then took around 3 seconds to respond. Triggered again shortly later, and the response was back to around the 1 second mark.

I then left it waiting for the trigger for four hours, and the response was a bit over 3 seconds. Triggered it again a minute or so later, response back down to around one second.

Left it for 15 minutes - response 2 seconds.

Note, I don't currently have an accurate way to measure the response time, but I'm pretty sure that the longer it has been waiting, the slower it is to respond.

I then changed the camera setting to "M" to check that it still responds to the shutter button, and it does, but strangely, it did also respond to the USB remote trigger, but only once! With the camera set to "P" or "AUTO" I have never had it fail to respond to the trigger, but on "M" it is hit or miss, but mostly miss. Your guess is going to be better than mine as to what is going on there.
« Last Edit: 14 / May / 2015, 04:32:11 by ozcar »


Re: usb remote quick response
« Reply #8 on: 14 / May / 2015, 08:17:04 »
I may end up trying to do something with a script, but right now I'm just trying to make some sense of what I have been seeing.
Much of what you are seeing is indeed strange.   

Using a script has two possible advantages. 

In the first case,  the problem might go away. 

In the second, if the problem does not go away,  you can do some detaied logging with accurate timestamps down to the 10's of milliseconds of each step in the process from detecting the USB signal, through half press, full press and shot complete.  That could give us a much better answer about where things are slowing down.
Ported :   A1200    SD940   G10    Powershot N    G16

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Offline ozcar

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Re: usb remote quick response
« Reply #9 on: 23 / May / 2015, 22:09:27 »
I did not have much time to look at this again until yesterday.

I added a photo-transistor so I can detect when the camera flash goes off, and so measure the response time. What I have found since doing that:

Response time is typically around 2200 ms, but is quite variable - twice is was around 1350 ms. Setting the focus manually does not make any clear or obvious difference. The time does seem to increase if it has been waiting for a long time. The two times I left it for 60 minutes, I got responses of 2702 and 2947 ms, and after 10 hours I got 4094 ms.

I will keep plugging away...

 

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