What is the fastest motion sensing possible for an SD1100? - Script Writing - CHDK Forum
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What is the fastest motion sensing possible for an SD1100?

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Offline LabMonkey

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What is the fastest motion sensing possible for an SD1100?
« on: 21 / April / 2010, 05:22:01 »
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Hello everyone, I have decided to join these forums after doing some research into the capabilities of my SD1100 and CHDK.  I have had this camera for about a year now, and when doing some experiments in my physics classes I thought it would be very helpful to take high-speed photographs.  Unfortunately I confused shutter speed with pictures per second, and it wasn't until a few hours ago that I read through a lot of forum topics about the limitations of cheap cameras.  I have been trying to use the motion detection script written by fudgey+BarneyFive+MLuna to capture photographs of sparks between electrodes or the collapse of bubbles during cavitation.  What I am looking for is a script/configuration with the following properties:

It needs to work on an SD 1100 IS.
It should have as fast a shutter speed as possible (with the caveat that the SD1100 has no aperture or TV settings, only an ND filter).
It should detect motion (blue light intensity changes) as quickly as possible.
It takes a sequence of photographs as fast as possible after motion is detected.

Right now I am having trouble getting better results than just recording the event with the camera's video option.  It would be really nice to get more than one image using the camera, since only one frame of the video has the event.  I wrote a script that simply takes a series of no-flash photographs, but even that had significant delay between shots.  Am I totally out of luck here?  Should I be investing in a much more robust camera?  Thanks for any help you can provide.
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Offline fe50

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Re: What is the fastest motion sensing possible for an SD1100?
« Reply #1 on: 21 / April / 2010, 07:24:21 »
Hello & welcome, LabMonkey !

Quote from: LabMonkey on 21 / April / 2010, 05:22:01
It needs to work on an SD 1100 IS.
It should have as fast a shutter speed as possible (with the caveat that the SD1100 has no aperture or TV settings, only an ND filter).
It should detect motion (blue light intensity changes) as quickly as possible.
It takes a sequence of photographs as fast as possible after motion is detected.
In general, this could be done with fudgey's fast MD script (see also here) and the correct camera setup...

Use the camera in custom timer mode, with fix ISO, optionally fixed exposure time (Tv override), either with flash (adjustable with the CHDK force flash setting) or with a strong light source.

Set up MD to your needs in the script settings, e.g. set up a mask if you want to use only a part of the screen...

With Canon's custom timer mode the MD script starts capturing the images when motion is detected, IMO on the the SD1100 you can select up to 10 shots (in custom timer / "drive" menu, don't forget to set delay time to 0).

Quote
It would be really nice to get more than one image using the camera, since only one frame of the video has the event.  I wrote a script that simply takes a series of no-flash photographs, but even that had significant delay between shots.

The camera is to slow to capture such a fast series of images; a video typically has 25 or 30 fps - the SD1100 can take ~1.3 images per second in continuos mode, that's the highest fps you'll get.

FYI - the MD reaction time for the Powershot cameras is somewhere around 60 to 180 ms...
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Offline LabMonkey

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Re: What is the fastest motion sensing possible for an SD1100?
« Reply #2 on: 25 / April / 2010, 04:21:04 »
Thank you for the clarification.  I should have asked this question weeks ago (as it would have saved me a lot of time and allowed me to plan different experiments).  Do you happen to know if the cameras automatically shoot at as high a shutter speed as possible, provided they are set at the maximum?  Do I need to find out the exact maximum speed for the SD1100, or can I just shoot at the maximum available and have it work as well as possible?  Thanks again.
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Offline fudgey

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Re: What is the fastest motion sensing possible for an SD1100?
« Reply #3 on: 25 / April / 2010, 07:22:19 »
MDFB doesn't touch exposure settings at all. If you need a fast exposure and your camera doesn't have a Tv mode, you'll need to set CHDK Tv override before starting the script (remember to set ISO and ND filter manually too -- Canon's exposure automation will only hurt you once you override one parameter).
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