Question about shutter lag, and chdk

carl1864

20

« on: 24 / January / 2011, 18:16:01 »

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I'm going to buy a CHDK capable camera soon. I'm wondering, how can I know what sort of shutter lag to expect from the camera I buy? I'm not talking about the lag when when its focusing, etc, since I always do half click first on any shot I ever take (this seems to be what I generally find on spec sheets). I'm talking the amount of shutter lag from when the button is already half clicked, and you click it the rest of the way. Or more importantly, when using the usb remote, the amount of time the signal is sent till the time it goes off.

One of the biggest things I am hoping to use the chdk camera for is for high speed photography, triggered by sound triggers, laser triggers, pressure triggers, etc. I know normally this type of photography is done in a dark room, with camera in bulb mode, and a flash. However i'm hoping to be able to take advantage of the fast 1/10,000+ shutter speeds to take some nice high speed photos, outdoors and other unique places, without the need for a dark room setup.

I've tried reading specs on the prefocused lag of a few cameras, but that info is very hard to find and often varies greatly (one site said a particulat camera had a .06 lag and another said .02 for the same camera). And that's just with the stock firmware though, I don't know if chdk is able to make it any faster or not, since afterall I've heard chdk on its own, just using its own motion detector, is fast enough to capture lightning. How can I actually know how much lag to expect from a particular camera to help decide which one to get? Do any of these canon powershots have a short enough shutter lag to even make somewhat high speed photography realistic, or will they all likely have too much lag?

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reyalp

14079

Re: Question about shutter lag, and chdk

« Reply #1 on: 24 / January / 2011, 23:52:24 »

Quote from: carl1864 on 24 / January / 2011, 18:16:01

I don't know if chdk is able to make it any faster or not, since afterall I've heard chdk on its own, just using its own motion detector, is fast enough to capture lightning. How can I actually know how much lag to expect from a particular camera to help decide which one to get? Do any of these canon powershots have a short enough shutter lag to even make somewhat high speed photography realistic, or will they all likely have too much lag?

CHDK doesn't make it faster. However, the speed of fast MD should give an upper bound of the time it takes to go from half shoot to capturing the image. Note that while only some CHDK cameras have fastest MD support, this is based on whether the CHDK port knows where particular camera variables are or not. The cameras that don't have fast MD aren't slower, the CHDK port just isn't as complete.

So somewhere around 50-100ms is probably a good bet for all CHDK supported cameras.

It should be noted this isn't directly related to high shutter speeds, even the factory firmware can do <1ms exposures. A subject that requires a fast shutter speed doesn't necessarily require a low reaction time. If your subject does require reaction time on the order of the shutter speed, you are going to need to do some hacking and/or use external hardware to achieve anything approaching the maximum factory shutter speed, never mind overrides.

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Don't forget what the H stands for.

fudgey

1705
a570is

Re: Question about shutter lag, and chdk

« Reply #2 on: 25 / January / 2011, 13:35:31 »

As reyalp pointed out, the shortest achievable shutter delay from half shoot to full shoot is probably somewhere around the fastest observed MD reaction time (50 ms or so -- MD has lots of variation on top of that but that's largely because the live view update rate is slow).

But do note that even if this is too slow, the delay can be made highly accurate using a USB supply voltage remote trigger in CHDK/SDM sync mode, see http://stereo.jpn.org/eng/sdm/crt_synch.htm#synctest .

So, if you can trigger the camera slightly before you trigger whatever phenomenon you want to shoot, this may be accurate and fast enough for your purposes.

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