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Flash speed setting or custom AF light possible?

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Flash speed setting or custom AF light possible?
« on: 01 / June / 2011, 13:31:56 »
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Hi,
I shoot lightnings, and I think my lightning shots would be more interesting is I shot the rain droplets also, it would add a deepness to the images. I tried to flash them, and it works, but the flash is too fast, making the droplets just dots, not (white) lines.

Is it possible to change the speed of the flas, or make it to work differentially at shooting? For example, a AutoFocus light seems to be slow enough (and not too bright), if works. (The camera shoots by running a motion detection script, where the flash setting should be put).

Thanks

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Offline fudgey

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Re: Flash speed setting or custom AF light possible?
« Reply #1 on: 02 / June / 2011, 03:47:08 »
I shoot lightnings, and I think my lightning shots would be more interesting is I shot the rain droplets also, it would add a deepness to the images. I tried to flash them, and it works, but the flash is too fast, making the droplets just dots, not (white) lines.

Is it possible to change the speed of the flas, or make it to work differentially at shooting? For example, a AutoFocus light seems to be slow enough (and not too bright), if works. (The camera shoots by running a motion detection script, where the flash setting should be put).

First, why not use an external lamp, powered continuously? Then you can make it just as powerful as you like. It won't be able to illuminate the entire sky so it shouldn't interfere with lightning detection at all.


Flash is very short and no matter how long you set it you will probably only get brighter and brighter white spots instead of white lines. If the camera can fire a burst of small flashes, you might get what you want. But that is probably not available in the stock firmware and hasn't been experimented a lot in CHDK either (but it may be possible, ewavr probably once did it with eventprocs).


The AF light seems more viable, the set_led command may control it too once you find the correct number for the AF led in your camera. Then just modify the script to enable it right before (or right after) the full shoot command and add a suitable amount of sleep before disabling the LED.

Don't try to enable it permanently, it's possible the the LED or something around it could be harmed by the heat (it's not meant to be shining more than a second or so at a time during autofocus). Also, I wouldn't be surprised if the firmware doesn't like the idea of having the light enabled during a shot and goes on disabling it anyway or crases. Won't know until someone tries.

Re: Flash speed setting or custom AF light possible?
« Reply #2 on: 02 / June / 2011, 05:31:00 »
Thanks,

That's what I'm looking for. At night I shoot relatively long expos (10 secs), since, interesingly, these add more details to the lightnings themselves. But, for bringing out the rain droplets, I need 1/10 sec or so illuminations.

The same might work daytime too, with ND filter and low ISO providing an exposition of similar length (1/10 sec to allow droplets to travel a bit).

Otherwise, the flash is too bright, the droplets are as bright as the lightings.

Here is a test shot:
http://indafoto.hu/KGyST/image/11877653-53bfa733/user

A droplet can be seen down form the middle of the pic, flashed at the start of the expo and then travelled a bit unlighted.

Thanks

 

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