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Lightning

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Offline CanonBlue

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Lightning
« on: 17 / August / 2009, 08:57:42 »
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I just moved to the midwest and all of a sudden there are electrical storms in the summer! So in the middle of the night last night I was woken up by thunder, and I set up my camera to try to capture the lightning, but I didn't get anything. I'm not that surprised-- based on my motion detection photos of birds, it didn't seem nearly fast enough to capture lightning. But I've seen other people do it. So I'm asking-- what settings are needed to capture lightning? (It also keeps getting set off by trees waving in the wind, so I think next time I"ll try to frame the shot with no trees).

I have an SD1100IS/IXUS80 and I'm using the motion detector script found here: http://chdk.setepontos.com/index.php/topic,471.msg21328.html#msg21328

Thanks!
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Offline Anaglyphic

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Re: Lightning
« Reply #1 on: 17 / August / 2009, 12:01:42 »
You'll probably find this in the Script Writing when you return...

Yes MDFB-080914 will work fine, as will the SD1100. What you need to do is limit the amount of cycles spent on scanning the grid to 1. The best way for lightning is to setup a high pixel skip using large grids. The defaults work pretty well, actually. 6x4 pixelstep 6. I would increase that to 10 or even 16, you are looking for bright flashes, so it'll easily find some during electrical storms. Lower triggering delay to 0, obviously. Compare interval defaults to 7ms and is probably fine, but you can lower it all the way to 0 if you want - we're talking about catching instantaneous flashes of light. (not sure it makes a difference if you are < 1 cycle anyway)

Threshold is a bit tricky. You want it as low as possible without self-triggering off the LCD noise. But the LCD gain is tied to your exposure settings, and threshold is sort-of tied to the compare interval as well. So it does require experimenting. When it's nighttime lightning, you have some leeway and can be off by a wider margin, daytime storms require you to stand at the camera and keep adjusting... I don't know if this "hand tuning" aspect can be automated, just like a noise reduction program can't tell noise from details.

I usually use for nighttime shots out my window where 3/4ths of the scene is sky: threshold between 4-7, a 6x4 grid, pixelstep 10, compare interval 5, with all delays on 0. Look at this lightning image from a couple weeks ago. Notice the traffic in the bottom right. Compared to the cell size, those headlights are too tiny to ever trip the detection routine regardless of threshold level.

It's fun stuff. Soon you'll have thousands of lightning images. :^)
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Offline fudgey

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Re: Lightning
« Reply #2 on: 17 / August / 2009, 15:26:25 »
Whatever settings you have, it's good practice to test with a dry run. Simulate a lightning with a lamp, for instance. When it comes to shooting lightnings, the camera will usually be triggering because the lightning lights up the entire scene, not because it draws a tiny thread of white on the LCD.

For daytime lightnings it's probably better to push ev compensation all the way down (for greater contrast during the lightning -- a daytime sky is probably already nearly overexposed on the LCD and there's not much for MD to work with) and use CHDK overrides to circumvent it if photos turn out too dark.
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Offline CanonBlue

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Re: Lightning
« Reply #3 on: 17 / August / 2009, 19:17:18 »
Thanks for the responses.. Ill try it again next time there's a storm. Maybe it would be better to wait till its really dark-- today it was in the early hours of morning, really, and it was starting to get somewhat light. Anagylphic, I can't see the image you listed, it just gives me a graphic about hosting from remote or something.
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Offline mx3

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Re: Lightning
« Reply #4 on: 18 / August / 2009, 03:02:20 »
hm . I think it is possible to make threshold self adjustment script.
make one cell.
set very high threshold so it would not trigger at all.
set 1 second timeout interval.
read luminosity.
add to it some small number.
use it as threshold.
all night noise will be under calculated number.
same applyes for daytime handheld position...
« Last Edit: 18 / August / 2009, 03:03:53 by mx3 »
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Offline Anaglyphic

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Re: Lightning
« Reply #5 on: 18 / August / 2009, 07:27:19 »
Quote from: CanonBlue on 17 / August / 2009, 19:17:18
Anagylphic, I can't see the image you listed, it just gives me a graphic about hosting from remote or something.
Apparently Tripod is testy about direct linking... sorry bout that.
http://chdk.setepontos.com/index.php/topic,4008.msg38174.html#msg38174
« Last Edit: 18 / August / 2009, 18:48:58 by Anaglyphic »
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Offline sumoetx

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Re: Lightning
« Reply #6 on: 20 / August / 2009, 01:08:18 »
I'd really suggest practicing using Youtube videos! I just looked up lightning, and zoomed my camera in till the screen filled the LCD, lowered the lights and tested until I could get it to work! Had great success at night not so much during the day yet.
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Offline CanonBlue

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Re: Lightning
« Reply #7 on: 23 / June / 2010, 21:50:19 »
I have tried using the motion detector for lightning and I've really had no luck. It doesn't even seem possible that it could be fast enough, since even if I wave my hand in front of the camera it isn't fast enough to catch it. So I'm trying to think of other ways to do it.

There is a pretty amazing lightening storm going on outside my window right now. I set up my camera at the window running the intervelometer, hoping to just randomly catch lightning, but no luck so far. I wanted to make the shutter stay open longer with each shot, so that it would be more likely to catch lightning. The problem is that if I turn the exposure or shutter length up, too much light goes in and the photo just ends up completely white. Any ideas on how to fix that?

Thanks!
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Offline mx3

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Re: Lightning
« Reply #8 on: 24 / June / 2010, 00:05:23 »
Quote from: CanonBlue on 23 / June / 2010, 21:50:19
I have tried using the motion detector for lightning and I've really had no luck. It doesn't even seem possible that it could be fast enough, since even if I wave my hand in front of the camera it isn't fast enough to catch it.
Use manual focus
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Offline CanonBlue

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Re: Lightning
« Reply #9 on: 24 / June / 2010, 16:01:25 »
I do have it on manual focus... I have an SD1100, and it has an auto or manual mode. I have it on manual mode-- I'm not sure if you were referring to something else? Having it on manual mode doesn't help with the speed of the motion detector, or at least, its still not fast enough to catch lightning.

I did manage to get one good shot of lightning bolts last night out of hundreds taken with the intervelometer, without involving the motion detector at all. I just left the camera by a window in a dark room and came back an hour later, and by luck one of the shots had caught lightning bolts, but many more were missed.
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I use the chdk on my SX230 and SD1100 cameras, and I installed them using a Macbook, currently running 10.6.8.
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