Whoa! ****MAJOR**** High-Speed Shutter-Speed Discovery! - Creative Uses of CHDK - CHDK Forum
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Whoa! ****MAJOR**** High-Speed Shutter-Speed Discovery!

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Offline Woodsman

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Whoa! ****MAJOR**** High-Speed Shutter-Speed Discovery!
« on: 29 / November / 2007, 04:14:19 »
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edit by phyrephox: this thread is about high speed shutter.
« Last Edit: 22 / July / 2008, 04:14:59 by PhyrePhoX »
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Offline a710is

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Re: Whoa! ****MAJOR**** High-Speed Shutter-Speed Discovery!
« Reply #1 on: 29 / November / 2007, 06:05:55 »
I'm not an expert but I don't even know if that would be phisically possible...
I mean 1/500000 - the shutter would probably reach supersonic speeds and you'd hear a sonic boom :D
I believe there's another explanation
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Offline cybernut

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Re: Whoa! ****MAJOR**** High-Speed Shutter-Speed Discovery!
« Reply #2 on: 29 / November / 2007, 10:38:45 »
This sounds really good but a little iffy.  I think it might be possible (electronics-wise) to do something of the order of 1/125K but after that it might be shutter???  I don't think CCD's aren't known for high clock rates.  I'm not sure what the clockrate for the Arm processor used in the Canon cameras but I'm assuming there would be some sort of state-machine anyway.

A possible method to check whether it is time or aperture at those speeds would be to take the earlier shots out of focus and then see if the line becomes sharper as its DOF increased with a smaller aperture.  I'm sure there are better ways.

Even if it is a combination of time and aperture it is still a pretty fantastic discover.  Now we just have to wait for the next eclipse!

C
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Offline n6mod

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Re: Whoa! ****MAJOR**** High-Speed Shutter-Speed Discovery!
« Reply #3 on: 29 / November / 2007, 11:29:04 »
That's a *really* interesting result.

I had always assumed that the reason the high speeds only worked at small apertures with the stock software was that Canon was using a single iris as both aperture and mechanical shutter. As such, the blades have much further to travel when the aperture is wide open. I haven't taken apart the optical assembly on any of these cameras, so I don't know this. (Anyone have a dead camera?)

I suspect that exposures at speeds substantially beyond Canon's limits are in fact underexposed, and if you had a way to measure depth of field you would find they were taken at smaller apertures.

Here's the thinking:

Exposure begins with the shutter closed. The blades begin moving towards the desired aperture. If the exposure time is long enough, then the blades stop at the desired aperture. When the exposure time ends, the blades begin to close. If the blades move in both directions, the under exposure that happened while the blades were opening is corrected by the 'extra' exposure that happens while the blades are closing.

If the exposure time is too short, the blades never make it to the desired aperture, and start closing. So while it's very cool that the camera will attempt extremely fast shutter speeds (and leaf shutters are inherently fast), I think you'll find substantial underexposure and smaller-than intended apertures at those speeds. Doesn't mean they aren't real, but I think you'll find you need a lot more light than you'd otherwise expect.

Forgive me if you've posted this elsewhere, but which camera do you have?
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Offline cybernut

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Re: Whoa! ****MAJOR**** High-Speed Shutter-Speed Discovery!
« Reply #4 on: 29 / November / 2007, 12:22:02 »
Wouldn't the iris remain open so you can see the picture while composing?   Then when you take the picture they close to the desired aperture.  I think it is opposite to the way you described n6 - but then again I could be totally wrong as it happens all the time!   ;D ;D ;D

C
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Offline n6mod

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Re: Whoa! ****MAJOR**** High-Speed Shutter-Speed Discovery!
« Reply #5 on: 29 / November / 2007, 15:44:58 »
Cybernut: I believe that the shutter/aperture closes, the CCD is flushed, then it opens for the exposure, then closes again. It's possible that it might not close before the exposure, but I'd be surprised.

Woodsman: I don't doubt that the exposures are that short, I'm just suggesting that the shutter might not make it all the way open, therefore providing a smaller aperture than you expect. Indeed, based on what you've written, it looks like the exposure times you're actually getting are 1/6400, 1/12,500 and 1/25,000. After that, you're getting "one or two dimmer ones", which sounds to me like the same shutter speed but a smaller aperture.

Don't get me wrong, this is *really* cool.

I'll have to break out the dremel tool and do some testing myself. (Photograph a spinning dremel tool...I use a cutoff wheel with a line of white-out on it. :) )
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Offline fingalo

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Re: Whoa! ****MAJOR**** High-Speed Shutter-Speed Discovery!
« Reply #6 on: 01 / December / 2007, 06:55:08 »
Hi,
I checked in the SW when I added bracketing from Zosim. It would be possible to extend this by adding values for high speed settings. (If you display the propertyvalue 69, you can see that for higher speeds the value is above 1171 (the setting for 1/3200). Let me know what cams you have and I will see if I can fix an 'alfa' version with high speed settings for you to make tests.
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Offline fingalo

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Re: Whoa! ****MAJOR**** High-Speed Shutter-Speed Discovery!
« Reply #7 on: 01 / December / 2007, 06:57:06 »
Typo in last post should be 1117 (not 1171). (On my s3is)
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Offline a710is

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Re: Whoa! ****MAJOR**** High-Speed Shutter-Speed Discovery!
« Reply #8 on: 01 / December / 2007, 08:06:51 »
I guess Woodsman is right, I am also getting higher values in propcase 69 on my A710 and I took pictures of a CRT screen: indeed I am getting less and less lines and they are also getting darker. amazing. congratulations for the find, I guess that means soon enough we're gonna be able to take pictures of the sun :)

on the 10th shot in a sequence for example I got 1533. how fast is that?

edit: I also took some pictures of an incandescent light bulb (moving the camera so I wouldn't burn the CCD) and indeed I am getting darker frames than the ones I am getting at the regular 1/2000
anyway I read somewhere that you can burn the CCD if you're pointing the camera long enough to extremely bright light sources so be careful.
« Last Edit: 01 / December / 2007, 08:47:25 by a710is »
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Offline GrAnd

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Re: Whoa! ****MAJOR**** High-Speed Shutter-Speed Discovery!
« Reply #9 on: 01 / December / 2007, 09:50:07 »
Quote from: a710is on 01 / December / 2007, 08:06:51
on the 10th shot in a sequence for example I got 1533. how fast is that?

Generally the formula is:
1 / ( pow(2, (<value> / 96))

So, for 1533 it will be... 1/64132
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