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 LightRails - Dynamic External Exposure Control 
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Post LightRails - Dynamic External Exposure Control
(I know this isn't a motion-control project, but this seems to be the best place to put it!)

I finally got off my butt and posted all of the source code and some basic information about the External Exposure Control System I had been talking about for a while. I had intended to do a great job of writing it up, and solving all of the "how to use it in many different situations" problems first, but I kinda spent way more time than I think I should've already on this project.

Anyhow, it's rough, and it isn't perfect, but all the code's available here if anyone else wants to experiment with external exposure control: http://roamingdrone.wordpress.com/2009/ ... ime-lapse/

Let me know if you have any questions or comments!

!c


Wed Mar 25, 2009 7:37 am
Post Re: LightRails - Dynamic External Exposure Control
I still think it's the coolest thing since sliced bread.. :D


Wed Mar 25, 2009 8:51 am
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Post Re: LightRails - Dynamic External Exposure Control
Yep it's great! Now that I handed in my thesis, I have lots of time to do more interesting stuff :) I can't wait until the LCD screen arrives...

Quote:
I still think it's the coolest thing since sliced bread.. :D


Sliced bread?!?? Americans... :)

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Wed Mar 25, 2009 11:32 am
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Post Re: LightRails - Dynamic External Exposure Control
Hehe, I like bread too - sliced or otherwise. I'm not sure sliced bread was that great of an invention (I mean, c'mon - bread over beer?) - but I dig it anyhow!

If anyone gets to implementing it, and has any questions, let me know. I think a fully cleaned-up version is about 8-12 months out on my pipeline =)

!c


Mon Mar 30, 2009 8:07 am
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Post Re: LightRails - Dynamic External Exposure Control
shutterdrone wrote:
If anyone gets to implementing it, and has any questions, let me know. I think a fully cleaned-up version is about 8-12 months out on my pipeline =)
!c


I guess that means reverse engineering before that (with your help) :)

tmophoto wrote:
hey i am american and i make my own bread!! :)
!c


That looks great!

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Mon Mar 30, 2009 9:58 am
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Post Re: LightRails - Dynamic External Exposure Control
shutterdrone wrote:
If anyone gets to implementing it, and has any questions, let me know.
!c


I have my TAOS chip and shall attempt to put something together for the PIC microcontroller. I'll be sure to peruse your code. Many thanks.

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Mon Mar 30, 2009 2:16 pm
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Post Re: LightRails - Dynamic External Exposure Control
astronomerroyal wrote:
I have my TAOS chip and shall attempt to put something together for the PIC microcontroller. I'll be sure to peruse your code. Many thanks.


Always glad to help in any way I can! If you do get it to work on the PIC, the best thanks you can give is to share the code w/ others =)

!c


Thu Apr 09, 2009 11:14 am
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Post Re: LightRails - Dynamic External Exposure Control
Is anyone planning to build a unit like this that others can purchase?

I would be very interested in seeing some tests that go from sunset to like 10-second night exposures. Has anyone done any? Is this possible?


Fri May 22, 2009 6:14 am
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Post Re: LightRails - Dynamic External Exposure Control
id be interested in making one of these, are you willing to put up the wiring diagram, im pretty handy with the soldering and building things off of specs. having a wiring diagram would save a lot of time, however i can even imagine how much time you put into researching this project.. thank you for putting it up.

Cheers


Mon Jun 29, 2009 5:55 pm
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Post Re: LightRails - Dynamic External Exposure Control
timescapes wrote:
Is anyone planning to build a unit like this that others can purchase?

I would be very interested in seeing some tests that go from sunset to like 10-second night exposures. Has anyone done any? Is this possible?


I'm also curious to know if it has enough latitude to solve the day-night transition problem. None of the cameras I've used (both film EOS 3, Elan7 and digital 300D, 40D, 5DII) can be fired in Bulb mode with shutter speeds greater than about 0.02 second, so that's where you'd have to start during the daylight phase. I believe this is a fundamental limit set by the velocity of the shutter curtain, and is sort of related to X-sync speed.

I've shot sunset test sequences and have found that the light levels can drop by a factor of more than 10,000 by the time it's night, resulting in unusably long exposure times. My guess is that you'd have to preconfigure ISO and aperture to get 10 second exposures at night, then start the device. Early shots will be horribly overexposed because it wants faster shutter speeds than 0.02s, but can't manage them. Eventually light levels will drop into the usable regime, and you end the sequence with properly exposed night shots. That said, 10s/0.02s = 500x drop in light levels, which is a respectable chunk of a sunset.

Combining this with a mechanical aperture driver would obviously help, but the effort would probably be better spent on getting a firmware solution, as Flyvholm advocates.

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Tue Jun 30, 2009 6:16 am
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Post Re: LightRails - Dynamic External Exposure Control
timescapes wrote:
Is anyone planning to build a unit like this that others can purchase?

I would be very interested in seeing some tests that go from sunset to like 10-second night exposures. Has anyone done any? Is this possible?


Tom, in the early thread I posted, it showed just that (with a minor problem in the middle, unfortunately) - well, up to 8.6 seconds =)

Here's the video:



shawn_peaire wrote:
id be interested in making one of these, are you willing to put up the wiring diagram, im pretty handy with the soldering and building things off of specs. having a wiring diagram would save a lot of time, however i can even imagine how much time you put into researching this project.. thank you for putting it up.

Cheers


Shawn,

At this time, I'm unfortunately short on time to do anything =( Been working 70+ hour weeks, and am also in the middle of a move at the moment. The best I can offer at this moment is to answer any questions you have =)

astronomerroyal wrote:
Combining this with a mechanical aperture driver would obviously help, but the effort would probably be better spent on getting a firmware solution, as Flyvholm advocates.


I understand completely what you're saying - and I think that it's one of the drawbacks that we have to interface with the camera via an analog method, and all of the problems that comes with it. (De-bounce has been a bigger issue for me than shutter curtain time - it de-bounces out random shots at less than 70ms exposure on my pentax, and requires up to 100ms between triggers.)

Obviously, I would prefer a firmware-based solution, but until pentax or canon or nikon opens up their firmware fully for the dSLRs... That's going to be a lot of hacking!

!c


Wed Jul 01, 2009 9:26 am
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Post Re: LightRails - Dynamic External Exposure Control
I've put a shutter ramping bulb mode into my custom intervalometer and it has not realistically solved the day-to-night problem. It let's me get a bit more of the sunset, but to get the shutter times down to get full daylight I have to run at as high of an f-stop as possible, hence making my shutter times unrealistic for night shots. The fastest shutter I can trigger via bulb mode on my mark ii is 15 ms.

Ben

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Wed Jul 01, 2009 9:31 am
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Post Re: LightRails - Dynamic External Exposure Control
Shutterdrone, as I understand it this gadget is absolutely perfect for something like an approaching thunderstorm, where the light changes by a few stops and manual exposure can't be used to good effect.

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Wed Jul 01, 2009 10:13 am
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Post Re: LightRails - Dynamic External Exposure Control
Regarding the limitations in extreme exposure latitudes, I understand that Canon's tethering software has the ability to control all aspects of the camera including ISO, shutter speed, and aperture. Perhaps if you could tap into that, you could have more control over the system.

(I'm guessing changing the ISO would be more desirable than changing the aperture since it's more exact, and you'll still be able to lock the aperture down for dof and flicker.)

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Sun Aug 01, 2010 5:43 pm
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