Mechanical vs Electronic (w/ Mirror lock) controls possible with CHDK?

boboche

« on: 18 / September / 2012, 13:34:35 »

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Hello everyone,

I'm trying to figure out if it's possible to do the following (and how) with CHDK:

I want to use the electronic shutter to prevent burning my mechanical shutter, this is in a controlled environment so dust is not an issue. What I would like (but not limited to):

- Ability to position the mirror in lock-up mode for long period (i.e. script start: lock up mirror, run script (10,000+shots), unlock mirror)
- Having an external event triggering the image capture (if impossible, I can use a timer)
- Process everything in RAW

I currently have a t2i and SX130 that I can take apart for this project, I could use any other cameras if the CHDK controls are more solid on another one.

Background:

I am currently working on a R&D project, and the requirements & challenges I have are similar to shooting long HDR timelapses, meaning having to control exposure (bracketing), removing the mechanical shutter out of the equation because I will kill it in less than a week, and also having to deal with workflow/stacking/post-processing.

I'm okay with the workflow/stacking/post-processing portion of the project, a lot of this has already been covered in the forums for those who are reading this and are curious.

If it's camera-dependent, I am willing to purchase the best supported camera to do the job.

Thanks for anyone's help on this.

« Last Edit: 18 / September / 2012, 15:54:38 by boboche »

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waterwingz

11991

Re: Mechanical vs Electronic (w/ Mirror lock) controls possible with CHDK?

« Reply #1 on: 18 / September / 2012, 15:05:17 »

Quote from: boboche on 18 / September / 2012, 13:34:35

I'm trying to figure out if it's possible to do the following (and how) with CHDK:

Minor point - CHDK does not run on DSLRs.

« Last Edit: 18 / September / 2012, 15:07:57 by waterwingz »

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boboche

Re: Mechanical vs Electronic (w/ Mirror lock) controls possible with CHDK?

« Reply #2 on: 18 / September / 2012, 15:53:54 »

Good point, completely missed checking... I've thought CHDK has been ported on DSLR since last time I checked.

There's a silent timelapse feature with the MagicLantern Firmware but I'm not sure it will allow for easy HDR bracketing without shutter abuse...

This said, I have an SX130 camera to experiment with and if I need more quality I can always ramp up to the Gxx series. So is there a way to leave the shutter always opened and switch to electronic shutter?

Thanks for your input

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outslider

Re: Mechanical vs Electronic (w/ Mirror lock) controls possible with CHDK?

« Reply #3 on: 18 / September / 2012, 16:46:09 »

I've been shooting thousands photos on sx130, even running the script that simply keeps the shutter button down for few hours, so camera was shooting 1 photo per seconds. And my shutter hasn't die yet:)

I know that's not really an answer. Thing that you want to acheive is not supported by CHDK itself. In general CHDK doesn't really affect the shooting procedure, it rather sets some parameters before shoot is taken. Shooting procedure is done almost completely by the Canon firmware. However, in theory everything that camera can do can be acheived by native function calls:

http://chdk.wikia.com/wiki/Lua/Lua_Reference/Native_Function_Calls

The problem is, that you'd have to take your time for guessing which function has to be called, when to call it, which parameters it needs and so on.

The other option is maybe to block the mechanical shutter mechanically. I don't know, whether there are any sensors, that check the shutter position, but if they are not present this could be very simple (as far as you can take camera apart as you mentioned).

Mechanical shutter isn't probably really used to determine the shutter time. The electronical shutter plays this role. Mechanical one probably only helps that. This can be assumed, since the CHDK allows you to have shutter times as short as 1/40 000 s, which is rather not possible with mechanical movement of such simple mechanism.

Regards!

« Last Edit: 18 / September / 2012, 16:50:25 by outslider »

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lapser

1093

Re: Mechanical vs Electronic (w/ Mirror lock) controls possible with CHDK?

« Reply #4 on: 18 / September / 2012, 19:46:02 »

On a CCD sensor, the mechanical shutter has to be closed to read the image out of the sensor accurately. If you could hold the mechanical shutter open, the images produced wouldn't be as high a quality. CCD sensors produce video this way, but a very bright light, like the sun, will mess up the entire sensor column, producing purple vertical lines.

The amount of time the CCD sensor is collecting light is controlled electronically, and by CHDK, so very fast shutter speeds are possible.

CMOS sensors collect light all the time. They can be reset and read out instantaneously, so you reset it, wait the desired shutter time, and read it out. However, you can't read the entire sensor all at once, so the maximum shutter speed is determined by how fast you can read the entire sensor. It takes longer to read high megapixel sensors than low megapixel ones.

The other problem with CMOS electronic shutters is that the camera doesn't expose the entire sensor at the same time, called the "rolling shutter" effect. It's a big problem with flash photos, so that requires a mechanical shutter to work right.

It should be possible to use only the electronic shutter on CMOS cameras and disable the mechanical one. Taking video is done this way (with rolling shutter artifacts visible sometimes). I think the Nikon 1 V1 camera has the option to turn the mechanical shutter off.

On my sx-260 cmos camera, the fastest Canon shutter speed is 1/2000, which I assume is done by the mechanical shutter. I've experimented with going faster with CHDK, and the maximum it will do is 1/3200 (2/3 ev faster).

The mirror in an SLR is just there to be able to see exactly what you're shooting. It pivots out of the way before the mechanical shutter (which is also the aperture control iris) takes over. Point and shoot cameras don't usually have mirrors, since they use electronic viewfinders. The "silent timelapse" feature of Magic Lantern sounds like it may be holding the mirror out of the way like you want.

Thanks for bringing up an interesting topic. If someone knows more about the various shutters, please add your comments.

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boboche

Re: Mechanical vs Electronic (w/ Mirror lock) controls possible with CHDK?

« Reply #5 on: 20 / September / 2012, 11:09:06 »

Very interresting points brought up... I do not plan on shooting at very fast speed, but you do bring up a very valid point about CMOS integration time and non-uniform exposure... I won't be shooting in video mode and if any visible (or measured) "rolling" luma discrepancies are found, I can always batch correct in post with a mask with After Effects since my setup will shoot with several constants (exposure time, F-stop, lighting and zoom will all be constant), as long as it's not over-saturating the sensor (I will shoot in raw, should give me a tad more room to maneuver).

The only thing I would be worried about is if integration starts at different time in the "rolling" process... does anyone know if when you issue a "take picture" in still mode, the sensor always does its pass starting at the exact same pixel coordinates?

I guess I'll have to experiment by removing the mechanical shutter and abusing the sensor through various exposures and analyse the resulting images...

Hopefully someone will have messed a little more on this and report his findings because I'm starting to wonder if I shouldn't just go grab a CCD frame grabber... would have been an easy choice if there would be 4K+ sensors with single-shot RAW HDR supporting a wide gamut for under 2K$ out there

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Brane212

Re: Mechanical vs Electronic (w/ Mirror lock) controls possible with CHDK?

« Reply #6 on: 20 / September / 2012, 11:35:52 »

Interesting. I was about to pose the same question but for a different purpose.

I have an EOS 350D and two 400Ds.

A few days ago I decided to check the noise of the sensor on 400D that gets recorded, so I took a couple of dark frames at each ISO setting and each exposure time with noise filtering on ( It's under Custom Functions- function number 2 "Long exp. noise reduction" ).

This filter works by repeating each shot without opening the mechanical shutter and taking effectively dark shot and then subtracting it from the previous shot. The idea is that sensor noise will largely be the same and subtraction would reduce noise levels in the picture.

But even with this, remaining noise has clear structure and quite strong non-random component, so I thought that if I could play with this a bit more I might gain some further noise reduction.

I thought it would be usefull to repeat this with and without a filter, with various timings between shots and at various temperatures.

But this would take awfull lot of shots and probably kill my shutter.

So it would be nice if I could just take a dark frame and save it...

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