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Exposure bracketing time lapse (not HDR) question.

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Offline vostok

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Re: Exposure bracketing time lapse (not HDR) question.
« Reply #10 on: 29 / July / 2008, 07:46:35 »
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Quote from: fudgey on 29 / July / 2008, 07:27:54
Yes, that's the mode dial position. Remember to disable flash, though. I'd use P with auto ISO and custom white balance to better compare the shots (unless you are going to ditch the JPEGs and only use RAWs, in that case WB doesn't matter at all).

Note that the script will not give you a constant sampling rate since it just sleeps a constant time after shooting, and the shooting takes a variable time. You'll have to either fix the script to use get_tick_count for the delay (like some "accurate" intervalometer scripts do) or dig the datestamps out of jpeg filenames or exif tags and plot xy.

So am I missing some overriding stuff here, or how is P/AUTO-mode compatible with my goal of shooting a constant-exposure-setting timelapse movie? Shouldn't I be using M?

Constant sampling rate isn't required, but if it's far from constant, it would be nice to have it timestamped in some way. Isn't it possible for example to print get_tick_count or get_day_seconds to the output file instead of the p index?

I'm eager to get home from work and start testing all this stuff. Friday might be clouded out in Finland, but luckily intensity measurements can be done anyway.
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Offline fudgey

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Re: Exposure bracketing time lapse (not HDR) question.
« Reply #11 on: 29 / July / 2008, 08:05:04 »
Quote from: vostok on 29 / July / 2008, 07:46:35
So am I missing some overriding stuff here, or how is P/AUTO-mode compatible with my goal of shooting a constant-exposure-setting timelapse movie? Shouldn't I be using M?

Ah... you indeed will not get a constant exposure timelapse movie in P or AUTO mode. But if you like that measurement code (which uses Canon's exposure automation and saves the resulting exposure settings), you need to be in P or AUTO mode.

Then you can set the manual exposure you wish using CHDK overrides. I'm not sure what happens when you use CHDK  Tv+Av+Sv override AND CHDK continuous mode Tv bracketing override simultaneously. I hope it brackets from the override. If it doesn't, I'd report it as a bug.

Quote from: vostok on 29 / July / 2008, 07:46:35
Constant sampling rate isn't required, but if it's far from constant, it would be nice to have it timestamped in some way. Isn't it possible for example to print get_tick_count or get_day_seconds to the output file instead of the p index?

I'm eager to get home from work and start testing all this stuff. Friday might be clouded out in Finland, but luckily intensity measurements can be done anyway.

The camera stores a datestamp in JPEG exif, you can extract them from there with e.g. exiftool. But of course you can quite as well print the tick count...probably your best option. And storing an initial value and printing a subtraction result in seconds is probably a good idea:

X=get_tick_count
...
Y=get_tick_count
print (Y-X)/1000,B,S,A,T

The exif tags are however more accurate if shooting takes a lot of time (unless a continous shot series gets the same date stamp, I've never checked).
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Offline vostok

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Re: Exposure bracketing time lapse (not HDR) question.
« Reply #12 on: 29 / July / 2008, 11:44:49 »
Quote from: fudgey on 29 / July / 2008, 08:05:04
Then you can set the manual exposure you wish using CHDK overrides. I'm not sure what happens when you use CHDK  Tv+Av+Sv override AND CHDK continuous mode Tv bracketing override simultaneously. I hope it brackets from the override. If it doesn't, I'd report it as a bug.

Finally got home to test things out. The Continuous mode Tv bracketing indeed overrides the Av and Tv overridings, which in turn override the Program mode exposure settings. Just the way I want!

Thank you all very much for helpful advices. I'll now start working on the script to both measure intensity and make bracketed timelapses. I'll be back to bug you as soon as I encounter problems. :)
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Offline fbonomi

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Re: Exposure bracketing time lapse (not HDR) question.
« Reply #13 on: 31 / July / 2008, 17:40:19 »
Vostok, sorry if I didn't reply before but I was out of country for a few days....

I haven't read all the thread yet, but just to clarify what bv_log does:
this script is meant to mainly to log data, and will only shoot a picture every 10 minutes or so

it's where it says:
Code: [Select]
if (p%60=0) then shoot

p is the counter of the measurements being take: the script measures about every 10 seconds, each time increasing the value of p
The line above means:
if p is exacly divisible by 60, then shoot.

So, the script will log information every 10 secods, but shoot every 10*60 seconds, i.e. 10 minutes

if you want to shoot every measurement then change
Code: [Select]
if (p%60=0) then shoot

to a simple

Code: [Select]
shoot

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Offline vostok

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Re: Exposure bracketing time lapse (not HDR) question.
« Reply #14 on: 04 / August / 2008, 11:28:04 »
Quote from: fbonomi on 31 / July / 2008, 17:40:19
Vostok, sorry if I didn't reply before but I was out of country for a few days....

I haven't read all the thread yet, but just to clarify what bv_log does:
this script is meant to mainly to log data, and will only shoot a picture every 10 minutes or so

Luckily I figured the script out in time. :) I modified your script to let the user select sampling interval and shooting interval. I also used bracketing in continuous mode and exposure overriding to get the three bracketed timelapse movies.

The eclipse shows very well in the luminance graph I measured with CHDK:

http://www.ursa.fi/~lkangas/kuvat/080801/pimennys/ps_valokayra.png

There are other light curves measured with a photodiode in the same directory. File names and labels only in finnish, sorry! Once I finish the documentation of my project, I'll also write an english abstract or translate the whole thing. The movies are also still in progress.

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Offline fbonomi

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Re: Exposure bracketing time lapse (not HDR) question.
« Reply #15 on: 04 / August / 2008, 11:45:39 »
vostok, thanks for showing the results.
It's interesting to see CHDK put in use in different ways!

Quote
File names and labels only in finnish, sorry
I think diodi_setuppi is all the finnish I can manage to undestand :-)
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