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night sky timelapse video with shutter speed override

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Offline chuckheron

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Re: night sky timelapse video with shutter speed override
« Reply #20 on: 19 / February / 2008, 15:08:03 »
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Very cool stuff!
Timelapse is lots of fun!

I created a Long Exposure Intervalometer page on the wiki: UBASIC/Scripts:Long Exposure Intervalometer - CHDK Wiki
(not as fancy as the Shutter Speed Stack, but it gets the job done..)

Here are some of the timelapses I've done as well:
chuckheron wiki / TimeLapse

As far as video hosting, I recommend http://archive.org
They don't have any size limits on uploading videos (go to Open Source Movies) and they convert your videos to a flv/flash format so you can embed them.. (although I couldn't figure out how to embed it in this post :( )
They have lots of other cool stuff as well, including Petabytes of Live Music to listen to while your TimeLapses are being captured.

For video processing, I like VirtualDub, you can open an image sequence, apply filters, add an audio track and write out the video to a variety of formats.
http://virtualdub.org   

All are open source/public domain/free!

-chuck
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Offline mcx

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Re: night sky timelapse video with shutter speed override
« Reply #21 on: 04 / May / 2008, 19:53:50 »
i've just got a question. i found this script today and i wanted to make a long exposured picture directly. so i turned all the lights in my room off und took a picture with 15min exposure from outside. for the iso i set 80.

now the picture is not that bad, but it has a lot blue sparkles on it.. from where did they come?

Sorry if i'm stupid, but why shouldn't i take pictures from "hours and days" ? Does it damages the CCD or why? Is that the reason why my image has those sparkles on it? Or can i take a picture with 3-4 hours exposure at night without risking anything?

thx
MCX
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Offline BB

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Re: night sky timelapse video with shutter speed override
« Reply #22 on: 04 / May / 2008, 21:36:05 »
Are you sure that you took a 15 minute exposure? Generally, as far as I know, around 60-65 seconds is the maximum exposure time allowed by all of the Canon cameras that support CHDK (even if you set a longer time with CHDK--the camera will time out at ~65 seconds).

Don't know about the sparkles... There is a possibility of a purple fog in parts of the picture (when the sensor heats up, the purple will increase). For exposures longer than 2 seconds, the camera will automatically take another exposure of the same length with the shutter closed (your 65 second exposure will take about 130 seconds to complete) and subtract the second exposure (with sensor noise) away from the first exposure.

CHDK also supports turning off NR shots too (you can do it manually, or once every several pictures to save time, etc.).

The longer exposures you are seeing here are typically adding of multiple shots together (or time lapse of 60 second shots turned into a video).

-Bill
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Offline mcx

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Re: night sky timelapse video with shutter speed override
« Reply #23 on: 05 / May / 2008, 12:19:42 »
Well i can't say it 100% correct, but i took a shower while the picture was made. Then i came back and the cam seemed to be turned off, but then the display "woke" up and another picture was about to shot. So i took out the batteries, because you cannot stop the process, and restarted the cam. After that, there was only 1 picture on my card... So i thought it must be the one with 15min exposure.

So here it is:
my picture


It has (at least i think so) 15min exposure and ISO 80. It was absolutely dark, only 2 lights or so.

Now again: Does a long exposure damages my CCD chip?
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Offline chuckheron

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Re: night sky timelapse video with shutter speed override
« Reply #24 on: 05 / May / 2008, 13:54:16 »
I would suspect that the NR is off and the blue sparkles are hot pixels and ccd noise showing up in your images. (In the long exposure clicker that I posted above, NR is off by default.)

If you set the noise reduction setting to either 0 or 2, you will probably get fewer hot pixels and noise.
The other approach is to take a bunch of dark frames, and subtract those out when you are processing your images...

WRT to the warning about letting it run hours or days...
That warning was in the original script that I modified, so I just left it..
I can make a couple of guesses about what could be detrimental..
- Since the camera has a mechanical shutter, that could wear out after clicking alot. (probably the most realistic cause for concern)
- The CCD could maybe exhibit some sort of 'image burn in' if the subject was bright and exactly the same for many thousands of shots... (that's just a guess, no idea if this could happen)
- If you are running the Long Exposure clicker script, I've always been worried about it still going when it gets light out.. fully saturating the ccd...

Having said all of that...
I have clicked 10's of thousands of shots on both of my cameras (S3 and A560),
they have done long exposures into the daylight (not too much, but I've seen pure saturation)
And so far, they both appear healthy, and still clicking!

-chuck


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Offline BB

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Re: night sky timelapse video with shutter speed override
« Reply #25 on: 05 / May / 2008, 14:03:10 »
Nice picture...

From my very little experience, I would say that this exposure is much closer to 1 minute than 15 minutes...

1. The lighting around the homes would probably be blown out at 15 minutes and the sky much brighter (although the exposure number is only about 4 stops different--a big, but not huge, difference).
2. The angle of the star "streaks" would be much longer:

360d/(24hr*60min)= 1/4 degree
360d(24hr*4expperhr)= 3.75 degrees

If you can measure the angle of the star trails (I don't have anything on my computer to do this), you can see how long the shutter was open.

From what I understand, the CCD may be damaged by heat--and that heat could be generated by operating the shift registers a t high speed (like video)... As far as I know, as long as you are not pointing it at a bright light source (like the sun--which can cook the sensor directly), long exposures will not cause any harm at all.

-Bill
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Offline chuckheron

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Re: night sky timelapse video with shutter speed override
« Reply #26 on: 05 / May / 2008, 14:19:05 »
Quote from: mcx on 05 / May / 2008, 12:19:42
Well i can't say it 100% correct, but i took a shower while the picture was made. Then i came back and the cam seemed to be turned off, but then the display "woke" up and another picture was about to shot. So i took out the batteries, because you cannot stop the process, and restarted the cam. After that, there was only 1 picture on my card... So i thought it must be the one with 15min exposure.

So here it is:
my picture

That's a nice shot..
Judging from the length of the star trails, that looks like a typical 65 second exposure..
Also, if you used the script unmodified, the line:
  set_tv96_direct -576
sets the camera to do 65 second exposures.
And, as BB said, so far, there is no way to get a longer shot than 65 seconds straight from the camera.
I'm a little surprised that there was only 1 shot on your card, if you used the script without
changing anything, I would expect about 9-10 shots (65+30)*10 = 15.8 minutes
Did you change the 'Interval (minutes)' to 15 or so? Then you would only get 1 shot..


It has (at least i think so) 15min exposure and ISO 80. It was absolutely dark, only 2 lights or so.
A 65 second exposure can gather quite a bit of light...

Now again: Does a long exposure damages my CCD chip?
I haven't seen any degradation... but I can't guarantee anything  ;)

Also, try turning on the noise reduction setting (a single exposure will take twice as long (130 seconds)) but you will see less noise...

About stopping the script:
Pushing the shutter button again will interrupt a running script.
It won't interrupt an exposure mid-way, but it will stop the script once the exposure is finished.

Hope that helps
-chuck


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Offline fbonomi

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Re: night sky timelapse video with shutter speed override
« Reply #27 on: 05 / May / 2008, 16:32:57 »
To have longer trails, you should do more of shots, and stack them together.

This is made of about 120 shots of 20 seconds each, for a total of nearly an hour.

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Offline mcx

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Re: night sky timelapse video with shutter speed override
« Reply #28 on: 05 / May / 2008, 17:00:01 »
thx for the answers!

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Did you change the 'Interval (minutes)' to 15 or so? Then you would only get 1 shot..

Nope... i've read about this interval after taking the picture.


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About stopping the script:
Pushing the shutter button again will interrupt a running script.
It won't interrupt an exposure mid-way, but it will stop the script once the exposure is finished.

Yup i know. But I saw the cam taking a new picture immediately... and because i thought it would take 15min to stop, i preferred to take batteries out :)


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If you set the noise reduction setting to either 0 or 2, you will probably get fewer hot pixels and noise.
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Also, try turning on the noise reduction setting (a single exposure will take twice as long (130 seconds)) but you will see less noise...

NR was on 1. So i should take a higher level, but how high can i set the NR ?... It seems to have no end in the script :D


@fbonomi:

The picture is very great! How do you stack them together?
« Last Edit: 05 / May / 2008, 17:03:56 by mcx »
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Offline chuckheron

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Re: night sky timelapse video with shutter speed override
« Reply #29 on: 05 / May / 2008, 19:47:16 »
Noise reduction is either on or off, you can't set it high or low..
If it is on, the camera will take a shot (for 65 seconds in this case), and then it
will take a second shot of equal duration but with the shutter closed (a dark frame)
and then subtract the dark frame from the actual photo, so that camera noise will be removed.

Here are the possible values for NR:
@param e Noise reduction (0=auto 1=off 2=on)
@default e 1

So if you set it to 2, it will always be on.
If you set it to 0, it will be on 'auto' mode, which will automatically do NR for shots longer than 1 second (or maybe 1/2...)

You can set it in the 'scripting parameters' menu before you start the script.

-chuck

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