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Crash Course in HDR Night Time Lapse Sequences

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Crash Course in HDR Night Time Lapse Sequences
« on: 13 / March / 2013, 15:01:23 »
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I'm heading out to the desert for a week (leaving in a couple days) and I've been trying like hell to figure out how to make the most of the really dark skies and beautiful sandstone backdrops that will be available out there. I have CHDK loaded on an old A590 and very little experience. I'm technically-inclined but definitely not a photographer. Basically I have to learn enough in the next 48-72 hours to do all of the image capturing I can, without having a laptop around to get a look at how the images are turning out.

The issues I'm having boil down to software and photography:

0) There are like a dozen scripts out there that claim to do time lapse / intervalometer work. Is there one that will do _everything_ that I want to do?

I would want: auto exposure bracketing, long exposures for dark skies, ability to compensate automatically for dramatically changing light conditions (e.g. moonrise, sunrise), power-saving by not refocusing every shot, and some degree of idiot-proof setup (or at least a very simple guide for tweaking a couple parameters and letting things run).

1) How do I get long shots AND shot-to-shot continuity when the camera spends so much time doing dark-frame-subtraction? I'm a little intimidated by the thought of trying to do the dark frame subtraction thing manually. If the shutter is closed >50% of the time, aren't I likely to end up with jerky motion?

2) How do I get the bracketing to work out with the time concern? In other words, if taking a single long exposure will have stars and clouds moving in the shot, wouldn't bracketing with a couple more exposures be useless? How do people manage this - especially with the added time cost of dark frames?

3) Is Tv, Av, or M the right thing to use? Which setting should be varying in response to changing light (and can the script change it intelligently)? How about ISO?

4) What should I expect to use for intervals? 10 sec? 20 sec? More?


It feels like I'm under a lot of pressure to get this working in a short period of time, and without much chance to test things out beforehand. We're getting rain and overcast weather where I am, plus tons of light pollution, so much testing before leaving may not be possible. I do expect to be able to get long battery life by adding an external battery, so this is not a primary concern at the moment.

Thanks in advance!

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Offline lapser

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Re: Crash Course in HDR Night Time Lapse Sequences
« Reply #1 on: 13 / March / 2013, 17:28:59 »
Rather than attempting bracketed shots, it would be better to get one raw shot exposed correctly. Then you can process the raw shot to get HDR. CHDK can save raw, so you'll need to get that working correctly before you go.

If you really want to create a smooth time lapse, you need to keep the delay between shots to a minimum. That means turning dark frames off, and removing the hot pixels from the raw file later. That will take some learning, but you can do that after you get back.

As for what script to use, I think shooting in continuous mode with manual exposure and focus is the way to go. Set the focus on infinity, and take some test shots to get the right exposure. ISO should probably be 100 for lowest noise, and the aperture should be as wide as possible. CHDK has a long shutter time override which will be helpful.

The easiest part is the script. Here it is:

Code: (lua) [Select]
press("shoot_full")
sleep(1234567890) -- 14 days


I've been experimenting with day/night time lapse scripts and CHDK modifications, but it's not quite ready to use yet. Take a look at this thread if you're interested:

http://chdk.setepontos.com/index.php?topic=8997.msg97841#msg97841
EOS-M3_120f / SX50_100b / SX260_101a / G1X_100g / D20_100b
https://www.youtube.com/user/DrLapser/videos

Re: Crash Course in HDR Night Time Lapse Sequences
« Reply #2 on: 13 / March / 2013, 19:54:54 »
There are like a dozen scripts out there that claim to do time lapse / intervalometer work.
There are a lot more than that  :blink:

Quote
Is there one that will do _everything_ that I want to do? 
Probably not.  What you are looking for takes time to tweak and get right for your needs.

This might be an acceptable option though :

http://chdk.wikia.com/wiki/Meteor_Intervalometer_with_Dark_Frame_Managment
Ported :   A1200    SD940   G10    Powershot N    G16

 

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