Night timelapse (was Re: considerations for SX260 external power supply for time lapse situations)

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Offline udo

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The plan is to, hopefully in 2016, visit Australia once more and do some night time timelapses.
Which script would be the ultimate solution to do night time, starry timelapses with this setup?
« Last Edit: 27 / August / 2015, 11:52:22 by udo »

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Which script would be the ultimate solution to do night time
Why not rawopint?
You can run it at night until 30s and ISO1600….

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Offline udo

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Which script would be the ultimate solution to do night time
Why not rawopint?
You can run it at night until 30s and ISO1600….
With an S110 I'd do 20 seconds at ISO800 max (no trails and not too much noise I hope).
But how to go about the black frame noise reduction thing, interval timing for smooth star movement and do aperture issues exist for nighttime photography?
« Last Edit: 27 / August / 2015, 12:46:32 by udo »

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to go about the black frame noise reduction thing, interval timing for smooth star movement
All what I have seen on YouTube, dark frame was switched off. I think this is more important for single pictures as for timelapse (see videos from drlapser, OK the videos made with G1x). Same with smooth star movement. Aperture has to be the smallest. Would be interesting to have a comparable run with and without dark frame…


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Which script would be the ultimate solution to do night time
Why not rawopint?
You can run it at night until 30s and ISO1600….
Not too sure why you'd want to use rawopint for this?  It was designed to shoot pictures as quickly as possible with exposure adjustment between each shot.  Not really necessary for shooting in the night sky.

This might be more appropriate : Meteor Intervalometer with Dark Frame Management
Ported :   A1200    SD940   G10    Powershot N    G16

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Offline reyalp

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A bit off the original topic. I can split it if desired.
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Which script would be the ultimate solution to do night time
Why not rawopint?
You can run it at night until 30s and ISO1600….
I agree with waterwingz, if you are only shooting at night (not doing sunset/sunrise) rawopint may be overkill. In many cases a simple fixed exposure will work fine, and give more consistent results without a lot of testing and tuning.

I use a clunky script somewhat similar to the meteor intervalometer that I should clean up and post somewhere.

All what I have seen on YouTube, dark frame was switched off. I think this is more important for single pictures as for timelapse (see videos from drlapser, OK the videos made with G1x). Same with smooth star movement. Aperture has to be the smallest.
For clarity: smallest F number, largest opening.

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Would be interesting to have a comparable run with and without dark frame…
Dark frame depends on the camera and exposure length. Modern cameras should give quite good results without dark frame up to at least a minute. I'm not sure where the cut-off is, my D10 (2009) has very bad amp glow, while sx160 (2012) doesn't. It probably depends on the sensor as well, but Canon seems to have improved even the very low end cameras at some point.

See http://chdk.setepontos.com/index.php?topic=12295.msg121437#msg121437 for some comparisons

If you do need (or want) dark frames, you can create stand alone dark frames by shooting with the shutter closed, and then subtract them afterward in your workflow. This will work better with raw than jpeg.

Star trailing depends on your exposure length, zoom and what resolution you are rendering the final video at.

With 30 sec at a wide angle you'll see some trailing if you look at a full res jpeg, but it probably won't be very noticeable in a video. It's worth noting that without tracking, you won't get "deeper" image once the star trail is significantly longer than it it is wide. After that you just accumulate more noise and stray light.

Image 3900 in https://app.box.com/s/sjj9a6kiyx95qeda9ixubxpkmuhuol3u is an example of a 32 sec exposure at 28mm equivalent.
Don't forget what the H stands for.

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In many cases a simple fixed exposure will work fine,
I'm not sure if does not yet change the exposure at night. At least during the transition to the dawn would have to adjust the exposure. But I have not much experience about this. I think at least an overexposure control would be helpful.

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Offline udo

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Ideally the nighttime timelapse would run from dusk until dawn.
So yes in such case some exposure control is necessary.
Once darkness has come, the exposures could be done with constant settings (e.g. 20 seconds at ISO800, open aperture, focus at infinity).
When dawn comes the exposure control should help us getting decent pictures.

Does such a script exist?


This discussion is diverting from the small powerbank mod but for me it is very interesting.

In-camera noise reduction doubles the time to take a picture, would the frequency of once every ~45 seconds be sufficient?
(If not: how to do black frame noise reduction externally on the PC in batch?)



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Offline reyalp

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Ideally the nighttime timelapse would run from dusk until dawn.
So yes in such case some exposure control is necessary.
Once darkness has come, the exposures could be done with constant settings (e.g. 20 seconds at ISO800, open aperture, focus at infinity).
In this case, rawopint may be useful. You can set the night exposure just using the Max Tv and Max ISO values, once the scene gets dark enough it will just stay on those values.

If the moon will be up, you have to decide how you want to handle it. If the moon is properly exposed, the rest of your scene will likely be pitch black. If you want lots of stars, the moon will be totally blown out. For a wide field of view, I'd suggest it's better to let the moon be blown out, but it's a matter of preference.

In rawopint, you can control how the moon is handled by setting the over "overexp thresh". If it's significantly smaller than the fraction of pixels occupied by the moon, then it will try to keep the moon from being blown out. If it's significantly larger, then the moon will be ignored. Clouds will complicate this. If sunrise or sunset are also in the field of view, you'll have to consider that too.

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This discussion is diverting from the small powerbank mod but for me it is very interesting.
I will split it into a thread in the scripting forum to make it easier for others to find.
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In-camera noise reduction doubles the time to take a picture, would the frequency of once every ~45 seconds be sufficient?
Probably the best way to tell is to do some tests. However, I would say that for a 30 second exposure on a reasonably new camera like the sx260, you can probably just disable it and still get acceptable quality.
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(If not: how to do black frame noise reduction externally on the PC in batch?)
You need software that supports it. raw therapee and dcraw are examples of programs that do. I don't know off hand if they will let you do it using jpegs.

You may also find useful resources on astro-photography sites. Here's an example of subtracting dark frames with imagemagick https://astrofloyd.wordpress.com/2013/10/27/astrophotography-with-imagemagick/

Here is one I did using fixed exposure on D10.
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Note some of the jerkyness is due to the video being 15 FPS, just because there were so few frames. Settings were
Shutter: 32 seconds
ISO 80
F/2.9, 35 mm (35 mm equivalent, really)
CHDK raw
+2 Ev in raw processing
Dark frame disabled, subtracted in raw therapee batch

The actual time between exposures was ~36 seconds (32 for the exposure 4 to save the raw)

Note I used ISO 80, because adding the equivalent number of stops Ev compensation in raw processing gives pretty much the same result as high ISO, but avoids the jpeg processing time associated with using high ISO (this may not apply to all cameras). The high ISO processing time is separate from the canon dark frame. If you don't use raw, you'll want to use a higher ISO.
Don't forget what the H stands for.

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You can set the night exposure just using the Max Tv and Max ISO values, once the scene gets dark enough it will just stay on those values.
Does it helpful, for dark scene, only to use overexposure control of rawopint? So ignoring the meter window. I think, the meter window should be not helpful for dark scenes. Right now, I can’t switch off the meter window. I can only playing a little bit with the weight. But without the meter window, the exposure will probably not increase...

« Last Edit: 29 / August / 2015, 07:09:59 by c_joerg »

 

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