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Astral Timelapse


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#1 James Mann

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Posted 04 April 2010 - 02:40 PM

Okay.

I am shooting a documentary. We are doing a series of timelapses (ala Baraka, Koyaanisqatsi, etc...). We are trying to do a timelapse of the stars twirling in a circle.

We will be on a remote island in the pacific, so light pollution will not be an issue.

But is there something that I should know going into this?

We will be shooting on the timelapse stuff on the Canon 5d.

What type of exposure should I expect?

What are the effects of reciprocity?

Thanks

James Mann

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#2 John Sprung

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Posted 05 April 2010 - 01:57 AM

You want true North, not magnetic. And elevation = latitude.




-- J.S.
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#3 Thomas Dobbie

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Posted 05 April 2010 - 03:53 AM

Hi James,

you should check out http://timescapes.org,lots of how to do,and technical info there.
Very friendly and helpful forum,I'm sure you'll find what you're looking for.

Tom.
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#4 Oliver Christoph Kochs

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Posted 05 April 2010 - 08:24 PM

5d - be it old or the newer mark2 - will have lots of noise from long exposure. To make things worse: the noise will increase with the sensor heat. You might want to go the "film" route here as an add-on to the 5d. It's just a thought.
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#5 James Mann

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Posted 06 April 2010 - 12:02 AM

You want true North, not magnetic. And elevation = latitude.

-- J.S.



Okay, John. I see the words on the screen but I can't quite ascertain their meaning. Can you please go a little further into detail here.

Thanks

James.
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#6 Tom Lowe

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Posted 06 April 2010 - 12:23 PM

5d - be it old or the newer mark2 - will have lots of noise from long exposure. To make things worse: the noise will increase with the sensor heat. You might want to go the "film" route here as an add-on to the 5d. It's just a thought.


Not my experience at all. I regularly shoot dark skies at ISO 3200 with absolutely jaw-dropping results once downsampled to 1080p/2K.

Film cannot touch digital these days for astro timelapse, unless you want to shoot 5-perf 65mm or 15-perf frozen in liquid nitrogen.

As far as circling skies go, just aim for Polaris. There are many, many handy iPhone apps that can tell you where celestial objects are. pUnivirse (aka Pocket Universe) is a really cool one, especially if you have an iPhone 3Gs with compass and accelerometers.
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#7 John Sprung

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Posted 06 April 2010 - 03:10 PM

Okay, John. I see the words on the screen but I can't quite ascertain their meaning. Can you please go a little further into detail here.


The earth has two North poles. One is the axis it spins on, and the place we use for the top of globes and for latitude and longitutde on maps. We call that one true North. Straight up from there is the place that all the stars will appear to circle around, so that's the one you want. There's a bunch of molten iron inside the planet, spinning around and creating a magnetic field. The iron doesn't quite line up with the rest of the planet, so it has its own pole, the place where magnetic compass needles point to. That's magnetic North. The charts that navigators use at sea tell them how to correct from magnetic to true. The magnetic pole also moves around over time, so that's in the instructions on the charts, too. They say things like so many degrees East, minus however many per year starting from 1977.... (That's about when I was messing with navigation.)

Once you're facing true North, you need to know how far up in the sky to look for the place all the stars circle around. At the North pole, it's 90 degrees straight up. At the equator, it's zero degrees up, right on the horizon. In between, the angle you want to tilt up from horizontal is equal to the latitude of your location. For instance, here in the LA area, we're mostly pretty close to 34 degrees North, so we'd want to tilt the camera 34 degrees up to get the center of the circles in the picture. You can find your latitude and longitude from a map or from a *good* GPS -- not those crappy car navigation ones that don't give you numerical lat/long. (Check your cell phone, many of them have GPS built in.)




-- J.S.
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