Star trails, how to set up camera?

[Pinarelloman]

I will be camping this weekend and the nights will hopefully be dark enough to try some star trail photography.
How to set up the camera.
I have a 5dmk3.
70-200f 2.8is.
A 24-105 F4
A Giga t to keep the shutter open.
Heavy tripod.

When I tried this before, after keeping the shutter open for about 30mins, the red light stayed on the camera for quite a while as it processed the image. The battery then died. How long does it take for the camera to process the image? Is it normal, to wait a long while?

I would think I set the camera up with the lens wide open, maybe iso 400? How much time do you allow to get the full rotation.

Someone said you set the camera up facing north.

[Warbler]

Are you trying to get a single exposure, or did you mean 30 seconds and not 30 minutes? You'd be better to take 30 second exposures over many hours and combining them using the available free software out there. As for the light staying on, that's your long exposure noise reduction working.

Others do this more than I do, but I'd set up before it gets dark and take an exposure that gives me a twilight image to start. Then I'd wait for it to get fully dark and start my series. The Giga t will look after this. I'd just set my lens to manual focus and the camera to burst, lock the Giga t to on and let it fire away as many 30 second shots as you want 300-400 should do it. Make sure your battery is fully charged. Settings I've used with my 5D3 were f2.8, ISO 3200, 30 seconds. Use Manual. Take a dark shot (lens cap on) at the end. Turn off your in-camera noise reduction. Don't forget to cover the viewfinder to stop light entering. Take a good book or listen to the footy on the radio. Watch out for dew.

Oh, and point the camera at the south celestial pole. You'll get a circular pattern then. Try for a still night if you're going to have foliage in the foreground, or use something that won't move in the breeze.

[hakka]

Good advice above, but iso3200 is too high, try iso1000. No need for darkframes if you're stacking multiple images, the stacking process will eliminate the noise.

[nardes]

>snip
When I tried this before, after keeping the shutter open for about 30mins, the red light stayed on the camera for quite a while as it processed the image. The battery then died. How long does it take for the camera to process the image? Is it normal, to wait a long while?
>snip



The long “wait” time is probably due to the camera shooting an equal length (automatic) “noise reduction” or “dark frame” if you have in-camera noise reduction enabled.

Basically, the camera takes an equivalent “dark frame” of the same exposure time as your “light frame”.

So, if you exposed a 30 minute star trail shot, the camera then internally blocks light to the sensor and then exposes a shot for 30 mins which is a record of the thermal noise of the chip and electronics with no outside light falling on the sensor.

The camera then subtracts this “dark frame” (i.e. thermal noise) from your real image so that you end up with the real data from the other side of the lens not being polluted by the internal noise from long exposures.

This noise only becomes noticeable at exposures of maybe 1 sec or longer.

Cheers

Dennis

[Pinarelloman]

Thanks to all, I will try on the weekend & post some results.
Will I be better with the wider angle lens? I know it is f4 and alot slower than the f2.8.

[hakka]

Thanks to all, I will try on the weekend & post some results.
Will I be better with the wider angle lens? I know it is f4 and alot slower than the f2.8.

Yes, f4 will be fine, but bump up the iso to around 1600.