Photographing star trails help (amature)

[mattscreative]

Hi guys,

I have just started photography and have a Nikon D5000 and am trying to photograph star trails. I have the stacking software so am taking the "multiple, short(ish) exposure time" technique, and stack them, over the one long shot.

I took some on Sunday night and when I stacked them, there were gaps in the star trails. I am taking them at 30sec intervals, (on the "S" setting) not sure what the aperture was im afraid, with a cable remote. I noticed that on the test shot (to make sure scaffolding I was getting in shot was in focus) that after the 30 seconds of shooting, there was another pause, possibly a further 30 seconds before the photo showed in the live display. I presume this is the reason for the gaps in the stars, but im wondering if there is anything I can do to stop these gaps? I was thinking of going down to 10 second exposure, so more photos to stack but no issues with the software doing the work.

Any ideas greatly appreciated.

Thanks

Matt

[CJK]

I am not an expert by any means but if you are waiting any time over 10 seconds or so between shots you will actually get gaps from the rotation of the earth. I know 10 seconds doesnt seem like a lot but its enough to blur the moon, ie show the earths rotation.

I might be wrong but if you took a 30 second photo, then waited even 10 seconds before taking your next shot you would have a gap since the stars location would have shifted from the rotation of the earth.

I enjoy taking night photos the best, I usually pick M mode so I can adjust the aperture as well as shutter speed. Usually pick an F stop of around 8 to let the most amount of light in without losing all depth and a shutter of always more than 20 seconds or so, depending on what I am after and conditions (if the moon is out), I use bulb so I can experiment. I dont go over 200ISO.

As far as stacking, never tried it in night photography but it is on my list to try. If you are interested, bring a high powered flashlight and try light painting, you can get some cool stuff by just illuminating certain foreground subjects for a few seconds. Even better if you have different color filters and ways to disperse/diffuse the light so its more even... if that makes sense.

Also, don't wait until hours and hours have passed after sunset, you can get some cool colors about an hour after the last visible light has settled, mainly in the westerly direction, your camera will still pick up some light from the sun even though its dark to you.

Here is a link to one of my shots a while back, I think this particular photo was F 5.6, 200 ISO and 324.5 second shutter speed.

Mini Competition #1668

[Wayland]

The gap between shots is caused by the camera's noise reduction processing, which makes a dark frame subtraction using a second internal "exposure" the same length of the first.

This can usually be turned off somewhere in the menu settings.

For most star trail shots I find that the noise reduction is not needed because the stacking tends eliminate most of the noise anyway.




If you do need to apply a dark frame subtraction you can produce one yourself by making an exposure of the same length with a lens cap on before or after the sequence and making the subtraction with software. This may be possible in your stacking software or be done in an editing package in needed.

[mattscreative]

Thanks for that, it felt like the camera was doing something, like processing something. I will flick through the menu and see if I can turn it off and try again

Thanks

Matt

[Wayland]

No problem.



It really is a lot of fun so good luck with your next shots.

Welcome to the Forum by the way.

[mattscreative]

Yeah,

is a very interesting and fun part of photography. Im just starting out really, with my first camera, but am loving just playing about and trying things out, but I really want to get a great star trail photo or 2

Love yours by the way, utterly stunning. Really makes me want to get out there and do some of my own!!

Thanks again

[Wayland]

Biggest issue I have had is battery power.

Multiple long exposures eats batteries very fast and depending how your camera is mounted on the tripod you might not be able to change cells without moving the camera.

I've been working on an external power pack that should solve this problem so I hope to be doing a lot more as the darker nights creep back in.

[Dave Humphries]

Hi Matt,

Welcome to the CiC forums from me.

Look for "Long Exp NR" in the D5000's Shooting menu and turn it 'off' - p151 in the manual.

Says you'd need to go to 8 seconds or shorter if you want to avoid it (if left switched 'on')

Cheers,

[darekk]

I wanted to ask question whether Polar Star is in the middle, but found myself

http://en.wikipedia.org/wiki/Circumpolar_stars
http://upload.wikimedia.org/wikipedi...mpolar_ani.gif
Wikimedia Commons, author: user:Mjchael

.
(Polaris, the bright star near the center, is almost stationary)

But how the sky looks like in southern hemisphere, in Australia or New Zeland for example ?
Should the camera also be directed towards the north if someone wants to catch the center of such rings ?

[CJK]

Gary and Dave, good call on the NR on the 5000... its the same camera I use and I totally spaced about the NR option. I never knew about it for a while and started to get discouraged after taking a 10 minute exposure than having to wait another 10 mins to see it.

I started to just turn off the camera when it did this so I could keep shooting... I started to notice that there wasn't much difference between the shots I let the NR do its thing and when I turned the camera off, so I finally researched it and turned the NR off in the menu... chalk another one up for learning by doing.

[Wayland]

Dareckk, that's a great gif you found there.

I will have link that to some friends on another forum to explain how these star shots work.

As for the Southern Hemisphere your circle centre will be closer to the Southern Cross I believe.

I'm sorry I don't know the precise Southern polar axis but hopefully someone else can help on that front.

[darekk]

for the Southern Hemisphere your circle centre will be closer to the Southern Cross I believe.

Cook or Magellan knew it very well, but they are dead unfortunately ...

[Wayland]

Here you go.

Lifted from here: http://kvmagruder.net/bcp/aster/general/southern.htm



The south celestial pole actually lies within the constellation Octans the Octant, which is devoid of bright stars. The nearest easy-to-spot star to the south pole is Beta-Hydri in Hydrus the Little Snake. No brighter star than Achernar (alpha-Eridani) is closer to the south celestial pole, which lies midway between Achernar and Crux.


Not quite as easy to find as Polaris in the North I'm afraid.

[darekk]

Just above equator star tracks are probably linear, because this is border of northern and southern star paths. Here are images from southeastern France:
http://www.astronet.ru/db/xware/msg/apod/2009-03-14
and southern California:
http://www.dennismammana.com/spow110623.htm
Not equator, but two groups of circles are visible.


Very difficult seems to be correct exposure of land and stars in the same picture.