Capturing Star Trails on a D-SLR

Suburban Swirls.

I wrote a tutorial on how to capture star trails like the ones above for the WelshFlickrCymru group on Flickr.

It is repeated here for posterity!

Although I’m still learning too, I’d be happy to pass on some tips for winter night time fun.

#alttext#

First you will need..

A camera capable of manual focus, manual exposure, a cable release (I don’t know if you can use an IR remote or a wireless one, as long as you can lock the shutter open, you are ok..)

A tripod

Somewhere relatively dark – I’m still pretty close to Cardiff, so there is light pollution but trying to minimize it will help.. Trying just outside your back door in suburbia isn’t going to yield great results.

There are two methods for capturing star trails – you can do one very long exposure or you can do many shorter exposures and then some post production work in photoshop etc

First Method – One long exposure.

———————————————-

A] Set your camera to Manual Mode (M). Set the aperture to a small f number (large aperture), say f/4.0.

Then increase the shutter speed – past the normal 125,250 etc right up past 1″, onwards past 30″ until the display shows Bulb.

Bulb mode allows you to control how long the shutter opens manually. Try it. Bung in the cable release fire it, then release. You can open it up for less than a second or for many minutes.

B] You might want to try setting the white balance to Tungsten in areas where light pollution is a problem – other wise you will get a very orange shot at the end from the glow of the streetlights – going tungsten should cool the colours to a blue tone – or you can not bother and colour correct after if you prefer.

C] Next, for shooting in the dark you will need the camera to gather as much light as possible, so set the ISO to 400 or above. I usually use 800, but 400 will be ok if you start just after dark when there is still just a little light left in the sky, or if there is a lot of light pollution. By all means use ISO 100 but that will increase the exposure time by 4 from that of ISO 400.

D] The camera is set, now set the lens to manual focus, using the switch on the side, and manually set the focus to infinity (the symbol looks like an 8 on its side..)

Remember, you are at f/4, so you will not have much depth of field but the lens will gather more light the wider the aperture. To ensure that all is in focus with this depth of field, either bring a torch and light up an object to focus on, or ensure that there is nothing within 10 feet or so that needs to be in focus.

E] The last point is regarding noise reduction on some SLRs. Cameras like the Canon 400D have long exposure noise reduction. What this does is take another frame immediately after a long exposure, without opening the shutter, this so-called Dark Frame is then subtracted automatically from the exposed frame. Unfortunately this takes the same amount of time as the actual exposure… so for an hour long exposure the camera will then do an hours worth of dark frame – so charge them batteries! The dark frame doesn’t open the shutter, so you can safely pack up your kit and wander home but you won’t be able to do anything on camera till its finished. This will cause problems for method two but that’s for later!

I’m not going to tell you how to find Polaris, the star which presently is the celestial north star, you’ll just have to google it to find it in the sky. Its importance lies in that it is the one star in the northern hemisphere that stays still, whilst the motion of the earth makes the other stars appear to rotate.

OK. Camera on tripod, frame up, don’t leave the strap flapping about and lock the tripod up tight and ensure a firm footing and expose away whilst locking the remote shutter release.

#alttext#

The above is a single 8 minute exposure (I know – I should have gone longer..)

Then wait. And wait. And wait. …. and wait some more, you get the picture. Half an hour has gotta be a minimum for crowd pleasing swirls, but essentially the earth moves quite a lot in just 5 minutes – but the longer the better. Leaving it more than an hour in some conditions will lead to dew fogging the lens if the temp drops below the dew point. I’ve read suggestions of taping those pocket hand warmer doodads to the lens to stop fogging but I’ve yet to come across the effects of dew. [EDIT! As of late November, I had my first dew related incident… this is what happens…]

Fogger

Click to see the effects of dew on a larger scale.

Others tell tales of camping trips and overnight exposures on film cameras but a D-SLR will run of battery long before then!

After exposing for a while, release the remote, wait for the dark frame and hey presto, you should have trails. How well they come out depends on:

how long the exposure

how much light pollution

how much cloud cover – hopefully none but some might sweep past mid exposure

the effect of the moon – I aint gonna tell ya about the moon, again refer to google about moon rise and set times -but be warned the moon is much brighter than the stars and will ruin a trails shot just as much as city light pollution. Full moon = stay indoors. (Although I don’t always heed my own warnings… see the above dew soaked trails shot!)

Advantages of the Single Long Exposure Method

Its easy.

requires little post production (bar levels and colour balance)

Any wispy clouds passing through shot do the same as waves in long exposure – go to a misty cloud, which doesn’t happen in method 2, as we shall see.

Disadvantages of the Single Long Exposure Method

One shot. One battery. If it goes mid shot, you’ll have to start again. Noise reduction users better watch out for the dark frame – I dont know but chances are the whole shot fails if the noise reduction frame doesn’t complete.

This technique doesn’t allow for light painting experimentation in post production – if you go dancing around in the foreground to make some swirly patterns and screw it up – or maybe fire a separate flash into a tree to highlight foreground and get it wrong – you’ll be stuck with the effects in the shot. The multiple exposure method allows you to a certain degree to correct some of this in post production.

Second Method – Mulitple Shorter Exposures

————————————————————-

The idea here is to capture several short exposures and then layer the results up in software to produce a composite image that contains the trails. Each single image looks like a starry night and the movement is not really apparent until you flick through in playback mode on the camera!

You should set the camera up as detailed in method one, steps A,B,C,D.

Except in Step A set the camera to 30″ rather than bulb.

For this procedure however, you must disable noise reduction. If there is more than two seconds gap between the frames, then your trails will look like dotted lines, rather than streaks, so we haven’t got time to expose another frame for 30 seconds.

For shooting the process is similar, with one vital difference. Set the capture quality to highest quality JPEG, rather than RAW. RAW is great but the write speeds to the card between frames may cause problems – and do you really want to process 100 RAW files individually once you’ve finished?? Nope, me neither!

Lastly for this method, put the camera in burst mode, or continuous shooting mode. Usually you would use this in HDR to get 3 frames in really quick succession but here we will use it to get one shot every 30 seconds. You must use the locking feature on the remote shutter release once again to force the camera to keep taking shots in burst mode – when it exceeds the number of frames it can do, it writes one frame to the card and is then able to do another burst e.t.c ad infinitum.

So once you’ve set it off, sit back relax and listen to it clicking away every thirty seconds.

I say 30 seconds – this works well if there is enough light in the scene to produce an ok exposure in 30 seconds! If its really, really dark, you may need to go back to bulb mode and try several exposures at a minute or five minutes. However long the exposure, the stacking procedure is the same.

Once you’ve had enough, release the lock on the shutter remote and it will stop after the next exposure. Before packing up – chuck the lens cap on and do another 30 seconds frame – this will be your Dark Frame and any hot pixels and sensor errors from long exposure will appear here as well as on the individual frames and you can use this to subtract the dodgy artifacts from your finished shot.

Stacking the frames in Software

The easiest program to use is the Star Trails app, which is free (Hurrah!) from here

You open your JPEG frames and your dark frame and hit the trails button and as if by magic a fantastic picture is drawn before your eyes!

For large amounts of frames, try the movie button to get a movie clip of the sequence as a time lapse movie – oh the possibilities – you could extend this to a flower blossoming, or clouds over the mountains – time lapse stuff is possible on a SLR with this prog – there are a few good ones on Flickr (which then link to YouTube for the movie).

Another method which allows more control over the individual frames is to stack em in Photoshop. Open the images, copy and paste each one onto the first, using the “lighten” blending mode – except the dark frame, which uses the “Difference” blending mode in the Layers palette. This is more time consuming but worth it for flexible control.

There is a Photoshop action which automates the process of opening and stacking the frames and setting the “lighten” mode but it also flatten the finished layers at the end. I just deleted this line from the action command to allow me to fiddle with the layers before flattening.

You can get the PS action from here

#alttext#

Stacked trail above shows disadvantage of stacking – strange cloud patterns.

References.

—————-

I’ve by no means figured this out on my own.. Thanks to some google-ing (verb?) I’ve gathered lots of really useful stuff… I include here some references from whence this stuff came from should you wish to peruse further…

Naturescapes

Dan Heller

Flickr Star Trails Group

Word of Warning

———————–

I’m happy to give technical details about how to go about taking this kind of shot but I can’t sign off without mentioning that staying warm and safe is also essential!

Make sure you choose a safe location to get to / get back from in the dark and wrap up warm! Standing in the cold doing nothing is not as easy as it sounds – take an iPod (whilst also keeping an ear out for camera stealing undesirables….!!). I would hate to hear of any mishaps incurred whilst following this guide!

Update…

I’ve been off to the southern hemisphere in the African bush and got some nice south facing swirls, all on single exposure. I did come across some amp glow – a side effect of a long single exposure. The only way round it was to keep exposures short on the 300D but apparently the built in noise reduction on newer cameras is particularly good with amp glow.

Here’s some of the shots..

#alttext#

#alttext#

Advertisements

9 thoughts on “Capturing Star Trails on a D-SLR

  1. Thanks for this comprehensive guide.

    This guide is the best one I have found and I have read a lot of them, whilst waiting for a clear night.

  2. great blog, i got a lot from this guide. hopfully the stars will be clear tonight so i can have a crack at this

    Body warmer and coffe on standby

  3. have done quite a few of these but 30 mins with the balance shot on top is about the limit of my batteries (my kingdom for a battery grip!!) and I wanted to go longer .. by the sound of it I can go for as long as I want now .. thanks .. can’t wait to try it all =]

    Steev S

  4. The thing I won’t agree with is ISO setting. 400 is a lot and during long exposure night shots will result in a lot of noise. I would recommend switching noise reduction to off and move ISO to lowest setting available.
    No moon phase will be the day after tomorrow, hope there will be no clouds at all 😉

  5. Hey likedat, you are quite right – particularly in the case of the one long exposure like I mentioned above. I have no excuse it was a while ago I wrote this entry and also in the middle of winter – so going to ISO100 really extends the amount of time you have to stand in the cold!!

    If you go too low on the ISO when you are doing the multi exposure technique however you have to be careful as you will only gather light from the brightest of stars in the time of the short exposures needed for stacking. But the stacking method results in less noise anyway, particularly when backed up with a noise reduction plug in like Neat Image.

    Thanks for helping to improve this guide.

  6. Hi, found your guide when I realise it was a clear day and was going to stay clear. To get a descent brightness in one exposure at 30sec f3.5 I had to use iso1600. But, to my amazement the northern lights appeared (not visible to the naked eye). Did multiple exposures for star trails, 30sec f3.5 iso1100, the Nikon D300 lets you do interval shooting, but it would only do 9, then I had to reset it, worked OK though apart from the noise, but any lower and the stars didn’t show all that well. I’m thinking that the Nikon D3 would be great for this.

  7. Thanks for sharing your tips!

    Have had a few goes and enjoyed the fun (bit warmer in the southern hemisphere at the mo), but gearing up for another attempts soon!

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s