...Shoot Startrails

22/01/10

Here is a basic overview on how to photograph star trails. There are many fantastic articles online that go into great detail, and are far more comprehensive than this, but this will give you a good basis to get out and try. I will provide some links at the end to some good sites.

EQUIPMENT

DSLR camera (though most of what’s written here will work equally well for film) capable of exposures of 30 seconds or more
Fast lens - wide angle or standard zoom
Remote shutter release - wired or wireless
Sturdy tripod
Fully charged batteries
Warm clothes
Torch
A watch or timer to keep an eye on exposure times.

LOCATION

Plan your location ahead of time. The direction you are shooting will make a lot of difference to the types of trails you get. North will give you circular trails as the stars appear to rotate around Polaris, South will give you horizontal trails, and East and West will give you curving trails across the sky.

Stellarium is a great free downloadable program into which you can enter your coordinates and take a look at the night sky and its stars and constellations from whichever direction you choose.

Try to visit your planned spot during daylight so you can visualise your composition as once it gets dark it will be much harder. Some foreground interest in the shot will make it far more appealing.

Be aware that the earlier in the evening you shoot, the more aeroplane trails you will get tracking across the sky, not always a welcome added feature!

You will need to wait about 2 hours after the sun sets to start your shot, to ensure that you don't get too much light. If shooting in the early hours plan to finish a couple of hours before dawn.

Streetlights are not your friend! Even if you are miles away from a town, the ambient light from them will show up on a long exposure as an orange glow (UK) particularly if there are any clouds in the sky. The recommended minimum distance from a small town is 25 miles in order to eliminate the possibility of streetlight pollution, but in the UK that is not easy to achieve, so try to find somewhere with minimal lighting and aim your camera well away from any lights.

The other point to mention here is be aware of the moon phases. A full moon will throw far too much light out to allow for long exposures so aim for a night when the moon is new or not out at all.

SETTINGS

Set your camera up on the tripod in your location. Plug in your remote shutter release and in manual set the camera to bulb mode, single shot, ISO 100 and f/5.6. You want a wide aperture to let in as much light as possible from the stars. Set your lens to manual focus and switch off any image stabilisation. White balance is down to personal taste and will also depend on any ambient light that may be around. Often the tungsten setting looks most natural if there is pollution from streetlights, but if you shoot in raw you can adjust this setting when processing your shot.

Focusing in the dark can be a real problem, so a simple way to do it is to set your lens to infinity (the sideways 8 symbol on the lens focusing ring). It might help to test this in daylight. Set the lens to infinity, look through the viewfinder and slowly turn the lens back a little until almost everything you can see is in sharp focus. I have found the 'sweet spot' on a lot of my lenses is often just past the actual infinity mark. You can then mark this spot with a dab of tippex or light coloured nail varnish to make it easy to find in low light conditions.

If your camera has a noise reduction feature then turn it on.

IMPORTANT: If you use the noise reduction feature you must be aware that this will double your exposure time. When you finish your exposure the camera will then take a darkframe image for the same length of time, which it will then use to map any hot pixels and noise and eliminate them from the final shot. Make sure you don't run your first exposure too long to allow the dark frame to finish processing too, because if your battery runs out during this dark frame you will lose the entire image.
You can move your camera during the darkframe but you should leave it in the same conditions, temperature, humidity etc, as the original frame.

I have pushed a fully charged Canon battery to 2 hours and 2 minutes at -4C, the camera died the moment the darkframe finished processing so it was right at its limit. In warmer conditions your battery should last a little longer than that though.

TAKING THE SHOT

Once you are happy with your set up, it is worth taking a test shot to check your focus and composition before committing to a long exposure.
Set your exposure to 30 seconds, bump up the ISO to record as much detail as possible in the shorter exposure, and then take a shot. Once you are happy remember to turn the settings back for the long exposure.

Double check your settings, make sure the lens cap is off (an easy mistake in the dark!) and once you are ready, lock on the remote release and then find something to pass the time! This is where the warm clothes are essential, particularly if you are not near your car or house to warm up. A thermos with a hot drink is a good idea too as is taking a friend for moral support and company!

A 20 minute shot will give you decent length star trails, but you might want to leave it longer than that. Just remember that your battery needs enough power to complete the darkframe for the same length of time.

The above photograph of Penmon was shot for 61 minutes at ISO 100 and f/5.6.

STACKING

Another method of shooting star trails is by stacking multiple images into one final shot. This is sometimes preferable if there is a lot of ambient light around since you are shooting shorter exposures. This method can work well on moonlit nights or if there are a lot of streetlights around. It also eliminates battery worries because if your battery dies you only lose the last shot your camera was taking.

It is possible to stack the images in photoshop, but a much easier method is using a dedicated program. You can download a fantastic free one called 'Startrails' (link below). Just load in your images, hit 'build' and it does all the hard work for you.

It is worth noting here that if you shoot in raw for stacking your processing time at the computer will be much longer since the Star trails program only accepts tiff and jpeg files. You may find yourself with hundreds of raw files to convert before you can start the stacking. You can shoot in jpeg to save time but it will affect the final image quality.

Find a location and set up as for the long exposures. Set your camera to high speed multiple shots, ISO 200, 30 second exposure and f/5.6. Set the focus the same way as before.

Make sure your noise reduction is OFF, otherwise your camera will process a darkframe in between each shot which will result in gaps in the trails in your final image.

Take a test shot to check the exposure and focus. You want the image to record the light from the stars but not to be too bright if there is a lot of light around. You can adjust the ISO if the shot is too dark and the exposure time if its too bright.

Once you are happy, double check your settings and then lock on your remote release. Your camera will now take continuous 30 second shots until you stop it.

You can also 'lightpaint' a little during one or two of these shots. Use a torch to illuminate your foreground, making sure to keep the torch moving evenly to avoid any burnt out areas. Do this during your first or last frames so that if you are not happy with them you can eliminate them without affecting the final image.

Once you have finished shooting, replace your lens cap, and without changing any settings at all shoot 2 or 3 more frames. These will act as darkframes similar to the noise reduction setting when you come to process your shots. Just add these shots into the Startrails program in the 'darkframes' section.

SOME POINTS TO CONSIDER

Always keep an eye out for clouds. One or two small ones rolling through can enhance a shot, but if you can't see more than 80% of the stars you started with, its time to stop the exposure!

Watch out for the dewpoint, when moisture in the air starts to condensate onto the ground and anything low. Unfortunately I haven't found a way to accurately predict this, though many weather forecast websites can tell you at what temperature it will occur. If this happens whilst you are shooting your lens is likely to get fogged up and ruin your shot. Not so bad if you catch it in time, but on a long exposure if you don't spot it, it will mist over your shot and spoil it. It can help to place a hand warmer – the single use type, around the lens held in place by a sock with the end cut off, this may prevent some of the dew forming on the lens.

Carry some ID or a business card with a web address where you post your shots on it, or even a small print of your work. I have been approached and questioned a few times, as being out and about after dark with a camera can look suspicious. A simple explanation is usually enough but anything you can produce to confirm what you are up to is always handy to have.

Dress warmly, gloves, thick socks and a hat are a must as the temperature can drop dramatically on a clear night. Hand warmers are a welcome addition to your kit bag too. Ebay have a good selection of cheap reusable ones as well as the single use type. And don’t forget the thermos!

Remember all the advice here is what works for me. You may find that different settings work better for you, so don’t be afraid to experiment, its part of the fun!

LINKS

Naturescapes
A great comprehensive and more technical overview of how to take star trail images

Stellarium
A free downloadable program for finding stars and constellations

Startrails
A great free downloadable program for stacking star trails