Digital Cameras

Currently, digital cameras are less then ideal for taking Northern lights photos, but they can be made to work. There is one major problem that will cause poor pictures with a digital camera and that is Noise. Digital cameras generally aren't designed for taking pictures at night, so you have to be careful which ones you buy.

If possible, try before you buy.

When purchasing a digital camera for taking pictures at night, you want to look for a few things:

• High resolution. The better the resolution, the less visible the noise will be for the same size.
• Manual mode. You need a manual mode, ideally capable of 30 second exposures, but 15 seconds will do (just).
• Wide angle lens, or capable of threading on an adapter lens. Wide angle lenses take better aurora shots, as you can get more in.
• Economical on batteries.
• Accurate color reproduction at night.

Some of the higher end cameras (like the Sony DSC-F707) have noise reduction systems built in which is a big advantage as you don't need to process them afterwards.

Generally the more expensive the camera, the better it is for this kind of work. Isn't that always the way :-)

About Noise

Every CCD (the device that the image is detected on in a digital camera), produces a certain amount of digital noise on an image. If an image has a poor noise level, you will see it as color grain in the image, particularly in the darker sections.

When taking a daylight picture with a digital camera, the signal (the image) to noise level is high. I.E. The image you are taking has a high brightness, so the amount of noise you see is low. At nighttime, the reverse is true and the signal to noise level is high.

Evaluating The Camera

You don't need an aurora to evaluate the camera though it does help. To evaluate your camera for night work, try taking a few pictures:

• On a night with a full moon taken from a dark location (no nearby street lights and no moon in the picture). 30 second exposure. The ground should be lightish (grey) and you're looking for no color casts in the photo or the sky.
• On a night with up to a quarter moon, taken from a dark location (nowhere near a city, and no moon in the picture). 30 second exposure. Point the camera towards the sky, pick a nice constellation or star field. You're looking for no color casts and faithful reproduction of sky color and detail in the stars.
• Take a picture at night with the aperature set to maximum and a 30 second exposure. You are looking for vignetting (this is where due to the lens, you get a ring which gets darker towards the edge of the picture). This can be corrected for if you're prepared to do some digital processing.

On the first two tests you're looking for color casts (which can sometime be corrected via the White Balance control on your camera, or via your photographic software), and for a good noise (or rather lack of) level.

Image Processing.

Unless you have one of the higher end cameras, processing your image in a program like photoshop (or similar) is a must.

You can use this to correct color balance, improve contrast, reduce noise, remove vignetting and a host of other functions.

If you keep noise low, it will make your image processing easier. The colder the CCD is the better the signal to noise level (though most cameras don't like being too cold, and you can damage them this way).

If your camera doesn't take very long exposures you can stack them to produce an image with a lower signal to noise ratio.

Be careful with the Jpeg file format. It tends to compress the dark areas, i.e. the areas your aurora is in! So always keep compression to the minimum you can get away with.

Look at my Image Processing Guide to find out how to reduce noise, vignetting and find out about image stacking.

Batteries

The biggest headache with digital cameras is batteries. Digital cameras tend to use a lot of battery power, particularly the more you use the viewing screen on the camera.

When the battery can no longer deliver the current required, the camera shuts off. Quite often this will be before the battery is flat.

Here are some things you can do to eliviate the problem:

• Night tends to be colder than day. Try to keep your camera and spare batteries warm, as a battery delivers less current when cold. I keep my spare batteries in my inside breast pocket when working in the cold.
• Use Rechargeable NiMH batteries (Nickel Metal Hydride), or just ordinary rechargeables. The NiMH batteries have a high capacity. Rechargeables in general have a lower internal resistance than normal batteries, so they're better able to deliver the current that is needed to your camera, and your camera is less likely to switch off.
• Get a camera that uses a bigger rechargeable battery. I like the Sony DSC-F707 because it uses a camcorder battery, and has loads of spare power. I can use it for 2 hours straight with the viewing screen on for 75% of the time.

Practice

Practice makes perfect! You can get a lot of experience from just taking photos at night. Then when an aurora does happen, you're more likely to get that good shot. Take photos of the stars (you never know you might start a new hobby). Take photos of the city where you live. Try experimenting with man made objects in your pictures.