When taking pictures of northern light I like to use the shutterspeed as short as possible. This depend on the light and how fast the aurora moves on the sky. If the shutter speed is too long the light will be smeared out and more mixed. When taking pictures of the northern light a shutter speed between 3 and 20 sec. can be allright. Therefore is a tripod required to get sharp pictures. To get the picture the most realistic as i experience it on the sky I have to experiment with different shutterspeed and ISO to get a optimal result. As you can see on the pictures below the picture with 5 sec expousure is a bit less clear, and more blurred than the picture taken with 3,2 sec.
5.0 sec f/4.0 ISO 2500
3,2 sec f/4.0 ISO 3200
13 sec f/4 ISO 3200
Here is it not much northern light and it is not moving fast on the sky. A longer shuttertime/exposuretime was possible and I still get a quite clear northern light. It was almost full moon illuminating the landscape.
Best regards
Harald