A lot of nature photographers never have much need to use flash. If you don't need it, why bother?! But when you need to photograph at night, as I did during my bat class recently, flash can become a necessity.
Recently I did a short piece in National Wildlife Magazine about photographing nature at night. There is a huge amount of natural things going on at night but we see very little photography then, other than the now faddish (though still interesting and fun) night skies. After just taking a bat ecology and conservation field course, I realize even more how much we are all missing as photographers, naturalists and as the eyes of the public. When the public does not "see" things, such as through our photography, things really don't exist for them.
But photographing at night is challenging, to say the least. The timing is off for most of us, our eyes don't function so well in the dark, cameras are not made for the dark, and light is an issue. Regardless of your camera's high ISO capabilities, there is only so much you can do in the dark night. Landscapes with stars and landscapes in moonlight can be readily accomplished with today's cameras, but beyond that, you need to add light.
I have done a bit of night photography of spiders and and insects because many of these little animals are creatures of the night and will not be seen otherwise (either by you or anyone who sees your photos). I have used both flash and continuous light sources for this. The advantage of a continuous light source such as a quartz light or LED light is that it is always on as you shoot, making focus and composition easier (I don't use quartz lights so much anymore because of heat and power issues). This is a couple of labyrinth spiders, a male (small one upper left) and a female (larger, lower right in "trash" hiding spot), with the labyrinth of web showing in the background, shot with a strong backlight LED and a front fill LED.
In some situations, such as the bats, you can't simply set up lights, leave them on and expect all the action to be there (which was true for the spiders), so I used flash. Even with flash, you need a light for focus and composition, which can be a headlamp (which I used, but I am thinking about using a small, LED ring light for this purpose because this always puts a good light on the subject, especially close-ups, though I don't like it so much for the actual photo).
The quick and easy thing most people will do is to turn on their flash or maybe use a strong light from the camera position. While this will illuminate the subject, it won't always result in very attractive photos. Any light from the camera position will be flat and without dimension or form (which is one reason I don't like ring lights much).
The key to getting better light at night is to get the light off the camera. This creates dimension and modeling on the subject. With light coming from the side, above or even behind the subject, you give a three-dimensional quality to your subjects and you bring out texture.
I know flash can be intimidating to many photographers, but an accessory flash is easy to get off camera simply by using a dedicated flash cord and then holding the flash away from the camera. All of the bat photos from my class seen here were done that way. In addition, I added a small soft box to the flash (my complete set up is shown below).
I find that the built-in wireless flash systems of today's cameras are terrific as long as you are inside. Unfortunately, they do not consistently work outdoors, so even if you use them, it helps to have a cord. Plus a cord is easier to use for many people because the flash works the same as it does when it is sitting in your camera's hot shoe and you don't have to fiddle with wireless settings. The reason camera-based wireless flash struggle outdoors is that the camera has to send a signal to the flash (infrared or pulsed), and outdoors, that signal can go off into infinity without being seen by the flash.
So think about lighting up some night subjects. I am. You can get starts with a strong LED light from the hardware store and a high ISO, or just by getting a dedicated flash cord (i.e., a cord designed specifically for your camera and flash) to use with your accessory flash. I am going to be experimenting now and then with different night techniques to see what I can find.
Check out my book and video course combination at www.joyofnatureandphotography.com.