The day we arrived at the Victoria Falls in Zambia we heard that it would be full moon that night! Without any planning on our side we just happened to be there when we had a chance to photograph a moonbow (or a lunar rainbow). Never heard of a moonbow? Check out these tips to photograph a moonbow yourself (or just watch the photos).

Preparation to photograph a moonbow

Here we go. As said before it’s kind of essential that it’s full moon. Next to that there should be a clear sky, clouds would simply block the moonlight. Once the light hits the mist of a waterfall a lunar rainbow will appear in the middle of the night! It might come in handy if you visit the place during the day so you’ve got some sort of idea on where you want to be at night. It’s also good to find out at what time the moon rises that night. A nice little app to do just that is Magic Hour.

The gear that you need

To photograph a moonbow you’ll need to bring along the following items (next to a proper camera of course):
– A sturdy tripod: since we’re working with long exposures the slightest movement will end up in a blurry photo.
– A camera remote to ‘start’ your photo without touching your camera. This way you don’t have to touch the camera and it gives you complete control over the length of the exposure.
– A headlight to see what you’re actually doing (turn it off when shooting your lunar rainbow photo!)
– A watch (or phone) to check the exposure time.
– Spare batteries.
– A cloth to dry or clean your lens if necessary.

Composition

If you’ve been at the location during the daytime you might have a pretty good idea of where you want to be. Even if you’ve done that it might be worthwhile to shoot a couple of photos with an extremely high ISO and short exposure times to get an idea of your composition.

photograph a moonbow

Aperture and focus

Once you’re happy with your composition it’s time to dig into your camera settings. It’s important to open up your aperture as wide as possible (low F value, for example F2.8) so that enough light will get into your camera.

To end up with a sharp image of the lunar rainbow it’s important to set your focus on ‘infinity’, often represented with this ∞ symbol on your lens. Since it can happen that infinity isn’t really infinity here’s a little trick to accomplish an infinity focus:
– Select live view on your camera
– Zoom in on a distant and bright object (a star for example) using digital zoom.
– Focus on this bright object (either automatic or manual) and set your lens to manual focus
– Now you’re focussed on ‘infinity’. Be careful not to touch the focus ring anymore otherwise you’ll have to repeat these steps.

Exposure

Next to your aperture your exposure is equally important. The higher the ISO value the more noise your image will have. Be sure to check at what ISO the noise in your image is still acceptable.

However, the higher the ISO the shorter your exposure can be. Turn your camera on the bulb setting (so that you can expose your shot how long you want to do so) grab your remote and start your shot.

While the settings are different every single night you can take the following settings a starting point:

ISO 100:

  • 3 minutes at f/2.8;
  • 6 minutes at f/4

ISO 200:

  • 1,5 minute at f/2.8;
  • 3 minutes at f/4;
  • 6 minutes at f/5.6

ISO 400:

  • 1 minute at f/2.8;
  • 90 seconds at f/4;
  • 3 minutes at f/5.6;
  • 6 minutes at f/8

The longer you expose your photo the more likely it is that your rainbow will shift while taking the photo. It also means that you’ll get star trails instead of a crisp starry night.

photograph a moonbow

One last tip: Use your histogram

While it’s tempting to just look at your camera’s screen to see if the photo is good enough it doesn’t say that much in the middle of the night. It can look quite good but once you’re back home you find out that the image is underexposed and too dark. Therefore always use your histogram! It should ‘lean’ as much to the right as possible without touching the right border of the histogram. If it’s too light you can always edit it while post-processing your photo.

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