Tips for Photographing Lunar Rainbows

Half Dome and Upper Yosemite Fall with a lunar rainbow
Half Dome and Upper Yosemite Fall with a lunar rainbow

 

In Friday’s post on my other blog I described some of my experiences attempting to photograph lunar rainbows, but here are some tips for capturing your own moonbow images.

The moon will become full at 5:19 Wednesday morning, so Tuesday night will provide the brightest moonlight, and the best chance to photograph a lunar rainbow this month—if the weather cooperates. Unfortunately the forecast calls for rain. If the predictions are faulty, and some moonlight manages to break through the clouds, cool temperatures will probably limit the amount of spray on Upper Yosemite Fall, so Lower Yosemite Fall may work better. For the upper fall, you might be better off waiting for the next full moon on May 27th. For detailed information on times and places to photograph lunar rainbows in Yosemite, see Don Olson’s site.

For those who aspire to capture lunar rainbows, here are some tips.

Equipment

Any digital SLR will work, but full-frame sensors usually produce less noise and work better for the long exposures required at night. A sturdy tripod is essential, plus a locking cable release or electronic release. You’ll want a good flashlight or headlamp, a watch to time long exposures, and a cloth for wiping spray off the lens if you’re at the lower fall. Long exposures drain batteries quickly, so make sure your camera battery is fully charged—and your spare too.

Focus and Depth of Field

To make exposure times reasonably short, you’ll have to keep your aperture wide open, or close to it. That means you won’t get much depth of field, so try to exclude foregrounds from your compositions. This shallow depth of field makes focusing critical. It’s obviously difficult to focus manually in the dark, and autofocus won’t work either. In the past I’d just manually set the lens at infinity, but many lenses now focus past infinity, making the correct focusing point difficult to determine. The solution is to find something distant that’s bright enough to focus on, like the moon itself, car headlights, or perhaps a bright light that you place far away. Then focus on that bright spot, using either manual or autofocus. The most precise method is probably focusing manually during a zoomed-in look in live view. Once you’ve set the focus, turn autofocus off and don’t touch the focusing ring—leave the lens set at this distance for all your images. You might even tape the focusing ring so it doesn’t move.

Exposure

It’s tempting to push up the ISO and make your exposure times shorter, but you’ll get less noise with longer exposures at lower ISOs. Ideally you’d like to use your camera’s native ISO, which for Canons is 100, and most Nikons is 200. Since light meters don’t work under such low light levels, here are some recommended exposure times. You’ll have to set the camera on Bulb and use a locking cable release.

ISO 100: 3 minutes at f/2.8; 6 minutes at f/4

ISO 200: 90 seconds at f/2.8; 3 minutes at f/4; 6 minutes at f/5.6

ISO 400: 45 seconds at f/2.8; 90 seconds at f/4; 3 minutes at f/5.6; 6 minutes at f/8

I don’t recommend exposures longer than six minutes, as the rainbow will move while the shutter is open and the bands of color will blur together. On the other hand, most lenses are not very sharp at their widest aperture. So if your maximum aperture is f/2.8, I’d recommend stopping down to f/4; if your maximum aperture is f/4 I’d recommend stopping down to f/5.6—if you can do so without making the exposure too long, or pushing the ISO too high. There are always tradeoffs in photography. If your lens’ widest aperture is f/4 on a Canon camera, you could keep the ISO at 100 and expose for six minutes at f/4, or push the ISO to 200 and expose for six minutes at f/5.6. You’ll get better lens resolution at f/5.6, especially in the corners, but you’ll get more noise at the higher ISO. I’d try it both ways, and see if noise reduction software can cure your problems with the ISO 200 capture.

If you want pinpoint stars in the sky, rather than star streaks or trails, you’ll have to use shorter exposures and push the ISO up even higher. You’ll want to keep the exposures down to 30 seconds or less with a wide-angle lens, and 15 seconds or less with a normal or telephoto lens. With a wide-angle, try 20 seconds at f/4 and 1600 ISO. The photograph will be noisy, but with many cameras the noise won’t be too objectionable.

Many digital SLRs have a “long exposure noise reduction” option buried somewhere in their menus. With this on, after finishing a long exposure the camera will take another exposure of the same length with the shutter closed—a black image—then compare the two captures and try to subtract the noise out of the first one. Since it’s actually making two exposures, it takes twice as long to capture one frame. On my camera (Canon 1Ds Mark II) the noise reduction has no visible effect, so I leave it off. But I’ve heard that it may help on other models. The only way to know is to test your camera with this option turned on and off, and compare the results. I’d at least recommend keeping it off initially, while you test exposure times, then you might turn it on once you have everything set.

If you’re good at exposure calculations you can boost the ISO initially to shorten exposure times for some test shots. For example, try 20 seconds at f/4 with 1600 ISO. If this looks okay, then this is the equivalent of 6 minutes at f/4 and 100 ISO, so you can then try the longer exposure at the lower ISO with confidence that it’s correct.

When judging exposures, don’t rely on the appearance of your camera’s LCD screen. At night even a severely underexposed photograph will look much brighter on screen than the surroundings, fooling you into thinking that you’ve made correct exposure when it’s actually way off. Use the histogram! For most moonlight photographs, the histogram should be pushed as far to the right as possible without touching the right edge—that is, the image should be as light as you can make without overexposing anything. This will give you the most noise-free capture. You can, and probably should, darken the image later in software to create more of a nighttime feeling.

Unprocessed Raw file of a lunar rainbow photograph

Here’s the unprocessed Raw file of a photograph that I made last year. It looks too light for a nighttime image, but it’s noise-free.

Here’s its histogram. Note that the brightest pixels are near, but not touching, the right edge—ideal for most nighttime captures.

If the histogram is pushed over to the left, like this, the photograph is too dark. Make a longer exposure.

Here’s the final processed image. I darkened it overall, then lowered the sky values even further, to make it look more like a night scene.

 

Tags: , , , , , ,

15 Responses to “Tips for Photographing Lunar Rainbows”

  1. Ben says:

    Michael, I recently returned from Yosemite, and along with some great dogwood shots, I attempted some full moon star trail shots. Do you have a tutorial online somewhere that speaks about this process? My main struggle was sharpness. I have two great shots, but there are both slightly blurry, more blurry than accecptable. Focusing to infinity did not work for me. Perhaps a blog on star trails sometime? :) Just a suggestion – thank you!

  2. Michael Frye says:

    Ben, I don’t have a tutorial specifically about star trails, but the suggestions in this post about focusing apply to any night photos.

  3. [...] All this happens at just the right time for people hoping to photograph the lunar rainbow during the upcoming full moon. Once again, here’s a link to Don Olson’s site with his predictions for when the moonbow will be visible from the bridge below Lower Yosemite Fall, and from Cook’s Meadow. Note that the lower fall will probably be much too wet for photography—it will be impossible to keep spray off the lens. Also, here’s a link to one of my previous posts with tips for photographing this event. [...]

  4. Patti says:

    You didn’t just get a lunar rainbow. You got a double lunar rainbow!! You’re awesome!!

  5. [...] Posts: Photo Critique Series: Star Trails and Cathedral Peak by Rick Whitacre; Tips For Photographing Lunar Rainbows Michael Frye is a professional photographer specializing in landscapes and nature. He is the [...]

  6. [...] Related Posts: Photo Critique Series: Star Trails and Cathedral Peak by Rick Whitacre; Tips For Photographing Lunar Rainbows [...]

  7. [...] focusing, and general suggestions about equipment and techniques for night photography, see this earlier post about  photographing lunar [...]

  8. [...] aperture should you use, and how long should you keep the shutter open? Here’s a link to a previous post with answers to all these [...]

  9. [...] Whether you’re an experienced night photographer or a beginner, I recommend reading Lance Keimig and Scott Martin’s excellent book Night Photography: Finding Your Way in the Dark. Also, you can find tips about focus and exposure for moonlit landscapes in my post about photographing lunar rainbows. [...]

  10. [...] be in Yosemite trying to do just that. If you’re one of those people, last year I wrote some lunar rainbow photography tips that you might find [...]

  11. [...] Thanks to Jim Goldstein and the folks at Borrowlenses for their help! And for more information about night photography techniques read this article about photographing lunar rainbows. [...]

  12. […] on photographing moonrises and moonsets, I’ve also written about photographing by moonlight. Tips for Photographing Lunar Rainbows delves into the specifics of moonlight photography: camera settings, shutter speeds, and how to […]

  13. David M says:

    Here’s the unprocessed Raw file of a photograph that I made last year. It looks too light for a nighttime image, but it’s noise-free
    I pulled the above from you notes above. Is the comment you made of the “noise free” shot coming from observations of the histogram or from the picture itself?
    Love your subject and love your work!
    David M

  14. Benjamin says:

    Though the federal law requiring court oversight in the particular proceedings helps protect you,
    it and delays you from receiving the money as soon as you might
    haave hoped. The Annuity is decided depending on the nature of injury, time normally taken to fully recover, type of immobility of the
    victim, the status of the victim, etc. Payment streams purchased through Pattriot offger higher rates
    of return than otherwise available from banks, treasury bonds or other
    fixed income investments.

    Also visit my page; Structured Settlement Cash Now Company;Benjamin,

Leave a Reply

Notify me of followup comments via e-mail. You can also subscribe without commenting.