Lunar Rainbows and the Milky Way
There will be a full moon this Saturday, and I’m sure many photographers will be heading to Yosemite to photograph the lunar rainbow. Astronomer and “Celestial Sleuth” Don Olson has updated his website to include predictions for when the moonbow will appear on Upper Yosemite Fall from Cook’s Meadow, in addition to his previous predictions for Lower Yosemite Fall.
I think there should be enough spray to make the rainbow visible on Upper Yosemite Fall this month, but probably not in June, when there will be less spray. The Lower Yosemite Fall bridge might work in June, because you don’t need as much water to see a rainbow from that spot, but I expect the bridge will be rather wet this month, which will make it hard to keep spray off the front of your lens. Of course the weather always plays a role, and there are showers in the forecast for this Friday and Saturday nights, so the moonlight might get blocked by clouds. But if you want to try your hand at either location, here are some tips for photographing lunar rainbows.
This is also the beginning of Milky Way season here in the northern hemisphere. The brightest part of the Milky Way can now be seen rising just after 10:30 p.m. here in central California, and will be visible in the evening sky through September.
The Number One Problem in Night Photography
With all of these upcoming opportunities, I thought this might be a good time to address one of the most difficult aspects of night photography: focusing in the dark.
First, just turning the focusing ring to infinity doesn’t work. Most modern lenses are designed to focus past infinity, so you can’t just turn the ring all the way until it stops and hope for the best, or you’ll get fuzzy pictures. Also, with modern ED or fluorite glass, focus varies with the temperature, so you have to find the right focusing point anew every time you go out to photograph the night sky. And because you’re usually using wide apertures at night, the depth of field is quite shallow, and any slight focusing error will make the photographs look soft.
You could try autofocus, as most cameras should be able to autofocus on the moon, and some might be able to autofocus on a bright star. After you’ve acquired focus, make sure you turn autofocus off, otherwise the camera will refocus, or hunt for something to focus on, when you press the shutter (unless you’re using back-button focus). And if you’re using a zoom, you need to refocus every time you zoom in or out, because the focus may shift slightly. (That applies to any situation, day or night, when using a zoom lens.)
But many times you can’t find a star that’s bright enough to use autofocus on. And even if it works, your autofocus has to be perfectly calibrated, as, again, any slight focusing error will make the image soft. (This isn’t an issue with mirrorless cameras, but mis-calibrated autofocus is a common problem with SLRs. Most SLRs have an autofocus micro-adjustment option.)
Focusing in Live View
The most consistently accurate method of focusing at night – the one I’ve used for many years – has been to use manual focus, and zoom in on a star in live view. First, in order to see the brightest live-view image possible, set your lens to its widest aperture (lowest f-stop number), push the ISO way up (at least to 3200), and set a long exposure (at least 15 seconds). Also, make sure your lens is pre-focused somewhere near the infinity mark, otherwise everything will be so blurred you won’t be able to see any stars.
Then switch to live view, find a bright star, and magnify the view to zoom in on the star. It will help if you don’t zoom in too far at first. Zoom in a little bit, find the star, center it, zoom in more, and repeat. When the star gets big enough to see the focus clearly, adjust your focusing ring until the star looks sharp. Try to make the star look as small as possible – like a pinpoint, not a blob.
This technique works better with fast lenses (that is, lenses with wide maximum apertures); the more light the lens lets in, the brighter your view, and the easier it is to focus. It also works better on some cameras than others – typically very well on Canons and Sonys, and not as well with Nikons. Canons and Sonys can transmit a live view image at lower light levels than Nikons, which makes it considerably easier to focus and compose at night in live view. I’ve been able to use this technique with Nikons, but it’s challenging. You need a fast lens and a very bright star, and even when you find such a star it can be hard to tell when it’s in focus.
If you can’t find a bright enough star to focus on, look for another light source, like distant streetlights, lit buildings, or the moon. Or you can try shining a flashlight on a tree or rock. With the wide-angle lenses typically used for night photography, a tree that’s 50 feet away will be at infinity, so if the tree is in focus the stars will be too. You could even walk out 50 feet or more from the camera and set a flashlight down on a rock, pointed back at the camera, and then focus on the flashlight.
But even zoomed in with live view, many people have trouble telling exactly when the star (or tree) is in focus. I’ve had a lot of practice with this technique, yet I still sometimes miss the focus slightly.
I recently learned about a product that attempts to solve this problem called SharpStar2, by Lonely Speck. I’ve had a chance to test SharpStar2 pretty thoroughly, and it works very well. It takes some practice to use it properly, and it doesn’t work under all conditions, but it works most of the time, and when it does it removes any doubt about whether the focus is accurate.
SharpStar2 slides into a filter holder (like a Cokin P-Series holder, or a Lee holder). SharpStar2 uses a Bahtinov Mask to create three fine spike lines around a star. The idea is to adjust the focus until the middle line is centered between the other two. Here’s what that looks like:
As I said, it takes a bit of practice, so here are some tips for using SharpStar2:
The more contrast between the star and the surrounding sky the better. That means SharpStar2 works best with a bright star and dark skies. It can work on moonlit nights, but usually only with the very brightest stars. On dark nights it can work with moderately-bright stars – at least with some cameras.
If you can’t see the spikes clearly in live view you can focus as best you can and take a photo with SharpStar on to confirm focus (this requires a filter holder). If you don’t get the focus right the first time it could take some trial and error to get it right, but eventually you should be able to nail the focus.
I also found that I could focus with SharpStar2 even when I couldn’t see the spikes. The star itself becomes a slightly-elongated oval when it’s in focus. But it takes some practice to focus this way!
You can also focus on off-center stars with SharpStar2, but this also requires some practice. With off-center stars, turn the focusing ring until you see a single, elongated spike, like this:
Ian Norman, the developer of SharpStar, told me that any point light source will work – it doesn’t have to be a star. In fact he said that he used a laser pointer when doing his initial testing. That got me thinking. On moonlit nights, or times when there are no bright stars visible, what about using a laser?
Rick Whitacre recommended this green laser to me, so I ordered one. When it finally arrived I tested it with SharpStar, and it worked very well. You just point the laser at something more than 50 feet away (again, that should be far enough to get infinity focus with wide-angle lenses), put the laser dot in the center of the lens, and adjust the focusing ring until the middle spike is centered between the other two. Here’s what it looked like in my test (the spikes don’t look that crisp here because I couldn’t hold the laser perfectly still for 15 seconds when making this exposure, but the spikes were very clear in live view):
The hardest part about using the laser is holding it steady while you adjust the focus. I just brace it against my tripod. But the laser makes it possible to focus accurately in any situation, even when there are no bright stars visible – or no stars at all. And you can do so without turning on a bright flashlight, which will ruin your night vision and annoy nearby photographers!
I don’t know if this laser-focusing technique will work with Nikon cameras. I hope so, because it might provide the best option for focusing at night with Nikons. If any of you Nikon users get a chance to try this, please let me know.
There are no simple, foolproof options for focusing in the dark. But SharpStar2 is the best tool I’ve found so far, and it’s earned a permanent place in my camera bag. And just to be clear, I didn’t get paid to say this, nor do I make any commissions on SharpStar2 sales. Lonely Speck did give me a free copy to try out, but with no obligation to say anything positive about it – or to say anything at all. I just think it might be helpful to those of you who do night photography. If any of you have tried SharpStar2 please post a comment and let us know how it worked for you.
— Michael Frye
Michael Frye is a professional photographer specializing in landscapes and nature. He is the author or principal photographer of The Photographer’s Guide to Yosemite, Yosemite Meditations, Yosemite Meditations for Women, Yosemite Meditations for Adventurers, and Digital Landscape Photography: In the Footsteps of Ansel Adams and the Great Masters. He has also written three eBooks: Light & Land: Landscapes in the Digital Darkroom, Exposure for Outdoor Photography, and Landscapes in Lightroom: The Essential Step-by-Step Guide. Michael has written numerous magazine articles on the art and technique of photography, and his images have been published in over thirty countries around the world. Michael has lived either in or near Yosemite National Park since 1983, currently residing just outside the park in Mariposa, California.