*A quick note before we begin: I teach these techniques as well as many, many others in my night-sky photography workshops. For more information, check ’em out here: http://www.bencoffmanphotography.com/star-photography-workshops-and-lessons/*
My last blog on focusing in the dark was kind of a primer, so now we’re going to dive into something a little more advanced. So unbuckle your camera bag, extend your tripod legs, and hang on tight—we’re about to dive into (insert echochamber voice) HYPERFOCAL DISTANCES…Distances…distances…distances…
To keep this discussion clear, I’d like to define a couple of terms below.
•Landscape astrophotography: Landscape photography that also features one or more elements of the night sky (stars, shooting stars, the moon, aurora borealis).
•Fast lens: A lens with a particularly wide aperture.
•Fixed focal length lens/prime lens: A lens that doesn’t zoom.
•Wide lens: A lens wider than about 28mm or so.
•Native ISO: The ISO at which your camera was designed to take photos. For Canons, this would be ISO 100.
•Shooting wide open: Opening your lens’s aperture as wide as possible (to its lowest f-stop number)
•Stopping down: Narrowing your lens’s aperture
So by now you have a few tools in your metaphorical tool belt, the last tool added being your ability to focus your camera in the dark. Hopefully, by now, finding your focus this way feels natural. Let’s go ahead and assume at this point that you’re a fairly dedicated landscape astrophotographer, which means that you’ve invested in a wide and fast prime lens. (I know that I haven’t exactly delved into this topic before, but a wide and fast prime lens is a fairly essential tool for the type of landscape astrophotography in which you “freeze” the movement of the stars in the sky.)
Sharpness is a fairly important aspect of photography, particularly in landscapes in which you’re seeking maximum depth of field (ie, you want everything in your image to be in focus). Your photo has to be sharp if you want to print it large (and who wouldn’t want to do that?). Landscape astrophotography is much the same way, except that sharpness is even more important. Why? Because many landscape astrophotos require high ISOs, and noise reduction is a critical part of post-processing. What happens during noise reduction? Well, sharpness is sacrificed in favor of a “cleaner” or more noise-free image.
Whereas a soft photo at a camera’s native ISO can be sharpened to make it more acceptable, sharpening a high-ISO image (like in landscape astrophotography) only adds to the noise in an already noisy image. In short, you don’t want to do it. (I’ll delve more into post-processing techniques for my landscape astrophotography some other time.)
So sharpness is critically important, and that means getting it right in the field since we may not be able to sharpen it up much in post. If you only want the stars for your image to be in focus and don’t care about your foreground, that’s a fairly easy scenario: just focus on the stars. But that’s not exactly landscape astrophotography, is it?
So we’re going to create a make-believe scenario, and in this make-believe scenario, you’ve discovered, while hiking, the most awesome tree ever, miles away from anywhere, and it’s begging you to take its picture beneath the starry night sky. Further, you’ve decided that in order to make the most effective composition, you need for both the tree (with its super cool gnarly trunk and twisted branches) and the stars above to be in focus.
If you use the ol’ landscape photography rule of thumb “focus one-third of the way into your scene,” you might get a little confused—after all, what’s one-third of the way into your scene when the background is millions of miles away? Using this rule, you might find that your stars are in focus, but the Most Awesome Tree Ever is still out of focus. Worse yet, the Most Awesome Tree Ever (henceforth: MATE) might look like it’s in focus on the back of your camera, and you might not notice that the MATE is soft until you zoom in at 100% while you’re post-processing at home the next day. But by then you’ve hiked out of the place where the MATE lived, and the notes you made in your hiking journal are gone because you accidentally lit your hiking journal on fire with your camp stove while you were absentmindedly talking to your buddy about whether you’ll make next month’s front cover of both National Geographic and Outdoor Photographer, or just National Geographic. And now you can’t remember where that tree was, exactly.
So where does that leave us? How can we reliably know for sure that everything in the shot will be in focus when we’re so often fooled by the tiny, awesome images on the backs of our cameras? Hyperfocal distances and depth of field calculators.
In the olden days, this might’ve involved pulling out a rather large chart, turning on your flashlight, and cross-referencing a couple of figures—all in the field. Nowadays, there are smart-phone apps that can give you this info in the field. How awesome is that? Let’s all take a moment to pat ourselves on the back for living in the digital age. Of course, whipping out your phone still involves adding an artificial light to the scene, killing your night vision, and, if you’re out shooting with a buddy, creating a light that may or may not end up in someone else’s photo.
So here’s what I do: Since I shoot my night shots with two different fixed focal length lenses at one of two or three apertures, I simply memorize the hyperfocal distance most applicable to my particular situation.
For instance, if I’m out with my full-frame camera and my 14mm lens, I know that if I shoot wide open (f/2.8), I can focus 8 feet in front of me, and everything from about 4 feet in front of me to INFINITY will be in focus. How I do I know that? Check out this handy hyperfocal distance calculator online. Cherish that link. It’s magic.
So let’s say I’m shooting on my Canon t3i (a crop sensor camera) with my kit lens, which has a maximum aperture of f/3.5. If I’m shooting wide open (at f/3.5), I need to focus about 16 feet in front of me to ensure that everything about 8 feet in front of me to infinity is in focus. This means that as long as I place the MATE (remember the MATE?) at least 8 feet away from me, I’m golden. The tree is in focus, the stars are in focus, life is good, and I won all photography forever.
This, my friends, is the magic of hyperfocal distances. If you want to, you can trust the “infinity” symbol on your lens (if your lens even has an infinity symbol), but be warned: your lens’s focus can change with the ambient temperature (if it was even correct to begin with coming from the manufacturer). In a certain temperature, that infinity symbol might be dead on. In a radically different temperature, you might not be in focus. Why risk it?
Personally, I’ve memorized the applicable hyperfocal distances for two of my lenses. I don’t need apps, and I don’t need charts. And the great thing about these principles is that they translate perfectly well to standard, daylight landscape photography too. The only difference is that, when you stop down to an aperture that isn’t wide open (as you hopefully would when not shooting star photos), you 1) bring the near limit of acceptable sharpness even closer and 2) you probably create an even sharper photo, since not all apertures are equal when it comes to sharpness. But I’ll get more into that second part in another blog post…..
Until next time, may the clouds part and the stars shine on, my friends!