<If a rock star can repackage previously released material in a "Greatest Hits" album, I can repost an image from a previous blog because it best conveys today's message. For the story of my capture of this image (and an easier read), check out my March 18 blog.>
"Is that the way it really looked?" (fifth in a continuing series)
I'm asked that question quite frequently, and my response is always an emphatic, "No!" The camera and the eye see the world differently; it's silly for any photographer to claim an image is "exactly the way it looked when I was there." A camera's dynamic range, visual depth, and range of focus (to name a few) are all inferior to the human eye. A good photographer doesn't submit to these limitations, he or she turns them into an advantage. Conversely, there are wonderful things the camera can do that the eye can't. All these differences combine to give the experienced landscape photographer an opportunity to create evocative, artistic images in the camera, with very little post-processing required. Today's post continues an ongoing series expressing my thoughts on using your camera's vision to your photographic advantage (and without having to resort to Photoshop enhancement).
Is this exactly what I saw that night in the White Mountains? (What do you think?) The first four posts in this series deal with the camera's limitations and how to turn them to your advantage. But here's something the camera can do that the human eye can't: Expand time.
While your eyes send your brain a series of consecutive images to connect into a continuous moving picture, the camera can capture all that motion in a single fixed frame, creating effects the eye/brain can't. Holding your camera stationary (on a tripod!) and leaving the shutter open, you can juxtapose sharp fixed objects and blurred moving objects. The most common examples of this are blurred water and star trails.
Blurring water is so popular that some consider it cliché. But sometimes it's impossible to freeze the motion of streams, rivers, and waves in shadow, making blurring the most aesthetically appealing approach. There is no magic formula for blurring water, as the effect varies with shutter speed, subject distance, and focal length. But doing it is fairly straightforward in that, aside from the water's motion, the scene will appear quite similar to the resulting image. Once you get the exposure right, you can play with the other settings (ISO and aperture) to vary the shutter speed. The more you try it (don't be afraid to fail), the more you'll start to identify opportunities when you're in the field, and know how to handle them.
Star trails are a bit trickier, as the long shutter speeds will record a world significantly different than your eye registers. Success requires some understanding of these differences, and of the reciprocity of exposure. It also requires a solid tripod, locking remote release, and a camera that supports bulb mode. (And a warm jacket.)
(And reading about star trail photography exhausts copious brain cells, so if you proceed from here, sit down and hold on tight.)
I've found the star trail compositions that usually work best are silhouettes, like this bristlecone. For a silhouette to succeed, the silhouetted subject needs to stand out against something brighter, like the sky or water (even though the sky looks dark, it is lighter than the foreground, a difference that will be revealed by a long exposure).
The correct exposure varies significantly with factors like the phase of the moon, the time of night (the sky is darkest right around the midpoint between sunset and sunrise), the amount of light polution, the direction you're shooting (even if you can't see it, the western horizon is brighter when sunset is closer than sunrise; the the eastern horizon is brighter when sunrise is closer), and the effect you’re going for. Unfortunately, conventional metering pretty much goes out the window with star trail photography—there simply isn't enough light. Fortunately, digital shooters have a solution….
(Now the fun begins.)
Digital shooters, a test shot will help you determine the exposure settings you'll need. Start by bumping your ISO as high as it will go and opening your aperture to its widest opening (you can even use your fastest lens for this test). Point your camera in the direction of your planned composition and meter--keep adjusting the shutter speed longer until the meter registers, and shoot a test shot (on a tripod, please!). If you don't get any response from your meter, try a one minute exposure
Review your LCD and adjust the exposure (using shutter speed) lighter or darker, continuing to take test exposures until you get one you like (this shouldn't take too many shots)--don't worry about image quality or critical focus for these tests. Once you get the test exposure you want, you can choose the desired shutter speed by reducing the ISO and aperture, counting the stops as you go--remember, halving (or doubling) the ISO subtracts (or adds) one stop of light; the 1-stop f-stop steps are 1.4, 2.0, 2.8, 4.0, 5.6, 8.0, 11.0, 16, 22, ... (it's handy to note that the 1-stop f-stop sequence is just two sequential sets of doubling numbers: 1.4, 2.8, 5.6, 11, 22, ... and 2.0, 4.0, 8.0, 16...).
So if you found 1 minute gave the desired exposure at ISO 3200 and f2.8, and you want 32-minute star trails, you can compute that 32 minutes is 5 stops more light than 1 minute (do the math—getting from 1 to 32 requires doubling 5 times). Armed with this knowledge, you know that reducing the light by any aperture/ISO combination of 5 stops will allow a 32 minute exposure that matches your test exposure. That’s the beauty of photographic reciprocity. In this example, to reduce my light by 5 stops I could drop down to ISO 400 (3 stops less light than 3200) and f8 (2 stops less light than f2.8), or ISO 200 (4 stops less light) and f5.6 (1 stop less light). Both total 5 stops less light, allowing me to reciprocate, adding 5 stops of light by going from 1 minute to 32 minutes.
(Are you still there?)
Now you’re ready to compose (and I’m exhausted). I find it easier to compose and focus off the tripod. Focus is a total pain, usually involving flashlights and lots of guessing. In my exposure settings I usually opt for a higher ISO to allow a smaller aperture, just to allow more depth of field (increasing my margin for error). A shorter focal length (wide angle) also increases your margin for focus error. And if your subject is at infinity, you can sometimes find a distant light (such as headlights or the moon) to autofocus on. Just be sure when you’re ready to shoot that you put your camera in manual focus mode—otherwise it will forever hunt for focus.
And now it’s time to shoot. I’m not going to talk much about in-camera noise reduction (black-frame subtraction) except to say that some photographers use it and some don’t—turning it on (it’s usually buried deep in your menu system) doubles your exposure time by taking a second picture of equal duration with the shutter closed, then subtracting noise it finds in the black frame from the actual frame. In my example, using black-frame subtraction, I’d have to wait another 32 (or so) minutes after my initial exposure while my camera did its processing.
Put your camera on the tripod (stabilizing it with your camera bag or some other weight isn’t a bad idea), adjust the tripod head to position your camera (but don’t change your focal length or you’ll mess up your focus—trust me on this), put your camera in bulb mode (if it isn’t already), click your shutter (if mirror lock-up is set, don’t forget to click a second time to release the shutter), engage your remote lock to hold the shutter open, and check your watch. Now there’s nothing to do but sit back and take in the sky.
Questions? Hey, where'd everybody go?
* Website: Eloquent Images
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