April 20, 2010................................................................................HOME.................................................................."Star Light, Star Bright..."
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Technical details
Nikon D3s
Nikkor 14-24mm F 2.8 lens
ISO 3200, Long Exposure Noise Reduction
20 second exposure @ F 2.8
Really Right Stuff BH-40 Ball Head
Velbon El Carmagne tripod legs
Photoshop CS 4
Nikon D3s
Nikkor 14-24mm F 2.8 lens
ISO 3200, Long Exposure Noise Reduction
20 second exposure @ F 2.8
Really Right Stuff BH-40 Ball Head
Velbon El Carmagne tripod legs
Photoshop CS 4
What better way to open a photography blog about taking photos of the night sky than a “wish” from our childhood. But rather than wish for a great photograph, let’s talk about making one instead!
I’m just back from my fourth trip to Death Valley National Park. if you’d asked me before my first visit how many times I’d go back, I’d likely have tilted my head and looked back with some confusion. Death Valley? All that’s there is HEAT and a lot of nothing, right? Wrong. Dead wrong (couldn’t pass that up).
The first two times I went I was all about photographs between sunrise and just after sunset. But before my trip in 2009 a friend had begun writing me about his recent interest in astronomy. He had turned his passion for photography in that direction and was excited. It made me consider the potential for Death Valley in a whole new light... darkness.
Prior to leaving for the trip I decided to do a little research. There is no shortage of information about night sky photography on the internet. I was able to download a trial version of a software program that previews the night sky at any hour on any date. Knowing the day and optimal early morning hour with the most potential made it a little easier to force myself out of bed at 3:00 am. While the advice of others about suggested exposure provided a starting point, I discovered that like promises of gas mileage, “your results may vary.” With a little trial and error, one exposure adjustment led to another and things got interesting. I shot for about 45 minutes and at the tail end was very glad I had swung my feet over the edge of the bed and headed out the door.
I’m hoping somebody out there besides me said, “Wow!” when they looked at this image. That’s what came out of my mouth when I saw it come up on the LCD in the dark. While the basic premise is (a) put the camera on a tripod, (b) crank up the ISO, and (c) make a long exposure, there are a few considerations that will make your foray into the dark a little smoother. Although far from an expert in this area, here are my thoughts about how I made this shot.
Location: As much as I’d like to say “head for Death Valley!”, you don’t need to go that far. But you do need to get well away from the light pollution typical of even small towns, much less large urban centers. You need a really black, clear sky. Check the weather in advance.
Timing: Like everything else “out there” in space, viewing the milky way means waiting for it to “rise”. The software program I referenced was StarGazer v4.5 from Carina Software ( http://www.carinasoft.com/ ). The program lets you adjust a clock on a specific date, facing any compass heading and preview what will be visible. You could just get up and check things out but unless you’re a real night owl, you might appreciate the extra sack time a little planning will provide.
Equipment: High end equipment is not absolutely required, but better is better. While the earth’s rotation seems slow as you stand and gaze up, in fact the earth is hauling ass. 1000 miles per hour. That means the stars aren’t really very still, at least your camera won’t think so during a long exposure. Let’s consider focal length of lens first. For my shot I wanted a dramatic sky full of stars and a nice wide swath of milky way galaxy. That meant a wide angle lens. As it happens using a wide angle also helps minimize the perception of star movement during the long exposure. If you use a longer lens, the movement of the star due to the earth’s rotation will be more obvious because of the magnification. Astronomers and serious celestial photographers use a sophisticated, motorized camera mount to move the camera in perfect synchrony with the apparent star movement so everything stays "still". We need to work around this consideration and make good compromises. You’ll find all sorts of different shutter speed recommendations out there. Remember that shutter speed is only 1/3 of the equation. Aperture and ISO are the other variables. A wide open aperture will help you “quickly” collect the photons you need. (Stop and think about how long the photons have been traveling through space to arrive inside your camera. Light from many of the stars you are photographing took hundreds of thousands of years to get here. When you open your shutter they collide with your sensor and their energy is converted into your photograph. If you weren’t there, their journey would just end in the darkness, so your photo memorializes a remarkable phenomenon) A high ISO will be needed to amplify the signal of these relatively weak photons. Full frame sensor cameras excel at minimizing noise in the dark sky because their pixels are larger and so each can collect more photons. The current champion for high ISO file quality is the Nikon D3s. You can still get excellent results with a D300, and files from earlier digital cameras or compact cameras can be processed with noise reduction software to yield good images too.
Settings: I will give you those I found useful using my D3s and the Nikon 14-24mm f2.8 lens. I shot at ISO 3200, f 2.8 for 20 seconds. Even at 20 seconds when you zoom in at 100% magnification you begin to see very early star movement. While a longer exposure will give a brighter result, it also will create more star movement which I found unacceptable. A processing technique in Photoshop ( see below ) can enhance brightness of the stars, so you can produce a sharper star capture with a shorter exposure. Experimentation is the catchword here ( “your mileage may vary” ). One other setting on your Nikon is useful: Long Exposure Noise Reduction. Noise is an artifact of high ISO, especially accentuated in long exposures. The Nikon long exposure noise reduction technique uses an elegant approach to minimizing this artifact. You take a long exposure. As soon as the exposure ends, the camera takes another “exposure“ of the same duration but with the shutter closed. Any color noise generated in this shutter closed exposure is the artifact that should not be in your picture. Before recording your file, the camera subtracts each pixel of artifact color from your photograph. As you stop and think about what is happening inside your camera and the 12 million pixels being evaluated and manipulated, it is simply staggering. This is why your camera seems to be working slowly when this feature is enabled. The exposure takes twice as long because of the blank exposure and processing.
Final details: You won’t think about this in advance, which is why I mentioning it. Focusing in total darkness is harder than hell. You’d think, well just twist the lens to infinity and bang away. That will get you close but if you’re striving for the excellence (and we all are aren’t we?) you want precise infinity focus. My suggestion is this. At the end of daylight, when you’re planning your night shoot, focus on something at infinity and then turn off autofocus on the lens, and/or turn on manual focus on the camera body. Put your camera on the tripod to minimize handling which might bump the focusing ring. You might consider using Live View on your Nikon and even more accurately fine tune the infinity focus point. As for looking at camera settings when you’re out in the dark, don’t forget your Nikon has an LCD illumination function to light things up. It is built into the On-Off switch surrounding the shutter button. Just push the switch past On as far as it will go. The light will illuminate for a brief time and shut off automatically. Another useful idea is to carry a tiny flashlight. Not something big and bright. Bright will affect your night vision after your eyes have adjusted to the near total darkness. Some flashlights come with colored lenses you can snap on the front for effect. Using the red filter will provide red light which does not affect your night vision at all, but still provides usable illumination to adjust camera controls.
Post Processing: Pick your shot and then open in Photoshop. Duplicate the background layer once or twice, then change the blend mode of each additional layer to ”screen“. Adjust layer opacity to taste for overall brightness. Adding a contrast adjustment layer is also desirable for snapping up the contrast and making the black area of the sky darker while retaining the brightness in the stars and milky way clouds.
Whew! See how easy it is to take a simple picture of some stars! LOL
The first time you may feel a little clumsy. Each time you venture out it gets easier and your results will improve. Next time I’m going to work on ”light painting“ a foreground subject for even greater drama. Isn’t photography interesting! Enjoy.
PS ... Someone is thinking, ”That orange glow from behind the mountains... I thought he was away from cities and light pollution...“ That glow is called zodiacal light. It is light from the sun (still well below the horizon) that goes out into space and is reflected back off ”space dust“. It wasn't even visible to my eye during the shoot, but it registered in the long exposure. True sunrise was still a couple of hours away.
Mark Alberhasky is a Nikon Mentor for the Mentor Series Worldwide Photo Treks.
Join him as he travels and share his enthusiasm for photography and learning.
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