Back in January of 2010 I published a blog post titled.
Ten Tips for Exciting Nighttime Photography
Now, I don’t profess to be an expert on nighttime photography. But the month of October provided a number of great opportunities to do some night shooting with some people who know what they are doing. October started off with a trip to Grand Portage in Northern Minnesota near the Canadian border. There I shot with Travis Novitsky and my brother Roger Nordstrom. Both are experienced at shooting star trails. And my friend Wally Pacholka is world renown for his astrophotography. And while I haven’t had the pleasure of photographing with Wally I figure during the associations I’ve had with him something must have rubbed off.
I’ve put together some thoughts on nighttime photography that I’d like to share with you.
There are two kinds of nighttime photography, at least the kind done with digital cameras. First is star trails, something we all have seen and perhaps tried at some point. The other is astrophotography where we attempt to capture the wonders of the sky as we see it. I’d like to propose a technique here that combines the two and gives you the best of both worlds.
Please Note
Before getting in to this technique, let me point out that the masters like Wally use digital cameras that are specifically adapted to astrophotography. This involves monkeying with the filters on top of the camera’s sensor. I haven’t taken the time to fully research this topic. I do know that there are companies out there that will do the modification for you. You can search for them on Google. Such modifications are one way streets however. Once done you cannot return the camera to its original condition.
Nighttime Shooting with an Unmodified DSLR
OK, so let’s assume we’re going to use our unmodified digital SLR to do some night shooting. I’m going to describe a technique for capturing night sky photographs and then extend the technique for doing star trails.
To capture a night sky photograph you must effectively stop the stars in their tracks. Now, that’s impossible. No matter what you do the stars just keep on moving. So the trick is to use a shutter speed that is long enough to capture enough light to see the starts but short enough so that their movement is so slight that it appears they haven’t moved.
Exposure Length
If you think about it you will quickly realize that if you use a telephoto lens the star movement will be much more apparent than if you had used a wide angle lens. So to stop the stars in their tracks with a telephoto lens you will need a much shorter exposure time than you would need with a wide angle lens. Now, there is a simple formula to calculate the exposure length based on focal length. It’s 600/focal length. So if you shoot with a 100mm lens your exposure would have to be no more than 600/100 = 6 sec. If you shoot with a 20mm lens then your exposure length can be 600/20 = 30 sec. So for that and other reasons most night sky photography is done with a wide angle lens.
Aperture
For night sky photography you want to capture as much light as you can. So you’ll be shooting wide open. Obviously f/2.8 lenses have an advantage over f/4 lenses. The problem with shooting wide open is you have a shallow depth of field. Now, the starts are at infinity but how do you focus on them in the dark?
Focus
Clearly, autofocus will not work. There’s not enough light for the camera’s autofocus sensors to work. If there’s a moon in the sky you can focus on that. Set your lenses focal length, put the lens on manual focus, point toward the moon and adjust the focus ring until it’s in focus.
If there’s no moon but a nearby object 100 feet or more away, and if you have a bright flashlight (for light painting maybe?) you can focus on that object. At 20mm or so 100 feet is the same as infinity.
If you don’t have any object to focus on adjust the focus ring so it’s just shy of infinity and take a test shot. View the results on your LCD and zoom in to see if the stars are sharp. If not, make and adjustment and repeat the process until your stars are tack sharp.
ISO
You’re going to need to use very high ISOs for this. OK, I can hear you groaning now. What about noise!? Well, the answer is simple. If you want the shot you have to use a high ISO. The thing that surprised me was that with a little testing I was able to determine that I didn’t need to use my camera’s highest ISO (which is 3200). I was able to get good exposures at 1600.
The moral here is test. Take test shots at different ISOs to determine the lowest ISO you can get away with and still capture all of the stars.
High ISO Noise Reduction
Speaking of noise, your camera probably comes with a High ISO Noise Reduction setting. Turn it OFF. You think I’m crazy, don’t you. You need to turn it off because if you don’t the camera will take as long to process the image as your exposure was. What I’m trying to say if you take a 30 second exposure the camera will process the image for another 30 seconds, during which time you won’t be able to take any more exposures. This will have a huge impact when we get to the topic of star trails below.
So what do you do about all that noise? Simple. Slam the Luminance Noise adjustment in Lightroom to 100 and be done with it.
Composition
Composition is an interesting challenge when you can’t see anything through the viewfinder and live view is useless. Again, you need to take test shots and review them on your LCD to know which adjustments to make to get your composition down.
Light Painting
One of the things that’s really fun with night sky photography is light painting. For this you will need a very bright flashlight. I picked up a small model with 125 lumens of output. It works for relatively nearby objects – 100 feet or so. If you want to light paint more distant objects you’ll need one of those mega-powerful spotlights.
Light painting is an art mastered through trial and error. So, again, keep on testing till you get the results you want.
Star Trails
So far all this talk has been about night sky photography. But what if you want to do star trails? Well, I have a suggestion. Many star trails photographers are taking many smaller exposures instead of one long exposure. That way if the battery runs out of juice you haven’t wasted the whole evening.
There are several techniques for this approach. One is to use an intervalometer that will fire off exposures of a predetermined exposure length for a predetermined period of time. For example, you can set the intervalometer for 2 minute exposures and run it for 90 minutes. (You need to set your camera’s mode to Bulb.) To make this work you need to add a 1 second gap between exposures. When you are done you stack all the files together into one magnificent star trail photograph. With 2 minute exposures you can reduce the ISO even more from the 30 second exposures we’ve talked about up till now. And perhaps you can even reduce your aperture to add a little depth of field.
In addition to offering protection against the battery running out of juice, this technique also gives you the option of selecting just one photograph should a shooting star come streaking through.
The problem is with the 1 second delay between images. Believe it or not, when the files are stacked together this one second delay is noticeable. There are software solutions that address this. I’m not familiar with them because I use a different star trails technique that avoids this problem.
My Star Trails Technique
There’s another way to make star trails from multiple exposures. Your camera has a maximum 30 second exposure length. You can use that and a wide angle lens of 20mm or wider to shot your star trails (actually a 24mm lens won’t make enough of a difference to worry about.) This amounts to taking a series of night sky photographs and stacking them together. You’re back to the higher ISOs but we’ve addressed that issue with the Luminance Noise adjustment in Lightroom.
So, get your ISO, focus and composition dialed in. Also practice a little light painting if you want (that comes in later). Set your exposure mode on Manual and dial in 30 sec at your widest lens aperture. Put your drive on Continuous shooting mode – high if you have a fast and slow setting. Now, with your remote control, lock down the shutter and sit back for 30, 45, 60, 90 minutes or whatever. The camera will take 30 second exposures for as long as you keep the shutter locked down.
This is a great time to lay back, point your head to the heavens, talk with friends and perhaps even listen to classical music (quietly of course). I set timer on my iPhone to tell me when the desired length of time is up.
Now, here’s the cool part. When you have total exposure length you want (45 minutes, 90 minutes, whatever) keep the camera going for just a few more exposures and do some light painting. You will be able to stack one of these light painting images on the star trail images for a truly magical effect.
Other Considerations
Here are a few other things to take into consideration.
Regardless of which technique you are using for nighttime photography, make sure you start with a fresh battery. The normally cold temperatures will decrease your battery life significantly so don’t be caught in a situation where your battery runs out after a half an hour of shooting.
Make sure you have plenty of storage if you’re going to use the multiple exposure technique. you don’t want your memory card filling up half way through the shoot.
As a reminder, turn off High ISO Noise Reduction. Otherwise your camera will delay the next exposure while it processes the one it just took.
Set you white balance to a manual setting. Daylight works as well as any. You just don’t want it changing during the exposures.
Lens fogging can be a problem at night, especially if there is a bit of humidity in the air. One way to deal with this is to wrap a hand warmer around your lens and hold it in place with a cut off sock or something. This will keep the lens warm and the fog away.
Stacking Your Files
If you use the multiple exposure approach to shooting star trails you need a good way to stack them. You can import them one at a time into Photoshop, stack them as layers and set the blending mode to Lighten. But that’s way too hard.
There is good software help with this.
I like StarStaX. It’s fee, fast, flexible and available at http://www.starstax.net/ It runs on PC, Mac and Linux.
Another popular program is StarTrails. It is free, works on PC and is available at http://www.startrails.de/html/software.html.
There’s even a free Photoshop action that does the stacking for you. It is called Photoshop Stacking Action. It is found at http://www.schursastrophotography.com/software/photoshop/startrails.html.
You can read about each of these solutions on their respective websites. They all work well.
Summing It Up
Nighttime photography can be a lot of fun. And the photos that result are always a joy to create and share. There are many techniques that those of use without specially modified cameras can enjoy. I’ve shared with you the technique I find to be the most flexible and rewarding.
Let’s hear from you. What experiences have you had with nighttime photography? What techniques have you used and how happy are you with them? Also, if you don’t mind, perhaps you can share some of your photos with us.
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