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Sunday, April 3, 2011

How to Make Star-Trail Images with your Digital Camera

First Let us discuss what is a star-trail; in the evening because of the earth’s rotation the stars in the night sky slowly move (from our perspective) in a circular motion around the North Star (Polaris). So a star-trail image is essentially a long exposure ranging from minutes to hours during the night with your camera left pointed at the sky. The stars leave long beautiful streaks across the sky.

Cayo Costa State Park Florida, ISO 200, F5.6, 25min, 17mm

Some things to consider when shooting a Star-Trail Image:

Being able to find the North Star is essential because all the stars move around Polaris. This is important when composing your image because you can end up with a large bulls eye design in your sky or if your shooting more in a southern direction you will get what looks like a rainstorm of falling stars in your image. Any direction you point your camera is OK, but I usually like to keep my North Star off-center for a more interesting image unless something in my foreground strongly suggests a symmetrical composition.

*More often than not anti-symmetry is what you want for an attention-grabbing composition.

So how do you find the North Star? First look for the Big Dipper, which is one of the easiest constellations to find in the night sky. The end of the ladle on the Big Dipper will point you directly to Polaris.

I like to get a free sky map every month from

When and where to shoot a Star-Trail:

· I try to get as far away from city lights as possible, even miles away city lights will show up in your exposure illuminating your horizon.

· Cities also cause “light pollution”. Light pollution is when streetlights and other sources of light keep you from clearly seeing the stars in night sky.

· Elevation is also a factor in seeing the stars; the higher in elevation you are the clearer the night sky.

· If you are near civilization it is also a good idea to wait till after 11pm to start shooting your star-trail because of air traffic. Airplanes will put many a blinky light across your frame.

· Clear nights are good, check the weather forecast.

· Civil Twilight can also be a factor, the hour after Sunset (dusk) and the hour before Sunrise (dawn) are times when there is still light in the sky that can be picked up by your exposure even if it is not visible to you. This can be a positive or a negative. For example, an exposure taken around 1 am will usually give you a dark sky and foreground but an exposure taken closer to dusk or dawn can add some pretty interesting colors to your sky or foreground, essentially adding a little of that colorful sunrise or sunset light to your exposure.

Some Equipment and Camera Settings to consider:

Focal Length of your lens; The wider the better for me when shooting a star-trail and that is because the further away I get from the north star, the farther the stars appear to move in a shorter amount of time, so less time is needed to create that surreal image. If I take a 30 minute exposure; stars closest to the North Star will not appear to travel very far in my image but the further away from it I get the longer the trail of light is on my image.

Exposures can range anywhere from 5 minutes to all night long (depending on battery life) so you will probably need a Shutter Release Cable (or Cable Release). Most cameras are set so that 30 seconds is the longest exposure you can take and after that comes the “bulb” setting. This is the setting you want, it basically means as long as you hold down the button the camera, the camera will take an exposure. But if you’re like me you probably have better things to do than hold that button for and hour without letting go. So getting a good cable release with a shutter lock on it is important. A shutter release cable can range from $10 for the off-brand EBay variety to $100, depending on the bells, whistles and brand. My only recommendation is NOT to buy the wireless versions; they seem like a great idea but often do not have that shutter lock feature that is so important. How else can you walk away from you camera and have some hot cocoa or a nip of Scotch?

*Remember to make sure you camera has that “bulb” feature if you want to shoot star trails.

Tripods are essential and the sturdier the better. These are long exposures and you do not want your camera to move at all, which makes another great argument for the shutter release cable in that it keeps you from touching (and moving) your camera when you press the shutter.

If it is really windy weigh your tripod down. This can be done with a rope, a carbineer and something heavy like a rock or your camera backpack. Tie the rope into one large loop and set it on the outside of each tripod leg, between each tripod leg pull the rope into the center of the tripod and clip it with the carbineer, then set something heavy in the center to weigh down your tripod.

Another thing that I never leave home without when I am shooting a star trail is a hand warmer (that’s right those little pocket sized hand-warmers that hunters use). Often between 3-4 am or on really humid or moist nights you can have a big problem with condensation on the lens. To solve this problem, I take a hand-warmer and wrap it once in a hand towel and wrap that around the barrel of my lens secured with a rubber band. Problem solved, no condensation on the lens.

With such long exposures you may get some pretty heavy noise in your image. So you may have to consider turning your noise reduction on in the camera menu. Noise reduction takes a second blank frame or in camera dark frame, analyzes the frame for hot or stuck pixels, and then applies that dark frame to areas of your images that need it. This can often help your images out tremendously, but for an hour-long exposure your camera will take a dark frame of equal time making it a two-hour exposure. However, if you choose to leave the noise reduction mode off in your camera you can then use Photoshop, Lightroom and other software programs. They do a pretty good job of noise reduction. Choices!

You never know when a car will drive by or you forget your headlamp is on while checking your camera settings, so ALWAYS keep your lens-hood on to avoids lens-flares.

Shoot in RAW! There is a lot of information in a RAW file and therefore a lot of room to play around. If you shoot in JPEG mode you cannot adjust your settings such as temperature. Color temperature is a big one, you can leave it on auto or set your camera to a precise temperature but in the evening the color temperature changes dramatically from the day and it’s a good idea to have the ability to play around with it after the fact.

I also like to play with the Fill Light slider, Recovery slider and the Blacks slider, these can really bring out a lot more information in exposures that are too dark or light. All other processing for RAW star-trail files is normal.

If you are adjusting your exposure or levels using a Histogram it is ok to clip your highlights, as most of these will be stars and it is acceptable if they are blown out. This will help the contrast in your scene overall.


ISO 100 at F4

ISO 200 at 5.6

You can play around with this formula but I find this to be a good starting point. It is best to use your camera’s native ISO or the ISO that your camera performs its best at. For many Nikon cameras it is ISO 200 for other cameras it is ISO 100, you can find out in your camera manual.

The moon will greatly affect your exposure time with a DSLR; here is my rough guide on exposure times.

Full Moon Up to 10 Minutes

Half Moon 15-25 Min.

Quarter Moon 30-40 Min.

New Moon 50-120 Min. or until your battery runs out.

Try to train your eye to look for ambient light in the scene, wait for your eyes to adjust if you have to. In this image I saw just a hint of green light in the fog below and it adds a great eerie element to the photo.

Red River Gorge, Kentucky ISO 200, F5.6, 25 Minutes

If you don’t have any ambient light you may want to create some to add an interesting foreground element to scene. This can be done with flashlights, fires, strobe lights and don’t forget some colored gels. The night is like a blank canvas for photographers and lights are our paints.

In this image taken at Red River Gorge in the fall, my LED headlamp gave off such a cool blue that the color temperature of the night sky becomes a warm orange.

ISO 200, F5.6, 25 min, 17mm

This was quite a dark night on a rocky ledge in a small campsite so I made sure to find my composition during the day so that I was not fumbling around at night.

Remember to bring a flashlight; this will help you to find the hyper-focal distance on the distance scale in your lens at night. The hyper-focal distance is the distance on your lens where you have the most in focus at one time. To find it set the distance scale on your lens to just inside the infinity symbol (it looks like and 8 that got drunk and passed out). This will help you get the most in-focus in your image instead of relying on your eyes or auto-focus at night. The wider the lens, the more distance you can keep in focus. Remember you can always set everything up during the day and come back to your camera at night if you are worried about the focus or any other settings on your camera.

Digital vs. Film when shooting Star-Trails:

While most of us have sold or packed up our film cameras there are some unique differences when shooting a star trail on film. The biggest differences is time, here is a 4-hour exposure done on a medium format Mamiya 7 film camera.

ISO 100, F4, 4 hours

As you can see it was nice not to have to worry about battery life, I got some nice long star trails and a little bit of residual dawn light coming into my sky. I was also able to do a 4-hour exposure during a quarter moon (light on the trees) because of something called “Reciprocity Failure”. Reciprocity Failure is any exposure over a second long has to be doubled to compensate for how long it takes the light to reach the film. So I could leave my camera out as long as the battery was good and let the exposure “soak” in light all night long.

Digital sensors do not have reciprocity failure, if your meter says it will take 1 hour to reach middle grey on an exposure then it will take 1 hour. Although most of our meters do not work well in the dark so we end up guessing exposures when in the dark.

*It is also important to remember that each “stop” or change in exposure time is double the amount of light than the previous one, so the difference between a 1 hour exposure and a 2 hour exposure is really only one stop. Overexposure is not something we really need to worry about when the exposure is that long.

List of things to remember:

· Camera with a wide lens

· Tripod

· Shutter Release Cable

· Lens Hood

· Extra Camera Batteries, freshly charged

· Memory Cards

· Hand Warmer, Hand towel, Rubber-band

· Rope and Carbineer

· Bubble level

· Flashlight or other light-sources with extra batteries

· Watch with Alarm for timing exposures

· Compass

· Turn off image stabilization/vibration reduction, it will drain your battery and does not work on long exposures, it can cause your image to drift left.

· Find your Hyper-focal Distance

· Remove camera straps and anything else that can blow around on your camera and cause your tripod set-up to move.

· Turn on long exposure noise reduction if you don’t mind doubling your exposure time. It will help any pixel problems due to long exposures.

· RAW image format

· Camera on Manual Mode

· Shutter speed on Bulb

· Look for ambient light that may be in your exposure

· Check the weather report and sky map.

· IPod or other entertainment source (hey, sometimes it’s scary out in the woods alone).

Remember to experiment a lot and bring some coffee. Have Fun!