One of the reasons I like photography so much is because it allows you to capture moments in time that are impossible for us to perceive otherwise either because they are too fast or too slow for our eyes. Among the "too slow" examples are light trails left by cars and also how stars "travel" through the sky during the night (and I put "travel" in the metaphorical sense so my astronomer friends don't kill me...).
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| Arches National Park, Utah |
First things first: what do we need? Actually the minimum requirements are fairly small:
1. Digital Camera: Duh! Obvious, but actually any digital camera with a manual mode will suffice (meaning that at least you should be able to control the exposure time). Of course one of those expensive DSLRs with gazillion automatic functions will make your life much easier, but any camera in which you can control exposure time will do.
2. A Sturdy Tripod: I don't know how to emphasize more the "sturdy" part, but it is fundamental. No matter how much you try to stay still and not touch anything, even if you are using a remote switch to take the photos, it is inevitable that some vibrations will occur and you need a strong tripod to minimize that shake. Just a mildly strong wind can make your tripod vibrate if it is not sturdy enough... and these photos require at least 15 to 30 minutes of exposure. Any shake will reduce your image sharpness... and we don't want that. So please, specially if you already invested a lot of money in your top-notch camera and sharp lens, don't be cheap and buy a $40 dollar tripod.
3. Patience... and most likely strong will and a hot beverage, because you will have to wake up between 2 and 4 in the morning, and most likely you will be sitting in the cold for a long time. For the photo above I woke up at 3:30 am, spent a good 30 minutes composing and then another hour shooting. So be patient.
There are a couple of optionals that I highly recommend:
4. Flashlight: you will be shooting in the middle of the night, and if you really want stars in your photos you probably are also in a place where there is almost no light... hence the flashlight. You can also use it to "paint" your foreground if there is no external light available and you don't want just a silhouette in your photo.
5. Remote switch: Not all cameras allow these, but if yours does, it is highly recommended. The basic switches will allow you to take the photo without pressing the camera's shutter button, and thus less camera shake. The more advanced ones will actually allow you to program the exposure time, number of photos, etc. It can simplify your shooting a lot.
Now that you have all you need the next thing on the list is... research. Indeed, this should be on your list every time you decide to go out somewhere to shoot. Today you can easily research your travel destination in Google Earth, Panoramio, Flickr, and so many other sites. There you can find what people have already shot, and thanks to the magic of geotagging you can even know where those images were taken. That will always help you prepare your trip and take advantage of the best spots to get a good photo.
Even if you don't care about this there is another set of important things you need to check out before you leave to make sure you can take these photos: the ephemerides of the place you will be visiting. There are several sites online where you can get them, so make sure you take a list with at least sunset, sunrise, moonset, moonrise and moon luminosity. As a side comment, if you are having a full moon during most of your trip, you will most likely not get a lot of stars. That is because when we have a full moon the Earth is in between the sun and the moon, hence as soon the sun sets, the full moon will rise and vice versa, so the really dark (and useful) part of the night will be minimal. But that is not bad... you can still do wonders when the moon is out, so just be creative. Remember that the amount of stars you can see depends on how much light is out there, so knowing when the sun and the moon won't be polluting your star-filled sky is essential. You definitely don't want to be waiting for 2 or 3 hours in the cold at 2 AM in the morning because the moon is still shining... and by having the sunset times you also know when to go to that great overlook you found earlier to take sunset pictures.
All set? Ready then, off you go. Once you arrive to your destination, while hiking around, look for interesting places. You need to do this during the day, otherwise you will waste your valuable night time looking for what to shoot instead of actually shooting. Even take a couple of photos to see if you find something interesting, but always remember that there will be little or no light, so think of shapes more than colours. If you are in the northern hemisphere, make sure you look for interesting places by looking to the north, and vice versa if you are in the south. That is if you want to get those concentric circles you see in the picture above. In that case I made sure I was pointing my camera to the NNE to have the circles centred to the left of the photo (and you can see the Polar Star in the centre). If you don't, then you will end up with lines streaks instead like in the photo below. Also notice that in that photo the moon was up when I took it, so the amount of stars was reduced significantly.
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| Balanced Rock, Arches National Park, Utah |
Ok, so now that you have a couple of cool spots to take your photos you just need to wait until the desired time during the night, but prepare to get there at least 30 minuted before to set up everything. Once you put your tripod and the camera in place the first thing you will notice is how hard it is to compose and focus when there is no light. So how you do that?
The composition part I do it by trial and error. I remember from my search during the day more or less what I want to put in the shot and where to put my tripod, so I start there. Then I take a couple of test shots and recompose accordingly. These shots have two purposes: one is testing your composition and the other setting the correct exposure. In general I take 30 second exposures to check these two things, and since almost all cameras have at least a maximum exposure of 30 seconds (without using any additional triggers) it is a good bet. With 30 seconds you will be able to record small trails that can indicate you where the star trails will be, where the centre is and so forth. For the rest of the settings I start with a large aperture (generally f/4 if I'm using a wide angle) and ISO 800. Of course everything will depend on your sensor, so use these values as a starting point and play around until you get something you like. The histogram will not help you much in this instance, since most of the sky will indeed be totally dark, so you must trust a little your instincts and check if what you see in the screen is relatively decent. More importantly, once you go back home and start processing your images take note of the ones that worked, so you can use those values when you go out again in the future. That is how I got the 30 sec., f/4.0, ISO 800 as a starting point for my Canon.You will need to tweak it of course because it depends on your own personal taste (e.g. how many stars you want to record, if you want more then increase the ISO, or reduce the aperture), the camera's sensor, and how much light is in the sky (any cities around, the moon might be out, full moon, new moon, etc.), among other things.
Once you set those numbers correctly you need to make your second important decision (composition being the first): stars or star trails. If you want static stars (maybe even a cool photo with the milky way or just stars during dawn like in the photo below) you will have to reduce your exposure time, depending on the focal distance of your lens. For example if you are using a wide angle (around 14 mm) I've been able to take photos of 15 to 20 seconds without any noticeable star trails, so the stars actually look like dots and not small lines. Of course once you start increasing your focal length, and thus zooming into your subject, the trails become more noticeable and you might require to reduce your exposure time even more. In order to compensate for that exposure reduction you will need to crank up your ISO and suffer with the wrath of the sensor noise. Depending on how good your camera is, you can go really high on your ISO and still be able to pull it off (via noice reduction in post-processing), so play around with your camera beforehand to see how far can you go. You don't want to come back and realize the amount of noise made your photo unusable. In general the fancy DSLRs have a much better ISO performance than the cheaper point-and-shoots, so this will make a huge difference in the final quality of your photo. Now going from 30 seconds to 15 reduces exposure (and thus the amount of "light gathered") in half (also known as 1-stop down), hence we need to double our sensor's sensitivity, which implies going up from ISO 800 to 1600 (1-stop up in ISO, and thus keeping the total exposure the same). This will increase your image noise, so don't be too disappointed if it doesn't work.
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| Stars at Dawn, South of Chile |
One the other hand, if you want star trails, you will need to increase the exposure. Here is where the remote switch with a timer saves the day. You put your camera in bulb mode and leave the remote shutter pressed for as long as you want. The problem is that the longer the exposure time, more noise will creep into your photo, since the sensor will become hotter. The solution is taking many shorter exposure photos and combine them in post-processing. I generally don't go for more than 3 minute exposures. Going from 30 second to 3 minutes (180 seconds) implies you will gather 6 times more light (that is a little less than 3-stops up), so we need to reduce the sensor's sensitivity 6 times too (i.e. about 3-steps down), to ISO 100 to keep the same nice exposure we calibrated in our test shots. Easy right? Now you can take all the 3 min. pictures you want, without worrying about noise and then put them all together in Photoshop later (I'll explain how in a second).
What about the focus? Ok, this one is trickier. If you own a high-end lens this part can be very smooth. Those lenses come with markings that indicate the distance, so you just need to set it to the correct value. Given that you want to have both your foreground and your nice starry background in sharp focus, you need to set the focusing distance and the aperture to make sure that happens. This is material for a whole other post but the summary is the following: the aperture and focusing distance will set your depth of field, which is the range between the closest and furthest distances to your camera that will look sharp and in focus in your photo. The larger the aperture (the wider the lens opens) the smaller the DOF, the smaller the aperture, the larger the DOF. So why don't we just put the aperture all the way down to make sure that we maximize the DOF? well because the smaller the aperture, the less light we get into the camera, and thus we need to increase something to keep the exposure correct: that means either increase the ISO or the exposure time, and both of them are bad ideas since they will increase the amount of noise in our photos. So we want to reduce the aperture just enough to keep our subjects in focus. The answer to what aperture and at which distance to focus is given by the hyperfocal distance. In simple terms this is the closest distance at which you can focus and still make sure that objects at infinity (i.e. our starry background) are still in focus. Anything less, and your stars start to become blurry. The hyperfocal distance depends on your lens size (its focal length) and the aperture, so given your lens, you need to reduce the aperture such that your subject is further away from your camera than the hyperfocal distance. Of course this will imply that you need to estimate the distance to your subject, but with a little practice you can do that more or less accurately. You can google "hyperfocal distance" and you will be able to find charts for different focal lengths and apertures or if you are the proud owner of a smartphone, download one of those free DOF calculators that are out there (DOF Calculator for Android works like a charm, and you get it for free at the android market, here) and use it to determine the aperture. Again recall that the smaller the aperture the larger the exposure or ISO, so once you determine how many stops to reduce the aperture, you will have to do the same to either the ISO or exposure (or combine both) so that you increase the same amount of stops that you lost in the aperture. Then you set your lens to focus at your subject (which should be at the hyperfocal distance for these new settings) and voilà, all will be in focus. What if you don't have a fancy lens? then the flashlight comes into play, as you can use it to focus your camera. Just illuminate your subject, so your camera can focus, and then set the aperture accordingly. Remember to set your lens to manual focus after that, since you don't want the camera trying to re-focus on every shot. Note that you can do the same procedure if you are using a fancy lens. In that case you can use automatic focus to make sure that the closest part of your foreground subject is sharp, and then read the distance that appears on the lens and use it to determine the correct aperture.
Finally, the only piece missing is the white balance. If you have a DSLR, please shoot in raw and forget about it. You can then tune it in post-processing. Now if you prefer (or are forced) to use the JPEG road, make a couple of test shots with different settings to see what you like the most. I prefer to set mine to incandescent or tungsten to give a slight bluer glow to the ski, but you might like it warmer, so play around beforehand.
After that is just shooting and enjoying the night. Have warm clothes and/or a hot beverage at hand because it can definitely become really cold.
Once you have all your pieces it is time to put them together, to make those large start trails. The steps are easy, but you will need special software like Adobe Photoshop to do it. Here is the procedure:
1. Open all photos in Photoshop, and select one to work in.
2. Copy all other photos into the selected photo. They will be copied as layers over the selected image, covering it. Don't worry, we will fix that in the next step.
3. Once you have all the photos as layers in a single file, for each layer you need to set the "Blending Mode" (just under the "Layers" tab on the right) to "Lighten". This will superpose the light parts of each layer, effectively adding all the trails.
4. Do this to all the layers except the one at the bottom, which should be the "background" layer.
5. In the top menu select "Layer" and "Flatten Image" to squash everything into a single layer and you are done!
Here is another examples of star trails I took back in Chile.
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| Remains of a Chapel after the 2010 earthquake, Tapihue, Chile |
I hope that although the post is a little long it was clear enough and gave you good tips to make cool star or star trail photos. If you want to add a link in the comments to show your results or just add your personal experiences, feel free to do so.