Field Report
by Gary Gray
Downtown Denver /1 sec, 35mm, ISO 400, F/8.0
For the purposes of this write up, I'm assuming you are using a digital SLR or 35mm Film SLR. Myself, I use Canon Digital SLR's for my night photography. My camera of choice is the Canon EOS 5D.
Hopefully, if you are new to this subject and looking to get started without excess fumbling around, you'll find this article of interest. I'm not going to address astrophotography, mainly because I don't know much about it.
First, lets start with basic equipment. In addition to your camera and lens, you'll need the following.
Sturdy tripod.
Enough can't be said about your choice of tripod. I use Bogen/Manfrotto tripods, mainly because they are reliable, sturdy and have never let me down. Stay away from using el-cheapo aluminum & plastic tripods if you can. The camera must stay steady. Also, I try to place my tripod on solid earth. I never try shooting from a wood deck or platform, or concrete/asphalt. These surfaces can all transfer vibrations from nearby movement. The heavier the tripod the better vibration resistance. Some folks go so far as to hang weights from their tripod to give them more stability from ground vibration and wind vibration. Wind is a big enemy. Try to work on nights with little or no wind or shield your setup from the wind as best you can.
Remote cable release.
On many DLSR's, you can attach a remote shutter release. If you can't afford one, try using the timer function on your camera. Some cameras will only do a maximum of 30 second exposures without using bulb mode. Sometimes this isn't long enough. You also want to avoid moving the camera when you fire the shutter. A remote release allows you to fire the shutter without going near the camera and it allows you to do exposures longer than the camera default. In addition to using a remote cable release, you may wish to get to know your camera's mirror lock-up function. Digital SLR's have a mirror between the lens and the sensor which is used to reflect the light (image) from the lens up to the viewfinder. Before the camera takes a picture, it must raise the mirror to allow light to hit the sensor. As a result of this movement, vibrations occur. They aren't significant vibrations but none-the-less, can result in the camera vibrating for an instant when the shutter is released. The mirror lockup function allows the mirror to be raised with the first press of the shutter release. The camera is allowed time to dampen the vibration and you then fire the shutter. This is typically a manual process and a normal wait time between mirror raising and shutter release can be anywhere between 2 to 10 seconds. The end result is a cleaner sharper image due to mirror vibrations not interfering with the exposure. I recommend you learn to use this feature of your camera.
Light weight non-opaque black cloth.
Why do you need a black cloth? Sometimes when making a long exposure, a source of light may come into the camera's field of view. You can save the exposure by having a cloth handy. If you see a car's headlights approaching, simply drape the cloth over the front of the lens to shield it from the interfering light. Once the light is gone, gently lift the cloth and continue the exposure. Of course you'll want to use a cloth that doesn't weigh much to prevent camera jiggle and you certainly don't want a opaque cloth that allows light through.
Backlit stop-watch/timer
For those shots over 30 seconds, you'll need to know how long your exposure is taking. Personally I like a watch with a built in timer and alarm with a green back-light.
Extra Batteries
One thing to make sure of is having a fully charged battery and perhaps an extra battery or two. You'll be doing long exposures and you don't want to run out of juice. Keep the spares in your pocket next to your body to keep them warm. Cold batteries drain quicker.
Small Flashlight
It's nice to see what you are doing when you aren't taking photographs. Since you'll be working in the dark, a flashlight makes it easier to find things, like flash chips, lenses, and the buttons on your camera. You can also use your flashlight to paint objects while making exposures. I'll talk more about painting later.
Hotshoe flash.
Yes, I usually take my hotflash with me. Most hotflash units will allow you to fire them manually when not mounted to the camera. You can get some interesting effects by firing a flash in your scene when making long exposures. It's one way to do a double exposure. You can have a person appear as a ghost or in multiple locations on a photograph by using your flash manually.
Coffee – optional
I never go out at night without a thermos of hot coffee. It gets cold at night in Colorado, even during the summer.
Portable chair – optional
I like to be comfortable while I'm making long exposures. I use those portable camping chairs that fold up into a nice little bag with a shoulder strap.
Lenses
One thing of importance is allowing your lens and camera to temperature stabilize. If you are going to be moving outdoors from inside, a sudden shift of temperature can cause your lens to fog with condensation. I normally allow my camera and lenses to acclimate to the environment for at least a half hour before I try to do any photography. You can do night photography with virtually any lens. I prefer wide angle lenses for the most part but sometimes use telephotos for shots of the moon or comets and such. You'll want to understand certain basics though, and much of this you will learn through trial and error as you progress and become more proficient.
13 sec, ISO 400, 42mm, f/9.0
If you are photographing the night sky and intend to include stars and celestial bodies in your image, you will want to be aware of the “Rule of 600.” In a nutshell, if you want to make the stars appear static in the sky (in one spot without movement), you must calculate your exposure time based roughly on this rule. To calculate a proper exposure time, you simply divide 600 by the effective focal length of your lens. The result is the maximum number of seconds you can expose without obvious star trails or blur due to the earth's rotation.
30 sec, ISO 400, 16mm, f/2.8
955 sec,ISO 400, 16mm, f/2.8
This calculation may vary depending on the type of camera you use.
For the Canon EOS 5D, I know that it has a full frame sensor. Thus, a 50mm lens on the 5D has an effective focal length of 50mm. There is no focal length multiplier to consider. Maximum exposure time will be 600/50 = 12 seconds. Any exposure over 12 seconds and I know the image will show movement of the stars. So, as you can see, the longer the focal length of your lens, the less time you can expose and keep the stars in one place. This presents other challenges, which I'll discuss a little later in the article.
Many digital SLR's use what is called a crop sensor. For the APS-C sensors, such as the Canon EOS 20D, 30D, 350D, 400D, the focal length multiplier is 1.6. A 50mm lens mounted on one of these cameras will produce a field of view 1.6 times longer than the lens rating, ie...80mm effective. Thus you calculate 600/80 = 7.5 seconds. As you can see, this is less time using these bodies.
For many of the Nikon bodies, your crop factor will be 1.5. Nikon and Canon bodies aren't using the same exact sensor sizes, unlike 35mm film. With 35mm film, your focal length stays the same with any body/lens combination. So, a 50mm lens mounted on a Nikon D300 will give an effective focal length of 75mm. Rule of 600 says, 600/75 = 8 seconds exposure time max.
You will want to examine your particular camera's specifications and use the proper focal length conversion for your particular brand.
Here is a shot using only moonlight. The intention was to get the light on the pine trees and maintain the position of the star-lit sky. In this case the moon was over my shoulder to my right and reflecting off the trees in perfection.
20 sec, ISO 800, 28mm,f/3.5
Now that you know about the rule of 600, you can see that the wider the focal length of the lens, the more exposure time you can achieve. Longer exposure times normally equate to more light and less noise in your images. You want to push your exposure times to the limit to get the highest quality images. For this reason, I like to use fast lenses between 16-50mm focal length. One of my most favorite night lenses is the Canon EF 24mm f/2.8 prime lens. Another is the Canon EF 16-35mm f/2.8 L, zoom lens.
If you are unconcerned with star trails, the rule of 600 doesn't really matter and there are other more important considerations to take into account.
Focusing can be a problem at night. I don't try to use autofocus. I put the lens in manual focus mode and try to prefocus at infinity. Different lenses rotate to focus in different directions, understand how your particular lens works before you get out in the dark trying to fumble around with it. Nothing worse than trying to focus on infinity and finding out you went the wrong direction after a 30 minute exposure. Don't assume that turning the lens focus knob all the way out is a good infinity focus. Some lenses will focus beyond infinity and this will not produce a sharp image. I find that by manually focusing on the stars, the foreground will stay fairly sharp unless there are objects very close to me. When I'm doing scenic landscapes, I try to manually focus on foreground objects instead. Distant objects will pretty much be in focus, even with low apertures, when you do long night exposures using wide angle lenses.
One of the critical aspects of night photography is getting the proper amount of light to the camera's sensor. In general, the more light you can put on the sensor the better. I seldom rely on the camera's auto-exposure setting to achieve the exposure I want. The metering in the camera isn't going to accurately determine a proper night exposure, so learn to use your camera in manual mode. Set your aperture, shutter speed and ISO manually. Keep control of your photograph.
There is also no need to worry about proper white-balance if you shoot raw format images. I won't get into the debate of raw vs jpg photography, but I will say that shooting with raw format gives you far more ability to adjust your image in post processing. For this reason alone, I always shoot raw format.
One thing I like to do when I find the time is to take pictures of the moon during its different phases and at different points across the horizon. I archive my moon photos and use them from time to time when editing by inserting them into other night shots. You can put a nicely exposed moon shot in just about any other photograph using photoshop or other digital image editors. Very handy thing and a good way to stay in practice as well.
Photographing the moon is no different than photographing any other low light subject. Remember that the moon is a sun lit object, so exposure times for getting detail of the lunar surface will actually be very low. You will find it difficult to get good detailed shots of the moon and have nice bright stars in the same shot. Why? The moon is much brighter. You'll want to use the rule of 600 on the moon as well, because the earth is still spinning and the apparent movement of the moon will create a blurry scene if you expose for too long a time.
One trick to get the moon and stars in the same shot is to do two different shots. One shot exposes the moon for proper detail and the second shot ignores the moon and concentrates on getting the stars they way you want. You can also frame the moon with buildings and other scenery. Multiple exposures of the same scene can be combined to make very dramatic photos.
The image above was taken during a full lunar eclipse in 2007.
1/3 sec, ISO 800, 800mm, f/6.3
The exposure time needed to keep this image sharp was less than 1 second. The Tamron 200-500mm lens I used doesn't give a very fast aperture, so I had to bump the ISO up to 800 just to get a basic exposure. The lens was actually rated at 500mm, but using the 1.6 x conversion factor, exposure was calculated at a effective focal length of 800mm. 600/800 = .75, so you can see the maximum exposure I could even consider would be 3/4 of a second.
Since the moon, even during an eclipse, is a sun lit object, it is much brighter than the stars. You can see a few twinkles of starlight in this frame, but at this exposure setting, you will only get the brightest stars to show up.
Other optical elements can also affect your image. One serious consideration is lens flare. Bright light sources in or near your field of view can generate a great amount of unwanted flare. One way to keep flare to a minimum is proper lens selection. All lenses are not the same. Some will be more flare prone than others. You'll have to experiment with your lenses and determine for yourself what is acceptable and what is not. I always use a lens hood at night. It helps to keep flare from out of frame lights to a minimum. I never use filters. Filters can add a great deal of flare to your images as you get more light reflecting between the front lens element and filter. Of course, if you are trying to be creative and wish to use lens flare as an element of your composition, by all means, filters may actually give you some interesting optical effects. Don't be afraid to experiment.
Your aperture setting will have an effect on your image. If you have light sources in your image, you may notice the star pattern that emanates from those lights. In general, the more stopped down your aperture, the more star points you'll get from those light sources. The number of aperture blades in the lens will affect this also. I normally shoot at f10 or higher (more close aperture) and as a result, I get a lot of star spines from lights in my shots. I kinda like the effect, your opinion and needs may differ. Something to think about when trying to be creative.
ISO is another important consideration. With low light photography, you run the risk of introducing sensor noise. Most DSLR's will go up to ISO 3200, but I don't recommend using that high a setting. For landscape work around city lights and buildings, I normally shoot at ISO 200. When I photograph the night sky, I may go up to ISO 800 if I need to, but most typically shoot at ISO 400. ISO 400 is a good starting point in my opinion. It's a good trade off between sensitivity and noise on most current camera bodies. As high ISO noise reduction improves on new camera bodies, we all stand to gain. The digital SLR is already leagues beyond 35mm film in this regard.
Another item of concern is sensor heat signatures from long exposures. In many digital SLR's, the sensor can actually heat up during long or repeated exposures and produce a red glow on the edge of the sensor. I find the Canon EOS 30D is prone to this, appearing on the right-center edge of some shots. One way to reduce this is to try and do your photography on nights when it is cooler out. Living in Colorado, I've not had much trouble at night in the mountains and higher elevations, when the temperature is below 50 degrees fahrenheit, but during the summer on hot nights, this can become an issue with exposures longer than 10-15 minutes.
This leads us to another question. Should you turn on long exposure noise reduction? The Canon cameras have the ability to reduce long exposure noise by doing a second exposure after the primary exposure has finished. This second exposure is basically a black scene of the same duration, the two images are merged electronically and the noise is reduced by an algorithm in the camera. This will reduce your image noise but it also doubles the time it takes to make an exposure. If you are doing a 30 minute exposure, you will tie your camera up for an hour. You better make sure you have a fully charged battery before you start this. Personally, I leave that particular custom function off for exposures less than 30 seconds and do my noise reduction in post processing. It saves a lot of time and I get more shots during any given evening that way. For very long exposures, it may well be worth the wait to have the camera's noise reduction turned on.
Review of basic tasks.
For photographing stars statically (no trails), use the rule of 600 and use as fast a lens (low aperture, f2.8 or more open) as possible. Try to keep your ISO to less than 800. I usually begin at ISO 400. The wider angle the lens, the longer length time you can expose.
For photographing stars with trails, the rule of 600 is of no value. Use lower ISO's when possible to keep sensor noise down. Use your black cloth to prevent stray lights from moving into the frame. For landscapes, wide angle lenses produce the best results. Don't rule out the use of telephoto lenses though. Telephoto shots of star trails can produce some dramatic effects and when shooting scenery from a distance, dramatic night scenes can be composed.
Pay attention to sources of light and be aware of the possibility of lens flare.
Keep your camera steady with a good tripod and use a remote shutter release to minimize vibrations. Try to sit your tripod on solid ground, not wood decks, concrete or asphalt. Shield it from the wind as best you can.
Try using your flashlight or hotflash to create unique images by painting objects in the foreground.
Explore creative possibilities.
Bring spare batteries and keep them warm.
Lastly and most important, have fun.
