There is nothing quite like the sight of a waxing crescent Moon hanging in the evening twilight sky - the classic Moon shape beloved of the movie makers and artists alike. Photographing the Moon is one of the simplest targets you can find in the night's sky, but this guide will show you how to get the best shots with your DSLR.
The moon can be a tricky subject to photograph. It is a very bright subject compared to the rest of the night sky. It is also a moving subject, and it moves just fast enough that it can be problematic. Its brightness changes depending on the time of the month.
The best areas of the Moon to photograph are along the terminator - the line that separates lunar day and lunar night. Along with this line, lunar features are most visible due to the low angle between the Moon and the Sun which creates long shadows over the lunar surface.
There is no single correct set of exposure settings that will always expose the moon correctly. Its brightness depends on a couple of factors, primarily its phase, its position in the sky if the Moon is at perigee (closest to the earth) or apogee (farthest from the Earth) and what exactly you want to expose (just the moon, or the moon with some earthshine.) Here is a table of base exposure for digital cameras, assuming an aperture of f/8, based on some of my experience (note that the difference between each phase is not exactly one stop, the scale tends to get skewed a bit as you reach the full moon). These are base settings to start experimenting with. You may find you need to adjust them for your camera, lens and seeing conditions. These settings are for a base aperture of f/8.
Blue moons, orange moons in crescent hung just above the horizon, etc. will all be dimmer than a white moon in the middle of the sky. Slightly longer exposures, maybe by a stop or two, will be necessary to compensate. When it comes to exposing the full moon, however, the reverse tends to be true... shorter exposures by up to a stop may be necessary.
If your camera does not support full manual, or you're not comfortable in full manual, you can still use auto exposures. Just set the metering mode to "spot". That should help your camera with the correct exposure for the Moon. If your camera supports exposure compensation, you can tell the camera that the scene needs to be underexposed by around 2 stops which should also help.
Photographing the Moon with a Telescope
You will need a T-mount adaptor to couple your DSLR to your telescope in order to photograph the Moon. These are fairly inexpensive and can usually be got for around £15. They are specific to certain brands of camera, so if you have a Canon DSLR you will need an adapter ring for Canon cameras. You will also need a barrel that will slide into your telescope focuser. These are generic and screw into the adaptor ring. You can also add a neutral density or variable polarizer filter to the barrel as you would an eyepiece. Adding a filter also has the benefit of sealing the insides of the camera from dust and moisture.
Once you have your camera setup and ready to go, you need to do the same for your telescope. This includes polar alignment if you are wanting to track the Moon for any length of time.
Now that everything is set up, insert your DSLR into your telescope and tighten the restraining screws. I think it is also a good idea to wrap the camera strap around the guide scope, just in case the camera should fall loose.
Once secured, set the camera's ISO to a low setting, say 100-200 and focus the camera as accurately as possible. I find it helpful to use a hartmann mask and a high magnification to aid focusing.
The exposure setting will vary depending on your telescope, but as a starting point try 1/200 second. Take a test shot and view the image. The Moon should be bright, but not overexposed and not contain any pure white. If the shot is overexposed decrease the exposure time if it's not exposed enough increase it.
When you have found the optimal exposure setting, you need to either use a remote shutter release or the camera self-timer. This is because when you release the shutter, you introduce tiny vibrations into the camera and telescope. These are magnified by the optics and introduce blur to the image. The remote shutter release or self-timer will allow you to take the picture without physically touching the camera.
Take plenty of shots as atmospherics can affect the quality of the images. The more you take, the better the chance of a great shot. Once you have some good shots of the moon, why not try increasing the exposure to 0.25 or 0.5 seconds and see if you can capture some Earthshine.
Earthshine is reflected earthlight visible on the Moons night side. It is observable when the Moon is a thin crescent, one to five days before or after a New Moon. Twilight is the best time of the day to capture this phenomenon, which is also known as 'the old Moon in the arms of the New Moon'.
With the right conditions, no special exposure adjustments are needed. A moon with Earthshine is a beautiful addition to any twilight shot.
The Moon in the Landscape
The Moon can be part of the landscape or it can be used as a source of light to illuminate the landscape at night. With a full Moon and moderate exposure time, you can make a night scene look like daytime - that's a good way to create an impact in a photo. If you decide to include the moon in the landscape you might find it difficult to balance the exposure. To get around this, shoot at twilight on a night when the moon is very thin, or shoot when the moon is really low in the sky. This will help to balance the exposure.