While you can take good pictures of the moon with a normal camera lens, a lens longer than 300mm will help you fill the frame with the moon. However, extremely long lenses are very expensive and unnecessary for most photographers.
Instead of paying for a big lens, you can turn to a less expensive alternative and take moon photographs through a telescope. Yes, telescopes can be very expensive as well, but good results can be achieved with a cell phone, an inexpensive telescope, and a bit of patience.
Afocal Telescope Photography
The most inexpensive method of taking photographs through a telescope is called afocal. This means that you focus the telescope on the object you want to photograph and then point your camera into the eyepiece to take the photo.
This method works well for point and shoot cameras and cell phones. It is highly dependent on the size of the eyepiece for your telescope. The larger the eyepiece, the easier it will be to aim the camera and avoid vignetting (a soft black frame around your image).
The trickiest part about the afocal method is keeping everything steady.
- For light cameras, you can carefully tape the camera to the telescope.
- For larger cameras, you may need to use a tripod.
Prime Focus Telescope Photography
A slightly more expensive method is called prime focus. It's easy but does require a couple of accessories.
You will need a T-ring and T-adapter that are compatible with your camera and telescope. These should cost around $25 each and will allow you to attach your camera directly to the telescope without the lens or eyepiece.
This method allows for sharper focus and less time spent lining up the camera with the telescope for each shot.
5 Telescope Photography Tips
No matter which method you choose, there are a few things to keep in mind when photographing through a telescope.
Minimum Focusing Distance
A camera lens cannot focus on an object that is closer than its minimum focusing distance. A small focal length lens (e.g. 50mm) can typically focus on objects closer than a lens with a larger focal length (e.g. 150mm). The smaller lens will be easier to use in conjunction with the telescope because you can put it closer to the eyepiece. If your lens has a macro setting, that will help reduce the minimum focusing distance as well.
If your camera has manual focus, use it. This will help you get a sharper image through the telescope. Smaller lens cameras such as cell phones generally handle the autofocus fine. Larger lens cameras like DSLRs see a good bit of the area around the eyepiece and will have trouble using autofocus.
If your telescope is not a large heavy one, the shutter motion on your camera might cause shake while using the prime focus method. This can result in a blurry photo. You can minimize this with good support for the camera or by using a cable release or remote shutter button. You can also lower your ISO and increase the time the shutter is open so there is a more stable recording time to overpower the time it shakes.
The Moving Moon
The higher the magnification, the more apparent the movement of the moon will be in your photography. If you have a 1000mm telescope and a doubler on your camera, the moon motion could be apparent in just a few seconds. Experiment with exposure times to see what works best for your particular set-up.
As discussed in the basic moon photography lesson, it is okay to underexpose the moon a bit. Even with the light lost through the telescope, the moon is so bright compared to the sky around it that the camera may overexpose the moon while it's trying to brighten the sky.