Astrophotography with a smartphone or small digital cameras is possible with the right adaptor and most of them can also be used on spotting scopes, binoculars and telescopes. There are various ways to connect your smartphone or camera to your telescope.
The first option is to simply hold your camera or smartphone to the eyepiece. This works best for the smaller sensor sizes such as those found in smartphones and for larger targets such as the moon. You will need to set the shutter speed quite fast to eliminate movement and you may get some vignetting around the edges depending on placement, eyepiece and lens size.
The best option for smartphones is a cheap adaptor which combines a clamp for the eyepiece and a universal smartphone holder which is commonly found in car phone brackets. These will allow you to accurately position the smartphone on the eyepiece and hold the phone steady.
Top Tip: When using a smartphone camera, you can also use hands-free earphones as a shutter release! Simply press the volume buttons to take a picture. This eliminates the need to touch the screen and potentially shake the phone while taking the photo.
For compact cameras and cameras with a fixed lens, a platform adaptor can be used. These combine a similar eyepiece clamp with a small platform upon which a light camera can be attached with the tripod screw. This allows you to position the lens and eyepiece accurately with thumb screws. You can also use some optical zoom to further magnify the image.
This platform adaptor can also be used with a smartphone by using a smartphone tripod grip, although you may not be able to get the smartphone close enough to the eyepiece to eliminate vignetting completely.
For DSLR cameras there are several options available. A T-Mount adaptor will allow you to directly attach the camera body without a lens to the telescope. This results in almost perfect alignment with the optical pathway and securely holds the camera in the focuser, although it is advisable to wrap the camera strap around something just in case the camera slips out the focuser. The telescope lens effectively replaces the camera lens.
Another option is an eyepiece projection kit. This allows the same level of alignment precision, and also allows you to use small eyepieces for greater magnification. The eyepiece sites inside the tube, which screws into the T-Mount adaptor for your camera and into the focuser.
When attaching a DSLR to a telescope in this way, bear in mind the weight of the camera and the distance from the focuser as the forces can cause the focuser to become bent or damaged, especially with eyepiece projection. You must make sure that your focusser is capable of supporting the camera weight. I would also highly recommend wrapping the camera strap around something on the telescope, such as the finderscope. In the event that it should come loose from the adaptors, it won't come crashing to the ground.