Observing the wonders of nature with a spotting scope or telescope is fun and exciting, but taking a picture of what you see in a spotting scope or telescope allows you to enjoy it over and over again. Astrophotography with a telescope, whether reflector, refractor, Maksutov or Schmidt-Cassegrain, is often a simple matter of adding an SLR or CCD camera to the telescope with the appropriate adapters . You can even view images on a TV or camcorder by using an electronic eyepiece. For many spotting scopes, adding an SLR camera is just a matter of an adapter and the appropriate t-ring. Currently, however, the most popular form of photography with a spotting scope is digiscoping.
You will need a motorized or GOTO mount to keep objects in the eyepiece during the long exposures required in astrophotography. This type of mount provides the necessary tracking accuracy where even a single hesitation or misstep in tracking over a period of many minutes can result in a blurred image. That's why serious astrophotographers value highly precise and accurate motorized mounts. Simply put, if you want to do more than take low power shots of very bright objects such as the moon, you will need a good motorized or GOTO mount.
The preferred type of mount for astrophotography has traditionally been the motorized equatorial mount or computerized equatorial mount. This type of mount eliminates something called field rotation. Field rotation is a blurring at the edges of a picture that occurs with mounts which move the telescope both horizontally and vertically to follow an object, rather than in one smooth continuous arc or curve like an equatorial. You can, however, add an accessory called a "wedge" or a "field de-rotator" to other types of mounts to duplicate the movement of an equatorial mount. In fact, if you use a CCD camera, exposure times are sometimes so short that field rotation may not be a problem.
SLR Camera or CCD Imager
These cameras have the necessary sensitivity to record faint objects and they also have the capability to acquire images over long exposure times, which run to many minutes. Digital point and shoot camera typically shut off after a period of several seconds, making them totally unsuitable for this kind of work. Unless you want to limit yourself to shots of very bright objects such as the moon at low magnifications, you will need a CCD or SLR.
Once you have the correct mount, you have a choice of several techniques for attaching a camera to a telescope.
Prime Focus Photography
In prime focus photography, you attach an SLR camera body directly to the telescope. No telescope eyepiece or camera lens is used. The telescope then becomes a giant telephoto camera lens. The advantage of this type of astrophotography is that magnifications are relatively low, so image brightness is high and exposures times can be minimized. This is the preferred way to take pictures of faint deep-sky objects, which are the most popular targets for astrophotography. Short focal length telescopes excel here because short focal length telescopes require shorter exposure times than long focal length telescopes. In photographic terms, these are "fast" lens systems. Long focal length telescopes designs such as Schmidt-Cassegrain are easily converted to shorter focal lengths, however, by adding a an accessory called a focal reducer.
More magnification is typically needed to get good pics of the planets, the moon and some of the smaller deep-sky objects. Long focal length telescopes, such as Schmidt-Cassegrains and Maksutovs are in their element here because longer focal lengths translate into more magnification. A popular trick to increase focal length and therefore magnification, on any telescope is to place a barlow lens in the telescope first, before adding camera adapter and camera. A 2x barlow thus doubles the focal length and the magnification of any telescope.
If adding a barlow still doesn't produce enough magnification, there is always eyepiece projection. In eyepiece projection, the camera takes a picture of the image in the telescope eyepiece. In theory, it's just a matter of using the eyepiece that delivers the desired magnification, assuming, of course, that your scope and observing conditions can deliver a good image at that magnification. In practice, though, this type of astrophotography can be very challenging. High magnification typically increases exposure times and, more importantly, makes tracking much more critical. Even the slightest tracking error at high magnification will result in a ruined exposure. Patience and determination are required.
CCD Imagers for Beginners
If you are a beginner, you might want to take a look at CCD imagers if you don't already have a camera. CCD imagers have changed the face of astrophotography. These are correctly called "imagers" rather than "cameras" because they cannot store images like a camera. Instead, CCD imagers deliver images directly to a computer and the computer captures, stores and processes the images. Obviously, then, you need access to a computer with this type of astrophotography. CCD imaging offers many advantages, though. On top of all the digital advantages, you also get something called "stacking". In stacking, the CCD imager takes a series of snapshots and the computer then stacks the images one on top of the next. The beauty of stacking is that tracking accuracy is far less critical - the computer can compensate for tracking errors that would ruin a shot with an SLR. Exposures times are also typically much shorter with a CCD imager. Astrophotography has never been easier, thanks to CCD imagers and many of these are now more affordable than a digital SLR.