Optics
The telescope can be reflector, refractor or catadioptric, but it is important to have large aperture (114 mm or more) and low focal length (900 mm or less).
The greater the aperture greater the light gathering capacity and therefore you will be able to photograph fainter objects or use shorter exposure times.
With a smaller focal length your camera will cover more apparent field, it may be able to cover nebulae of certain size without having to mosaic multiple pictures and it will also capture more light, allowing to photograph fainter objects too.
Based on the above, the Newtonian telescope design are often the most used, as they get large apertures and low focal lengths for relatively little money and may even be home-made.
Mount
The mount should have sky tracking capability to compensate for the apparent rotation of the celestial sphere. Equatorial mounts are preferable to azimuth mounts because, if they are polar aligned, they have no visual field rotation, allowing long exposure times, simplifying image processing and using the entire field of the camera.
Camera
You can use modified webcams, digital single lens reflex cameras (DSLR), compact digital cameras (digicams) or astronomical CCD cameras.
- Modified Webcams. They are the cheapest option. They are quite sensitive but somewhat "noisy", they are mainly used in primary focus. Webcams must have CCD sensor, the most popular molels are Philips Vesta and SPC900.
- Digicams. They are of intermediate cost. Often used with the afocal technique, but some of them can be modified for use in primary focus. The most important feature is the capacity to take long exposure pictures. The most popular are some Canon models.
- DSLRs. Their cost is much higher than that of webcams or digicams, but have larger sensors, covering more field. Commonly used in primary focus, the most widely used brands are Canon and Nikon.
- Astronomical CCD cameras. They cover a very wide range of costs, from similar to a digicam to much higher than DSLRs. They are used in primary focus and there is a lot of brands.
