The job of a telescope is to gather light, never to magnify an image (the eyepiece will do that job). The bigger the goal (the part that gets the light) is, whether it is about the lens, in refractors, or a reflection, in reflectors, the greater light the telescope will accumulate. The more light you can accumulate, the more comprehensive you’ll be able to capture, and also vital for astrophotography, the shorter your exposures will have to capture this detail.
The types of telescope tubes most people imagine when they hear the word telescope is the ‘Refractor’. This is what Galileo used for his break-through discoveries. A refractor comes with an objective lens at the front end which moves the light right through the back of the tube, emphasizing this light for astrophotography a camera or at an eyepiece.
-No central blockage (see more in the reflecting scopes), providing better contrast.
-Due to the simple design they need little maintenance.
-Incredible for planetary and lunar photography and viewing.
-Incredible for wide field observation and astrophotography, especially in shorter focal lengths.
-As the goal is permanently mounted and aligned, there is no requirement for collimation.
-Incredible colour in apochromatic and ED (Extra Dispersion) designs.
-Expensive per inches of aperture (goal) than a catadioptric telescopic tube and reflectors.
-Can become heavy and hard to handle, especially in bigger lens designs.
This design was designed by Sir Isaac Newton. Rather than a lens at the front end of the pipe this telescope design runs on the concave, parabolic reflection to accumulate light reflecting it back again towards leading of the pipe to a set diagonal reflection which displays the light out the medial side of the telescope to the eyepiece or camera for astrophotography.