| Basic Telescope DesignsThe job of a telescope is to | | | | such as collimation (discussed in another article) which |
| collect light, not to magnify an image (the eyepiece | | | | is vital for great results in your astrophotography, |
| does that job). The larger the objective (the part | | | | although you will learn how to do this quickly with |
| that collects the light) whether it be a lens, in | | | | practice.Schmidt-Cassegrain TelescopesThis is a very |
| refractors, or a mirror, in reflectors, the more light | | | | popular design, with a high tech look. Also known as |
| the telescope will collect. The more light you can | | | | a CAT (Catadrioptics). They use a combination of |
| collect, the more detail you will be able to capture, | | | | lenses and mirrors to collect and focus the light onto |
| and also important for astrophotography, the shorter | | | | the eyepiece or camera. The light enters the |
| your exposures will need to be to capture this | | | | telescope through a thin 'lens' called a schmidt |
| detail.Refractor TelescopesThe type of telescope | | | | corrector plate, goes to the back of the scope to a |
| most people visualize when they hear the word | | | | spherical primary mirror which reflects the light back |
| telescope is the 'Refractor'. This is what Galileo used | | | | towards the front. Here the light strikes another |
| for his break-thru discoveries. A refractor has an | | | | mirror, the secondary mirror which is mounted on the |
| objective lens at the front which passes the light | | | | corrector plate. This secondary mirror then reflects |
| straight through to the back of the tube, focusing | | | | the light back towards the back where it is focused |
| this light at an eyepiece or for astrophotography a | | | | onto a hole in the primary mirror where the light is |
| camera.Advantages:-No central obstruction (see more | | | | collected by an eyepiece or your astrophotography |
| in the reflecting scopes), giving higher contrast.-Due | | | | camera.Advantages:-Compact and portable.-Low |
| to the simple design they require little | | | | maintenance although once again collimation is |
| maintenance.-Excellent for planetary and lunar viewing | | | | required for top performance.-Many, many |
| and photography.-Excellent for wide field viewing and | | | | astrophotography accessories available.-Cheaper per |
| astrophotography especially in shorter focal lengths | | | | inch of aperture as compared with |
| (more on this later).-Because the objective is | | | | refractors.-Excellent all-round telescope, good to very |
| permanently mounted and aligned there is no need | | | | good for both visual and astrophography.-Very good |
| for collimation (again more on this in another | | | | for planetary and lunar viewing and |
| article).-Excellent color in apochromatic and ED (Extra | | | | astrophotography.-Very good to excellent for DSO |
| Dispersion) designs.Disadvantages:-Costlier per inch of | | | | (Deep Space Object) astrophotography with a |
| aperture (objective) than reflectors and catadioptric | | | | caveat (see the disadvantages).-Very good to |
| telescopes.-Can become bulky and difficult to | | | | excellent optics, both Meade and Celestron are |
| manage, especially in larger lens designs.Newtonian | | | | putting out excellent optics on a consistant |
| TelescopesThis design was invented by Sir Isaac | | | | basis.Disadvantages:-Costlier per inch of aperture as |
| Newton (he of the apple on the head fame). Instead | | | | compared with Newtonian telescopes.-Loss of |
| of a lens at the front of the tube this telescope | | | | contrast due to the central obstruction which is even |
| design uses a concave, parabolic mirror to collect light | | | | larger than that in the Newtonian scopes.-Due to their |
| reflecting it back towards the front of the tube to a | | | | longer focal lengths the field of view is smaller and |
| flat diagonal mirror which reflects the light out the | | | | longer exposures are required for astrophotography, |
| side of the telescope to the eyepiece or camera for | | | | although a lens known as a focal reducer is available |
| astrophotography.Advantages:-Lowest cost per inch | | | | which minimizes or removes this problem. The longer |
| of all the telescope designs.-More light gathering | | | | focal length is actually an advantage in planetary and |
| power per dollar because of the lower cost | | | | lunar photography.Maksutov-CassegrainThe |
| design.-Absolutely perfect color rendition.-More | | | | Maksutov-Cassegrain telescope design is basically the |
| compact design compared to a refractor of similar | | | | same as the Schmidt-Cassegrain design except it |
| light gathering ability.-Excellent contrast for planetary | | | | uses a meniscus lens at the front instead of a |
| and lunar astrophotography and viewing in longer | | | | Schmidt corrector plate. The main advantage to the |
| focal lengths.-Can get excellent wide-field astrophotos | | | | Mak telescope design is you will get sharper higher |
| and short exposures in shorter focal | | | | contrast planetary and lunar images when compared |
| lengths.Disadvantages:-Slight loss of contrast due to | | | | with the Schmidt design.Carl Gilbertson has been |
| the central obstruction (the flat secondary mirror) as | | | | involved in amatuer astronomy for over 30 years and |
| compared to a refractor.-Requires more maintenance, | | | | astrophotography for over twenty-five years. |