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