COMPARING TELESCOPE STYLES
Refractor (Galilean) Telescopes
- Sharpest, highest contrast images • Most expensive
- Well made units – minimal spherical aberration • Large refractors are heavy, can be
- Rugged awkward
- Easy to maintain • Chromatic aberration
Reflector (Newtonian) and Dobsonian Telescopes
- Least costly means for bright images • Spherical aberration
- Well made units – limited chromatic aberration • Large reflectors can be heavy, awkward
- Small central obstruction • Open ended design allows air
- Bright images & accumulation of dust in telescope
- Good contrast and resolution requiring occasional cleaning
Catadioptric (Maksutov and Schmidt) Telescopes
- Compact and lightweight • Larger secondary mirror obstruction
- Durable, low maintenance limits light gathering, contrast, resolution
- Bright images • More expensive than reflectors
- Good contrast and resolution • Some field curvature exists
- Well made units have low aberration • More system light loss – reflections
- Less expensive than refractors • Exposed corrector plate collects dew
WHICH ONE FOR YOU?
1) If your primary requirement is viewing over the land or water with a “spotting scope,” refractors and catadioptrics best meet your needs. Since there is limited vertical maneuvering necessary for your telescope, altazimuthal mounts enhanced with slow motion controls permitting easy horizon scanning are ideal. Altazimuthal mounts have vertical and horizontal axes of rotation and can easily pan the horizon or be tilted up and down to place the desired image in the field of view of the eyepiece.
2) If you wish to view the stars, planets, and deep-sky objects, an equatorial mount permits effortless tracking of celestial objects as the Earth rotates. Equatorial mounts have an axis of rotation (right ascension axis) that can be tilted to match your latitude. When this axis is pointed north, adjustment of the slow motion control on the axis will facilitate tracking of celestial objects as the Earth rotates. You can even utilize a clock drive motor in order to track automatically! A tracking telescope is necessary if you plan much long time exposure astrophotography.
If you live or observe where the Milky Way is visible, you can use the telescope for deep-sky viewing and should consider a larger diameter reflector or catadioptric telescope with which you can collect large amounts of light for a limited investment. Dobsonian mounts provide lower cost access to deep space visual observation. Dark sky conditions create great contrast of the background sky and most deep-sky objects thus reducing the need for a more expensive high contrast refracting telescope. Such highly corrected, short focal length, wide view refractors may also be advantageous in this situation.
If you have to observe in or near a city or other light polluted area, or if you intend to concentrate on viewing the bright planets and the Moon and Sun, a refractor which produces high contrast, sharp images is an excellent choice.