1. Telescopes
Overview
MAS
April 20, 2017

4. Three Basic Types

5. Refractors – Typical 3” to 6”
Disadvantages
- Generally have small apertures, typically 3 to 6 inches Smaller apertures mean poorer viewing of distant galaxies and nebulae Heavier, longer and bulkier than reflector and cassegrain telescopes of equal aperture Good-quality refractors cost more per inch of aperture than any other kind of telescope.
Advantages -Easy to use and consistent due to the simplicity of design. - Images are very sharp - Excellent for lunar, planetary and binary stargazing especially with larger apertures. - Sealed tube protects optics and reduces image degrading air currents. -Great for wide field deep sky astrophotography. - Rugged, needs little or no maintenance and its sealed tube protects optics from image degrading.

6. Refractors Chromatic Aberration filters CA Killer or Fringe Filter
<-Single Lens
<- Achromatic or Doublet
<- ED or well corrected doublet or poor triplet
<- Apochromatic or Triplet/Quad
Chromatic Aberration filters
CA Killer or Fringe Filter

8. Types of Refractor Glass
Abbe is a measure of the material's transparency or dispersion, higher is better.
Here are the Abbe numbers (Vd) of some commonly used ED glasses:
Crown & Flint (Schott): 60
FPL-51 (Ohara): 81.54
H-FK61 (CDGM): 81.61
FCD1 (Hoya): 81.61
OK-4 (LZOS): 92.1
FCD100 (Hoya): 94.66
FPL-53 (Ohara): 94.93
CaF2: (Fluorite)

9. Refractor Quality
There is more to quality than the type of glass. There are different quality levels for each of the types of glass. It is basically how much imperfection is allowed. You can get very high quality FPL51 glass that is better than low quality FPL53. So the types of glass is only one thing to consider. Add to his how well the glass is ground or figured. On top of this there are coatings to prevent reflections and enhance transparency.

10. Reflectors – Typical 4” to 36”
Disadvantages
- Images are a little softer than a refractor
- Generally, not suited for terrestrial applications The tube is open to the air, which means dust on the optics even if the tube is kept under wraps Reflectors may require a little more care and maintenance (collimation)
- May require a Coma Corrector
- They are large and possibly heavy and storage space and transportation need to be considered.
Advantages - Usually have larger apertures and long focal lengths which mean excellent viewing of faint deep sky objects (remote galaxies, nebulae and star clusters). - Low in optical irregularities and deliver very bright images. - A reflector costs the least per inch of aperture compared to refractors and catadioptrics since mirrors can be produced at less cost than lenses

11. Reflectors
Long focal length
Longer focal length

12. Compound – Typical 3” to 16”
Disadvantages
Images are a little softer than a refractor
More expensive than reflectors of equal aperture
Required DEW prevention
Mirror flop on some designs, focus is achived by moving the primary mirror
Heavy weight on some designs, especially with fork mounts
Its appearance may not be suited to everybody's taste
Advantages
Generally considered the most versatile type of telescope with excellent lunar, planetary and deep space observing plus terrestrial viewing and photography.
Best near focus capability of any type telescope
Very Good for deep sky observing
Ideal for planetary astrophotography
Closed tube design reduces image degrading air currents
Compact and durable
Very long focal lengths

13. Compound

14. Variations
Catadioptric telescopes (Catadioptrics) Argunov–Cassegrain telescope
Catadioptric dialytes
Klevtsov–Cassegrain telescope
Lurie–Houghton telescope
Maksutov telescope
Maksutov camera
Maksutov–Cassegrain telescope
Gregory (Spot) Maksutov-Cassegrain telescope
Rutten Maksutov-Cassegrain telescope
Sub-aperture corrector Maksutov-Cassegrain telescope
Maksutov Newtonian telescope
Modified Dall–Kirkham telescope
Schmidt camera
Baker-Nunn camera
Baker-Schmidt camera
Lensless Schmidt telescope
Mersenne-Schmidt camera
Schmidt–Cassegrain telescope
ACF Schmidt–Cassegrain telescope (Meade Instruments)
Schmidt–Newton telescope
Schmidt-Väisälä camera
Refracting telescopes (Dioptrics) Achromatic telescope
dialytic refractor
Apochromatic
Binoculars
Opera glasses
Copyscope
Galileoscope
Monocular
Non-achromatic
Galilean telescope
Keplerian Telescope
Aerial telescope
Superachromat
Varifocal gas-lens telescope
Baden-Powell's Unilens
Reflecting telescopes (Catoptrics) Cassegrain telescope
Dall–Kirkham telescope
Nasmyth telescope
Ritchey–Chrétien telescope
Gregorian telescope
Herrig telescope
Herschelian telescope
Large liquid mirror telescope
Newtonian telescope
Dobsonian telescope
Pfund telescope
Schiefspiegler telescope
Stevick–Paul telescope
Toroidal reflector / Yolo telescope