The 127/130 is the diameter of the mirror in mm in a newtonian or cassegrain style scope and is the measurement equivalent in reflecting scopes to the measurement across the diameter of the from lens in a refracting scope,. In Newtonian types it is the aperture. In other reflecting scopes that use a combination of lenses and mirrors, the aperture can be the from glass element, or corrector plate.
Newt(onian) and Cassegrain (SCT-, Schmidt-Cassegrain, or Mak(sutov Cassegrain or Richey-Chretien) are reflecting scopes that use a mirror as part of the optical path.
The Newtonian, including the Dobsonian, use mirrors exclusively to present the light to the eye-piece for magnification.
Cassegrain types use a combination of mirrors and lenses in various configurations.
Both types are reflecting and these two articles should give u a good overview.
http://en.wikipedia.org/wiki/Reflecting_telescope
http://en.wikipedia.org/wiki/Cassegr...idt-Cassegrain
The Cassegrain type is the dearer because of the often large glass lenses, and often much dearer than a Newtonian type.
Hope this helps, but please don't hesitate to ask. If I cannot help then someone else will.
I am famous among my friends for taking the time to decide. That bodgy alt-az took about 2 days to build after thinking the process thru for 2-3 months. But I think the time spent thinking helped make it the best it could be. Same with scopes when you don't have a never ending supply of money to throw at them.
I know the Celestron 127 (and I think the Vixen 130) use an element in the bottom of the focuser to increase the magnification and allow the tube to be very short.
Trev
P.S. Here is the review that makes me think seriously about getting one for my self as a grab-and-go with a bit more aperture than my 150 f12 Maksutov-Cassegrain (Mak)
http://www.universetoday.com/35759/v...-comfort-zone/