Due to the certain views most people have about optical design, i though a post soley for optical discussions be started.
RC's are NOT the best optical design, contrary to many peoples beliefs. But by placing a lens correcting setup, it puts it close to perfect!. But then the scope becomes a Cataioptric (Cat).
The Corrected Dall Kirkham (CDK) is corrected to remove many abberations.
To an RC, the CDK is a better optical design..
Telescope Type: ................Spherical: .................Coma: ..................Field Curvature
Classical Cassegrain.................... Corrected ......................Has coma ........................Has Curvature
Corrected Dall-Kirkham ..............Corrected ......................Corrected ........................Corrected
Ritchy-Chretien ..........................Corrected ......................Corrected ........................Has Curvature
Schmidt-Cassegrain ....................Corrected ......................Has Coma .......................Has Curvature
Further a mention was made on another post about spot diagrams
" More importantly, again we see a manufacturer (PlaneWave Instruments) who compares their products to the RC optical design through spot diagrams, etc. just like Meade and Anssen Technologies have done in the past. It is the statements and figures conveyed that have the potential to fool the prospective buyer"
This is partly correct, this is because manufacturers tend to only toot the good points and leave out the drawbacks. Problem is ALL manufacturers do it. Yes even RC Optical and RCOS, so we cant just say Meade or Anssen have done it in the past. Just to nip it in the bud, Anssen has a manufacturing problem, and nothing to do with the spot diagram or design of the scope. The scope is designed correctly, just other forces producing bad images.
Further, the Spot diagram is the process of comparing telescope performance, and every telescope manufacturer designs their optical systems using Spot diagrams as its proof of performance.
Even the Vixen VC200L is a CDK type, so read about it.
Lastly, one question was asked about why do they prefer the RC over other designs.
Well, the RC only uses 2 mirrors, so you get NO loss or abberations introduced by passing light thru glass, plus ALL optical wavelenghts are also reflected. Not to mention the size and weight of the correcting lens's for a 2 meter or larger telescope.
This is why they dont make big Schmidt telescopes. The glass on the 48" Schmidt is hugeious enlargicus !!!!. So corrector plates are out of the question.
Any other views most welcome, anyone..