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Originally Posted by sejanus
hey guys out of curiousity, does a dobsonian of equal size to a SCT absolutely kill it optically?
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I wouldn't say `kill' but SCT's usually suffer from rough optical surfaces and the 40% obstruction at the secondary baffle lowers image contrast significantly over the smaller Newt obstruction. A 33% obstruction for example lowers the contrast curves equivelent to an unobstructed system with about 1/2 wave wavefront error. Throw in some surface roughness , and real optical errors and even good SCT's are struggling to get a Strehl ration in the low 0.70's. A well made Newtonian with small obstruction and single smooth primary surface can easily keep a Strehl above 0.95 ( Strehl ratio of a perfect system is 1.0).
Mark