?? re: optical performance given a certain configu

Gang: I know this is a real elementary question but here goes anyway-when a manufacturer gives a set of optical performance specs for a particualr set up: do they routinely take into account say if there is a central obstruction or not? here is an example: Compare the limiting visual magnitude as well as teh resolving power of say an 8" S-C with central obstruction VERSUS say an 8" refractor with no central obstruction---
THanks ahead! Rich M

>>>Compare the limiting visual magnitude as well as teh resolving power of say an 8" S-C with central obstruction VERSUS say an 8" refractor with no central obstruction---
THanks ahead! Rich M
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IME, Not normally. Limiting visual magnitude is highly dependent upon the observer as well as the conditions, a 30% difference in light through-put results is 0.3 magnitude difference at best, not a great deal.

As far as resolution goes, to a first order, resolution only depends on aperture, given equal quality optics, a 8 inch SCT and a 8 inch refractor "should" split the same double. It normally doesn't work out quite that way.

Jon