Wavefront error of an average C8??

Does anyone know what the wavefront error is of an average C8?? I'm interested in buying an C8 OTA if expected wavefront error is better that 1/4 wave p.t.v. Thanks.

Francisco, there is no known correction error average for C8s. Exessive correction error usually is not the main problem with SCTs (it is normally possible to bring it within diffraction limited by a small change in primary-to-corrector/secondary separation). The "big uknown" is fabrication quality (mirrors/corrector surface roughness) and proper positioning/centering of the elements. It may be good - or very good - and may not. If it's not, it may be "fixable" to some extent, and may not, at least for an average amatuer. If you can return it, no problem, if can't, try to check it out before you buy. Otherwise, anything's possible - expect the unexpected too.

If this data was available, you should be concerned with the RMS wavefront error. PTV doesn't say very much about the overall quality of the mirror.

If you have access to ap-ug, check out a set of interferograms that Roland just placed there, number of scopes are tested including a typical 8" SCT, the iterferogram clearly shows the rough optics, this particular one tested at PV 0.57 and Strehl of 0.80, this one is really a good representative of what you can expect if you bought one.

Thanks,
Vahe