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Post by Watcher3 on Dec 21, 2011 2:26:11 GMT -5
The following is a statement I made at CN, quoted and responded to by ValeryD (vendor from Airies) I thought we had established that an R30 would have the CA of a scope with a 30% longer focal length? What are the facts? -------------------------------------------------------------------------------- Quote: -------------------------------------------------------------------------------- I've gone a different route to the same need. I'm anxiously awaiting my ISTAR 150mm F/4.7 R30. At F/4.7 it will have wide field views to die for, great optics, and the color correction of an F/5.9 scope. Should be very nice! -------------------------------------------------------------------------------- The math is not correct. Chromatism is proportional of a second order of focal ratio. If the chromatism is 30% less, then such chromatism will be in telescope F/5,36. Difficult to note the difference in useful FOV and telescope length. F/5,36 scope will have flatter field as well as less steep lenses curves - better surfaces. It seems that R50 will be more wise choice. Read more: istarscopeclub.proboards.com/index.cgi#ixzz1h9R4JADu
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Post by Ales - iStar Optical on Dec 21, 2011 13:34:21 GMT -5
Hello again, the best way is to compare the spot diagrams on R30 and Classic as well as to talkl to someone who has one of these R30 doublets and is able to comapre with similar scope with Classic doublet in it.. so talk to Mike Carman who recently purchased the 250 F11 and comapred to his older doublet... his calculation and visual experience can not be any clearer. Istar R30 doublets show CA reduction as in Classic Achromatic scope of 30 percent longer FL. Valery is correct of course but we came up with this simple way of comparing the optics without confusing everyone. We would not produce such doublets if they showed such insigificant reduction in CA. I hope it explains. cheers, Ales
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Post by Watcher3 on Dec 21, 2011 18:59:12 GMT -5
Thank you Ales.
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