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My 127mm iStar Anastigmatic R30 f12 is very clean with no detectable (to me) CA but it does require a fair amount of swing room in the observatory. Unfortunately iStar does not make R30 objectives in long focal length sizes anymore, the longest being a 250mm f11 which has a focal length of 2712mm and weighs a wopping 14kg for the objective cell. I wish they would stay in the market but low demand from people willing to take on building a large acrho seems to have closed that line down, however i am hearing that they will build custom R30 objectives in your chosen focal length as special orders. A 250mm R30 f11 objective cost $5995 USD these days, still its reasonable for a refractor of that apeture.
Btw, iStar are running out their production 150mm f10 achromat scopes, with a 2.5" Moonlight focuser for $1750 USD - seems like a bargain to me!
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