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I've also wondered how good these new range of doublet APOs that are on the market these days.
Tak has several fluorite doublet scopes again, 100mm aperture range, and then there are FPL51 and Lanthanum doublets some up to 150mm aperture.
I have had 3 doublets in the past - an FS102, an FS152 and an Orion ED80.
They were all quite good for visual but lacked in imaging being a bit poor in the blue channel. Blue rings around bright stars was where they were weak.
Whereas the oiled triplets I have had were all much more perfect, TEC110 F5.6 Fluorite, TEC180 F7 fluorite, AP140 F7.5 FPL 53 oiled triplet.
Colour correction is not an issue with AP Riccardi Honders 305 F3.8 and Planewave CDK17 F6.8 and these scopes have lensed correctors. The Honders has a large objective plus a corrector (a triplet I think).
I have not noticed in any of the telescopes I have used that had correctors/flatteners/reducers that colour correction became an issue. So this APO aspect is more about the objective lens not the lenses at the imaging/visual end of the scope so much it would seem.
Anyone used these new Tak doublets for imaging or are they regarded more as a visual instrument? Also these new FPL51 and Lanthanum doublets? They are marketed by Teleskop Services, APM, AstroTech and probably Skywatcher and maybe others (Sharpstar etc).
Greg.
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