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Thanks Bert,
The Pentax 6 x 7 300mm and 400mm ED IF are very good astro lenses.
I saw a Rho Ophiuchi taken with the 300mm ED and a FLI Proline 39 megapixel camera and it was very very nice.
I am told the non ED version is still good for narrowband but has some chromatic aberration.
The 300mm ED seems almost impossible to find. I have been looking around and couldn't find any for sale. There is a 400mm ED but its US$3650 which seems a lot for a lens (may as well buy a Tak refractor).
My FSQ106ED with reducer is 330mm and gives pinpoint stars to the corner of the 16803 chip so more looking for about 200mm or less in focal length for astro work.
Greg.
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