Post by alcofribas on Jan 27, 2011 3:50:35 GMT -5
Hello
I'm building a 6" F/12 refractor, from a ISTAR achromat.
This focal ratio is a compromise between optical quality (chromatism) and length/weight, and with a 40mm 70° eyepiece, the object field is around 1.5°, which is enough for me most of the time. I will use the instrument mainly for unar/solar/planetary observations, and even for deep sky observations, there are not so much objects larger than 1.5° (but the exit pupil may be a bit too small for efficient DSO: 3.3mm)
But if I want occasionnaly more field and a larger exit pupil (observing M31 for example), which focal reducer could I use to increase the field to 2.5°, even 3°, without too much vignetting ?
Only for visual observation, I don't need flat field as required for imaging, and as it is for occasional use, I don't think I will spend more than 150-200$.
Any idea or reference ?
