3 Feb
2012
3 Feb
'12
3:57 p.m.
On Fri, Feb 3, 2012 at 3:24 PM, Hutchings, Mat (H USA) < mat.hutchings@siemens.com> wrote:
Having a relatively slow (for a dob) f-ratio of 5.5 gives me outstanding views of everything from the moon to tiny planetary nebulae.
I remember Vaughn Parsons telling me once that he thought f/5.5 was just about the best f-ratio for largish mirrors. It's an excellent compromise between keeping the overall tube length manageable, yet not so short that it results in ridiculous amounts of coma in low-powered views. IMO, it's not particularly slow for 16 to 20 inch mirrors. The ladder is still on the short side. I think you nailed the optimum f-ratio for a 16-inch, Mat.