What happens at f6?

[Avocette]

I started a topic in the Equipment/Eyepieces section today hoping that the SGL experts there would be able to answer my question about the differences in eyepiece performance with Newtonian reflector scopes of identical focal length but different mirror size, and hence aperture ratio. I realize it's a more general question than just one about eyepieces, and it's certainly a confusing subject for those who are just Getting Started! So are there any other responses out there? The original posting is http://stargazerslou...-and-f6-scopes/ Thanks for your help.

[rowan46]

I don't know if this will be any help http://www.umich.edu/~lowbrows/reflections/2002/cnielsen.2.html

[ronin]

Nothing happens at f/6.

We simply like to draw a line and for whatever reason that line we talk about is f/5 or f/6.

A triplet apo will still show CA, all you have to do is to try make an f/4 scope and the properties of the glass are unable to perform as we would like and you get CA and SA and you no longer have an apo.

An f/5 scope is generally pushing the boundry of what we can accomplish and get good results, oddly that seems to be true of a good parabolic mirror or a good apo refractor.

[John]

I don't know if this will be any help http://www.umich.edu...cnielsen.2.html

Thats good information. From the same people:

http://www.umich.edu/~lowbrows/reflections/2007/dscobel.27.html

I've posted the above link in the other thread too because I think it's a good one.