Essentially correct, Patrick, but as Daniel pointed out, it can vary slightly depending on where you place it. Generally, most focal reducers/extenders are designed to be placed in one position in order for the stated multiplication factor to be correct. Check the literature that came with your reducer to make sure you are placing it where the manufacturer recommends. Cassegrains are funny animals. If the secondary is a "3X" secondary, you end up with a final focal length 3 times the primary's focal length. You can think of the secondary in a Cassegrain as a reflective Barlow. It works the same. And like a standard Barlow placed ahead of an eyepiece, you get the stated magnification factor only at a specific spacing. Same with the Cassegrain. Change the secondary spacing, and you change the magnification factor. On 5/8/10, Patrick Wiggins <paw@wirelessbeehive.com> wrote:
So in the case of a C-14 which operates native at f/11 and 3,910mm focal length if I add a .5 focal reducer between the back of the scope and the filter wheel I end up with f/5.5 and 1,955mm focal length.
Have I got that right?
Thanks for your help,