<https://stargazerslounge.com/topic/82057-low-profile-focuser/#comment-800434>
<http://schema.org/text>
"The diagonal I have is 3\" minor axis, 25% of the primary diameter. The scope was used for DSO imaging back in the 1970's so I suspect the oversize secondary was to ensure  max light to the camera with slightly reduced contrast. I want the scope to be a better all rounder so I plan to get a 2.25 or 2.5\" secondary. This puts the obstruction in the &gt;20% area. Newt says this will still ensure 100% illumination with the existing focuser. I think I also need to learn about some of the terminology used to describe this dark art. \n"
<https://stargazerslounge.com/topic/82057-low-profile-focuser/>