<https://stargazerslounge.com/topic/82057-low-profile-focuser/#comment-800347>
<http://schema.org/text>
"If you have a secondary already, try to compute what the fully illuminated field and the edge of field illumination will be for your largest field eyepiece using  Mel Bartels' Diagonal Calculator Note: the radius for the objects at the edge of the field is, of course, half the field stop size of the eyepiece. And the tool works with off-axis distances, i.e. radii. If you get a reasonably sized fully illuminated field (a couple of millimetres) and more than 70% at the edge of the widest field eyepiece, then there's no pressing reason to change focusers, unless you also want to use a smaller diagonal. \n"
<https://stargazerslounge.com/topic/82057-low-profile-focuser/>