[ATM] Calculating Focuser Length and Travel

[clement.focuser at verizon.net (Don Clement)]

With a focuser with a draw tube the length of the tube is fixed. Putting a
riser under the focuser or allowing the tube to go below the focuser base
does not help wrt vignetting, since the fixed diameter and length tube will
protrude into the riser or below the focuser base. In some cases the fixed
tube moves into the light path. Some focusers are deceptively labeled "low
profile" when the fixed tube is the same length as other fixed tube
focusers, only some of the focuser body and/or fixed tube protrude below the
focuser base.  There are focusers  (e.g. my focuser)  that do not have a
fixed tube  and where focuser parts do not protrude below the focuser base.
In the case of a focuser with no fixed tube, a riser with an opening larger
than the focuser aperture would allow the focuser to be spaced farther out
from the telescope tube without vignetting.  A tall focuser with a low
profile :-{)



Don Clement

Running Springs, California

http://www.clementfocuser.com