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Help verify my calculations

Started by Craig Burlette, 07/26/2003 02:49PM
Posted 07/26/2003 02:49PM Opening Post
I’m just about to finish a wooden tube for my 10” f5 scope, could yall help me doubble check my calculations before cutting the hole for the focuser? The mirror is 10” f5 with an actual focal length of 49.25”, the tube inside dia is 11.25” the focuser is a JMI dx2 with a fully racked in height of 2” to 3.5” fully extended. I figure with 3/4” extra on the focuser height would give me 8 3/8” off the focal length to net a focuser hole 40 7/8” from the face of the mirror. I currently have a 2.14” secondary but my calculations would indicate a 1.83” to be preferable. Any comments or suggestions will be greatly appreciated.
Posted 07/26/2003 04:35PM #1
I plugged the info into Newt and came up with essentially the same distance as you ( I got 40.675") However, using the 11.25" id newt says your 75% rays are vignetted at the front aperature, meaning the tube id is too small. That was using the 2.14" diagonal which I agree would be a better choice. The vignetting is gone with the smaller secondary but the fully illuminated field is only 0.10". It sounds to me like your tube id is too small. However, I seriously doubt you would ever be able to see it at the eyepiece.