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Lumicon finderscope ??

Started by falsetto, 11/13/2005 03:28PM
Posted 11/13/2005 03:28PM Opening Post
I purchased a 50mm Lumicon r-angle finderscope on AM. It came with no eyepiece and I can't seem to marry it to any eyepiece that will come into focus. They all reach focus without the diagonal? Any Suggestions would be helpful...I'm feeling a bit out of focus myself, Thanks
Posted 11/19/2005 06:03AM | Edited 11/19/2005 06:07AM #1
Scott,

The older Lumicon finders are sold two configurations - one with a diagonal and one without. Both of the older models have a helical focuser at the rear of the OTA. The newer versions come with optional tube extenders that must be removed if the diagonal is used. These have a barrel focuser on the front of the OTA. For older models the tube length was a fixed length - you had to decide at the time of order which one you wanted. The straight through had a tube length of about 8 or 9 inches. The right angle model that came with a prism diagonal had a shorter tube length to allow for the optical length of the diagonal.

A 25mm Kellner was the standard crosshair eyepiece sold with the complete setup - If you have a Kellner or Plossl in the 25-30mm range that comes to focus without the diagonal I would highly suspect the Lumicon is a straight-thru and the diagonal is adding too much length to the optical path. You can verify this by measuring the length of the tube from the center of the objective to the plate the focuser is attached to. The focal length of the 50mm Lumicon finder is 200mm (about 7.8 inches) A right angle finder has to be roughly 2 inches shorter than this for a diagonal to function.

If this is a new model - simply remove the tube extender!

-Gary

-Gary
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