Re: My latest review - nPAE Precision Astro Engineering 1.25 Ruby Turret

Jay Freeman

It is certainly possible to design an eyepiece holder in which the eyepieces not in use are not "pointing down". I regret that my software and/or drafting skills do not allow me to post a sketch (or maybe I am just lazy), but let's see if I can describe what I mean.

Consider a TEC or Unihex style eyepiece turret: The axis of rotation of the eyepiece cluster is the optical axis of the OTA, thus the optical axes of the eyepieces installed all lie in a plane perpendicular to the OTA.

Now consider a different arrangement of the installed eyepieces: Let's put their optical axes equally spaced around a conical surface of half-angle 45 degrees. The barrels of the eyepieces all point in toward the apex of the cone. In this configuration, the cluster of eyepieces resembles the cluster of up-and-outward pointing prongs of a World War II naval mine, and anyone looking through an eyepiece is looking down through the detonating end of such a prong.

That describes the rotating part of my proposed turret. Now let's see how it attaches to the fixed part of the turret, that plugs into the OTA's focuser:

First, imagine that our cone is positioned with its axis coinciding with the optical axis of the OTA, with the eyepieces pointing generally up. THIS IS NOT THE FINAL CONFIGURATION. In this arrangement, you could stick the point of the cone into the ground and precariously balance the OTA on it, with the eyepieces pointing diagonally upward like the stalks of a plant.

Now tilt the axis of the cone by 45 degrees. As the cone now rotates, the eyepieces' optical axes one by one become at right angles to the OTA's axis, and any eyepiece opposite to one at right angles is pointing up and parallel to the tube, toward the sky.

Now move the cone slightly sideways and install a diagonal mirror at 45 degrees to the OTA axis, to reflect starlight into the eyepiece at right angles to the OTA.

The part of the turret that holds the diagonal mirror plugs into the focuser, and the part that holds the eyepieces attaches thereto with a bearing that allows rotation about the axis of the cone.


Disadvantages of this arrangement include (1) it looks weird, and (2) the upward-pointing eyepieces might collide with parts of the OTA or focuser.

Just a thought ...

-- Jay Reynolds Freeman
(personal web site)

On Jul 11, 2022, at 11:59 AM, Andrea Salati <andrea@...> wrote:

[...] the concern related to 2 of them potentially falling down at any time was such I never felt 100% at ease.

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