Tag: Primero

Rotating Tube Rings

No project is ever completely done, even one “finished” decades ago… My 6″ f/5 RFT is the current incarnation of my first telescope, Primero. Built into an 8″ irrigation pipe this ‘scope is a rich field ‘scope that is just fun to use. And yes, I worked on this telescope again.

A set of new 3D printed tube rings for Primero, the 6" f/5 RFT
A set of new 3D printed tube rings for Primero, the 6″ f/5 RFT

One feature I have always meant to change is the tube rings. Simple aluminum straps that I kept loose enough to allow the ‘scope to be rotated to keep the eyepiece at a convenient angle for viewing. The issue is that in use the tube would constantly slide down through the rings throwing the mount off-balance.

I finally got around to fixing that. A set of 3D printed rings along with a stop mounted to the tube that prevented this sliding, keeping everything centered and balanced. The rings are attached to each other by the two dovetails and a handle forming a cage.

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Primero

Every astronomer has a first telescope, mine is a 6″ f/5.1 Newtonian I first built as a teenager. As life progressed I was forced to dismantle the telescope and it dwelt for a time as a pile of parts in a box. Eventually I had an opportunity to rebuild the telescope, but as both my technical capability and my financial means had increased I was able to do a substantially better job.

Primero
Primero setup at TIMPA outside of Tucson
The result is the instrument you see to the right, Primero, or simply ‘first’ in Spanish. The original mirror was used but little else from that first telescope was reused. A completely new mount, a new tube and all new fittings. The only purchased parts are the focuser, the Telrad and the secondary mirror. Several parts of the mount were removed and reworked from a previous mount, this includes both the bearings, shafts, counterweight and saddle. The entire tripod, tube, mirror cell, spider and secondary holder were produced by hand for this scope.

The optical design of the telescope is standard Newtonian with a f/5.1 primary mirror of 6.0 inches giving a focal length of 777mm. The mirror was hand ground when I was a teenager and thanks to expert help during figuring is an excellent mirror.

The RFT design is deliberate and has proven to be a good choice, particularly with modern eyepieces that perform so well in short focal length scopes. With a 35mm Tele-Vue Panoptic eyepiece the scope provides a 22x image with just over a three degree field.

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