Eyepieces – Unitron History Project

The Unitron name was familiar to me having grown up with the iconic 1960-1970’s S&T full page ads and the Unitron catalogues on my bookshelf. I owned two short focal length (9, 12mm) Unitron orthoscopic eyepieces in the 1980’s when I was utilizing a Parks 8″ f/4 reflector. At the time they weren’t anything special to me because I was mostly interested in wider field views. They did offer up wonderful narrow field views of M42 in that 8″ scope but at some point I rotated out of them into Naglers.

Fast forward to the late 2000’s. At that point I was only utilizing refractors and had picked up a 60mm Unitron. This little scope could punch above its aperture with double Jupiter moon transits a fun challenge to chase across the winter evening sky. The .965″ eyepieces could be a hit or miss quality proposition (as I came to learn) but the set I had left nothing to be desired in this aperture and chasing these very low contrast features.

For the first 30+ years the standard eyepiece offering by Unitron was a suite of .965″ barrel eyepieces in Orthoscopic, Achromatized Symmetrical, Kellner, Ramsden and Huygens designs. I’ve seen a photograph of a Polarex eyepiece, the European branding for Nihon Seiko telescopes, of a .965” Plossl but never a Unitron brand advertised. In Unitron’s words an Achromatized Symmetrical is “An eyepiece composed of two achromatic doublets which gives a wide field with long eye relief (ie: the eye does not have to be placed uncomfortably close to the eye lens)”. Their orthoscopics were marketed for “high power planetary viewing with wide, flat fields with large eye relief”. Obviously, they never used their 4-7mm orthos. Presumably they were comparing their orthoscopic design to Huygens or other earlier designs. The early Unitron .965″s apparently had brass barrels and tops. The engraving for branding and focal length on the top was thru the paint into the base metal which has tarnished over the years to a nice golden hue earning the moniker “gold tops”. These eyepieces are noticeably heavier than the later ep’s (presumably with aluminum construction). There were changes in the writing style of “Unitron” on these eyepieces with the lettering either being block or slanted. Discussions continue as to time periods these styles were in production. For the latest theory check the Cloudy Night Classics Forum. There are also variants of the early, early sets without the Unitron branding.

In addition to individual sales, the eyepieces were supplied in sets with the telescope offerings. The smaller and more basic scopes might have 2-3 eyepieces with a .965″ diagonal, better appointed 3 and 4″ telescopes might have a boxed set of 5-7, a scope ordered with a Unihex would have a larger box to accommodate a 40mm Kellner or Monochromatic. The 4″ photo-equatorial came with even larger selections up to and including all eyepiece offerings of the time. The Super Unihex had a screw in port for a 60mm or later a 50mm Kellner eyepiece. These two were in 58mm diameter barrels with adapter rings, offered decades before 2” eyepieces were normal fare for the average astronomer. By the time of the 1956 catalogue issue the eyepiece range was pretty well established with nine .965”, a couple of 40mm 1.25” variants for the Unihex with the larger, longer Kellner’s reserved solely for the Super Unihex or direct screw onto the super focuser drawtube. In later year’s there were also illuminated eyepieces, I’ve seen a photograph of the 12.5mm in this variant.

Dave Komar’s research with original sources confirmed that Unitron sourced their eyepieces through Nihon Seiko, a Japanese marketer of astronomical equipment. The full suite of 1.25″ eyepieces were a late addition to the Unitron catalogues, in the post 1980-time frame. My research indicates these later eyepieces were exclusively a volcano top offering with slanted letter branding and straight letters for focal length and eyepiece type. These 1.25” eps were offered in a range of orthoscopics, Erfles, Koenig and Plossls. The one exception to this was the 40mm eyepiece. Over the years the 40mm appeared with a variety of lettering styles, flat and volcano top, plain and double crosshair. This eyepiece first appeared in 1955-1956 and served as their wide field eyepiece in the Unihex B accessory. It’s been engraved as a Mono, Monochro, OR and K(elner). Unitron came out with a Super Unihex circa 1955-1956 with a screw-in port for the larger format 60mm Kellner, one barrel for a 1.25″ eyepiece, the remainder .965”. The 60mm eyepiece (and later a 50mm) were threaded into an adapter to be semi-permanently mounted to the Super Unihex or removed and screwed into the back of their drawtube for straight thru viewing. It is also apparent that in the waning years of Unitron telescope sales the US distributer imported some eyepieces from Nihon Seiko without branding. This has been demonstrated either by identical measurements to branded eyepieces, N-S stickers on the barrel or purchases from first owners who described the eyepieces.

I’ve been able to document, either in ownership or via photographs posted on two CN threads, a small selection of 2” eyepieces. These are included on the following list. Dave has a copy of the original Excel file so for those who can send a photo or other documentation of additional 2” format eyepieces I’m sure he’ll keep the list updated.

Not eyepieces per se, but glass in the optical path would include the slip or screw-in barlow lens associated with the Unihex and a projection eyepiece for photography.

Jim Curry, December 2016

Unitron eyepiece list

Part 1: Photos of .965 Eyepieces:

Some older “gold top” brass barrel eyepiece sets:

And the more modern sets:

A complete Photo-Equatorial set:

Part 2: Photos of 1.25 inch Eyepeices:

The attached photos courtesy of Jim Curry:

Photos courtesy of Chuck Mitchell:

The attached photos were provided courtesy of Dave Komar; it is a complete set of 1.25 eyepieces (minus the 18mm Ortho) that came with his original 1989 vintage Unitron Model 152 plus a 20mm Erfle: