In the more recent past, most of the early 18mm Kellners we see with Celestron are indeed from Vixen. But some of you don't realize that in the 1971-1983 era, before Vixen dominated the Japanese products from Celestron (Nihon Seiko and Daiichi Kogaku to also be included), Towa and Carton were the big boys; Mizar not to be included as I have never seen a (M) kellner from this family unless it is the coveted 25mm.
Towa and Carton era kellners would arrive in pale gray-to-smoky gray boxes. Mizar and Daiichi Kogaku would be in lime-green boxes with white labels. And the Vixen ones would always arrive in orange boxes with white labels, and later white boxes with a white label.
This is a 3rd generation of the 18mm kellner and the 2nd generation of the 18mm kellner by Vixen. We know this because in the 1st gen models, the body would be much taller and the characters would be silver-etched. In the 2nd gen models, an unusual, thread-on, hard nylon eye guard would be present in lieu of the conventional aluminum caldera (as seen on this one). And as with the 1st gen kellners, it would almost always have a longer chrome barrel that was 60% of the height of the black body (not to include the thread-on eye guard). Only in the 3rd generation are the characters painted and the Celestron font italicized.
And it should be noted that the 3rd generation is the final generation of the Japanese-sourced Celestron .965-inch kellners.
So the 18mm, which has the most generations I know of, could be quickly concluded:
* 1st gen high chrome, silver-etched, aluminum caldera "CELESTRON" on top
* 2nd gen high chrome, silver-etched, thread on nylon eye guard (usually lightest in weight)
* 3rd gen near equal chrome-and-body, white-painted, aluminum caldera
Unlike the larger 30mm, which was widely popular in its 2nd generation guise, and sometimes 25mm relatives, the 18mm was never an inclusive eyepiece to the C90 unless it was of the very earliest C90 Astro models (orange). For the most part it was most commonly acquired in the "C90 Visual Package", an accessory kit Celestron offered in a turquoise box (or cream-white) that featured a .965-inch 90 degree prism diagonal, the 18mm kellner, and either a 2.5x or 2x "long neck" barlow, also called "EXTENDER".
By the time the C90 had moved into its all black-gloss generation (the turn into 1985), the 18mm was still included along with the 30mm. But by 1987, this practice was omitted and we now see only the 30mm as being the standard model's inclusive eyepiece (and we can see this reflected by one of Celestron's strongest dealers, Orion).
Celestron catalogs always advertised the 18mm kellner in their master and general catalogs from at least 1973 until very late 1996. If you are looking to complete the entire .965-inch kellner family, the full set (never offered as a complete set) would be:
40mm (rare and labeled as an AH-40, which is still a kellner)
30mm
25mm (rare)
18mm
16mm (very rare)
12mm (rare)
10mm.
These eyepieces were fully removed from production right at the turn of 1995-into-1996 when the Super Modified Achromats AND the Halloween Plossls took stage as the choice .965-inch eyepiece. Interestingly enough, they did exist side-by-side with the emerging .965-inch Halloween Plossls.
Barrel size: .965-inch
Design: 3-element kellner (2)(1) configuration
Optics: fully coated
Field of view: 46 degrees
Eye relief: 8mm
Exit aperture: 14.0mm
Threaded for filters: yes
Materials: milled aluminum and brass, glass
Weight: 1.8 ounces
Aside from Pentax, this is probably the very best kellner in this focal length money can buy; especially in the 1-inch class as images in the correct telescopes are always very sharp and clear. And unlike your much older Towa, Yamamoto, Apollo Labs, and Eikow kellners, this entire line from Vixen has BIG exit aperture and eye relief by comparison. This 25mm, for example, has double the size exit aperture and almost double the field of view as a Towa 21mm kellner coming on your 1977 Jason 313 Discoverer or 1982 Tasco 17T equatorial refractor.
The 18mm is rewarded with having an unusually wide field yield, 46 degrees, and is only tied by the very rare 16mm for giving the largest window view. You will feel like you are looking through a plossl more so than a typical kellner.
In 60mm to 80mm refractors in the f/11 to f/15 range and 80mm to 102mm cassegrains in the f/10 to f/12 range it produces very sharply-resolved views of objects like M42, M13, M22, M8, M37, M35, and M29 to name a few. The focal length it provides is perfect for using as an up-close view of your bright galaxies and nebulae (also planetary) without over doing it on your limited light gathering ability to the point of the image becoming too dim. It will comfortably frame the Moon at half phase, easily show Jupiter with its moons AND show the brightest cloud belts, and it should definitely be used on those dense open clusters; the Double Cluster, M29, M35, M37, M52, and M11.
Perfect telescopes to utilize this kellner in would be the Sears 6333, Carton Aerolite 60, Towa 339, Unitron 142, Carton 100 f/13, Celestron C90, Parks Jovian 4, Meade 1040 and 97E, as well as the long, old-boy reflectors. These reflectors would be the Optica b/c 4 DTC, Edmund Scientific Palomar Jr, Criterion Dynascope 4, and Vixen Sky Scope NP-R114E.
As a daytime observing eyepiece, this is an EXCELLENT ocular for use as high magnification in your vintage spotting scopes like the Celestron C90 and C5, Meade's 97 Series, and any 60mm f/11 to f/12 on a decent altazimuth yoke mounting; the Unitron 114, Shrine Manon 60 and the rare Orion TeleVista 60. The 18mm will be perfect for getting those nearby hills front-and-center, identifying feather head characteristics in your aviary studies that would not be possible with the 25mm, and you'll be able to possibly pick-out individuals on nearby ships, boats, and jet skis in the harbor.
Images will be crips to the edge, with VERY controlled secondary spectrum in long achromats. For upper-end maksutovs and schmidt-cassegrains, color will not be an issue. It is the perfect eyepiece for these observing activities as magnification will be comfortably high enough to get those much finer details in your subjects, but not so high that your image is ruined by low air turbulence.
And that 46 degrees field of view is going to make clocking your objects quite easy on your brain.
Eye relief is moderate and so those who must keep their spectacles on, but do not have very thick prescription lenses will be able to appreciate the views without being in the back seat. Those who are forced to deal with thick lenses (astigmatic glaucoma, for example), may wish to forgo this 18mm. It will work with your eyes for sure, but you may have to settle for a 30 degree field of view experience. It depends on what you consider as acceptable.
For beginners at the eyepiece, this kellner is made for you as positioning will be easy and straight forward with no fear of the "black-outs".
Just remember, kellners are fantastic eyepieces in all telescopes with focal ratios above f/8. The slower objective or primary figure gets, the crisper and purer the views will be.