I bought this lens in a "blind date". One day when I was browsing the KEH Camera Brokers (of Atlanta, GA) web page, I came across this lens: Navitar golden 3" f2.5 f/Kodak, demo, new, $129. That's all the information I had before I placed the order. (I have, though, heard of the reputation of Navitar as among the bests in projector's lenses before.) The lens didn't come with a specification sheet either.
The lens is solidly built, although I would not use the word "craft". The marking on the lens says O. D. Industries Golden Navitar 3" f/2.5. The way of focal length designation indicates that the lens is really old: the modern designation would have been 76mm, or round up to 75mm. Lens elements are all glass, and the barrel is mostly metal. The lens barrel actually consists of two sections, which can be taken apart revealing the lens construction: 4 elements in 4 groups. The rear section consists of two layers. The outer layer is plastic molded with a gear rack that meshes with the pinion in a Kodak carousel projector. The inner layer is metal that holds lens elements. The lens comes to soft caps (probably made of LDPE) for both ends but neither actually fits.
Optically, this is a fabulous lens. It is a flat-field lens and is extremely sharp and extremely bright. I even felt that it might be too bright that my images are loosing color intensity when projected. A flat-field projector lens means that it requires the slide to be perfectly flat. In other words, it works best with glass-mount slides. Its short focal length produces a large image in a short distance -- best for home use where the room is usually small. The short focal length also makes the alignment of the optical path of the slide projector be of critical importance. The minor shortcoming is that its image field is not perfectly flat: the far corners are very slightly blurred, but not due to the unsharpness of the lens, and the area and the amount of blur is hairy small.
On the other hand, the quality of the projected image could be dismal for glassless slides. Only a small portion of the slide can be in focus at a given moment. And, without glass, slides literally pops, and my nerve gets ticked, in just a few seconds in the projector. Although Kodak's literature that comes with the projector suggests that a flat-field lens is most versatile for mixed slide mounts, I found that the lens would not give any better image than a cheesy (Kodak's) plastic lens for anything other than the glass mounted slides.
Overall, I am very happy with the lens. Perfect for professional quality home slide shows, with glass mounted slides. And it forces me to use only dupes on glass mounts for projection.