Celestron Orthoscopic 4mm

4.0 Celestron 4MM Orthoscopic

Very sharp and undistorted views; Very well built; Made in Japan; "Circle T" series.

Very short eye relief; Small field of view; May be difficult to find.

When it comes to viewing the Moon or planets, it's hard to beat a good orthoscopic eyepiece. Almost a year ago, I acquired a vintage Celestron 4mm orthoscopic ocular from a seller on Ebay. At that time I really hadn't had that much need for an orthoscopic, but I wanted to see what all the hype was about and took the plunge.

First, the eyepiece was solidly built. It has what is known as a cone or volcano-top, housing the very tiny eye lens. Eye relief is very short, near the the focal length of the eyepiece itself....give or take a few millimeters. Field of view is between 40 or 50 degrees. Even with the tight eye relief, the views were very sharp and contrast was outstanding. From my research I discovered that this eyepiece was made in Japan by the Kokusai Kohki company. That is why it wears the the famed "Circle T" inscription on the barrel.

This is an exceptional little ocular that can duke it out with the best of plossls and other similiar designs. I'm not sure about the coatings on the lenses. However, the eye relief and small field of view does keep me from using it more often, and reaching for the more modern long eye relief, wide FOV oculars in my case. But I do like having it around for those rare occasions when I want to see a colorless and undistorted view of lunar and planetary targets.

Yes, I like this eyepiece very much.