Orthoscopic Eyepieces

The Orthoscopic design was developed by Ernst Abbe in 1880. Since the Orthoscopic eyepiece design is so old, why is it still so popular? Because they can deliver high contrast, distortion free and high resolution images. These characteristics make them the eyepiece of choice for many planetary observers.

Orthoscopics are a 4 element design with a cemented triplet field lens and a single plano/convex eye lens. The field lens is in a convex/convex, concave/concave, convex/convex array. It is the lower amount of glass elements that make these such great eyepieces for planets. Less glass means less distortion, higher through put, and higher contrast. Sometimes simple is best.

This isn't meant to dismiss more complex designs, such as Naglers and other wide field eyepieces. I own and have owned and use many types of eyepieces for different types of observing. But for high-power, planetary and lunar work I still love the Orthos.

In fact the Carl Zeiss Abbe Orthoscopic Eyepieces, which are no longer in production can still fetch $600.00 and more on the used market! They are a true classic and one of, if not the best, example of Ortho oculars ever produced.


But if you are on a budget don't despair. Baader Planetarium has a line they call "Baader Planetarium Genuine Orthoscopic Telescope Eyepieces" and they offer terrific performance especially for their low cost (around $100). Although, like all orthos, they have a narrow apparent field of view, when doing high powered work on planets and the moon I don't care about great vistas. I want clarity, high contrast and no distortion and these do deliver.

The Reflecting Telescope

Unlike refracting telescopes, which use a lens, reflecting telescopes use a combination of curved mirrors to produce an image which can the be magnified using an eyepiece. The first reflector was designed by Sir Isaac Newton (of apple on the head and gravity fame) in 1668. This simple and elegant design is still in use today.

The biggest advantage reflecting telescopes have over their refractor cousins is size. The largest refractor in operation is a 40 inch professional scope at Yerkes Observatory in Wisconsin. However the largest single mirror reflector is a whopping 323 inches! Of course these are professional instruments.

For us amateurs the big advantage reflectors have is price per inch of aperture. You can find a nice 6 inch Newtonian reflector on a decent quality equatorial mount for around $500. A fair refractor on the same mount would cost at least $1000. You can buy some nice eyepieces with 500 bucks!

Another plus on the reflectors side is their lack of false color. Refractors are notorious for halos of color around bright objects. This is due to the physics of lenses, the different wavelengths of light focus at different points. This can be mostly eliminated in modern apochromatic refractors, but this can add greatly to their price as well. For example my 90mm APO cost almost $1000. Beautiful scope, and you couldn't pry it out of my fingers but still...

 Of course the basic design of Sir Isaac has changed over the years and now there are many different types of reflecting telescopes available to both professional astronomers and the amateur community.