Frequently asked questions

In addition to Newtonian telescopes, coma-correcting eyepieces will work well on any telescope with a long focal ratio. In a typical 6" f/8 refractor, the performance of the Houdini eyepieces will be very good, and in a typical 8" f/10 SCT, the eyepieces will be near perfect. This means that most popular SCTs and long refractors will be well served by the Houdini eyepieces. The overall optical excellence and great ergonomics of the eyepiece will make it a very good choice for all these telescopes.

Houdini eyepieces will not work well on fast refractors in the f/4 to f/5 range, the coma-correcting eyepieces would show inverse coma. For example, we do not recommend using Houdini eyepieces on a 4" f/5 APO refractor.

No, the coma correction is built-in and does not require any special positioning. You can focus a coma-correcting eyepiece just like a normal eyepiece, and you'll get the optimum view.

For comfort all Houdini eyepieces are designed to be essentially parfocal. You'll appreciate the fact that changing eyepieces requires only the slightest of touches of the focuser.

The 20 mm is the first of a full line of premium 86° coma-correcting eyepieces starting from 30 mm down to 4 mm - including 12, 9 and 7 mm focal lengths.

We also have plans for 5.3 mm and 4 mm eyepieces, and a coma-correcting 2X telecentric barlow.

The series will present a nice continuity: 86° AFOV (except the 30 mm which will be closer to 80°), 20 mm eye relief, flat and distortion-less field, weight between 300 and 600 gram, close to being parfocal, and with similar housing length, eye lens and comfort.

It may take some months before all these items can be taken in production, but we are in this for the long run.

For your eyepiece collection we recommend the following scheme.

At lower powers, relatively large steps make sense; a factor of about 1.5 or 1.6 between the eyepieces is nice for quickly zooming in on an object.

At higher powers it's useful to have a closer spacing between the eyepieces to better respond to atmospheric seeing conditions; a factor of about 1.3 between the eyepieces is useful.

For even higher powers you can add a 2x Barlow, but unless you live in excellent seeing conditions you will not use this very often.

The focal lengths of the Houdini eyepieces have been chosen according to this scheme. At low power you have 30, 20 and 12 mm eyepieces with about 1.5X between each eyepiece. At high power you have 12, 9, 7, 5.3 and 4 mm eyepieces, maintaining the 1.3X factor that allows you to fine-tune to atmospheric seeing conditions.

Correcting coma in the eyepiece is the most efficient, economical, and ergonomic solution.

The alternative, using a separate coma corrector inside the focuser, has significant drawbacks - there's extra weight, significant cost, reduced field of view, reduced focusing comfort, and need for focus in-travel. See the Benefits of Coma-Correcting Eyepieces.

The Pretoria was a coma-correcting eyepiece produced in small quantities in the 1980s. It was a 50° eyepiece, which even in the 1980s was not really widefield. Other than its coma correction, in many ways it was inferior to competitive designs with wider fields. It was also very expensive - over $USD 200 back then, for what was still only a 50° eyepiece.

In contrast, Houdini eyepiece designs are very modern and state-of-the-art; they present all the features we expect in premium eyepieces in 2025. This means not just tight star images to the edge, but also an ultra-wide flat field without distortion, that is easy to view with a comfortable usable eye relief.

Even without the built-in coma correction, a Houdini eyepiece would be one of the finest eyepieces currently available, at an affordable price.