The Great Houdini Zoom

A new Widefield Zoom eyepiece for telescopes and spotting scopes
featuring 18-7 mm focal length and 69° to 81° field of view

On several astronomy forums I have met people expressing interest in zoom eyepieces with greater power ranges and wider fields of view than are currently available. Most astronomical zoom eyepieces have a power range of around 2X and a field of view up to 60° or 65°, with only a couple of exceptions going above 70° at their highest power.

The concept of a wide-field, large-range zoom eyepiece is quite an interesting challenge. With the help of our Eyepiece Designer software we created an optical design from scratch that the engineers at KUO called "somewhat unique". The zoom eyepiece is intended for telescopes and spotting scopes, offering the following exceptional combination of features:

  • A 2.6X power range from 18 to 7 mm focal length. In a typical astronomical telescope this eyepiece covers the most frequently used powers.
  • A wide field of view, starting from 69° at 18 mm up to 81° below 10 mm.
  • Well-corrected, sharp images across the field even in fast F/4 telescopes.
  • A comfortable eye relief between 17 and 20 mm.
  • Nearly parfocal with less than 1.5 mm of focus difference across the entire zoom range.
  • Click stops at convenient focal lengths (probably 18 - 16 - 14 - 12 - 11 - 10 - 9 - 8 - 7).

The field stop at 18 mm would be similar to a Televue Delos 17.3, and at 7 mm it would be similar to a Nagler 7. The eyepiece should reach focus in nearly all telescopes; requiring 10 mm of inward focus travel in a 1.25" focuser, and 5 mm of outward focus travel in a 2" focuser.

Someone at CloudyNights coined the term "The Great Houdini" for this design, which sounded like a fitting name for the project.

Crowdfunding Campaign

Premium zoom eyepieces are expensive to manufacture; the cost of a production run of our design exceeds USD 100,000. Since we are currently investing heavily in the Houdini coma-correcting eyepiece lineup, we are turning to crowdfunding to bring this new zoom eyepiece to market.

We've created a Kickstarter campaign with a funding goal of €85,000. The money raised will fund the creation of a prototype and enable an initial production run.

Backers who pre-finance the project will receive the Great Zoom eyepiece for €599 or a pair for €1,149. About 140 backers are needed to reach the funding goal and make the eyepiece a reality.

The campaign will run for 30 days, ending on June 20. If the target is reached it would take four months to create the prototype, one month for in-field validation, and then four months for the production run. Delivery would be expected in March 2026.

If you like the idea of this innovative zoom eyepiece, please visit Kickstarter today and pledge to the campaign. Spread the word about it wherever you can. The eyepieces can be shipped worldwide, so anyone can participate.

The power of the zoom

The images below simulate the operation of the zoom eyepiece in astronomical telescopes and spotting scopes, to demonstrate the 2.6X power range and the variation of the apparent field of view.
From top to bottom: the globular cluster M3, a kingfisher, the Whirlpool Galaxy M51, a pair of flamingos, the Moon, a deer, and the Orion Nebula M42.
From left to right: 18 mm, 11 mm, 7 mm focal length with resp. 69°, 80° and 77° field.

 

Detailed Specs

Some of the numbers below may change when the prototype will be finalized and validated, but we guarantee the main specifications: an 18 to 7 mm focal length with an apparent field of view from 69 degrees to over 80 degrees, and comfortable eye relief.

 

 

Standard 1.25" and 2" barrels are integrated in the eyepiece body. The focal point lies 10 mm above the top of the 1.25" barrel, and 5 mm below the top of the 2" barrel. The eyepiece should easily reach focus in most telescopes.

Physical Dimensions: 145 mm high and 62 mm diameter.

Timeline

Manufacturing the prototype is expected to take four months. After a one-month period of in-field validation, the actual production will take another four months. Delivery is expected in March 2026.

The eyepiece will be manufactured by Kunming United Optics, a reliable source of premium telescope eyepieces. We have worked with them before to create the Houdini series of coma-correcting eyepieces. They have great know-how and produce some of the best eyepieces on the market.

The zoom eyepiece reinvented

Most zoom eyepieces operate through movement of two internal lens groups: a "compensating" group and a "zoom" group. We designed a zoom eyepiece from scratch with only one moving group. The manufacturer's optical engineers wrote us that they found the Houdini Zoom design "somewhat unique" ;-). The design simplifies the zoom mechanism and allows for greater flexibility in the optimization process. 

We optimized this eyepiece using our Eyepiece Designer software, which takes multiple zoom positions into account during the optimization process. The end result is an exceptional eyepiece with a large field of view across the entire range, surpassing any zoom eyepiece currently available for astronomical telescopes. This was achieved without the use of exotic glass types or special elements, such as aspherical surfaces.