Houdini Eyepiece Specifications
| Eyepiece | Focal Length mm | AFOV ° | Field Stop mm | Layout | Eye Relief mm | Weight g | Diameter mm | Height mm | Barrel | Barrel Length mm | Focal Point mm | Flatness diopter | Angular Magnification Distortion |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Houdini 30 | 30 | 80 | 42.0 | 8 / 6 | 20 / 15 | 580 | 64.5 | 140 | 2" | 38 | +2 | < 0.7 | < 3% |
| Houdini 20 | 20 | 86 | 30.0 | 8 / 6 | 20 / 15 | 570 | 64 | 140 | 2" | 35 | +2 | < 0.7 | < 2% |
| Houdini 12 | 12 | 86 | 18.0 | 9 / 7 | 19 / 15 | 330 | 51 | 121 | 1.25" | 34 | -0.5 | < 0.5 | < 3% |
| Houdini 9 | 9 | 86 | 13.5 | 9 / 6 | 19 / 15 | 300 | 48.5 | 127 | 1.25" | 31 | -0.5 | < 0.5 | < 2% |
| Houdini 7 | 7 | 86 | 10.5 | 9 / 6 | 19 / 15 | 290 | 47 | 129 | 1.25" | 30 | -0.5 | < 0.5 | < 2% |
| Houdini 5.3* | 5.3 | 86 | 8.0 | 9 / 6 | 18 / 14 | 47 | 128 | 1.25" | 28 | -0.5 | < 1.0 | < 2% | |
| Houdini 4* | 4 | 86 | 6.0 | 9 / 6 | 18 / 14 | 47 | 138 | 1.25" | 28 | -0.5 | < 1.0 | < 2% |
* Expected in 2027
AFOV = Apparent Field of View
Layout: Number of Elements / Number of Groups
Eye Relief: Theoretical Eye Relief (center of field, to glass) / Effective Eye Relief (edge of field, to body)
Diameter: Maximum diameter of the aluminum body - the rubber grips add around 1 mm to the diameter
Height: Includes the height of the eyecup
Barrel: Standard size 2" = 50.8 mm or 1.25" = 31.75 mm
Focal Point: Position of the focal plane with respect to the barrel. Positive values are above and negative values are below the top of the barrel
Houdini Eyepiece Performance
The following graph illustrates the performance of the Houdini eyepieces in an f/4 Newtonian telescope. Spot diagrams with 3,000 rays are shown for the center, halfway point, and near the edge of the field.
The spot diagrams have been strongly magnified to make them easier to see. At the center of the field, a spot diameter smaller than 2 arcminutes is considered nearly perfect. Near the edge of the field, a spot diameter smaller than 10 arcminutes is considered very good, while 5 arcminutes is excellent. The top left shows reference circles of 2' and 5'.
There is no trace of coma remaining in the Houdini spot diagrams. Some spherical aberration and lateral color remain, which are visible only on very bright objects, such as a magnitude 1 star or Jupiter, near the edge of the field. These aberrations are not visible in a typical deep-sky field that does not contain such bright objects. As a result, the field appears essentially sharp from edge to edge.
The following diagram shows the star images produced by these spots. Real star images are not point-like, but instead consist of a diffraction disk (Airy disk) surrounded by diffraction rings. In an F/4 telescope, an observer will start to see the diffraction pattern at around 12 mm focal length. At higher powers, the diffraction disks become larger than the spot diagrams of the eyepieces, at which point the eyepiece can be considered “diffraction-limited.”
Houdini Barlowed Eyepiece Performance
The Houdini 2× coma-correcting Barlow is optimized for use with the 1.25" Houdini eyepieces. The Barlow corrects 75% of the Newtonian coma, while the remaining 25% is corrected by the eyepieces.
Below are the star images produced by the Houdini 12, 9, 7, 5.3 and 4 with the 2× Barlow, producing the equivalent of 6 mm, 4.5 mm, 3.5 mm, 2.65 mm and 2 mm focal lengths, respectively, compared to the Houdini 7, 5.3 and 4 without a Barlow. At the shorter focal lengths, the entire 86° field becomes diffraction-limited.
