- Designed for use with the Howie Glatter Laser Collimator
- Screws into the laser aperture and diffracts the laser beam into 9 concentric circles spanning 10 degrees
- Recommended for superb collimation accuracy - especially with f/5.7 or slower Cassegrain telescopes
- Useful for checking and aligning interior baffles
- Allows accurate verification of mechanical centering and aligning the internal elements of the telescope to each other
The flexibility of the Howie Glatter Laser Collimator is evidenced by this optional holographic attachment that screws into the laser aperture. The attachment has a white screen front surface. It contains an optical element that diffracts much of the laser light into a series of symmetrical rings around the central beam. The projected pattern is useful for centering optical elements by making them symmetrical with the edge of the optic.
The holographic attachment’s pattern’s nine-concentric circles span 10 degrees and reach to the edge of f/ 5.7 optics. This pattern is recommended for scopes having approximately this focal ratio or slower. It is brighter than the standard square grid pattern because the laser light is spread over a smaller area. This makes it particularly useful with Cassegrain telescopes where the pattern is sometimes seen on the mirror surfaces.
All of the optical elements of the telescope should be centered and made square with the optical axis which should ideally coincide with the mechanical axis of the telescope tube. In practice the procedure may be complicated by restriction of the beam by baffles inside the tube and the refractive elements in some designs. With the holographic attachment, baffles can also be checked and aligned using the projected pattern.
The projected reticle pattern from the collimator is perfectly symmetrical around the central beam so it can be used for verifying mechanical centering. The position of the reticle pattern or central beam projected from one element onto another can be used to align the elements with each other.
Here is the general procedure as prescribed by Howie:
- Check drawtube or back centering with a ruler or caliper
- Check drawtube or back squareness by projecting the single beam down the tube and checking beam centering at the front by measurement from the tube walls
- Check centering of the secondary mirror by measurement from tube walls
- Check that reticle pattern is centered on secondary
- Check centering of the primary by measurement to the tube structure
- Adjust the secondary to reflect the reticle pattern symmetrically onto the primary. This should also fold the central beam back on itself.
- The pattern reflected by the primary is projected in a parallel beam out the front of the telescope.
- The angular adjustment of the primary is done by projecting the pattern onto a surface or screen in front of the telescope and adjusting the primary to center the pattern around the shadow of the secondary or secondary baffle (If a baffle, its centering should be checked).
Some collimation adjustments require observing the position of the reticle pattern on the primary and secondary surfaces. Viewing is done from far enough off-axis so that the reflected reticle pattern is not aimed towards your eyes. The reticle beam dot or pattern on a mirror (or lens) is only seen by light that is scattered from dirt, dust, or optical roughness on the surfaces. Be aware that visibility of the pattern impact can easily wash out in daylight, room light, or low ambient light, especially if the mirrors are clean. Because of this it is recommended that the brighter 635nm collimator be used for Cassegrain collimation in conditions other than darkness.
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