This unique 2” Glatter holographic laser collimator makes it easy to collimate any type of telescope. Optics that are out of collimation (with optical elements that are not all exactly aligned on the same optical axis) cannot produce good images. Stars will be elongated or lopsided, planetary details will be hazy and low in contrast, and binary stars will be difficult to split cleanly. Regular collimation with this highly accurate laser collimator will make sure that you get the best possible image contrast and resolution every night you go out to observe.
Precisely centered inside this 2” Howie Glatter Laser Collimator’s 3” long machined aluminum body is a solid-state 5 milliwatt laser diode. This emits an intense beam of red laser light exactly along the central axis of the cylindrical collimator body. A transparent removable diffractive optical element (the “hologram” generator module) is threaded into the body of the collimator, in front of the laser emitter, as seen in the picture above. This diffracts the single beam of light from the laser to project a diverging rectangular grid pattern around the still-visible bright central beam. This pattern is exceptionally useful for centering optical elements (the telescope lenses and mirrors).
The pattern is a ten line by ten line grid, forming a large square box enclosing eighty-one smaller squares. Each of the eighty-one smaller squares is further faintly divided into four smaller squares, a pattern that extends outside the boundaries of the large ten by ten box and gradually fades out as it gets further off-axis. The feature illustration below shows the actual pattern as projected.
The grid covers a wider angle (21°) than any other holographic collimator, which allows direct centering of optics as fast as f/2.7 to as slow as f/35. The rectilinear grid pattern of multiple lines is more sensitive to decentered circular optics than other patterns. If a mirror or lens is decentered by only a small amount against the grid pattern, it produces a proportionately larger and more easily-seen asymmetry of the perimeter of the optic against the intersections of the multiple grid line pattern. Cross-hair patterns do not have this property and a concentric circle pattern can only be as accurate as the grid method if one of its rings happens to be very near the optic’s edge.
Because there are some collimating situations in which the diffracted hologram pattern is unnecessary or unwanted, or maximum power in the central beam may be desired, the hologram generator module unscrews from the laser aperture and can be replaced by a single beam aperture insert.
The beam from all red diode lasers used in collimators is fuzzy-edged and elliptical in cross-section. When collimating, you sometimes must judge the location of the center of the spot by eye. To improve collimating precision, the single beam aperture insert has a 1mm hole surrounded by a matte white circular target. It produces a tiny, circular beam which allows more accurate alignment. With the single beam aperture threaded into the collimator, the beam impact on a flat surface at a distance of one meter or more looks like a star diffraction pattern, with a central dot surrounded by diffraction rings. The surrounding rings can help in centering the beam very accurately. When the single beam aperture is removed, the holographic generator module retains its alignment accuracy when it is screwed back into place in the collimator body.
Each hologram generator is individually fitted to its laser collimator for maximum alignment accuracy. Be careful not to switch hologram generators with someone else’s collimator. If switched, each collimator’s 15 arc second alignment accuracy in the holographic mode is likely to be lost, However, even if switched, both collimators will still fall within the several arc minute alignment tolerance of most other laser collimators.
The laser emits monochromatic red light at a wavelength of 635 nanometers. This wavelength appears two to three times brighter than the more common 650nm laser collimators, due to the human eye’s greater sensitivity to the shorter wavelength. This allows collimation under higher levels of ambient light, such as during twilight when first setting up your scope, so you don’t lose valuable observing time when darkness falls. A rotary switch in the end of the body turns the laser on and off.
In use, the collimator with the holographic generator is placed in a reflector, refractor, or classical Cassegrain telescope’s eyepiece holder and turned on. Catadioptric telescopes such as Schmidt-Cassegrains and Maksutov-Cassegrains generally do not have mirrors that can be user-centered, so the hologram generator is not used with these scopes.
The laser’s grid image is projected from the front of the telescope against a flat surface a few meters away. This lets you check and adjust the centering of the optical elements. Once the centering is checked, the laser (either with the holographic generator in place or with the single beam aperture) is used to check the collimation of the correctly centered optical elements. The laser beam travels through the scope, reflects off the scope’s optics, and returns to fall back on the flat end of the collimator. If the returning laser beam falls exactly on the small black aperture that is emitting the beam, the scope is in collimation. If the returning beam instead falls on the face of the collimator that surrounds the emitting aperture, the scope is out of collimation. There is a pattern of three concentric circles etched into the 2” face to help in centering the returning beam. Out-of-collimation optics are simply adjusted until the returning beam lands squarely on the aperture emitting the beam.
CAUTION: The Class IIIa laser in this collimator has a maximum output of 5 thousandths of a Watt (5 mw). This is quite safe if it is used with reasonable precautions. However, direct or mirror-reflected eye exposure should be avoided! Detectable eye damage can occur if the laser beam is focused on the same area of the retina for as little as 0.25 second. Therefore, take care when collimating your scope to be sure that the beam does not enter anyone’s eye directly, including your own. Keep it locked away when not in use and out of the hands of children. It is not a Star Wars light saber for them to play with.
There is no danger in viewing the beam’s impact on a surface that produces a diffuse reflection, such as the face of the laser collimator itself. The beam impact may also be safely viewed on a mirror or lens surface, if the reflected or transmitted beam is not directed towards your eye. A Newtonian or Cassegrain that is badly out of collimation may allow the beam to exit the front of the telescope, so when collimating these scopes, check first by pointing the telescope at a wall or screen to see if the beam is getting past the secondary or diagonal mirror. With a refractor, the beam will always exit the front of the telescope, so run a strip of masking tape across the diameter of the dew cap opening as a safety beam stop.
Two important considerations in choosing a laser collimator are the accuracy and stability of the laser beam alignment to the cylindrical axis of the collimator body. This collimator’s alignment tolerance is an impressive fifteen arc seconds. In order to ensure that this level of accuracy is always available, the collimator is designed – and tested – to withstand a shock equivalent to dropping the collimator from the eyepiece position on a tall Dobsonian telescope, without altering the fifteen arc second alignment. Most other laser collimators cannot withstand this kind of accident without loss of alignment.
The collimator comes with a single CR123A lithium battery that will power the laser for approximately 40 hours. Lithium batteries maintain a stable output voltage for their entire lifetime, giving maximum laser output. Replacement batteries are widely available (they are commonly used in point-and-shoot cameras) and usually sell for about $6-$7. The collimator is supplied with one battery, a plastic storage case, press-on collimation “donuts” for use with Newtonian reflectors, and very complete instructions for collimating telescopes of all optical types.