Howie Glatter Laser Collimator for RC or Cassegrain (1.25-2" 532nm Bright Green)
This Glatter 1.25-2” stepped bright green laser collimator is the best tool for imagers using Altair Ritchey Chretien’s (RC’s) or Cassegrain telescopes.
Laser collimation of an imaging scope saves you time because you can get the Lion's share of collimation done during the day.
This is because it has a bright 5mw green laser beam at 532nm wavelength, which, unlike red beams, makes the circular target pattern (produced by the optional attachment) easily visible in the daytime when projected against a flat surface such as a wall*. This is most suitable for imagers, who tend to perform basic collimation during the daytime, with final tweaks on a star-image at night, with the camera running, so we recommend this as the best way to collimate an Altair RC or Cassegrain telescope.
This collimator produces a dot-style beam pattern if used on it’s own, therefore we recommend you order this collimator with the concentric-circle target pattern attachment which makes collimation of your RC or Cassegrain primary and secondary mirrors possible. This is achieved projecting the target against a surface such as a wall, while adjusting the primary and secondary mirrors. Choose the circular diffraction target option opposite when ordering. There are several online resources and methods for collimating your RC using this method.
How to collimate your telescope with a Glatter Laser Collimator: There are many methods and procedures to do this and it's often a case of what works best for you. Therefore, we aren’t going to recommend one approach over others as there are many, and we can't take responsibility for content on the web, however we would suggest you at least view these You Tube Videos done by a very helpful British gent. Often if this procedure is followed, tweaking the collimation on a star isn't required, but sometimes the introduction of imaging accessories necessitates it.
Without further adieu, here are the videos: (all open in new windows)
Why collimate with a laser? In order to achieve the best possible resolution and contrast, the optical elements of a telescope must be put into near-perfect alignment. Collimation is the adjustment of the position and orientation of the optical elements to achieve best performance. Laser collimation is a relatively new way to accurately and precisely collimate a telescope. When practised with accurate tools and correct techniques the various methods of collimation will converge to the same result, but laser collimation has several unique advantages. The laser collimator provides its own light source, so collimation can be readily accomplished or checked after dark without additional equipment. Unlike passive collimation tools, your eye position is not constrained by a peep-hole and cross hairs, and you don’t need to scrutinize elements at different distances simultaneously.
Laser alignment and Shock Resistance: In use, the laser collimator is placed in the telescope’s eyepiece holder and clamped. A laser module inside the collimator emits an intense, thin, parallel beam of light, which exits a front aperture and projects along the central axis of the cylindrical collimator body. The beam acts as a reference line from which alignments are made. The most important thing about a laser collimator is that the beam be aligned with the collimator's cylindrical axis. If the beam alignment with the collimator body is off, the collimation will be off and the telescope will not achieve its best performance. For a collimator to serve as a reliable reference tool over the long term, the internal laser alignment must withstand mechanical shock. My collimators incorporate features to make them highly shock resistant. After I align the laser to the collimator body within 15 arc seconds, I test the collimator by whacking it against a block of urethane, striking at least a dozen times on three axis. I then check the alignment, and if it hasn’t changed the collimator goes into stock.
The collimators usually withstand drops from eyepiece position up a ladder without losing alignment. Glatter collimators are unique in this respect. If the laser inside a collimator is misaligned, rotation of the collimator on its axis will cause the beam impact to trace a circle. However, rotating a collimator in an eyepiece holder is not the best test of a collimator's alignment due to the small space between an eyepiece holder and the collimator. The collimator may wobble like a top as it is rotated, and then even a good collimator's spot can travel in a circle. For a valid test the beam impact location should be carefully noted, then the collimator unclamped, rotated, and re-clamped, and the beam location checked to see if it has wandered. An engineer’s V-block is the best way to tell if a collimator is mis-collimated.
Collimator sizes: Howie Glatter produces collimators in three different body sizes: a 1¼" only, a 2" only, and a combination 2"-1¼" size. The combination size is 2" at the back, and steps down to 1¼"at the front. The 2"- 1¼" or 2" collimator is recommended for accurate alignment in a 2" eyepiece holder, but the 1¼" collimator is o.k. in a 2" holder if used with an accurate adapter. The adapter can be itself checked for accuracy with the collimator by rotating the adapter and re-clamping it, and seeing if the laser spot wanders. The combination type is the most common solution, allowing any type of telescope to be collimated.
Wavelengths offered and what they are recommended for:
Red 650nm or 635nm wavelengths: The red collimators are offered with a choice of either 650 nanometre or 635nm wavelength. Both lasers have the same beam power output, but because the human eye's sensitivity to the shorter (red) wavelength is greater, the 635nm. red laser appears about two or three times brighter. The 635nm laser is more expensive, but it enables Barlowed or holographic collimation in higher levels of ambient light. In darkness, and for visual observers, the 650nm laser is adequate and it’s a “deeper” red colour, so it doesn't degrade your night vision as much as the other types.
Green 532nm Wavelength: Glatter also offers a 532nm green collimator, much brighter than the red ones. In most circumstances it is overly bright for night time collimation, unless you are an imager, but it is useful for Barlowed or holographic collimation daylight or room light. It is stocked in the 2"-1¼" combination size only. Seeing that imagers tend to do their main collimation in the daytime, and need a visible beam pattern projected onto a surface, the 532nm 5mw “bright Green” collimator is the best solution for RCs and imaging scopes.
The included 1mm stop Attachment: The beam produced by red lasers used in collimators is fuzzy-edged and elongated. When making collimating adjustments you will have to judge the location of the center of the spot by eye. To improve adjustment precision I supply my collimators with a detachable aperture stop accessory having a knife-edge 1mm pin hole and a white screen front. The stop is included in the basic collimator price. The stop screws into the laser aperture and restricts the beam, producing a tiny circular impact surrounded by a series of concentric rings. The edge of the pinhole diffracts some of the laser light, forming the concentric rings, which facilitate precise centering. With the stop attached to the collimator, the beam impact looks like a star diffraction pattern. The diffracted light that forms the rings is divergent, and this fact allows the stop to also be used to implement a low-contrast form of “Barlowed” collimation, explained below under the heading of Barlowed collimation.
The Holographic Attachments: The optional holographic attachments screw onto the front of the laser, and have a white screen front surface. They contain an optical element that diffracts most of the laser light into a diverging symmetrical pattern around the central beam. The projected pattern is useful for centering optical elements by making it symmetrical with the edge of the optic.
Three different types of holographic attachments are available:
• A nine-concentric circle pattern is available that spans 10 degrees and will reach to the edge of f/ 5.7 optics. This pattern is recommended for scopes around this focal ratio or slower. Because the laser light is spread over a smaller area it is brighter than the square grid pattern, and this makes it particularly useful with Cassegrain scopes, where the pattern impact is sometimes scrutinized on the mirror surfaces. The projected pattern is seen only by light that is scattered from dust, dirt, or optical roughness, so a brighter pattern is better, especially if the mirrors are very clean. (Recommended for Altair Astro RC & Cassegrain telescopes).
• A cross-hair and circle “scope” pattern is available that spans 10 degrees. It has utility for non-Barlowed, conventional Newtonian primary collimation, where the primary is adjusted to return the reflected central laser beam back into the laser aperture of the collimator. The cross-hair intersection makes it easier to see when the return beam is centred on the collimator face.
• A 10 x 10 line square grid pattern is available offering the widest pattern. It spreads 21 degrees which allows centering of optics as fast as f/ 2.7. This pattern is recommended for general use because it can be used with the fastest telescopes likely to be encountered. Recommended for fast Newtonians to correct mirror offset.
Laser collimator safety: The lasers in the “Bright” Glatter collimators have a maximum power of 5 milliwatts, and are quite safe if used with reasonable precaution. Direct or mirror-reflected eye exposure to any laser beam (regardless of power) should always be avoided, so be careful when collimating to ensure that the beam doesn’t enter anyone's eye. The beam's impact on a surface can be viewed with no problem if the surface produces a diffuse reflection. The beam impact on a mirror or lens surface may be safely viewed if the reflected or transmitted beam is not directed towards your eye. A badly miscollimated Newtonian or Cassegrain may allow the beam to exit the telescope, so check first by pointing the telescope at a wall or screen to see if the beam is escaping. With unobstructed telescopes such as refractors the beam will always exit the front of the telescope, so a strip of masking tape should be run across the dew cap or lens cell as a safety beam stop.
Collimator alignment within the eyepiece holder: Inconsistent registration of the collimator in the eyepiece holder is a main cause of laser collimation difficulty. When the collimator is clamped, a small sideways displacement may occur, but that won’t cause a problem if the collimator and holder axis remain parallel. However, significant problems do occur when the eyepiece, collimator or camera adapter tip, and the two axis go out of parallelism. If the tipping is consistent and repeatable, collimation can be accomplished, but if the eyepiece holder does not provide a stable pointing direction for the collimator, consistent results cannot be expected. Get a self-centering eyepiece holder or “parallelizer” and leave it in the scope after collimation.
Focuser stability: The collimator, with its long light beam as a "lever arm" is a very sensitive tool for detecting focuser problems. All too often the laser beam impact travels in a circle as a helical focuser is rotated, or jumps back and forth as focus direction of a rack-and-pinion focuser is reversed. Whatever focuser axis instabilities exist should be fixed or minimized, up to and including focuser replacement. However, even if the problems are not fixed, laser collimation of the telescope can be accomplished if the focuser is adjusted to a stable position and not disturbed over the course of collimation.
*The human eye is many times more sensitive to green than red – some suggest this is linked to evolutionary biology because foliage is green. Some suggest that green wavelengths have more energy, and therefore affect our retinal receptors more efficiently. Without coming down on either side of the debate, all we know is green is way more visible than red...
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