In summary, our SCA adapter serves three critical functions.
First, its expansion rings accommodate almost all focuser's manufacturing tolerances.  Second, it automatically centers the adapting laser.  Third, it provides at least two evenly distributed circular contacts on the focuser's inner tube surface preventing the adapting laser from pivoting.  Once the slop factor is taken away, you can quickly collimate your telescope in confidence to achieve perfect collimation every time.


The Problem

1. The Thumbscrew Gap:
The thumbscrew pushes the laser collimator off to one side of the adapting eyepiece focuser.  This off-axis distance creates a gap between the collimator's outside diameter and the focuser’s inside diameter.  No matter how accurately the laser is internally aligned, the displacement gap offsets the laser when fastened with the thumbscrew.  The displacement may seem small, but the misalignment grows when the laser beam travels a relatively short distance.   With slightly off, miscollimated mirrors in a fast telescope (F/5 or faster), the problem compounds substantially.  The illustrations below show how the laser beam is offset in three scenarios when the laser travels from the collimator to the primary mirror (in red line) and returns back to the laser origin (in blue line).

In figure 1, the primary and the secondary mirrors are collimated but the laser is installed offset, by the thumbscrew, from the true optical axis.  The laser only travels roughly parallel along the optical axis, but not on the axis, and returns with the same initial offset distance (assuming the focuser tube is parallel to the optical axis).  In this case, the user will be tricked into adjusting the secondary mirror first to center the laser dot on the primary, then adjusting the primary to point the laser back to the center of the true optical axis.  The attempt ruins a perfectly collimated telescope by adding astigmatism from the tilt compensation.

                                            
                                                    collimated                          misaligned

In figure 2, the primary is off 1 degree and the secondary is square to the focuser, and again the laser is installed offset from the true optical axis cause by the thumbscrew.  The deviation of the returning laser dot from the primary increases compared with the figure 1 scenario.

In figure 3, the primary is collimated, the secondary is off 1 degree to the true optical path, and the laser is installed offset from the true optical axis caused by the thumbscrew.  The deviation of the returning laser dot from the primary increases even more.

2. Adapting with Unified Compression Ring:

The unified compression ring actually does not do what it states.  The mechanism simply uses a thumbscrew crushing (but not uniformly contracting) an internal brass ring to clamp on the inserted tube.  When you take a closer look, it only forces the brass ring to bend into an off-centered oval ring creating two clamping points (not 360 degrees surface contact as you thought would be) on the inserted eyepiece tube (see photos below).

  
   

This spells disaster for a laser collimator.  With two sides clamping down creating two linear contacts, the compressed ring actually opens the other two sides wider even with a relief cut in the ring.  In addition, by design, the brass ring has to be larger than the adapting tube, so the total widened gap is even wider than the simple thumbscrew method.  The two-point clamping allows the inserted tube to wiggle/pivot on the wide/tangent sides. The only thing preventing it from pivoting is making sure the shoulder of the laser collimator is flush against the rim of the focuser and is tightly locked down with the compression ring.  But when you wiggle the laser collimator just a little more, you will find it starts to loosen up which allows the laser to dance around on the projecting mirrors in the orthogonal directions of the clamping points.  This “dancing laser spot” problem gets real frustrating because the user cannot repeat the laser collimation consistently.

Problem Solved with SCA Adapter Technology 

Many laser collimator manufacturers give users the wrong impression, “big and heavy means rugged and stable.”  Instead, HoTech engineers successfully cut the unnecessary weight on the laser collimator because we understand that additional weight on a telescope (especially open structure Newtonians) will create imbalance and structure sagging.  In addition, the heavier the device is, the more inertia it will have during an impact from an accidental drop.  In such an accident, the inertia force can cause more damage to the internal alignment mechanism because there is more energy required to dissipate from the impact.  Therefore, the lightweight design on our laser collimator makes you gain reliable precision collimation.  And of course our laser collimator uses aero-space grade lightweight aluminum material and CNC machined with the tightest tolerances, then sand blasted and anodized to protect from harsh environment.  Nothing has been sacrificed while you get a long lasting state-of-the-art collimation instrument.

More Technical FAQ on laser collimation

Includes 45º Faceplate Viewer with Laser Engraved Targeting Grid

The faceplate viewer helps to display the returning laser spot with a clear visual reference during adjustment.  The faceplate allows you to align your primary mirror from the rear of the telescope eliminating traveling to the front of your scope repeatedly during collimation.  HoTech understands the importance of this, so the faceplate is a standard feature in our laser collimator.  All astronomers deserve to have it without paying any extra! In addition, our faceplate viewer’s pattern is laser engraved to ensure a long lasting sharp targeting grid.  Unlike other collimators, the target is not a sticker that will peel, or paint that can rub off or chip.  We understand that you are paying for a precision instrument that is supposed to be well made.

Finest Projecting Laser Dot

Keeping the laser dot to the finest point is the key to precision collimation.  But when you look closely at the laser dot from brand to brand, most laser dots appear large, not really a fine point as you imagined.  This means there is guess work involved when you try to center the dot; not just centering the laser dot to the center of the faceplate, but also centering the center of the dot itself.  This does not make any sense when you are trying to take the advantage of the collimated laser beam's characteristic "which has a low beam divergence, so that the beam radius does not undergo significant changes within moderate propagation distances."  In other words, the laser beam size within the collimation distance (laser collimator to

the primary mirror and back to the faceplate) should remain a constant fine point.  As you know, most laser collimator brands are not really laser manufacturers.  They install an off-the-shelf laser module or pointer and align the laser in a tube without REALLY considering the user’s application, namely the operating distance for a laser beam size.  HoTech has been designing and building laser modules and systems for over 10 years for various professional industries.  We know exactly how a laser should work.  We limit our laser beam to the finest size in the correct operating distance for optimal effect.  Our understanding and experiences with the laser design permit you to have an effective and precision collimation.

High Accuracy Laser Alignment