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3" MacroGlide ALPHA/OMEGA Docking Focusers

Manual, DC Servo (analog) & Auto-Focus Stepper (digital) Motor Control

Without Comparison, the Finest Feature-Packed Focusers on Planet Earth

If you're THINKING "larger than 2 inch" FOCUSER, THINK GLIDERS for the FOLLOWING REASONS

Mount any VSI Focuser to any Scope - Not just Meade & Celestron

AP, Borg, OGS, RC Optical, Takahashi, TeleVue, TMB, Vixen, etc., etc. - Just Call VSI

MACROGLIDE Features & Specifications:

Introducing VSI's GIGANTIC 3" MacroGlide ALPHA/OMEGA Docking Focusers. The huge dual 3" diameter custom machined knobs and smaller dual micro-focus knobs (5 to 1 ratio reduction), now copied by many, have made a comeback on this mega-focuser. These giant 3" focusers conform to the existing 2.7" SAE and 72mm (2.835") metric threaded standards set by these established formats. Our focuser's moving tube, TRUE internal clear aperture is a full 3 inches. In fact, our proprietary output adapter format diameter is 3.1 inches (see Output Adapters link above right). This massive focuser is available for refractors (ALPHA model) with a whooping 5" of tube travel (primary focuser), and SCTs (OMEGA model) offering 1" of tube travel (secondary focuser). Custom tube travel lengths are available by special order.

MacroGlide focusers can couple directly to our Zerotators, Sidewinders, or Targetrons using the same 2.9" flanged format, so port rings are 100% interchangeable. You can stack components (see picture at left) in any configuration you want using coupling port rings (see Output Adapters link above right, and Sidewinder Docking Port Rings link) that only consume 1/8" of profile. Add a [1-inch profile] Zerotator (see Rotators link) to your MacroGlide and gain rock-solid, zero-flexure, super-fluid, radial ball-bearing Z-axis rotation of your entire imaging train. And our ATLAS Zerotator can handle any load you throw at it - guaranteed!

Each of the ALPHA/OMEGA focuser models have been optimized, for their specific function, from the ground up. The OMEGA has been designed with the shortest profile possible (2.75") as a secondary focuser for SCTs, etc. In fact, it's the same profile as the 2" MasterGlide M1 through M3 focusers, but much "fatter." The ALPHA model was designed for maximum rigidity as a primary focuser for refractors, etc. It has a slightly longer minimum profile (3.5") due to extended spacing between the massive Crayford bearings, and extra metal between those bearings, that are mounted on the focuser housing. This design creates a stronger, more rigid moving tube to better support the ALPHA's 5" of tube travel.

As you can see by the 3" diameter knobs, the OMEGA SCT model has only 2.75" of profile (same as our 2" MasterGlide focusers M1 through M3). Of course, DC servo (w/hand paddle) and/or autofocus stepper motor control are available (purchase stepper motor electronic hardware package from Technical Innovations, $295, see Autofocus link for more info). Interchangeable docking and output rings (optional) are available for every telescope and application possible.

Over the years VSI has continually taken the best features of all our previous focuser designs and incorporated them into new "super focuser" models. We do this not only to continually improve our products, but to [also] leave copy-cats in the dust. Of course, these VSI knock-offs are the greatest form of compliment!  It tells you that VSI products are always the best by design, function and application. The only way to keep ahead of these imitators is to design new and creative focusers faster than they can copy our designs and incorporate them into their product lines. This unique design philosophy has pioneered our Crayford focuser development since John Wall first invented it back in the early 1970's (see "Brief History of the Crayford Focuser" below), and kept VSI on the "cutting-edge" of focuser design for decades.

What we consider to be the most important mechanical feature is the dual pressure points on the Crayford rod. Instead of one pressure point, which has now been copied by just about every focuser manufacturer around, VSI now uses two identical Teflon pads with two large set screws (see picture right). This design upgrade literally doubles the pressure applied to the Crayford shaft, in effect doubling the holding power. By applying equal pressure along a full 1-inch length of the Crayford rod and the entire 1-inch width of the moving tube's machined flat, you create a more positive rack & pinion-like movement, while cutting your tactile contact, necessary to move the focusing tube, in half. In other words, all our Gliders have super-smooth, true feather action control. This creates an incredibly soft-touch, tactile manual focusing function that no other focuser can begin to offer.

Our QUAD-LOCK system is incorporated in our 2" reducer output port insert ring  (item #A312R pictured right) offering astroimagers a rock-solid coupling between a MacroGlide focuser's moving tube and your 2" barrel nose. Four tightening screws lock your 2" barrel nose into the focuser's moving tube - two 10-32 Nylon thumb screws and two [hidden] 8-32 set screws. The first two thumb screws, opposed by 90 degrees, lock your barrel in place from one end of the tube, and the other two set screws lock from the other end of the tube. This 4-screw application allows any 2" barrel nose to meld with the MacroGlide focuser's moving tube, creating a zero-flexure coupling. See VP Accessories link for more info on VSI's exclusive adapters.

VSI's massive 3" focusers are designed for astroimaging. So creating a rock-solid coupling between the focuser's moving tube and your extended imaging train is mandatory. As you know, 2" and 1.25" barrel nose formats are the "weak link" between your focuser and long extended imaging trains. These barrel nose formats are for eyepieces but, somehow, all standard focusers have always been created to accept this [less than adequate] format - even VSI focusers. Very seldom do you insert an eyepiece directly into a focuser, unless you are using a Newt/Dob for visual observing. You [at least] have a standard diagonal between your focuser and eyepiece, when using catadioptric and refractor type scopes. Now you can convert a MacroGlide focuser's standard 2" barrel-nose insert reducer (Item #A312R) to solid, low-profile [industry-standard] threaded formats (2"-24tpi threads, or standard 42mm-0.75mm thread pitch T-thread) with the simple use of VSI adapters (item #A2LT & #AT2, see links). And the coupling is [now] rock-solid so you can stack an extended, long profile imaging train onto these threaded couplings without flexure!

These two hidden [captive retaining] set screws on the MacroGlide focuser's insert adapter (pictured right) are also designed to hold our Hexagonal 1 or 2 in the focuser. A specially grooved barrel nose on the Hexagonal (see Hexagonal link for details) allows you to freely rotate the active eyepiece position to obtain a more comfortable viewing position. This [dual-purpose] QUAD-LOCK system is a VSI exclusive, not found on any other focuser.

To further reduce noise and vibration, and better isolate the focusing motor(s) from the focuser housing, the motor's drive shaft is [now] coupled to the Crayford focusing shaft using precision Delrin spur gears. VSI is switching from metal to Delrin spur gears because Delrin (an indestructable polymer resin) is more durable and lasts longer. And, VSI uses only the best Delrin gears available, with double metal set screws that lock the spur gears securely to the motor and Crayford drive shafts.

MacroGliders are extremely massive in design and size compared to all other focusers on the market. The single pictures at this web site can't impress the “giant” proportions of these huge, rock-solid focusers (outer housing dia. = 4.25”). To illustrate this proportional difference, a Commercial 2" focuser Size/Mass Comparison was created below.

VSI focusers utilize the famous "Crayford" design, which is world renown for its zero-image-shift, zero-backlash and simple mechanical qualities. Unlike the other "Crayfords" on the market, that use a cylinder section to hold their four bearings in place (they also claim being first to do so, but this Crayford redesign was originally introduced by Paul Van Slyke and copied by others, see S&T Feb 1986, P199 or go to "Four-Speed 17.5" Newt" link for article re-print), the Glider's housing is a complete cylinder with four 1" diameter [Crayford] ball bearing secured to the housing on both sides of all the bearings (patented), providing a much higher degree of stability and load handling capability. Instead of using two bearings [supported by a frame] at each end of the Crayford drive shaft to provide pressure on the moving tube, VSI's Crayford design uses a dual pressure point on the rotating drive shaft (supported with two pure virgin Teflon pads), which offers a fluid surface so near-infinite force can be applied with no possible warpage of the drive shaft (also copied by others). Previously, commercially available Crayford-style focusers offered a flimsy, flexure-ridden housing with [what I call] "slip & slide" focusing. These other focusers are adequate for casual sky observing with eyepieces, but critical astroimaging with heavier, leveraged imaging trains was impossible. No positive focusing action, like with R&P focusers, could be achieved - until now. The Glider movement is not only as smooth as a 20 year-old, single-malt Scotch whiskey, but the silky action is extremely positive and reactive to the slightest touch, especially with those GIANT 3" diameter focusing knobs.

Another exclusive VSI feature is the vibration dampening system. Note the brass motor bracket arm (see pictures). Brass, having a very high density, is the best material to dampen motor vibrations when a motor must be in close proximity to the eyepiece, like focusing motors. This undesirable vibration can easily transfer to what you see in your telescope's eyepiece.

WARNING: Be aware that all [so-called] Crayford focusers, are not really Crayford focusers. Deceptive advertising by many dealers, trying to take advantage of the Crayford's reputation, offer Crayford-type, Crayford-like or Crayford-style focusers that have very little to do with the true Crayford design. NO radial ball bearings, NO zero-image-shift, NO fluid motion, NO ultra-tactile sensitive control, NONE of the above functions that made the Crayford the finest precision focuser on Planet Earth. These non-Crayford focusers typically use plastic pads to simulate Crayford bearings and other inferior construction techniques that deminish the Crayford name. Only a focuser that uses four (or five, like VSI's MicroGlider) precision ground steel, radial ball bearings can [rightfully] be called a Crayford focuser. - PVS

Commercial 2" Focuser Size/Mass Comparisons

No words are really needed here, but do note the size of the Crayford bearings, where applicable.

Size Does Matter!

CYCLOID Crayford Disk Auto-Rotator w/MacroGlide Auto-Focuser Installed

Look interesting! See ROTATORS link above for details.

VSI's NEW Coma Corrector Insert Capability

Our MacroGlide ALPHA focusers can now accept all 3" outside diameter coma correctors on the market, including Astro Optik's Newton-Wynne 3" Coma Corrector (made in Germany), pictured at right. All ALPHA moving tubes have a 3.005" internal diameter to easily accept the insertion of these unique coma correctors. Pictured at right (left image) is a standard 3" coma corrector with an optional T-thread adapter bolted to the top that provides the exact 60mm distance between the corrector lens and your CCD chip. This one accepts any CCD camera that has a standard T-thread coupling, like the SBIG ST10 CCD camera (shown). Just screw the camera onto the coma corrector adapter (center image) and insert it in the MacroGlide ALPHA focuser (right image) and tighten the three thumb (or set) screws opposed by 120 degrees. You can also use the 6" long coma corrector's barrel as a push/pull drawtube, if desired. When not using the coma corrector, just remove it and drop in our standard output adapters. VSI's output adapters include 2" barrel-nose, T-thread, 2"-24tpi thread, and SBIG's new 2.156"-24tpi thread for their STL11000 CCD camera (see OUTPUT ADAPTERS link above).  Of course, custom machined output adapters are always available. Although our ALPHA's have a long 5" travel, shorter custom moving tube lengths/travels are also available by special order.

VSI's NEW Ramping Hand Paddle

Our new Mega-Power RAMPING hand paddle incorporates the new PWM2 chip with solid state duty cycle control and polarity reversal. This newly developed second generation [Pulse Width Modulation] circuitry also includes precision on-demand pre-loading of the motor. To overcome a loaded focuser motor's mechanical impedance, this new hand paddle instantly applies a 25% square wave duty cycle to the motor when either paddle button is pushed. This action instantly starts the rotation of the motor, even at it's lowest speed, as soon as a button is pressed. No more time lag between direction changes, like the other [now inferior] hand paddles. This new paddle delivers super-smooth, "power on-demand" low-speed torque capability that is light-years ahead of anything else available.

VSI's new circuit boards are custom designed and built, by Impulse Engineering, exclusively for VSI. The large [red-topped] knob is indiced on the face of the paddle (see picture at right), and this knob does what no other focuser motor controller can do. The more low-speed torque the motor needs, the more it gets - automatically and instantaneously. And it also RAMPS the speed applied to the DC servo motor, which is controlled by that indiced red knob. In other words, turn the knob all the way down and the motor runs very slow, but with full power and torque available, when you push either direction button. Hold the button down and the new "state-of-the-art" PWM2 circuitry delivers more and more speed to the motor - ramping faster and faster. Turn the knob up and the motor receives the power, speed and torque at a faster and faster "ramping-up" rate. Turn the knob all the way up and full power, speed and torque is delivered instantaneously to the motor - no ramping. A simple one-knob intuitive solution to complex "speed vs torque" motor control issues. The green/red light "ramps up" in brightness to indicate motor speed. When you press one of the large red buttons, the light is green. When you press the other button, the light is red, indicating direction of rotation and power levels at a glance. Uses 120vac wall-wart type power supply or 12vdc car cigarette lighter (optional). Operating voltage: 12 to 24vdc.

The Importance of Dual-Motor Controlled Focusers

VSI motorized focuser models offer two types of motor control - DC servo and stepper.  In fact, VSI focusers offer the only dual-motor control on the planet (that we know of), allowing both motor types of remote focusing control with a fast and easy "slide-out/slide-in" motor switch-out (see picture at left). You can also disengage either motor from the drive train for hands-on manual focusing with the instantaneous turn of a knob.

Why do we offer these exclusive motor features? Because DC servo motors are analog and introduce no vibration or noise into the drive train like autofocus stepper motors, which are inherently noisy and cause step vibration (even when microstepping). DC servo motor control offers smooth, remote hands-off eyepiece focusing via our new [super powerful] RAMPING hand paddle, that is custom designed and built by Impulse Engineering exclusively for VSI (see picture above right).

On the other hand, stepper motor control offers wonderful computer controlled autofocus for astroimaging, but is not capable of vibration-free driving of the moving tube, especially at resonant step frequencies, which cause your star images to jump all over the place when attempting to focus, making it impossible to remote eyepiece focus. This is why autofocus computer subroutines stop focusing, take a focus image, then do it all over again until perfect focus is achieved - a time consuming process, but acceptable. Although remote push-button control is offered on autofocus electronic hardware packages, via two push-buttons, you really can't use it for anything more than repositioning the focuser's moving tube to begin autofocus computer controlled focus procedures. It is simply a convenience feature. You can't do simultaneous visual eyepiece focusing with a stepper motor because it induces vibration when activated.

This little known motor control fact is very important when considering the purchase of a focuser that you want to use for both visual, remote eyepiece focusing and computer controlled astroimaging applications. You can't have hands-off remote eyepiece focusing and computer-controlled autofocus for astroimaging, unless you have a focuser with dual-motor control capability. This is something that the other single-motor focusers on the market don't want you to know, until it's too late. Unfortunately, this lesson is usually learned the hard way. Even though this info, that you are reading now, is buried [here] at VSI's Features link, you may be one of the lucky ones, if you were seriously considering a dual-purpose focuser for both remote visual focus and computer-controlled astroimaging.

Re-Engineering & Improving the Basic Crayford Design

Although most Crayford focusers on the market today utilize VSI's [original] central pressure point design, we continue to stay ahead of the game by continually improving our products, as noted by the myriad of improvements to our "new" MasterGlide Focusers. VSI has always maintained only the basic Crayford concept. Everything else has been thrown out the astro-portal and redesigned from the ground up. We have modified the four-bearing support platform by supporting the bearings from both sides (a feature others have copied for many years now), using hardened steel drill rod shafts and a complete cylinder instead of a cylinder section, providing more than twice the stability compared to single-end supported, bearing mounting systems. We have also made the entire structure more massive, and increased the typical bearing size (approx. 1" diameter bearings). The drive shaft support mechanism has also been re-engineered to eliminate the weak, flimsy, distortion prone standard drive shaft mechanism (see above diagrams) provided by many other manufacturers. The above left diagram explains the internet reports of ball bearings literally exploding due to over tightening a poorly designed drive rod tensioning mechanism. If the two drive shaft bearings remain fixed perpendicular to the drive shaft, while the shaft itself is allowed to warp [away from perpendicularity] from over tightening, then the bearings will bind causing locking of the drive shaft and danger of an exploding bearing. Even replacing the ball bearings with bronze bushing-type bearings will not eliminate locking or pinching of the drive shaft from normal tightening of the tension mechanism. Increasing the diameter of the drive rod will relieve some of the warping, but it will also give you a much coarser [ratio] movement of the tube, which is not acceptable, at least at VSI. The drive rod diameter must remain small to provide fine control of the moving tube. VSI uses a 1/4" diameter steel drill rod (concentric to 0.0004") machined down at the center to 0.15" providing a relatively fine focusing ratio of 0.47" of tube movement per revolution of the focusing knob.

To apply force at the center, instead of at the outer ends of the drive shaft, VSI uses two expedient and economical virgin Teflon pads backed by two adjustable, large Allen head set screws. Engineering studies have shown that, in this application, center mounted Teflon pads provide an inexpensive method to totally eliminate drive rod warpage and inherent concentric machining errors while allowing the user to adjust and apply a much higher FORCE between the drive rod and the moving tube, without warpage concerns. The more force you apply to virgin Teflon, the more "slippery" it becomes, making it an ideal and economical substance for Crayford drive rod applications. With the available increased force applied to the drive shaft, you can eliminate the typical "sloppy" action notorious to previously ill-designed Crayfords providing a more positive "rack & pinion" action, and a much higher leveraged load handling capability for astroimaging, etc.

A Brief History of the Crayford Focuser

The Crayford Focuser was invented by English amateur John Wall of Dartford, Kent, England in the early 1970's. His inspirational focuser was demonstrated at the Crayford Manor House Astronomical Society and described in the Journal of the British Astronomical Association (Feb, 1971). Also, several examples were published in Model Engineer magazine (May, 1972). Curiously, the Crayford focuser is not named after it's inventor, Mr. Wall, but after the Crayford Manor House itself. Even more curious is that he never patented the design, which rendered it unpatentable over the years because of his existing published "prior art." Others have acquired patents for various minor modifications to the basic Crayford design, but such patents pale in the light of the revolutionary, original Crayford focuser implications. FYI, an interesting article on the Crayford focuser appears in Sky & Telescope magazine, Gleanings for ATM's (Sept, 1972, p182). Mr. Wall's original Crayford focuser appears at right (courtesy Sky & Telescope magazine).

I would personally like to thank Mr. Wall for magnanimously donating his invention, the Crayford focuser, to the astronomical community. The Crayford focuser, and Mr. Wall, will live forever in the hearts [and hands] of amateur astronomers throughout the world. It is the only focuser mechanism that offers true zero-flexure tube movement. In my humble opinion, it is the finest, most ingenious focusing control mechanism ever created! - PVS

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