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MasterGlide* Docking Focusers (2" format)

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

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




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

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

Standard MASTERGLIDE Features & Specifications:

VSI's [2" format] MasterGlide Focuser has so many NEW features that it also demanded a new name to commemorate this completely redesigned super stable, ultra-high performance, secondary SCT focuser. 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 new 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 above 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, our Gliders now have super-smooth, true feather action control. Couple this feature with our new Spinners (see paragraph below) and you've created an incredibly soft-touch, tactile manual focusing function that no other focuser can begin to offer.

Probably the second most important feature is our new 4-inch diameter Spinner knobs (pictured at right). The Spinner arms are 1/4" diameter aluminum rods that protrude from the basic cylindrical knob every 60 degrees. With six Spinner rods to manipulate your focus position, you'll always have at least one or two in a comfortable position. Spinners not only increase your resolution by a factor of 4, they also provide 4 times the touch torque, making it that much easier to manipulate your focusing position manually. Ease of movement and feather action control doesn't get any better. I've found from experience that placing one spinner rod between two fingers allows for super sensitive, fine focusing control of your moving tube's position. Of course, not as fine as our exclusive Manual Micro-focus Tangent Arm. And for major changes in focus position, just spin the Spinner with one finger, it doesn't get any quicker! Spinners are also offered separately for your older model VSI Focuser or any aftermarket focuser with 1/4" diameter shafts.

Another exclusive and unique feature is our new internal [moving tube] locking splines (see picture at right). Every Glider moving tube now has 200 locking splines cut into their moving tube's inner wall. This machined splining operation provides a super gripping action with minimal applied thumb screw pressure. The holding action is comparable to a complicated, and difficult to machine, compression locking mechanism, but is much faster and easier to release when you need to rotate your imaging train to find that evasive guide star, etc.

Other NEW features include: 1) a repositioned moving tube locking thumb screw. When positioned conventionally [before], it allowed the Crayford moving tube to be cocked to the side when too much pressure was applied. Now, with central positioning between and opposed to our massive Crayford bearings, you can apply unlimited pressure to ensure a secure moving tube lock down; 2) weight reduction machining that doesn't impede the structural integrity of the focuser; 3) new ultra-precision digital turning and milling techniques that provide consistent perfect part mating every time.

Our NEW QUAD-LOCK system (pictured at right with the focuser extended to expose the two additional locking set screws) offers astroimagers a rock-solid coupling between a MasterGlide 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 MasterGlide focuser's moving tube, creating a zero-flexure coupling. See VP Accessories link for more info on VSI's exclusive adapters.

VSI's massive 2" 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 MasterGlide focuser's standard 2" barrel nose format 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 shown at right). 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 MasterGlide focuser's moving tube (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 NEW [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 brass insert hubs and double metal set screws that lock the spur gears securely to the motor and Crayford drive shafts.

The Glider's other standard features include an outer housing that docks and locks to the rear of your SCT's visual back utilizing the larger 3.25"-16tpi threaded format for Meade, and an adapter ring (#AMC33, $99) for Celestron 3.29"-16tpi visual backs. This very important large format docking totally eliminates flexure with even long, extended imaging trains. Unscrew your 3.25" to 2" Meade or Celestron Reducer on your SCT's visual back and take a close look at it. Do you really think that this thin, flimsy reducer can hold your imaging train without flexure. VSI won't even offer a focuser that attaches to this 2"-24tpi [wimp] reducer for this reason. Why do you think people like Dr. Frank Melsheimer of DFM, or John Stiles of OGS are so emphatic about massive visual back assemblies, etc. Because without a solid visual back, your pointing and tracking accuracy simply goes away. This flexure is mainly due to the effects of gravity on your scope as your pointing position changes over time. No matter how well a secondary focuser is built, if it is attached to this flimsy 3.25" to 2" reducer, it will induce unacceptable flexure into your imaging train, period. NOTE: John Stiles insisted that my custom machined mounting plate (to dock a customer requested MasterGlide focuser) on one of his 20" OGS Cassegrains was at least 12" in diameter and 1/2" thick minimum (see User Installations link, Leeward Community College). Gliders are extremely massive in design and size compared to all other 2” format 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. = 3.5”). To illustrate this proportional difference, a Commercial 2" focuser Size/Mass Comparison was created below.

The perfect marriage (if there is such a thing) between focuser and rotator! Combining our manual Zerotator and MasterGlide focuser (pictured at right) creates a rock-solid, stable rotating platform for astroimaging or just rotating your diagonal or Hexagonal to a more comfortable viewing position. The radial ball bearing loaded Zerotator can handle any load you stack on it, because it was designed to hold your entire imaging train - focuser, optical manifold, CCD camera, etc., etc. And it has a 2.75" internal clear aperture so vignetting is not a problem.

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 single center pressure point on the rotating drive shaft (supported with a pure virgin Teflon pad), 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.

The VSI MasterGlide Focuser is designed for the current generation of Meade/Celestron Schmidt-Cassegrain telescopes (10" and larger) that focus by moving their primary mirrors (which always have an unacceptable amount of lateral image shift when focusing), and accept accessories via their standardized threaded visual backs. However, Gliders can also be used with any other type of telescope using optional VSI screw-on or custom docking adapters. Since the Gliders are specifically intended  to be secondary docking focusers, and work in conjunction with scopes that have wide-range primary focusing mechanisms, the travel range is kept relatively short (around 1"), but more than adequate for any focusing application. The Glider's shorter focus travel is actually many times the amount required to adjust and pin-point focus your SCT, because your primary focuser's large focusing range can easily place the image at a "ballpark" point between the secondary docking focuser's lesser range. 

The blow-up picture at right illustrates the Glider's [ultra] micro focusing mechanism. This manual micro focusing tangent arm is [by more than a factor of 10] finer than any other focuser on the market (1 full turn of the Glider's micro focusing knob equals an incredible 5/1000" of tube travel). Even the dual coarse/fine control knob ones can't even come close to those specs. It is specifically designed for astroimaging focus control applications - not manual visual focusing. In fact, it's the only focuser control, I know of, that is fine enough to provide dead-on manual focus in conjunction with a computer/CCD focusing subroutine. This manual micro-focusing feature provides a 10 turn maximum range that equals a micro-travel range of 0.05 inches The bottom [slotted head] knob locks in the micro-control tangent arm at any point along the focuser's tube travel range. Then just turn the top larger knob (10 turn maximum range) for focusing so fine that you would have extreme difficulty seeing the focusing tube move even with a full revolution of the micro-focusing knob. Can you see a movement of 0.005 inches?

Another exclusive VSI feature is the vibration dampening system. Note the brass arms (see pictures at model links) on the manual micro-focus control arm and [most important] the motor bracket arm. 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.

The VSI Crayford docking focuser's analog and digital readouts (see M4 & M5 links) indicates focus position directly from the moving tube for accurate, repeatable positioning every time. Others indicate position from the Crayford's [slip & slide] focusing shaft providing a totally useless, decorative "bauble" that serves no purpose whatsoever. VSI's analog [M4] dial indicator has a rotating outer bezel with lock, two adjustable set mark indicators, increments of 0.001 inches (with interpolation to better than 0.0001"), and a smaller rotation dial that indicates a full inch of travel. VSI's digital [M5] read-out has inch/mm selection, zero and origin buttons with a digital numerical resolution of 0.0005" or 0.01mm. This model incorporates the same high quality Mitutoyo digital readout that was installed on our discontinued Monster and Super Power Focusers. You can also purchase an optional remote position display box (pictured below under M5 Options) that just plugs into the side of the local LCD digital readout on the M5 itself.

VSI MasterGlide docking focusers are available in five base models, with various motorized features available within each M3, M4 or M5 model (A, B, etc.) which are all pictured at their respective links above right: M1, basic [no-frills] with no options; M2, includes manual Tri-Focus control [only]; M3 includes manual Tri-Focus control and remote motorized control, hand paddle and power supply; M4 is a fully loaded unit with all of the above features plus Quad-Focus and analog readout; M5 is a fully loaded unit with all the above features plus Quad-Focus and digital readout. M1 through 3 have a 2.5" profile, where the M4 & 5 have a 3.25" profile to accommodate the analog/digital readout mechanisms. Glider docking bases are threaded (3.25"-16tpi, Meade format) to easily screw directly onto the visual backs of any 10" or larger Meade SCT except 16" Meade LX200, which requires a special ring converter (item #ACR43) offered at the Docking Converters link. For Celestron installation (3.29"-16tpi, C11 or C14), you need our Meade to Celestron converter ring (item #ACM33) offered at the Docking Converters link. VSI MasterGlide focusers will NOT dock with 8" SCTs because of their smaller 2" threaded visual backs (see MicroGlide focusers link). Custom machined docking mounts are available for your refractor or any other type of telescope. Nylon thumb screws, located at the base of the Glider housing, lock down the focuser [against your visual back's threads] in any rotational position relative to your scope's visual back.

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

Focal Reducer "HIDDEN CAVITY" Super Feature

All models of MasterGlide Docking Focusers have our exclusive Focal Reducer "Hidden Cavity" feature machined into the rear of their moving tubes. Just insert your Celestron or Meade focal reducer into the rear of your Glider, and your new, focal reduced profile has just been cut to zero. Then reinstall your MasterGlide focuser, insert a standard 2" diagonal or VP Slider in your [focal reducer equipped] Glider and you're ready for super stable, efficient, low-profile, wide-field operation.

You can also use this focal reduced configuration in your MasterGlide focuser mounted on other [similar focal length] scopes, not just commercial Celestron/Meade Schmidt-Cassegrains. Even if you don't use a focal reducer in your focuser's hidden cavity, the larger internal diameter provides an ultra-wide clear aperture that guarantees no vignetting, even with very fast scopes. Note that the internals of the above focuser were intentionally NOT flat blackened for demo purposes only.

This unique "hidden cavity" super feature has been around since the beginning of VSI. Over two decades. You may remember the old Monster focusers, now called MasterGlide. I changed the name because everyone and their brother was calling everything "monster this" and "monster that," etc. In fact, they still do. Maybe you remember my old "monster" display ads in S&T, with the picture of a monster coming out of my focusers that was a cross between "The Creature from the Black Lagoon" and a T-Rex? If you are at all familiar with VSI, then you know that I like to "march to a different drum." Honor, reputation and dignity are business and marketing traits that are unfamiliar to most.

Speaking of that, a relatively new focuser business, who seems to be filtching more than just my ideas from others, has "borrowed" my design and now features it in a small display ad in S&T's Market Place. Am I ever bothered by these unethical copycat activities? No, because it is the grandest form of flattery. A compliment that has no comparison. And it is not even a true Crayford focuser, so that makes the theft even more meaningless. As I have mentioned before, Crayford-type, Crayford-style and Crayford-like do not make a true [radial ball bearing] Crayford focuser, and VSI's bearings are five times the size of anyone elses. It is an insult to John Wall, the inventor of the Crayford focuser (see bottom of this web page), to use the "Crayford" name to describe a pseudo-Crayford knock-off at best. Besides, my unique products are never based on one or two features, like others. As with all my products, they are bases on an overall design concept that is timeless - a build-quality that will endure far beyond your lifetime.

Although I do have a couple of patents, this is not one of them. So rampant pilfering of many of my design features, including this one, is an on-going activity. Over the years I have found that patents are not worth the initial expense (i.e attorney's fees, patent fees, maintenance fees for the life of the patent, etc.). And you can literally go broke fighting patent infringements through the courts.

VSI's Exclusive Zenith Lift System

VSI's Zenith Lift System (patented), installed on all MasterGlide focusers, provides a unique lift feature that balances focus control at the zenith, or near zenith, observing/imaging positions. The Zenith Lift System (ZLS) was created so the astroimager, or visual observer, can easily take advantage of the more transparent overhead zenith arena. If balanced zenith lift is not needed, you can easily remove the springs by slipping the hooked ends over the Allen screws - instant gone!

FYI, this Zenith Lift System has nothing to do with backlash, as others have wrongly assumed in their display ads. They are trying to discredit the ZLS without even understanding its function. The more they try (desperately) to "poo-poo" VSI products, the more they humiliate and embarrass themselves. When will they learn that you can't destroy the reputation of a good product with words, especially words that only reveal their own jealousy and ignorance. A product can only destroy itself by its own actions. - PVS

We all know that you are looking through about 100 miles of atmospheric distortions on your horizon, but you are only observing through about 10 miles of atmosphere at your zenith. Obviously, you will obtain the best astroimages and visual observations when your scope is pointing straight up.

The mechanical apparatus comprises two heavy-lift springs (one is pictured at right) that are attached between the focuser housing and the moving tube on both sides of the focuser. Also, the Glider's mechanical spring-loaded lift system will greatly assist your autofocus stepper motor and DC servo motor when working around the zenith.

HINT: By setting your focus point further in, or further out, you vary the amount of lift capability to better balance your focuser's load. In other words, rack your focuser in most of the way, and you have light lift for a lighter load. Rack your focuser out most of the way and you have heavy lift for extended imaging trains. Just set your SCT's primary focus at the inner, or outer, point of your secondary focuser travel for different loads. Of course, if your load is light, and your're observing near the horizon (say, in your neighbor's window) you don't need the mechanical lift springs. Simply slip the springs over the Allen head screws to remove them.

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!

Miniature Slot Car Bearings vs Large-Diameter Precision Bearings

A Penny for your Thoughts

The picture above illustrates the difference in size between the bearings used in all other Crayford focusers (that I know of) compared to the bearings in VSI focusers. What you can't see in the picture is the lack of quality, but we'll get to that later.

Anyone can purchase these miniature slot car bearings on the internet for about a dollar or two each in quantities of 10, as pictured above. Dealers can purchase them for under $1 each in bulk quantities, so why do Crayford focuser dealers [gladly] sell you a replacement bearing for $25? Ouch! I hear that people need to replace them frequently. These slot car bearings are not even designed for loading. They are designed for hi-speed rotation, usually around 20,000 to 80,000 rpm. Whoa! That's fast! That means that their tolerance has to be very low to accommodate those extreme speeds. In other words, sloppy bearings designed for speed, not precision. Slot car bearing static load is [at best] around 13 lbs. and their dynamic load handling is around 44 lbs. That rating is for a precision bearing of the same comparable size because that is the only reference I could find. Slot car bearings don't even list their load bearing capacity, probably because they are way below the numbers that I referenced. What do you want for a dollar?

As you can see, almost two of these miniature slot car bearings can be dropped, side by side, through the center hole in a VSI bearing. VSI has always used precision radial, chrome steel ball bearings in all focusers since day one over 20 years ago. For simple comparison, each VSI bearing has a static load capability of 310 lbs. (slot car = 13) with a dynamic load capability of 740 lbs. (slot car = 44). That load rating is times four [bearings] when it's on your focuser. And precision radial ball bearings have much tighter tolerances because they are not designed for crazy hi-speed operation - a few hundred to a few thousand rpm max.

What kind of rotational speeds are we talking about for a Crayford focuser? Fractional, less than one, rpm. So why use hi-speed, low tolerance bearings in a Crayford focuser?  Maybe you would say cost. The large precision radial ball bearings I use are around $4 or $5 each. Not cheap, but not overly expensive either. Maybe it looks better to hide the bearings inside the focuser's housing? I would hide them too if they were that small. If the bearings were hidden inside the housing, they could even buy cheaper open-race bearings instead of shielded or sealed bearings. All VSI bearings are not just shielded, they are sealed so zero contamination can get inside the bearing's race, whether they are exposed to the elements, or not.

Another poor design on most Crayford focusers is their one-sided bearing mounting, using a shoulder screw. This causes the bearing to flex from the unsecured [screw-head] side of the bearing. VSI focusers use a 3/8" diameter stainless steel (SS) pin that is secured by SS screws from both sides of the bearing directly to the focuser's housing. This super secure bearing mounting provides ultra-secure, zero flexure movement of the travel tube. There are dozens of other reasons why VSI focusers are superior, expecially in load handling, to all other Crayford focusers on the market. This is just one more reason.

How does Tri-Focus & Quad-Focus Operate?

Why design all these redundant focusing controls into a focuser? Because we can, and to push the engineering envelope to a point where no one else would dare venture. But most of all, we do it for you, because we know that many of our clients love functional gadgetry as much as we do. Knobs, gadgets and gages are very "fresh" (aka cool). Others would also call it gaudy. We simply call it open-frame, functional versatility worthy of an Arlen Ness, Jesse James or Indian Larry (now deceased) chopper. However, you do have to be marginally driven to develop a focuser with FOUR different manual focusing controls. That's four different knobs that offer manual speed ranges from a moderately fine main focusing ratio (compared to other focusers on the market) to a micro-focusing tangent arm [for astroimaging] where one revolution of the control knob equals less than 0.005" of tube movement - Whoa!

Since VSI is the only one who has ever offered this extreme range of multi-focusing control, an in-depth explanation of these unique manual/knob controls is necessary. Of course, once you receive your MasterGlide focuser, operation of the various focusing controls is a no-brainer - just turn the knobs and enjoy the feature-packed, super-sensitive and smooth focusing capability no other focuser on Planet Earth has ever offered, or probably ever will.

On to the operation of the four levels of manual focus control, two of which are new. The main macro-focusing Spinner knob (see MACRO above left), with its six evenly spaced spoke-arms, is unique to itself and offers 4 times the tactile sensitivity of a conventional focusing knob, and directly rotates the hardened-steel 1/4-inch diameter Crayford shaft. This specially machined Crayford shaft is actually turned down to a central diameter of 0.15" where it contacts the moving tube's flat. This additional diameter reduction gives all MasterGlide focusers a much finer "coarse" focusing compared to other focusers.

The first gear-reduction (MEDIAN) is through a pair of Delrin spur gears with a reduction of 3 to 1, noted above left (REDUCTION 1). This moderate reduction is then transferred to the left side of the focuser through a second 1/4" diameter hardened-steel drive shaft, mounted directly below the primary Crayford shaft, where it terminates into a small aluminum knob (MEDIAN, shown above) on the Quad-Focus M4 and M5, and a large aluminum knob on the Tri-Focus M2 and M3. This intermediate reduction will probably not be used much on M4 and M5 focusers (see picture of Quad-Focus M5 below right) that have the further reduced mini-focus (crank-knob) directly attached, but decoupled from the main Crayford drive shaft, or [what we call] Quad-Focus, but it will be very useful on the M2s and M3s (see picture of Tri-Focus M3 below left). This [left-over] redundant median-focus control could have been removed in M4/M5 production, but since it was easier to keep, and ergonomically placed in relation to the further reduced mini-focus crank-knob, we decided to leave it in place for the time being, or until our valued clients tell us they don't like it, or they think it gets in the way of other functions, etc.

The second gear-reduction (MINI, aka crank-knob) is delivered through a second set of identical-ratio (3 to 1) Delrin spur gears to a third crank-handle knob that is the same size as the Spinner knob (without the six spokes) and resides on the opposite end of the main Crayford shaft. It spins freely on the left side of the main Crayford drive shaft, held in place by a lateral keyway, and is driven by a final 3 to 1 spur gear reduction. It rotates so easily that a crank handle was installed on the knob (like our MicroGlide focusers) to facilitate a choice of hand-rotation from the same knob. Since this control knob is directly installed on the opposite end of the main Crayford control shaft, it offers perfect ergonomic operation. In other words, turn the main focusing knob on the right side (Spinner knob) and you are provided with direct Crayford shaft rotation (1 to 1). Turn the focusing knob on the left side of the same Crayford shaft (crank knob) and you are provided with a 6 to 1 reduction. It can't be any simpler or functional than that!

There's more too! The crank-knob (see L1 above right) and the larger secondary spur gear (see L2 above right) have large [black] locking thumb screws - no tools required. By tightening the thumb screw on the large spur gear (L2), and loosening the thumb screw on the crank knob (L1), you engage a 6 to 1 gear-reduced control. Conversely, by loosening the thumb screw on the large spur gear (L2), and tightening the thumb screw on the crank knob (L1), the focusing knob on the left side of the M4 or M5 focuser becomes the same as the right focus knob, like any other standard two-knob focuser. And there's more! Either motor (DC servo or stepper) drives the large main spur gear directly connected to the Crayford shaft (see REDUCTION 1, above left). More about the importance of dual DC servo or stepper motor control below. Ain't gaudy wonderful!


M2 & M3 (above left) have Tri-Focus, M4 & M5 (above right) have Quad-Focus

See specifications list above for reduction ratios, etc.

VSI's 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 incorporates the new PWM2 circuitry and is custom designed and built by Impulse Engineering exclusively for VSI.

On the other hand, stepper motor control offers wonderful computer controlled, temperature compensated 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 all others have [literally] copied my central pressure point design improvements over the years, I continue to stay ahead of the game by continually improving my products in other areas, as noted by the myriad of improvements to our MasterGlide Focusers (formerly known as Monster focusers). Again, am I ever bothered by these unethical copycat activities? No, because it is the grandest form of flattery. VSI has always maintained only the basic Crayford concept. Everything else has been thrown out the astro-portal and redesigned from the ground up. I have modified the four-bearing support platform by supporting the bearings from both sides (a feature others have copied for many years now), using high chromium content, 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. I 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 now 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 applications, 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! - PBVS

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