Without Comparison, the most Loadable, Functional & Feature-Packed Focusers on Earth
THINK TOADLOADERS for the FOLLOWING REASONS
GIANT 2.5-inch "GUN" knobs with lightweight polymer cores and aluminum casings
MICRODIAL focusing offers the finest incremental focusing, by many factors, over any other focuser, period!
AUTO-FOCUS remote control hardware interfaces with MaxIm DL, CCDSoft & FocusAide, etc.
TEMPERATURE COMPENSATED Lunatico capability on all Hurst stepper motor models
Ultra-fine autofocus motor ratio - one motor step = 0.000052" of actual tube travel!
TOADLOADERS unique CRAYFORD design is the most stable and silky-smooth on the market, by a factor of 10!
TOADLOADERS can handle leveraged imaging train loads that others only dream of (unlimited).
Our exclusive QUAD-LOCK system secures your 2" barrel nose into 2" TOAD's moving tube like a ROCK.
All focusers have GIANT 1" diameter BALL BEARINGS for ROCK-SOLID operation.
All focusers have 3/8" thick-wall, solid 6061 alum. housings & moving tubes. NO other focuser even comes close.
2" TOADLOADERS screw DIRECTLY onto your Meade 3.25"-16tpi large format visual back - NO FLEXURE!
2" TOADLOADERS accept your FOCAL REDUCER (FR) inside it's moving tube, effectively reducing your FR's profile to ZERO.
Four models to suit any budget or application.
Best of all, VSI Focusers are [only] sold directly from the manufacturer to you, the customer, so prices are always WHOLESALE.
Need more proof? See "Unsolicited User Comments" link.
Still not convinced? Then go buy the other focusers and learn this expensive lesson the hard way.
Standard Features & Specifications:
GIANT 2.5" dia. focus knobs offer lightweight polymer cores for max focusing leverage & tactile sensitivity
MICRODIAL tangent arm offers the finest manual focusing on Planet Earth, nothing else even comes close
AUTO-FOCUS system for MaxIm DL, CCDSoft & FocusAide, etc.
TEMPERATURE COMPENSATED Lunatico capability
Dual motor control, accepts analog DC servo or autofocus stepper motors
For 8" and larger Meade/Celestron SCTs, or custom mounted to any scope
3.25"-16tpi threaded base for large format SCT docking
Refractor/Newt/Dob Docking Ring Converters install TOADLOADERS on any scope
Exclusive focal reducer "Hidden Cavity" on all models - zero-profile focal reducers!
Guaranteed zero flexure at any load factor
Solid stainless steel vibration dampening arm assemblies
Optional 12vdc auto cigarette lighter adapter (see Accessories link)
DUAL pressure point Crayford focusing mechanism doubles pressure and halves tactile sensitivity
Delrin spur gear trains that are quieter, smoother, self-lubricating and last longer than metal
Hardened shafts made from precision-ground A3 drill rod blanks with 5% chromium content
QUAD-LOCK [Zero-Flex] system secures your 2" barrel-nose in the focuser's moving tube like a weld
Built-in proprietary rotating barrel locks for our Hex 1 (see Turrets link for details)
Narrowest possible gap between housing and moving tube - only 0.025" (1/40th of an inch)
More durable "Glass-Bead" super finish - looks new longer!
Engineered weight reduction machining without sacrificing rigidity
Focusing tube locking thumb screws repositioned to improve holding power
Ultra-precision digital machining guarantees perfect fit on every part
Exclusive [balanced load] Zenith Lift System, all models (VSI trademark, patented)
Adjustable focusing tension with double set screws and Teflon pads
Dual control hand paddles on all DC servo models
Aircraft-grade 6061-T6 aluminum (NAS620 or AN960 aeronautics specs) or better
Military specification 18-8 stainless steel (MS15795, MS27183 or ASTM A693) or better
Four 1" diameter precision ball bearings - NO miniature (sloppy) slot car bearings
Double #10-32tpi extended Nylon equipment locking thumb screws + QUAD-LOCK
Thick-wall construction (0.375" approx.)
3" minimum profile
Unlimited imaging train loads
2" TOADLOADER housing diameter = 3.5"
2' TOADLOADER moving tube diameter = 2.75"
2" TOADLOADER travel (moving) tube internal clear aperture = 2.25" to 2" shoulder
2" TOADLOADER focusing tube travel = 1"
Docking: 3.25"-16tpi Meade SCT (see DOCKING CONVERTERS above right)
Custom machined docking available (see MACHINING link for details)
Adapter required for Meade 16" & Celestron SCTs, see Docking Adapters link above right
2" TOADLOADERS are compatable with 8" SCTs using our exclusive docking adapter, see link above right
Weight: less than 2.5 lbs. (approx.)
Over the years, VSI has continually taken the best features of all our previous focuser designs and incorporated them into new "super focuser" models. Just one of many of these super features is our huge dual 2.5" diameter custom machined "GUN" knobs incorporating lightweight polymer cores encased in thick aluminum shells (see picture at left). These giant knobs are easy to grip and rotate using minimal tactile pressure and resemble the rotating cylinder on a revolver, thus the name "GUN KNOBS." VSI products are continually improved to [also] leave copy-cats in the dust. Of course, 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 "bleeding-edge" of focuser design for decades.
VSI considers the most important mechanical feature to be the dual pressure points on the Crayford rod. Instead of one pressure point, which has been copied by every Crayford focuser manufacturer, VSI now uses two identical Teflon pads with two large set screws (see picture at 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.
Our exclusive QUAD-LOCK [Zero-Flex] system (pictured left with the focuser's moving tube extended to expose the two additional locking set screws) offers astroimagers a rock-solid coupling between a focuser's moving tube and the 2" barrel nose. Four tightening screws lock the 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 focuser's moving tube, creating a zero-flexure coupling under any load. See Slider Adapters link for more info on VSI's exclusive adapters.
VSI's massive 2" TOADLOADERS 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 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). Using VSI's exclusive QUAD-LOCK ensures that the coupling is rock-solid so you can stack an extended, long profile imaging train without flexure!
These two hidden [captive retaining] set screws on the focuser's moving tube (pictured right) are also designed to hold our Hexagonal 1 in the focuser. A specially grooved barrel nose on the Hexagonal (see TURRETS link for details) allows you to freely rotate the active eyepiece position to obtain a more comfortable viewing position.
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 has switched from metal to Delrin spur gears because Delrin (an indestructable polymer resin) is more durable and lasts longer than metal gears. 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 TOADLOADER'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 "lock & load" docking totally eliminates flexure with even long, extended imaging trains. 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. NOTE: John Stiles insisted that my custom machined mounting plate (to dock a customer requested 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).
The perfect marriage (if there is such a thing) between focuser and rotator! Combining the Zerotator and 2" ToadLoader (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 caged needle 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 TOADLOADERS utilize the famous "Crayford" design, which is world renown for its zero-flexure, 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 TOADLOADER's housing is a complete cylinder with four 1" diameter [Crayford] ball bearings 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). No positive focusing action, like with R&P focusers, could be achieved - until now. The TOADLOADER 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.
VSI's exclusive MICRO-DIAL (micrometer) ultra-fine focusing capability provides this focuser with the finest incremental focusing capability (by many factors) over any other focuser on the market (see picture below right). One full rotation of the micrometer's dial yields 0.00375" of travel with incremental indic interpolation that is repeatable to (better than) an unbelievable 75/millionths of an inch. VSI's Micro-Dial in not just another so-called fine focus control for visual observing like the ones offered on almost every other focuser on Planet Earth. To call a Micro-Dial fine would be like calling the space shuttle slow (17,500mph). Think thousands of times finer than anyone else's so-called fine focus control. A lot of experienced astroimagers, not familiar with VSI's relatively new Micro-Dial (with tactile sensitivity beyond any other) think that it is impossible to obtain critical focus without hands-off autofocus computer control. Not true! In fact, computer focus control is not as accurate or fine as VSI's manual Micro-Dial. Interpolation to better than 0.000075 inch. Do the math - indices vs steps. But only if you want to focus manually, as all TOADLOADERS can be equipped with temperature compensated autofocus so you can have the best of both worlds - ultra-fine manual and autofocus capabilities.
And you disengage the TOADLOADER's motor and/or engage the Micro-Dial with the turn of a knob. No dysfunctional [autofocus only] motor locked shafts or, worse yet, knobless focusers! Oh, you wanted to do some [analog] eyepiece observing too. Sorry, not can do! Did I mention dysfunctional? What are they thinking? Not.
VSI TOADLOADERS are 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, TOADLOADERS can also be used with any other type of telescope using optional VSI screw-on or custom docking adapters. Since 2" TOADLOADERS 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 TOADLOADER'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. Longer [moving tube] travel lengths are available by special order.
Another exclusive VSI feature is the TOADLOADER's vibration dampening system. Note the stainless steel motor arm (see picture at right). Stainless steel, 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 diminish the Crayford name. Only a focuser that uses four radial ball bearings can [rightfully] be called a Crayford focuser. - PBVS
Also see Miniature Slot Car Bearings vs Large-Diameter Precision Bearings section below for more info on this subject.
All models of 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 back of your 2" TOADLOADER, and your new, focal reduced profile has just been cut to zero. Then reinstall your focuser, insert a standard 2" diagonal or VP Slider in your [focal reducer equipped] 2" TOADLOADER and you're ready for super stable, efficient, low-profile, wide-field operation.
You can also use this focal reduced configuration in your 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 first VSI focusers called Monster focusers, then named MasterGliders, and now called 2" TOADLOADERS - 20 years plus is a long time! 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? Now you find that a "toad" has replaced the "monster."
FYI, 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 not always familiar to others.
Speaking of that, a relatively new focuser business, that 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 others. 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 based 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 "cavity" is not one of them. So rampant pilfering of many of my design features 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. - PBVS
VSI's Exclusive Zenith Lift System
VSI's Zenith Lift System (patented), installed on all 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. - PBVS
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 (pictured at right) that are attached between the focuser housing and the moving tube on both sides of the focuser. Also, the TOADLOADER'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 you'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.
No words are really needed here, but do note the size of the Crayford bearings, where applicable.
A penny for your thoughts. These pictures illustrate 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. A VSI bearing has never been replaced, ever! 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.
Our Mega-Power Dual Control hand paddle incorporates individual IN/OUT speed-torque control for balanced load even at zenith positions. Just turn the knob below the push button (see picture at right) to change the speed of the IN travel of the DC Servo motor. Turn the other knob to control the OUT travel speed.
Other hand paddles have one knob to control both IN and OUT speed, so when you are observing near the zenith and push the IN button, your motor strains to lift the load at reduced speed and torque, and drops the load at a much faster speed when you push the OUT button. With VSI hand paddles, you can balance your load by simply adjusting the two individual speed control knobs. Your IN/OUT speed can be precisely controlled for any load and any observing elevation from horizon to zenith with a simple turn of a knob(s).
This new VSI circuit design 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 other hand paddles. This new paddle delivers super-smooth, "analog" speed control that is mechanically and electronically near-indestructible.
This paddle is used to control our DC servo motor only. It will not operate the Lunatico stepper motor. Uses 120vac wall-wart type power supply (included when ordering appropriate focuser package) or 12vdc car cigarette lighter (optional). Operating voltage: 12 to 24vdc.
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 I 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 does VSI offer these exclusive motor features? Because DC servo motors are analog and introduce no vibration or noise into the drive train like digital 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 the Dual Control hand paddle.
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] in this 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.
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 TOADLOADERS. 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.
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.
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