Questions & Answers (FAQ) about VSI Products

with some CAUTIONS noted at the Bottom of this Web Page

Conducted by Paul B. Van Slyke

SLIDER 2 SKY & TELESCOPE Test Report (July 2002)

PLEASE read through the following questions before contacting VSI

Q: Which adapters do I need to create/build my imaging train?

If you can't create your custom observing/imaging train with the above, which is only a fraction of our available adapters, you can't create it, period! Click on the BIG METAL QUESTION MARK above for imaging train configuration ideas, click on the HELP! link, or see the individual product links for product specific port rings, couplings, docking converters, output adapters, etc.

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Q: How do I know which PORT RING/threaded adapter to purchase for my specific scope?

Good question! Because every scope manufacturer seems to create their own proprietary thread configuration, instead of adopting existing thread standards from those who came before, which can be very confusing (see "DANGER......." bottom of this page). To check your scope's thread configuration, you can use a simple 12" ruler, but a dial or digital caliper would be better. No, they're not expensive! You can purchase a dial or digital caliper for under $10 these days.

SAE Diameter Example: Measure your SCT's visual back thread diameter. Always measure the male outside diameter (OD) of a thread, never the female inside diameter (ID). If you have an 8" or smaller SCT, the diameter will usually be a few thousandths under 2 inches (industry-standard? - not really, but kind of). If you have a 10" or larger SCT, the diameter will be a few thousandths under 3.25" for Meade, and 3.29" for Celestron (you will need to unscrew the visual back 2" reducer to reveal the larger format thread configuration).

METRIC Diameter Example: Measure your refractor's visual back thread diameter. Some refractors have a rack or moving tube that has internal (ID) female threads (AP, Tak, Vixen, etc.). So you need to take the measurement from an adapter or accessory that screws into your focuser's moving tube and has male threads, as noted above. Your measured diameter should be [again] a few thousandths less than 72mm for Tak refractors, or possibly 90mm for Tak Mewlons. TMB has two different size focusers, a 3 and 4 inch. The 3" should measure slightly less than 85mm, and the 4" should measure under 110mm.

The above simple measurements will [at least] provide a "ball-park" reference that should take most of the confusion out of deciding which port ring/adapter/coupler/docking converter thread configuration you need to mount a VSI Toad focuser, optical manifold, etc. to your scope.

THREAD PITCH Example: If you want to go further, you can check the threads themselves by purchasing a SAE and/or metric thread gage at places like Harbor Freight or Enco. You can usually purchase both of the thread gages for under $10. Using the thread gage is a "no-brainer." Just touch the thread leaf to your scope's thread, either ID or OD, and the one that fits the best is the threads per inch (tpi) of your scope or adapter. Usually, the number stamped on the thread leaf will match the tpi or mm of the second number noted on all of our various adapters (i.e. 2"-24tpi, 3.25"-16tpi, M72-1mm, M110-1.5mm, etc.). This second number is called thread pitch, which can be either in SAE inches (tpi), or Metric millimeters (mm).

COMMENTARY: There are a myriad of non-standard proprietary adapters from individual manufacturers - no industry standards exist. Why can't these manufacturers adopt the closest standard set by their predecessors? There can only be two excuses; they're lazy or arrogant, or possibly both. Look at the three Tak, TMB and Vixen adapters (90, 85 & 88mm). They are all within 2 or 3 mm of each other. Why? Look at the two Celestron and Meade large-format adapters. One is 3.29" and one is 3.25" in diameter. Look at the two AP and Meade 2.7" adapters. Meade changed the existing 2.7" AP thread standard from 24 to 16tpi, but the 2.7" diameter remained the same. Again, why? Both of these non-conformity issues are Meade's fault for not adopting the existing Celestron and Astrophysics standards already established. And now SBIG has created a new 2.156"-24tpi proprietary thread standard for their large-chip CCD camera. Watch and see, no one else will adopt their thread configuration. They'll all create their own proprietary standard and you'll have a half-dozen different diameters and thread sizes that are within a few millimeters of each other - again. Do these manufacturers care about their customer's inconvenience and added expense? Never even crossed their minds! This kind of "diametrical dysfunction" creates confusion and costs you money, and it's totally unnecessary. Just wanted you to know, so you can take your own action  - or not? - PBVS

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Q: Should I be concerned about observing/imaging train clearance through my scope's forks?

NO! Unless you are concerned about impressing the relatives, neighbors, or your new girl friend. There is almost nothing around the North Celestial Pole (NCP) to observe anyway. 99% of all your observing/imaging efforts will be around the ecliptic or overhead around your zenith. To reiterate, no experienced observer or astroimager would even consider clearance through his forks, because he knows that any profile that clears the forks will give him a headache from continually banging his head into his scope's visual back - Ouch! If your computer controlled GO-TO mount happens to take a "nose-dive" toward your forks, abort the slew. If you want to polar align your scope, with a diagonal and eyepiece, by rotating your fork around the north star, then use a short profile 1.25" diagonal and eyepiece for polar alignment only. This method should only cause a slight headache. Afterwards, switch to your extended observing/imaging train. Or use the "Star Drift" method of polar alignment (basic Star Drift Alignment procedure below) where you don't need to observe through the forks or change your equipment. It takes a little longer, but what else have you got to do between astronomical twilight and total darkness? Don't answer that! - PBVS

Clearance Example using Hex1 and AHEX adapter: Conservation of profile only applies to imaging train configurations, not turret diagonals like our Hexagonals. You actually need extended profile for head clearance between your scope's visual back and the eyepieces installed in your Hex. This is the reason our Hex1 incorporates a long profile 2" format barrel-nose and our optional AHEX adapter (combo pictured at right), instead of a short profile 2" threaded slip-ring (like our Sliders). If we used a short profile slip-ring, you would [not only] loose clearance, but you would also loose our exclusive dual rotation feature, explained at our TURRETS link. If you are installing a Hex in a standard 2" format focuser, that accepts 2" barrel-nose accessories and consumes an adequate amount of clearance profile, then the Hexagonal's barrel-nose disappears inside your focuser's moving tube, becoming a profile non-issue.

Quick & Dirty Star Drift Alignment Method

Azimuth Adjustment (do first)

Insert a diagonal and illuminated reticle eyepiece into your scope's visual back. Find bright star on, or slightly east of meridian, a few degrees north or south of the celestial equator. Center star on eyepiece's crossed-lines. Watch the star's drift. If drift is north, azimuth is too far west. If south, azimuth is too far east.

Elevation Adjustment (do second)

Find bright star about 6 hours east of meridian, a few degrees north or south of the celestial equator. Again, center the tracking star on the crossed-lines. Watch the star's drift. If drift is north, elevation is too high. If south, drift is too low.

NOTE: How do I know where north, south, east and west is when my scope/diagonal turns everything upside down and backwards? Who cares! If you adjust your mount the wrong way, and the drift increases, go the other way until it doesn't. Of course, your scope must be tracking accurately to take advantage of the above. Eventually, after a few practice runs, you'll know your scope's idiosyncrasies.

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Q: Why aren't VSI products black anodized?

Anodizing hardens the surface of aluminum to better protect the product from scratches and abrasions. It can add substantially to the cost of a product too. The anodizing process also removes (from pre-etching) a product's surface material. This etching process can remove as much as 0.001" of material, making a precision "high-tolerance" product into an "out-of-tolerance" product. In most instances, this material removal is not a critical factor, but anodizing also deposits ferrous and other undesirable residues on the surface. This anodizing process damages our planet's fragile environment (If you want to know more about Earth's environmental disasters, visit BFO's "WHY SPACE" link).

At VSI, we use a different method of surface conditioning and hardening called glass sphere blasting, using actual glass micro-beads which, incidentally, removes no surface material and is as environmentally safe [natural] as the erosion of the blowing sands in the desert. You may have seen this unique lighter finish applied to hi-end firearms. That industry calls the finish "glass beading." This process, although not as durable as anodizing, actually "cold works" the surface, hardening and protecting it from wear induced from every day common use, and abuse.

The best way to preserve the glass-beaded finish on your VSI product, etc. is to keep a light coat of oil (WD-40, etc.) on the surface at all times, just like you do with firearms. Of course, any fine instrument that is constantly exposed to the elements should have a periodic application of preservative oil applied to its surface regularly, especially when the equipment is stored in an observatory structure for long periods, say over the winter. Even though all VSI products use stainless steel hardware, the bearings are hardened steel and will corrode and/or rust if left unattended in these harsh environments. A simple cover to prevent direct exposure to the elements is usually not sufficent, because humidity, moisture and dirt particles (not to mention bugs, as in spider webs, etc.) can penetrate these covers. My sincere recommendation is to apply a light external coat of oil to all metal parts that can rust. This includes anodized hardware, which are actually just as easy to corrode as unprotected metals. This is why VSI uses solid stainless steel hardware on all products. And cover and seal all your instruments before you lock your observatory door for the winter, etc.

Internally, all VSI products are also glass sphere blasted to provide a coarse, opaque [non-reflective] surface that randomizes light. The surface color is actually less important than the roughness of the surface because you are usually operating in darkness anyway. Where applicable, our internal glass beaded surfaces are also coated with hand applied ultra-flat black paint and/or permanent black dye. Myself and others have conducted reflection studies at the University of Colorado, where I taught, and at Black Forest Observatory, and the findings conclude that shiny black anodizing is extremely reflective, and must be anti-reflective coated on all interior surfaces where stray light can occur. Glass beading with, or without a final coat of flat black paint is very effective in reducing internal reflections. Under no circumstances, should a black anodized interior surface be left natural, without some kind of anti-reflective coating, because sensitive photometer tests have found that a black anodized [shiny] surface is almost as reflective as a bright polished or chrome finish.

Q: Does my scope have enough back focus to use a Slider? How do I  calculate the amount of back focus I need?

If you don't have a commercial SCT, you need to check your back focus before purchasing a Slider or Sidewinder. I'm finding that many seemingly experienced astrophotographers know very little about their own telescope's back focus (BF). They order a VSI optical manifold and find that it won't work on their telescope. This wastes my time and yours. Back focus is something that you need in abundance if you're going to do astroimaging. Unfortunately, many telescopes, like refractors and Newtonians, have very limited back focus and are designed for visual observing only. The only telescopes that have near infinite back focus are Cassegrains that move their primary or secondary mirrors, like the commercial Meade/Celestron Schmidt-Cassegrain or Ritchey-Cretien telescopes. For every inch that you move your primary mirror, you get an equivalent of about 6 inches of back focus change with catadioptric scopes.

How to check your back focus

If you have a commercial Schmidt-Cassegrain telescope (Meade/Celestron, etc.) you don't need to perform this test. Any TOADLOADER, Slider or Sidewinder will work with your scope. If you don't, then Rack [or move] your focuser all the way in. Then rack [or move] the focuser out about a quarter of an inch. Move the imaging camera or eyepiece out from the focuser, without moving the focuser position (a drawtube would be very useful at this point, but not always available), until you achieve focus at the camera/eyepiece. The distance from the outer edge/lip of the focuser's rack [or moving] tube, to the OD T-ring butt plate (not the end of a 2-inch adapter tube) of the camera is the profile (in inches) that you need (see BF diagram above left). To install a Slider or Sidewinder optical manifold you will need 3.5 inches of profile. If you don't have 3.5 inches of profile, then you can't use a Slider or Sidewinder, or anything else for that matter, until you extend your telescope's back focus.

There are many ways of modifying a telescope's back focus. Usually, you have to modify your scope's tube assembly by cutting a few inches off the tube, or machining some metal off your visual back, etc. Shortening your tube assembly doesn't change internal baffling, because you are not changing the focal point of your scope, just shortening the metal around it to accommodate components with longer profiles. This modification, done correctly, actually increases the value and versatility of your scope. You can always use an extension tube if you need less back focus, but the alternative is much more difficult. BTW, TMB addresses this problem most eloquently by offering a male/female 5" (or so) threaded extension tube that you use for visual observing, with a diagonal and eyepiece. When you need an extended imaging train, you simply unscrew and remove the tube and you have your needed back focus. Any manufacturer could install a similar threaded tube before or after the focuser. If you need to modify your tube assembly, you should "bitch" at your scope's manufacturer or dealer. Maybe they'll get the hint and make a shorter tube assembly at the factory, or do a TMB modification, so you won't need to deal with the "no back focus" problem. If you need advice, give me [Paul Van Slyke] a call and we'll talk about modifications to your telescope. Try not to send me a lengthy e-mail detailing your equipment, etc. It is simply not pertinent to determining your needs. Why? See CONTACT link, scroll to "HOMEWORK" section. You may not appreciate my answer?

Q: How do I attach my new Slider to my telescope?

Sliders have a standard SCT 2"-24tpi threaded slip-ring input format and standard 2" female output formats. Sliders standard 2"-24tpi threaded female slip-ring coupling on the input port allows you to screw your Slider directly onto your SCT's visual back, or insert a Meade or Celestron focal reducer between the two very easily. If you have a standard 2" focuser, like VSI's TOADLOADERS, you need VSI's 2" Threaded Barrel Adapter (item #A2LT, see ADAPTERS link) to couple your Slider to your 2" format focuser.

If you are considering a Sidewinder, that is designed to accept a myriad of different, interchangeable docking ports and output adapters, these issues need to be addressed on an individual basis, depending on your personal requirements. Call me [Paul Van Slyke] and we'll talk about it. Try not to send me a lengthy e-mail detailing your equipment, etc. It is simply not pertinent to determining your needs. Why? See CONTACT link, scroll to "HOMEWORK" section. You may not appreciate my answer?

Also reference The Art of Astroimaging and the BIG METAL question mark link above for more info on imaging train configurations.

Q: How does a Slider or Sidewinder achieve parfocus with my imaging camera, my guiding CCD camera and my various eyepieces?

Slider and Sidewinder optical manifolds can adapt to virtually any imaging configuration you can conceive, and some you haven't. You can attach a CCD camera, 35mm camera, video camera, and any other type of camera to any model Slider or Sidewinder by using the myriad of special adapters and port rings available at the ADAPTERS link for Sliders, and the various PORT RINGS links for Sidewinders. After attaching your new Slider or Sidewinder to your scope (addressed above), then attach your camera, using the appropriate adapter/port ring, to the rear imaging port. Adjust the telescope's focus on the focal plane, or CCD chip, of the camera. Without changing focus, insert a 2" or 1.25" (with reducer) eyepiece in the slide-mirror port and focus the eyepiece by push/pulling the eyepiece in and out until parfocus is achieved.

Typically, with a dedicated CCD camera for astroimaging, you will not need an extension drawtube using the (now discontinued) Flipper, Slider or Sidewinder (see lower left Flipper), but with a 35mm camera, that focuses about 1.5" further out from a standard CCD camera, you will need an extension drawtube (Item#AD22S or AD21S) between the top flip or slide port and your eyepiece (see lower right Flipper, area in red). Although not shown in the pictures at left, side pick-off ports may need to be extended to further achieve parfocus with a simple drawtube too. To further reiterate, note the two lower images just discussed. The red area noted on the lower right Flipper is an inserted drawtube that is needed to parfocalize your system when using a 35mm camera, and is not needed when imaging with a CCD camera (lower left Flipper). Conversely, the upper two images obtain parfocus by extending the CCD camera noted in the red area in the upper left [now discontinued] Micro-Slider image.

NOTE: Sliders and Flippers were beta tested for nearly 10 years at Black Forest Observatory before a production model was finally offered. We found that secondary helical focusing, offered by some others, is redundant, time consuming, awkward and literally useless when attempting to focus secondary eyepieces, since your eye can't observe perfect focus anyway. The push/pull method is easier to adjust, fast, accurate and more functional.

Also reference The Art of Astroimaging for more info on parfocusing your imaging train.

Q: Why should I buy a VSI product over other brands on the market?

VSI products were originally designed and built for college and research observatories around the planet. Tolerances exceed 50/millionths of an inch, where needed, and quality is beyond compromise. All VSI products are built with functional simplicity in mind. A discipline that others have lost in the "gizmo shuffle" and the necessity to swiftly produce and cheapen a product until it becomes dysfunctional. VSI uses the opposite philosophy, we build the best product possible, no matter what it takes [in time or cost] to produce that specific product. Then a lot of thought goes into the improvement and simplification of that product before every production run starts. Again, function and simplicity always make a better product. All VSI products not only have an unconditional 30-Day full money back guarantee, but a lifetime parts and labor warranty. We couldn't offer these kinds of guarantees, if our products weren't built to the highest industry and military standards. Anyone can say that their product is the best, but proving it is another story. Even if it is the simple truth, you need a qualifier. So, rather than going on and on "tooting our own horn," you should go to the "Comments" link and read through all the "after the sale" input from satisfied VSI customers. If that doesn't convince you to buy VSI, then you deserve the "other guy's" product.

Q: Can one use focal reducers in conjunction with Sliders, Sidewinders and VSI Toad focusers? Where would one place the focal reducer in the imaging train?

Yes, many different models of focal reducers have been used quite successfully with all models of VSI products, but it does take a bit of ingenuity. A Celestron/Meade f/6.3 or f/3.3 focal reducer's physical position, from the imaging camera, is not that critical (usually focal reducer back focus is a few inches, give or take). Therefore, commercially available focal reducers can be attached to the input or output (inserting item A2ST into the Slider's rear port) ports. Also, external screw-on focal reducers/field flatteners designed for various refractors can easily be used with Sidewinders utilizing the appropriate port rings.

A commercial SCT focusing mechanism always induces lateral image shift. If you're just going to casually observe with your SCT, then a secondary focuser is usually not necessary unless you are doing very high power observing. If you are astroimaging, then a sturdy secondary focuser, like the ones offered by VSI, becomes a necessity. As far as I know, there are no heavy-duty focusers, adequate for unlimited loads and serious astroimaging, on the market. Light duty focusers, such as the JMI models, are not suitable for serious astroimaging, because of the inherent focusing flexure introduced by heavier imaging trains.

And, don't forget that all VSI 2" TOADLOADERS have a built-in focal reducer "hidden cavity." This super feature is machined into the base of the focuser's moving tube providing you with a zero profile, and zero flexure, focal reducer.

Also reference the BIG METAL question mark link (top of this page) for more info on imaging train configurations.

Q: Can I interchange a CCD camera, video camera, and 35mm camera and still achieve parfocus with the Slider's top and side port eyepieces?

Yes, that versatility is designed into every optical manifold model that VSI offers. Sliders and Sidewinders offer this specialty camera flexibility, and the best selection of accessory port rings, drawtubes, coupling, and adapters, too. Even focal reducers can be used in conjunction with all our optical manifolds. Since a 35mm camera's focal plane is about 1.5" forward, compared to a dedicated CCD camera's [chip's] focal plane, you need to use various extension drawtubes to recreate a parfocal Slider assembly. Since the Sidewinder uses a different body port configuration, you can usually use a 35mm camera without extensions, but may need one of our short extensions on the rear port to achieve parfocus? VSI offers dozens of different port rings, adapters and couplings so you can build the imaging train of your dreams. No one else even comes close, and that's why we are at the "top of the food chain" regarding aftermarket focusers and optical manifolds. We "wrote the book" on easy, functional astroimaging focusers and optical manifolds over 25 years ago. And everyone else literally copied our "book" without permission. I just call it "flattery."

To elaborate on Slider installations, CCD cameras are designed to be close to parfocal with most eyepieces, so extension drawtubes are usually not needed. However, when you exchange a dedicated CCD camera for a 35mm camera (couples to the Slider's rear imaging port using a VSI Zero Profile T-Adapter, item AZP2T), you need to use extension drawtubes in the top and side ports to reestablish a parfocal system. You need to insert a VSI extension drawtube (many different types are available) between the Slider's top port and eyepiece, and another VSI extension drawtube between the Slider's side pick-off port and your guiding eyepiece or guiding CCD camera to achieve parfocus. A video camera attaches to the Slider's rear imaging port using a C-adapter (not available through VSI), and they are usually close to parfocal with CCD imaging cameras.

Q: What kind of filters can I use in the Hexagonal Turret and Slider built-in filter slots?

Any 2" format filter that screws onto the bottom of standard 2" format eyepieces. The slot aperture is 2" plus in diameter by 5/16"
(0.3125") thick. Most standard metal-celled 2" filters are less than 0.3" in thickness, but a few are much thicker than 0.3 inches. If you are going to use the Hex or Slider's built-in filter slot, ask the dealer for the thickness of any 2" format filter before you purchase. You can also purchase the thicker filter and switch the cell for a thinner one, or cut it down (carefully, if you can't/don't remove the filter glass first). Some filter cells are glued and difficult to remove.

Q: If I can't find what I need at the VSI web site, can VSI custom machine port rings & adapters according to my particular specifications?

Yes. VSI does not use external job shops to manufacture their various products, like others do. Every VSI product is designed and manufactured in-house. VSI not only has a fully equipped digital machine shop, and can create any port ring/adapter you can conceive, but VSI also has over 40 years of experience in designing and manufacturing telescopes and accessories.

Unfortunately, I can't machine items that are too complex or time consuming and maintain product availability. Again, I am only one person.

Q: How long does it take, between the time I place the order, and I have the product in-hand?

If the product is on-the-shelf, your order will usually ship on the following friday and you'll have it in about a week, possibly sooner (US). I strive to keep all VSI products available within a week or two. If the product is not immediately on-the-shelf, then I almost always have enough parts to finish, fit and assemble the product within a week from the time you place your order. Again, a week or two is the norm for all orders, not the exception.

Q: Are VSI products well documented?

Yes, all VSI major products are fully documented and individually serial numbered (hard stamped into the metal). When you receive your new VSI product, you will find one or more pages of color pictures, diagrams, illustrations and operating instructions. Most documentation/instructions are just a hard-copy convenience, and are already listed at this web site. Operational instructions (and much more) are offered at the various product FEATURES links.

Q: Why Space?

See "Why Space?" link.

"DANGER, Will Robinson, DANGER!"

A WORD OF CAUTION: I have noted an infestation of [other manufacturer's] optical manifold type devices on the market. Some claim that you can achieve pin-point focus using an eyepiece. This is untrue! The human eye can't "see" critical focus for astroimaging (see "The Art of Astroimaging" for more details), especially with an astigmatism, which afflicts half the people in the world. This has been confirmed by conversations with Dr. Dale Anderson, MD, PC, who is an ophthalmologist and noted eye surgeon. Minimum pixel count is the easiest [and accepted] way to achieve accurate focus with a CCD camera, but there is no quick and easy [lazy] way to achieve critical focus when doing film [35mm] astrophotography, period! You must use a knife-edge or Ronchi grating type focusing device. Otherwise, all your film astroimaging efforts will be soft, fuzzy, or indistinct (unless you get lucky from time to time), instead of masterpieces worthy of publication. Do you really want to waste all that time in the cold night air on guessing?

ANOTHER POINT OF CAUTION: VSI has always used first-surface mirrors in all their optical manifolds since day one. Why? Because they offer the most reflectivity, brightness and image sharpness as compared to prisms. If you think about it, prisms have three surfaces, instead of one like a first-surface mirror - 1) entering the glass prism, 2) reflecting off the hypotenuse of the prism (which should be silvered for maximum reflectivity, but usually isn't), and 3) exiting the prism. During this intrinsic excursion, your light cone is traveling through pure glass, that has to have [even] microscopic impurities in the glass itself. And, there are other disadvantages to a prism system. It's transparent so you can't distinctly see any incurred vignetting by the pick-off prism, just a fuzzy blop of blurred stars - Is that a galactic lens effect or........? With an opaque first-surface mirror, you [at least] know if your pick-off mirror is vignetting your imaging/film plane. It's obvious and, if need be, you can correct for the obstruction, instead of wondering if you need to call Brian Marsden.

AND YET, ANOTHER NOTE OF CAUTION: I have always been appalled at the industry standard manufacturing processes used by all the other companies that offer telescopes and especially imaging equipment. These industry standard techniques, that do apply to all the other terrestrial products in the world, can not possibly apply to any aspect of telescope or associated equipment manufacturing, but this earthly construction philosophy continues, and the astronomical community continues to purchase inadequate equipment that makes celestial observing and astroimaging a frustrating task, instead of a satisfying pleasure. And the quoted hype from so-called "people-in-the-know" (editors, well-known astroimagers, etc.) proclaiming these "wimp products" to be worthy of your hard-earned dollars, is ludicrous at best. I know of very few telescope products on the market today that construct their flat-walls [boxes, etc.] from larger than 16 gage, or even 20 gage sheet aluminum - again, standard manufacturing techniques. With any extended, leveraged imaging train connected to the rear of one of these devices, you have to encounter a minimum of many arc minutes of metal flexure. This is not tolerable in astroimaging! From the beginning, all VSI flat-wall construction has been 1/4-inch plate aluminum or better (Sliders, Sidewinders, etc.). Most VSI circular-wall construction is 3/8-inch wall thickness or better (Toad focusers, etc.). VSI's massive construction policy is not overkill. On the contrary, it is only adequate for astronomical pursuits. It is an "astronomical standard" that needs to be adopted by all telescope and associated product manufacturers.

These finer points, and many others, have been pain-stakingly acquired during the 15-year history (1986-2001) of Black Forest Observatory, and incorporated in the design and manufacture of VSI products. Many features, like the above, may seem like moot points, but if you put the above, and many other "moot points" together, they add up to a very superior product - like no other.

I hope I have provided you with more basic, simple insight into some of the finer points of astronomical product design criteria, because my job is [also] to try and take some of the frustration out of your astroimaging adventures, for all my astronomer friends out there in "astroland."

Paul B. Van Slyke