The following, will provide a general selection guide that will help you quickly understand VSI's item codes and the links at right will help decide what specific port rings and adapters are necessary to create your particular imaging train, or simply dock a major component (i.e. Slider, Sidewinder, VSI Toad focuser, etc.) to your scope.
You can build your own imaging train using these links, or just call VSI and I will help build it with you. However, before calling VSI, you should [at least] know your scope's visual back format. Especially if you have a scope from a manufacturer that has many different optical types and models, like Takahashi, TMB, Vixen, Borg, etc. That way, we have a place to start.
If you don't know your scope's visual back format, you can call the manufacturer or reference your owner's manual. If these are not available, then you can measure your scope's visual back threads yourself. Use a caliper and measure the outside diameter of the threads, not the inside diameter, because thread sizes are referenced from the outside diameter, not the inside. An example would be AstroPhysics 2.7"-24tpi threaded moving focuser tube, or Takahashi's 72mm-1mm visual back. Using an SAE caliper, you would measure a diameter of slightly less than 2.7 inches, and using a metric caliper, you would measure slightly less than 72mm. This simple method comfirms that the VSI port rings listed at the various links are correct. You don't have to measure the threads per inch, unless you have a thread gage.
ADAPTER = General term usually connecting or converting a 2" or smaller format component to your scope or camera. This type of adapter can be male or female threaded, or flanged on one end to be inserted in a female cavity locked down with double thumb screws,like the rear port of the Slider, etc.
MOVING TUBE = Also called Travel Tube. Always confused with the term "drawtube," even by other focuser manufacturers. A drawtube is not a moving/travel tube. A drawtube is a push/pull tube that is [usually] inserted into a focuser's moving/travel tube.
DRAWTUBE = Can be written as one or two words. Both are acceptable. A push/pull tube usually used for rough focusing an eyepiece or guiding CCD camera. Also used for extending the focus range of a focuser. Mostly associated with 2" or 1.25" eyepiece formats.
CONVERTER = Converts one format to another format. Usually an existing threaded format that converts to a different threaded format, but not always.
PORT RING = VSI's definition is a ring, usually threaded, the is larger than the standard 2" format (i.e. 2.7"-24tpi, 72mm-1mm, etc.).
DOCKING PORT RING = Docks a VSI major components (i.e. focuser, optical manifold, etc.) directly to your scope's visual back.
CAMERA PORT RING = Attaches a camera to the rear port of a VSI major component (i.e. Sidewinder, Targetron, etc.).
REVERSE PORT RING = Attaches to the rear port of a VSI major component to convert to the exact opposite of a [usually] threaded docking port ring. If a specific docking port ring is male threaded, then the reverse port ring is female threaded. Continues the same [threaded] format of the scope's original visual back format, before the VSI major component was attached.
COUPLING PORT RING = Connects two VSI major components together with the least possible consumed profile (i.e. Zerotator to Targetron, TOADLOADER to Sidewinder, etc.).
DOCKING CONVERTERS = Installs in the base of a focusers housing to convert it to your scope's visual back format.
OUTPUT ADAPTERS = Installs in a [larger than 2" format] VSI focuser's moving tube, like the 3" ALPHA/OMEGATOADS, to provide the shortest profile connection to an optical manifold, camera, or eyepiece.
ABBREVIATION REFERENCE GUIDE (click on product code below to go directly to link)
A??? = The letter "A" at the beginning of an item code refers to an Adapter (can also refer to a focuser docking port ring or converter (i.e. A2LT, A382, etc.).
RR??? = The letters "RR" at the beginning of an item code refers to a Reverse Port Ring for a Sidewinder or Zerotator. This item uses the same numbers as its "SR" mate, except with the opposite reverse thread. A good example would be the SR72 and the RR72, which are the same Takahashi M72-1mm thread pitch, but the SR72 has a male thread where the RR72 has a female thread. Again, continuing the scope's original output thread format.
CR??? = The letters "CR" at the beginning of an item code refers to a Camera Port Ring that attaches to the output of a Sidewinder or Zerotator to go directly into your camera. Example would be a CR35 referring to the industry-standard M42-0.75mm T-thread used for 35mm cameras, and now adopted by most CCD camera manufacturers like SBIG and Starlight Express, etc.
??123 = The number after the letter(s) usually refers to the manufacturer's threaded format of the adapter or port ring. EXAMPLE: the item code SR2724 refers to a port ring for the AstroPhysics 2.7"-24tpi format. This proprietary AP format is becoming an industry-standard that others are adopting, except for Meade and Celestron of course.
Sidewinder and Zerotator port rings are identical (2.9"). This means that any config you create will be directly interchangeable. The only difference is VSI component profiles. As the Sidewinder is longer than the Zerotator. Regarding configs, when referring to the Sidewinder, it also applies to the Zerotator. VSI offers a myriad of adapters, port rings, converters and couplings. If a specific connection isn't listed, call VSI. I can custom machine any threaded adapter using your scope part(s) as a reference template. I prefer to have your existing threaded part in-hand to better match the threads, rather than just cutting a sloppy chased thread.
Many have said that VSI has too many confusing adapters and couplings. This is probably true, because VSI has many dozens of different adapters that can be installed in various locations along your imaging train. VSI also has the best selection, by far, on Planet Earth. So your confusion is well justified, but I do believe that a good selection is important, simply because there are so many different types of telescopes and imaging equipment available to the modern astroimager. I hope the above will make your final imaging train decisions easier and less frustrating. After all, that's what VSI components are all about - creating an ultra-low profile, rock-solid imaging train, and removing the frustration from astroimaging. - PBVS