The above SCT imaging train consists of a Meade 10" SCT + A381 (not shown, mounted in base of OMEGATOAD) + 3" OMEGATOAD + A388 + TARGETRON + SR2156 + CCD camera (SBIG STL11000/4020/6303).
Many have said that VSI has too many confusing port rings, adapters and couplings. This is probably true, because VSI has 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 (now where have I heard that before?). 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 following 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
QUALITY ASSURANCE NOTE: It has come to my attention that others use less than adequate couplings on their products that induce flexure. They look very similar to VSI's exclusive docking/coupling systems. They are NOT! VSI's exclusive docking/couplings are not like any other flimsy, flexure-ridden connections used on other products. A good anology would be a comparison between a (less than) $50 and a $300 (and up) rifle scope. The lesser rifle scopes looks identical to the more expensive ones but, in operation, the differences are very apparent, optically and [especially] mechanically. Let the buyer beware, you receive quality and functionality only when you are willing to expend an appropriate dollar amount. VSI's proprietary flared flange (circular dovetail) docking inserts have extremely thick-wall construction and are locked in place by three set screws opposed by 120 degrees. When you tighten these set screws against this special [angled] flange, it not only pushes directly against the insert ring, but it also pushes laterally to compress the ring inwards against external and internal shoulders, which locks it in place like a good weld - rock-solid! - PVS
TAK scope+ A384 + 3" ALPHATOAD focuser + A388 + TARGETRON + SR2156 + CAMERA
TAK REFRACTOR (less focuser) + A384 + ALPHATOAD + A388 + TARG + SR2156 + CCD CAMERA (SBIG STL11 or similar)
AP REFRACTOR (less focuser) + A385 + ALPHATOAD + A388 + TARG + SR35 + 35mm or CCD CAMERA (42mm T-thread)
TAK REFRACTOR (w/existing focuser) + SR72 + TARG + SR2156 + CCD CAMERA (SBIG STL11000 or similar)
AP REFRACTOR (w/existing focuser) + SR2724 + TARG + SR35 + 35mm or CCD CAMERA (42mm T-thread)
COMMERCIAL SCT + A381 + OMEGATOAD + A388 + TARG + SR2156 + CCD CAMERA (SBIG STL11000 or similar)
COMMERCIAL SCT + A382 + OMEGATOAD + A388 + TARG + SR35 + 35mm or CCD CAMERA (42mm T-thread)
16" MEADE SCT + A383 + OMEGATOAD + A388 + TARG + SR224 + f/3.3 FR + A2T + 35mm or CCD CAMERA
ABBREVIATION GUIDE FOR ABOVE (click on product code below to go directly to link)
REFRACTOR (no focuser): Visual back ring only, no existing focuser
REFRACTOR (w/your existing focuser): Usually internal threaded moving tube (i.e. 2.7 inch, 72mm, etc.)
ALPHATOAD = Any model VSI 3" ALPHATOAD focuser (i.e. ALF1, ALF2, ALF3 or ALF4)
OMEGATOAD = Any model VSI 3" OMEGATOAD focuser (i.e. OMG1, OMG2, OMG3 or OMG4)
COMMERCIAL SCT = Meade/Celestron SCTs 10" and larger, mounts to 3.25" or 3.29" threaded visual back
A381 = Docking Converter for Meade to install OMEGATOAD (see FOCUSERS link, Docking Converters link)
A384 = Docking Converter for Tak Refractor to install ALPHA (see FOCUSERS link, Docking Converters link)
A385 = Docking Converter for AP Refractor to install ALPHA (see FOCUSERS link, Docking Converters link)
MPSW = Mega-Port Sidewinder Optical Manifold (see SIDEWINDERS link)
TARG = Accu-Port Targetron Off-Axis Guider (see TARGETRON link)
ZBR1 = ATLAS 4.5" Zerotator (see ROTATORS link)
SR29 = Coupling Port Ring, 2.9" to 3.1" back-to-back flange (see SIDEWINDERS link, Docking Port Rings link)
SR224 = Docking Port Ring, 2"-24tpi commercial SCTs, female (see TARGETRON link, Docking Port Rings link)
MR2729 = Coupling Port Ring, 2.9" to 3.1" back-to-back flange (see SIDEWINDERS link, Docking Port Rings link)
A388 = Coupling Port Ring, 2.9" to 3.1" back-to-back flange (see SIDEWINDERS link, Docking Port Rings link)
SR72 = Docking Port Ring to install Sidewinder to your existing Takahashi focuser (see TARGETRON link, Docking Port Rings link)
SR2724 = Docking Port Ring to install Sidewinder to your existing AstroPhysics focuser (see TARGETRON link, Docking Port Rings link)
SR2156 = Camera Port Ring, 2.156"-24tpi, SBIG STL11000 (see SIDEWINDERS link, Camera Port Ring link)
SR35 = Camera Port Ring, 42mm-0.75mm, T-Ring (see SIDEWINDERS link, Camera Port Ring link)
A2LT = 2" Threaded Long Barrel Adapter (see SLIDERS link, Adapters link)
A2T = 2"-24tpi Female to 42mm T-Thread Male Adapter (see SLIDEERS link, Adapters link)
NOTE: Sidewinder, Targetron and Zerotator docking, camera and coupling ports are identical (2.9"). This means that any config you create will be directly interchangeable. The only difference is profile. The Sidewinder is 1.5" longer than the Targetron and the Zerotator is 0.5" shorter than the Targetron. Regarding configs, when we refer to the Sidewinder, it also applies to the Targetron and Zerotator. VSI offers many other adapters, converters and couplings. If your specific scope isn't listed above, go to the various docking or camera links to find and build your specific imaging train. If your scope or camera isn't listed there, call VSI. We can custom machine any threaded adapter using your scope part(s) as a reference template.
Remember, a Targetron is a large-format optical manifold for larger than 2" format focusers and cameras. Targetrons are designed for 2.7" and larger focusers, like our 3" TOADLOADER, and 35mm or CCD cameras (like the SBIG STL11000) that have larger film/chip areas than 2" format. Usually, VSI's smaller 2" format Slider will accommodate up to 35mm format with no vignetting, depending on the f/ratio of your scope, etc. However, you can mount a Targetron on a 2" format focuser using an SR224 port ring and an A2LT, which will convert the input of the Targetron to a 2" barrel-nose format, like a 2" eyepeice.
A. Your primary concern will be the type, and number of telescopes you have now, and/or plan on purchasing in the future.
B. A secondary consideration is the number of stacked imaging accessories (i.e. focal reducers, filter holders, secondary focusers, etc.) that you are installing in your imaging train. In other words, how much back focus does your telescope have (see "Do you have enough Back Focus?" below)?
C. A tertiary concern might be size and weight. Not a single VSI product has ever been accused of being too small or too light. On the contrary, VSI products are quite "manageable" for their size, and built like a tank [to the extreme], because quality imaging equipment needs to be [normally] built to other people's standard of overbuilt, which I consider to be a prerequisite for any instrument used for astroimaging. Unfortunately, this overbuilt standard is not a standard at all in other domains (see specs for individual product weights).
D. A minor consideration might even be too much back focus. Every astroimager would like to have that "problem." As I've always said, "You can use a simple drawtube to extend your profile to meet a long back focus, but you're only alternative to an inadequate amount of back focus is usually too drastic to consider." Cut off your tube, move your primary, move your secondary, install a lower profile focuser, re-design your tube assembly, etc. Conscientious telescope designers always consider the astroimager, if they want to sell scopes.
If you don't have a commercial SCT, you need to check your back focus before purchasing a Slider, Sidewinder or Targetron. I'm finding that many seemingly experienced astrophotographers know very little about their own telescope's back focus (BF). They order an optical manifold, etc. 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 mirrors, like the commercial Meade/Celestron Schmidt-Cassegrain telescopes. For every inch that you move your primary mirror, you get an equivalent of about 6 inches of back focus change, depending on your f/ratio.
If you have a commercial Schmidt-Cassegrain telescope (Meade/Celestron, etc.) you don't need to perform this test. Any Glider/Slider, etc. 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 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. Some of these methods are briefly discussed above. If you need advice, give me [Paul Van Slyke] a call and we'll talk about modifications to your telescope.
Say that three times real quick. Betcha can't without spitting all over yourself? Anyway, I hope this section will provide you with a better understanding of parfocusing any imaging train, not just the Slider or Sidewinder. I selected the [now] discontinued Micro-Slider (MS) and Flipper because they were designed to parfocus "in-reverse" of each other, which should provide you with a better concept of parfocusing principles (oops! there's another P-word). The MS parfocuses [from 35mm to CCD camera] by adding length to the straight through imaging port (noted in red, upper left) which is the most inefficient method of parfocusing (like the Meade flip-mirror devices) because you are increasing your imaging train's profile. The Flipper, Slider and Sidewinder parfocuses [from CCD to 35mm camera] by adding drawtubes to the top flip or slide port (noted in red, lower right) and side pick-off ports (not shown), which is the most effective method to parfocus your system because you are not adding any length to your straight-through imaging train to parfocus your system, it remains the same for either CCD or 35mm cameras. Remember that a shorter imaging train is always preferred because it's simply more solid, eliminating system flexure problems as you move from object to object. After attaching your new Slider/Sidewinder to your scope (addressed above), attach your camera, using the appropriate adapter, to the rear imaging port. Adjust the telescope's focus on your 35mm camera's focal plane, or CCD chip of your imaging camera. Then, insert a 2" or 1.25" eyepiece in the top slide mirror port and focus the eyepiece by push/pulling the eyepiece in and out until adequate focus is achieved.
Typically, with a CCD camera, you should not need an extension drawtube using a Slider or Sidewinder (see lower left Flipper), because most CCD cameras are roughly parfocus with most newer standardized eyepieces. However, with a 35mm camera, that focuses about 1.5" further out from a standard CCD camera, you will need an extension drawtube (item code AD22 or AD21) between the top slide mirror port and your eyepiece (see lower right Flipper, area in red). Although not shown in the pictures at left, side pick-off ports will need to be extended with a simple drawtube, but not on the discontinued Micro-Slider models because of the inferior "reverse" design that Meade has now "adopted" that extends the imaging train profile instead of the top or side mirror port profile. To further reiterate, note the two lower Flippers above. 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 (see lower left Flipper). Conversely, the upper two Micro-Sliders obtain parfocus by extending the CCD camera's straight-through profile (again, a no-no) noted in the red area in the upper left Micro-Slider image.
NOTE: 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 on other brands is 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 functional.
Also reference The Art of Astroimaging for more info on parfocusing your imaging train.