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Focuser Heaven…the Moonlite Crayford Focuser and Baader Astro T2 System

Posted by Mike Strieber   03/03/2005 15:51:PM

Focuser Heaven…the Moonlite Crayford Focuser and Baader Astro T2 System

Having been serious about amateur astronomy for the last 15 years or so I’ve had the opportunity to own a variety of scopes and accessories. Until the last few years my interests were mainly focused (no pun) on visual observing while occasionally dabbling in imaging. I then purchased a Coronado Maxscope 40 (and eventually double-stacked it) and became addicted to solar observing and imaging. Within the last few months I decided to get “serious” about imaging at night also. With this in mind I refreshed my inventory of astro gear by selling some items (not the Maxscope!) and purchasing a Canon 20D and some other imaging related accessories. After a period of exhaustive research I decided the scope that best fit my scenario was the Vixen R200SS 8”, f/4 reflector. Generally speaking, I was looking for a fast, short tube, lightweight, Newtonian. It also had to be suitable for use with my beloved Losmandy GM8, dual mounted with a guide scope.

While not the intent of this piece, let me take a moment to discuss my view of this scope as it allows for a transition into the meat of the subject. Overall the scope is of fine quality. Very well made and mirrors to be proud of. My only complaint was the focuser. Perhaps for most the focuser would be just fine, it really wasn’t a quality issue. The focuser has unique threads and dimensions that pretty much limit you to using Vixen accessories. While those aren’t all that bad either, the coma corrector (required for this scope) didn’t allow for the use of filters. I had seen a number of forum discussions about this and it appeared to be a common theme. While searching for answers I came across suggestions such as gluing a filter to the coma corrector, references to bailing wire, etc. While that might be a suitable approach for some, I wasn’t interested in getting super glue anywhere near any of my optics. With great hesitation I decided to opt for a new focuser. Why with great hesitation? I am by no means mechanically inclined and the thought of drilling holes in a brand new telescope wasn’t real appealing to me. A common joke amongst my friends is that my toolbox consists of a screwdriver, ice pick, and duct tape. As a retired helicopter pilot I can assure you the last thing the crew chief wanted to see was me around the aircraft with a tool!

I had always admired the Moonlite focuser and decided this was the best approach for me to take. I followed the instructions at the Moonlite webpage on how to measure and order the right combination of adapters and drawtube length. Before I placed my order I contacted Ron Newman at Moonlite Telescope Accessories just to confirm I was on the right track. Next thing I knew Ron was all over it…"like ants on a candy bar”. He knew exactly what I needed and provided sound advice on not only the components but how best to conduct the surgery on my new Vixen. Without his help I probably wouldn’t have gone through with it. Once again, the Vixen focuser uniqueness came into play. The Vixen focuser min and max drawtube height did not conform to any of the adapters Moonlite currently had for options. Without hesitation Ron took it upon himself to make me a unique 1/4” spacer. This spacer is curved to fit various tube dimensions and allows for the proper standoff of the focuser, replicating as closely as possible the current min-max drawtube travel.

Since I was building my ultimate imaging machine I decided on the Model CR2 with a dual rate focus knob that allows for an 8 to 1 reduction. They also have a model that allows for a filter to be inserted into the optical train via a swinging device attached to the bottom of the drawtube. While this looked tempting I was concerned about too much drawtube being injected into the light path. It would be kind of like having another central obstruction if it protruded in too far. I also believe this design would be more suited for an open truss type reflector that allows for easier access to the filter. This model would have also created the need for me to increase the size of the existing drawtube hole, at least notch an area to accommodate the swing mechanism. Drilling four new holes in my new tube was bad enough. I already told you about me and tools, right? Since the Vixen tube is green (perhaps my only other complaint about it…but it’s growing on me) I decided to dish out the extra $25.00 for an optional color (Moonlite default color is red). In keeping with my tradition of trying to get my wife involved with my hobby I let her choose the color. She chose the anodized gold, and as usual, she was right on. It’s a beauty.

When the focuser arrived two things struck me hard. 1.) This thing is absolutely gorgeous. 2.) I’m that much closer to drilling holes in my new telescope. After careful consideration I decided that downing a couple of bottles of courage was probably not the preferred technique for prepping for surgery. Realizing the fact that the focuser wasn’t going to mount itself, I decided to get to work. The first decision to be made was whether to remove the optics or not. I chose the path of least mechanics and decided not to. I laid the tube on a blanket on the floor and propped it on both sides with towels to prevent any rolling motion. I then covered the secondary with a zip lock bag and placed a clean sheet of paper inside the tube to catch any metal shavings as I drilled. I oriented the tube with a slight incline with the primary mirror somewhat elevated to keep any material from falling in that direction. Unless you use an extremely long bit there is no danger of hitting the secondary as you drill through. Trust me, during the act of drilling you’re pretty careful about how far that drill goes in anyway. I then removed the original focuser. Easy enough, this is going great. Next I decided the best way for me to get the Moonlite hole pattern marked on the tube was to make a template. I traced the outline of the focuser on a piece of paper and very exactingly cut it out. I then placed this against the base of the Moonlite adapter, following the curvature of it, and poked holes in it that aligned with the screw pattern. This gave me a precise template of the adapter and I marked the tube with it. Next came the fun part. I took a fine nail (I decided against the ice pick) and tapped starter holes (more like nicks) in the tube. It is not necessary to go all the way through the tube. Chances are you’ll begin to crease the tube prior to making it through it. Make them just deep enough to keep the drill bit from slipping. I’m firmly convinced a variable speed drill is best suited for this application. It gives you much more control over what is taking place. I chose to use a very small bit first to just initially get through the tube. I then finished up the holes with the proper sized bit for the screw diameter. After wiping the sweat from my brow it was time to test fit the focuser. Wow, perfect! I was proud of myself. Once I had the Moonlite in place it was time to give it a test drive.

During my research I had decided on the Baader Multi-Purpose Coma Corrector (MPCC) and had previously ordered one from Alpine Astro. This had the capability of screwing directly onto my t-ring for the Canon and accepted 2”/48mm filters. So here we go, I plop in my Televue 20mm plossl (my favorite eyepiece) and start rack’n. Hmmm, I’ve hit the outbound stop and it won’t come to focus? What’s up with that? As I was wiping the tears from my eyes it dawned on me. When measuring I hadn’t factored in the “unique” Vixen 1.25” eyepiece adapter that sticks out of their focuser by about 8 feet. Actually it’s only about 2.5”, regardless it was a lot further out than my Moonlite drawtube would go. The good news was my Canon would come to focus with room to spare but at the other end of the drawtube travel. Time to regroup.

I conducted further research and narrowed my choices to two options. After further discussions with Ron at Moonlite I felt he had a viable approach that included a different adapter and longer drawtube. It would work but it heightened my concern (and his) about too much drawtube in the light path. During this research I came across the Baader Astro T2 System. I studied the Baader T2 system chart until my hair hurt trying to figure out the combination of adapters I would need. If you haven’t seen this diagram it’s kind of like the writing on the chalkboard you always see behind pictures of Einstein. I decided my best approach was to contact Bob Luffel at Alpine Astronomical. I could have saved a few gray hairs by contacting him sooner. I explained my situation to Bob (in a long convoluted story like this one) and he responded as if he conducted the surgery with me. You name it…if you want to connect a toaster to your scope…Bob can square you away.

The Baader T2 system is a work of art. Generally speaking it’s a series of adapters, extension tubes, couplers, t-adapters, etc. The system is based on the standard T2 thread (same as the M42 thread common to many T-adapters). The components of the T2 system are of the highest quality, machined to exacting standards, and allow for a tremendous amount of flexibility in varying configurations. Superb fit and finish to boot! As the MPCC is designed for a nominal distance of 55mm from the mounting flange to the film plane, Bob recommended the T2-17 (2” deluxe clamping eyepiece holder) and the T2-28 (expanding ring T2/2”). This combination also allows for the proper spacing between the coma corrector and the eyepiece field stop. The MPCC (with filter attached if so inclined) is then inserted into the 2” focuser drawtube and the system is setup for visual use with (hopefully!) plenty of focuser travel. My description probably sounds much more complex than it really is. Time to give it a shot. Bob, “you da man!” Now that my Canon 20D and my full range of eyepieces (including barlowed) come to focus I can sit back and enjoy my new focuser right? Of course not.

As this story was unfolding I had ordered a new ST-7XME with the intent of using it primarily as a guider. I chose this route instead of a dedicated guider as I figured I might at some time use it for primary imaging also. Time to try it out in the Moonlite. As I anticipated, I didn’t have enough inward focuser travel. This time I did something really stupid; I went back to the Baader-Einstein chart and tried to figure it out myself. You should be able to guess my next step by now. That’s right…get in touch with Bob. In a matter of seconds he had the answer for me. Of course it involved the T2 system again. I needed a 30mm extension tube to connect the SBIG camera to the MPCC. These are really nice as the Baader extension tubes are threaded on one end to fit the MPCC and the other end screws right into the standard thread of the CCD camera. It also provides the precise distance needed between the MPCC and the camera chip. Unfortunately Bob didn’t have any 30mm tubes in stock so he sent me two of the 15mm variety (what the heck, even more flexibility). Time to give it a shot. Bob, “you da man!”

Now back to the meat of this story. The Moonlite focuser is nothing short of top shelf stuff. The focuser is a low profile (1.45”), zero backlash, no image shift design. It is of the highest quality, perfect fit and form, built to the tightest specifications, and a pure joy to use. The focus knob and drawtube action is precise and silky smooth, and that’s not even the reduced side. The 8 to 1 inline reduction slow motion system makes precise focusing a breeze. Even with the narrow critical focus zone of my f/4 reflector the image truly snaps into an unambiguous focus. It has a vertical lifting capacity in excess of 5 pounds and is user adjustable, a really nice feature. Also included is a 1.25” eyepiece adapter. Not only are the mechanics superb, you’re tempted to put it in a display case as it just looks really nice. The flexibility in color (7 to choose from) allows you to configure a system distinctly tailored to your liking. If you’re picky about your equipment cosmetics like I am, this is a big plus. While my installation experience sounds somewhat harrowing it really wasn’t that bad at all, even for a guy who would never be confused with Mr. Goodwrench. Moonlite even makes standard adapter kits for a variety of common telescopes that preclude having to drill holes at all. My particular telescope led to some unique requirements and the Moonlite was flexible enough to make my system work. Top it all off with top-notch customer service and you can’t go wrong. I’m tempted to buy one of their crayford refractor focusers then find a new scope to attach to it!

How do you make a fantastic focuser even more flexible? The Baader Astro T2 System. If you can’t find the configuration you need with this system, what you’re trying to connect doesn’t belong near a telescope. The great reputation Baader enjoys extends to the T2 system. Unsurpassed build quality and craftsmanship at a very reasonable price. While not the focus (no pun again) of this article the MPCC is really a great coma corrector. Looking through my reflector without a coma corrector is like looking through a kaleidoscope. Pop in the MPCC and the view is cleaned up like a Hubble image (after the Shuttle repair mission mind you). Stars are crisp, like jewels, all the way to the edge both visually and on the chip. Once again, the only way to beat an extremely high quality product is to add extremely high quality customer service. Bob Luffel of Alpine Astronomical provided me with sound advice throughout this saga. I couldn’t have done it without his expertise and eagerness to get it right.

One day I’ll bore you more with my further exploits involving the turbo-charging of my Vixen. I removed and center-dotted the primary mirror (quite the adventure!), ventured into laser collimation, switched out the finder to a Tak 7x50, etc.

Thanks to Moonlite and Baader, I now have an extreme, lean, mean, imaging machine...the “Full Monty”. Now if I could only learn to image without the Sun up I’d be “da man”.

Mike Strieber

PS- I would be remiss if I didn’t take this opportunity to once again thank our fine Soldiers, Sailors, Airmen, and Marines, and more specifically our incredible Special Operations Forces, for quietly and professionally, conducting the nation’s business. God Speed.