Filter silde assembly viewed from inside the upper truss assembly.
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Over the past several months I have witnessed a pronounced increase in the use of binoviewers in amateur astronomy. One can hardly attend a star party without encountering them. Being the inquisitive type, I decided to investigate...
I began my investigation by just observing (pun intended). Every chance I got, I looked at and through the many binoviewers I came in contact with. I subscribed to the Yahoo group dedicated to the subject. I started reading the binoviewer forum on the Cloudy Nights website. I read the test reports and reviews posted across the Internet. I soon realized that there were two main manufacturers represented wherever one could find binoviewers on the observing field: Tele Vue and Denkmeier. There are a few others out there, such as Baader Planetarium (AP), B&W Optik, Celestron, LOMO, Siebert... but they are not as prevalent. Was this an anomaly or was there a reason for the proliferation of Tele Vue and Denkmeier?
As luck would have it, a very well known binoviewer reviewer lives in this very city... is a member of the same club (EVAC) and is a regular observing mate of mine. Naturally Jim lent his insight to my ponderings. At a star party one night Jim agreed to let me test his Denkmeier standard binoviewer in my TK-13. Much to my surprise, and disappointment, we discovered that the binoviewer would not seat fully in my Phase 4 focuser (this event occured before my focuser upgrade). The nosepiece of the binoviewer made contact with the filter slide mechanism, thereby preventing the binoviewer from fully seating and reaching focus. The filter slide cutouts are the same diameter (48 mm) as the nosepiece. This situation has since been addressed by Astrosystems -- the first filter position on current production TeleKits is slightly larger, thus allowing a binoviewer such as the Denkmeier to be fully seated in the focuser. This does remedy one problem, but it also introduces another: there now exists a trade-off between either having use of the filter slide or the binoviewer, but not both. It becomes a personal decision as to whether this compromise is acceptable. And Randy has informed me that TeleKits such as mine can be easily retrofitted to the new slide. Next Jim brought over his Tele Vue binoviewer, which worked fine when combined with one of the optical components from the Denkmeier rig. I joyfully spent the next several hours observing with the Tele Vue binoviewer equipped with a pair of 24 mm Panoptics. I decided on that night that I would eventually have to have a binoviewer of my own!
The above photo shows the view from inside the upper truss assembly. The filter slide assembly does double duty as the focuser board. The actual 5-position slide has been removed in this photo. This slight modification should allow the binoviewer to fully seat, a point I will confirm this weekend. Since I want to be able to use filters with the binoviewer, I have another project to attempt.
At this point in time I believe that my next step is to determine if the binoviewer will work in the TK-13 with the slide removed. If it does, I will have to either purchase or fabricate a couple of 'rails' upon which to mount the slide. These rails will have to be tall enough to allow the binoviewer to be seated.
All of my research led me to conclude that I would become a Denkmeier customer. On 3 June I placed an order for a Denkmeier II with self-centering diopters (SCD) and the new dual-arm power x switch. I was given an estimated ship date of two weeks... probably optimistic on their part, as a month has been more the norm. The helpful folks at Denkmeier suggested that I order the Newtonian kit, as this would work with both the TK-13 and my Intes MK66-DX Maksutov-Cassegrain.
While I wait for the binoviewer to arrive, I know that I'll have to address the issue of balancing the TK-13 again. The binoviewers (with eyepieces) will add a little over three pounds to the upper end of the scope. As I have done with such issues in the past, I contacted Jim Henson at ScopeStuff to see how he could help me out. He suggested a rail designed for a Meade LX90 SCT, as this was the most appropriate length for the size of my rocker box. The rail utilizes a system of little cars that ride along the rail... I feel like an engineer. I ordered this rail along with a one pound pancake weight and a close-mount kit that allows one to use regular dumbbell weights. In the photo below I have the pancake weight mounted on top, and below that is a 2½ pound weight. I also have a 5 pound weight that can be used instead, if necessary. Now I just have to wait for the binoviewers to arrive for further testing.
With a borrowed set of Denk IIs (thanks Jim) I was able to do further testing this past Saturday out in the Vekol valley. With regards to balancing, I found that I only needed to use the 2½# weight, and at times it was a bit much. I may need to order another 1# pancake weight so that I can employ a total of 2#. We'll see...
Counterbalancing proved to be the easier nut to crack on this night of testing. While the binoviewer can be fully seated in the focuser now, I was not able to bring any eyepieces to focus initially. After a trial-and-error period of adjusting part 'C' of the OCS, I was able to reach focus with 30 mm Ultimas, 24 mm Panoptics, 18 mm orthos, 16 mm Naglers and 15 mm Panoptics. Each set required adjusting of part 'C' to vary the amount of backfocus. Some pairs - the Ultimas in particular - just barely reached focus with the OCS extended to the maximum. In speaking with Russ (at Denkmeier) I've come to find out that the power switch adds about 3.175 mm backfocus, so further testing is required before any modifications are undertaken. Ideally, the OCS should be fully retracted so I'm thinking that I may get one of the Astrosystems truss extension kits. Further testing will reveal the optimum amount by which the truss poles should be shortened.
Last night saw, possibly, the arrival of the monsoon season. That could only mean one thing...
 The Denkmeier has landed. |
 Denkmeier II with SCD and dual-arm Power x Switch. |
It looks like any testing with the TK-13 will have to wait until the weekend. I have already set up the SVP and MK66 on the patio in anticipation of some MCT testing tonight, but it looks like another storm is already rolling in. The Moon doesn't set 'til after midnight, so hopefully I'll get a chance yet tonight... Well, patience is a virtue. By 10:00 PM the skies were clear enough to do some initial testing with the MCT. Following Russ' advice in assembling the rig -- part 'S' attached to the diagonal, part 'O' attached to the binoviewer, part 'C' unused -- I was able to enjoy using the Denks with my Maksutov.
Not even a waxing gibbous Moon (61% disk illumination) that didn't set until a quarter past one could keep me from getting out with the TK-13 over the weekend. About a half dozen club members met at Picketpost Mountain on Saturday. The day was mostly cloudy, but it cleared up quite nicely by 9:00 PM. After assembling and collimating the scope, I anxiously awaited darkness... almost. Since the Moon was already high in the sky, I decided to proceed with the testing.
The first test was to see if the fully-assembled binoviewer would fully seat in the focuser. Yes, it did. Next, I installed a couple of 24 mm Panoptics and set the binoviewer to low power (which should be around 1.4x), but I could not reach focus. Before adjusting the OCS, I tried the other two power settings on the Denk. Much to my delight, I was able to reach focus with either setting! I adjusted the OCS, but could not reach focus at the low power setting. I seem to need just a little more backfocus. Since it was Charles Messier's birthday (his 274th) I gleefully spent the rest of the night, until 3:00 AM, visiting old friends: M4, M6, M7, M8, M11, M13, M16, M17, M22, M27, M31, M32, M57... I also bagged NGC 7492 in Aquarius, the last globular cluster on an observing list I'd been working!
Russ was surprised that I could not reach focus at low power, and will be sending a spacer that he believes will remedy the situation. I can hardly wait for it to arrive!
The spacer arrived from Denkmeier... it's another part 'O' without the optical element. So, it looks like it should provide more than enough backfocus. Saturday night is clear -- nevermind that a waning gibbous Moon (97% disk illumination) is rising at 9:27 PM -- I've got some testing to do. I set up the Dob, collimated it, and went back inside to wait for darkness to descend. Speaking of darkness, SkyTools shows a grand total of 6 minutes of total darkness tonight (9:21 to 9:27). I went outside around 9:00 and there were already a few stars visible. I installed the binoviewer with 24 Pans and swung over to Antares... I can focus at all three magnifications! Wow! Since I was battling the clock, I decided to continue my testing in Scorpius and Sagittarius. It was quite nice to view the globular clusters M4 and M22 at a range of 90x, 125x, and 160x without changing eyepieces. Next up were a couple of open clusters: M6 and M7 -- followed by The Trifid and Lagoon Nebulae. Simply amazing! Two weeks until new Moon... I hope the monsoons hold off!
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© 2002-2004 Peter Argenziano, all rights reserved.
Page last updated on 4 July, 2004