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Taming of the Slew – Transforming Your Dobsonian into a Dutiful Companion
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Taming of the Slew – Transforming Your Dobsonian into a Dutiful Companion
Six years ago I got around to pursuing a long-held desire to educate myself on astronomy and cosmology. I started to learn the fundamentals with an inexpensive four inch reflector, learned the lay of the night sky, and read numerous books and resources. As a newcomer to the hobby I advocate the manual approach - the learning is in the doing, rather than having it done for you by a magical box with a motor. Give me a 1:24,000 topo map and quality compass any day over a GPS. Five years ago I moved on to a 12 inch reflector. I fully expected a beautiful mail order bride to arrive. Instead I received a monstrous, difficult to handle mistress in a casket-sized box. I was nevertheless certain she was the one for me…..with a little grooming. Perhaps some of my features and modifications may inspire you to make those changes to your outfit that will improve handling quality and make viewing more manageable and enjoyable.
Foundation:
Dolly - The fundamental issue with a large aperture Dobsonian is mobility due to the size of the OTA and the corresponding turret that must accommodate it. Let’s begin with the base and build upward. You can purchase a commercially made dolly, improvise one, or devise one yourself. I preferred to house the base plate of my turret down into the dolly and then attached it to the dolly from underneath with screws. The turret can also be mounted atop the dolly as well. Most turrets are typically MDF (medium density fiberboard, aka glued-up saw dust) or particle board (aka glued-up wood chips) laminated with Melamine for which you will want coarse threaded screws. Always drill an undersized pilot hole in these materials first to avoid bulging and break-out as they do not accept screws like solid wood. I recommend using wood glue in the screw holes when assembling the turret itself as this bond is intended to be permanent, and dispensing with the glue when attaching accouterments to the turret, facilitating later removal. I made my dolly from cedar and cherry. The cedar came from a tree in my yard I milled into lumber and air dried for years. Yours can more easily be made from readily available pine or poplar and needn’t be a hardwood. Although MDF and particle board lack the qualities of solid wood, they have the advantage of not expanding or contracting with fluctuations in humidity like solid wood. My dolly is 25.5 inches square (turret base plate is 24 inches in diameter). I keep it inside the house and use the front door as exit/entry, which is 35.5 inches wide. This gives me about five inches clearance on both sides. To prevent the turret from swinging and slewing on its own in transit I made a simple wooden dowel pin with square head that slides into aligned holes drilled in the upper/lower base plates.
Tires - Your choice of wheels will either be hard urethane style ones or soft rubber/inflatable tires. Hard tires ride well on hard surfaces (mine stay on concrete), soft tires for “off-roading.” I determined most of the off-road” versions were too big to reasonably work and I questioned the stability of their softer composition. Bear in mind the over-all height increase to the focuser based on the height of the dolly and choice of tires in relation to your stature. I chose 4” diameter urethanes and set them 6” in from the corners for two reasons: to avoid kicking them while standing close to the dolly at the focuser and to accommodate levelers. Bear in mind the balance point and weight-bearing location for the tires on your outfit to avoid a propensity to tip. Mine are just about in line with the vertical side walls of the turret and are very stable. I cannot get the platform to tip. I am an average bear at 5’10”. My tires and dolly raised the bottom turret base plate 6.5” inches off the ground. This additional height alleviates bending over the focuser at most viewing positions and increased comfort. However at positions near the zenith with various sized eyepieces I just have to get on my toes, which requires a step 3– 4” in height for comfortable, extended viewing. On occasion I view without deploying the levelers, which the hard tires accommodate just fine. Issue is I have a slope to my driveway, which is remedied by the levelers.
Levelers - I made the levelers from 3/8” threaded rod set in 2” from each corner edge. I mounted a 3/8” T nut on the underside of the dolly. T nuts come with either prongs for pressing into the wood, or screw holes in the flange. You will want the screw type for this application. On the top side I fed the rod through a 3/8: table leg top plate and drilled out the threads in each plate for a tight fit as a rod guide, just leaving the T nuts to actually connect with the rod threads to raise/lower the outfit. It is essential you have a swivel foot/toggle pad attached to the bottom to accommodate rotation of the rod while the foot remains stationary. I could not locate these even at two specialty places in town and ordered them online (see suggested sources at end of article). Ideally I would have liked leveler rods with a much larger thread pitch requiring far fewer turns, such as an Acme thread found on the rods of C clamps. However, if the extra thirty seconds to lower them is onerous, I probably should not be out looking at photons from celestial sources traveling hundreds to millions of light years to dance on my retinas. I added threaded handles and secured them by drilling through the handle and rod and inserting a roll pin. You could just as well swab some JB Weld on the threads and screw the handle on to prevent it from unscrewing itself from the rod on the lefty-loosey uptake rotations. Lastly, I made four leveler foot pads from cherry (3” square) to place under the swivel feet. A ¾” hole drilled with a Forstner bit for a flat bottom hole perfectly accommodates the diameter of the swivel feet. I avoided the metal feet eating into the wooden foot pad by applying epoxy and driving home a penny in the bottom of each hole, which was tight enough the epoxy is probably superfluous. A helpful feature to leveling is the two bubble levels I added to the sides of the top turret plate.
Bearing - The one upgrade necessary if you intend on adding storage features and “furniture” to your turret is an enhanced bearing. The manufacturer of my Skyline calls these the needle bearing and azimuth discs. They are sandwiched between the two base or ground plates of your turret. Your brand may have something comparable. It is essentially a lazy-susan bearing design and is surprisingly efficient and smooth if you do not add any weight to your outfit. However, additional weight will quickly render it ineffective. I replaced mine with a heavy duty lazy-susan bearing designed to accommodate up to 330lbs. It is 17 3/8” in diameter and 13/16” thick (bear this in mind when determining new height calculation to the focuser). This upgrade greatly enhanced the ease and smoothness of turret rotation to accommodate my modifications. You will screw this bearing to the bottom turret plate. The top plate will set atop it and be secured to it by the azimuth tension bolt just as with the original bearing. Other brands will likely have a similar construction, but may require a longer azimuth bolt or other modifications.
Furniture:
My intent with adding storage to the turret was to accommodate all my accessories, except the eyepieces and filters, which I relegated to Apache brand weatherproof cases with pick/pluck foam set out on a 5’ portable folding table. I added a touch of aesthetics by using cherry, cedar, and padauk with a few walnut, cocobolo, and myrtle burl accents. You needn’t get so fancy to have an improved system of organization and access to your accessories. Most turrets have ample surface space that lends itself well to attaching storage features that is otherwise empty real-estate. You can create wooden storage boxes or features, or even attach prefabed ones made from plastic or other materials. I recommend attaching the boxes to a back-plate and then mounting the whole unit to the turret. My boxes are glued and screwed onto the back-plates from behind in counter-sunk holes and then screwed onto the turret from the front side of the back-plates. If you create your storage units from solid wood, bear in mind the drastic changes in/outdoors throughout the seasons. I finished mine with teak oil and marine spar varnish topped with wax for maximum protection and ease of maintenance/touch-up.
My storage arrangements on the turret accommodate a Telrad and 2” riser for it, two finder charts for Messier objects for the Telrad, Wixie brand angle finder, light pipe, four leveler foot pads, 35mm extension tube, Glatter Parallizer, laser collimator, Astro-Systems collimator, Tele-Vue in-travel adapter, AA batteries for the Telrad and hex wrenches. Additionally, the second box has a sliding dove-tail receptacle to store the red dot finder when replaced with the Telrad. I managed this by screwing a Telrad mounting base onto the OTA between my focuser and Stellar-Vue 9x50 scope. I cut the wings off of an additional Telrad 2” riser and mounted the dovetail shoe and red dot finder onto it. Thus, one station can accommodate two very different optical accessories. In the spirit of economy I squeezed two narrow book racks on the inside of the turret between the walls and the OTA. My set up has a frog hair more than 1” clearance here on each side. My racks can accommodate materials up to ¾” thick, and hold a pocket atlas, moon map, and 2021 Almanac quite nicely.
Fulcrum:
I noticed most people attach ballast and counter-weights to the back end of large Dobs to address balancing the equation of varying weight at the front end. I chose to make a sliding dovetail control arm with locking knob that is anchored to the front of the turret and attaches to the OTA with four rare earth magnets. I removed the OEM handle on the front of the turret and utilized the two existing T nut locations to mount the base of the control arm. I could not get standard or metric bolts to fit these T nuts and so replaced them. The magnets very securely hold the head of the arm to the OTA against the front rim and permit easy removal of the arm. This arrangement allows me to instantly go from a 3oz. 1¼” Tele Vue 20mm Plossl to throwing a 1.2lb Tele Vue 2x Powermate under the Plossl, and everything in between. There is never a need to adjust counter-weights or re-balance. The arm has largely replaced use of the two OEM side bearings. I embedded an aluminum T track in the cedar control arm to receive the locking knob, articulated the upper and lower portions with knuckle joints to create hinges, and made my own hinge pins by cutting and drilling Clevis pins fitted with a Cotter key for retention/quick removal. I can remove/attach the entire arm in 20 seconds or less. The length of the arm portions are both determined by length of the hypotenuse from the rim of the OTA to the turret, and conversely determine the limits of attainable altitude. My arm permits movement from 90° (zenith) down to about 11° on the horizon. Between tree lines and turbulence, I seldom range this low. On occasion when I needed to go lower, it took 3 seconds to detach the magnetic head of the arm to get below 11°. However, holding a steady balance this low with any appreciable weight at the eyepiece is defeated. Lastly, a major minor improvement is a handle. It is the one thing I constantly hang onto throughout the night and use to slew the OTA with my left hand while operating the control arm locking knob with my right. I am fond of Rockler’s 41/2” jig handle that comfortably fills my whole hand rather than just a few fingers. I removed one of the screws in the rim and drilled out the hole to receive a black, low profile hex head bolt.
What is missing? An azimuth setting circle, which I will house between the two turret base plates and upgraded outriggers using veneer presses with large screws and Acme threads.
Suggested Material Sources: (most hardware available at local sources)
Lee Valley - (magnets, magnet cups, T track, knobs, T nuts, assorted hardware, lazy susan bearings)
Rockler - (T track, hardware, T nuts, jig knobs and handles, lazy susan bearings)
Harbor Freight - (Apache brand weatherproof cases with pick/pluck foam for eyepieces and accessories. Much cheaper and every bit as good as Pelican brand, except for the foam)
MS Discount Tool - (toggle pads/swivel feet for levelers)
The scope contains all necessary accouterments minus eyepieces and eyepiece accessories, which I maintain in two Apache brand cases and deploy on a folding 5 foot table. For quick reference I use the Orion Deep Map 600 clipped to ¼” Masonite on an artist’s easel. The depicted chart is laminated and attached to the OTA with adhesive strip magnets where it remains permanently and is readily visible under red light. Chart is included below.
morgan a.
Arkansas - 35°N latitude
(The S&T article which is derived from this document is copyrighted. However, this document is neither write-protected, nor copyrighted in the interest of disseminating ideas. Creating such a scope was a singular labor of love and not intended to result in the solicitation of production work for sale. I have no monetary interests in this information. Feel free to share.
304mm Aperture x 1500mm Focal Length – f5
|
Lens Aperture 1.25” |
X Magnification (60° AFOV) |
Limiting Magnitude |
2X Barlow Magnification |
Limiting Magnitude |
||
|
5mm (X-cel) |
300x |
0.2 |
15.2 |
|
|
|
|
7mm (X-cel) |
214x |
0.3 |
15.0 |
|
|
|
|
9mm (X-cel) |
167x |
0.4 |
14.7 |
333x |
0.2 |
15.2 |
|
12mm (X-cel) |
125x |
0.5 |
14.4 |
250x |
0.2 |
15.2 |
|
18mm (X-cel) |
83x |
0.7 |
14.0 |
167x |
0.4 |
14.7 |
|
25mm (X-cel) |
60x |
1.0 |
13.6 |
120x |
0.5 |
14.4 |
|
|
|
|
|
|
||
|
Lens Aperture |
X Magnification |
Limiting |
2X Powermate |
Limiting |
||
|
1.25” |
(50° AFOV) |
Magnitude |
Magnification |
Magnitude |
||
|
20mm TV (Pl) |
75x |
0.7 |
13.9 |
152x |
0.3 |
14.6 |
|
25mm TV (Pl) |
61x |
0.8 |
13.7 |
122x |
0.4 |
14.4 |
|
32mm TV (Pl) |
48x |
1.1 |
13.4 |
95x |
0.5 |
14.1 |
|
|
|
|
|
|
||
|
Lens Aperture |
X Magnification |
Limiting |
2X Barlow |
Limiting |
||
|
1.25” |
(62° AFOV) |
Magnitude |
Magnification |
Magnitude |
||
|
7mm TV DeLite |
214x |
0.3 |
15.0 |
|
|
|
|
|
|
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|
|
||
|
Lens Aperture 2” |
X Magnification (70° AFOV) |
Limiting Magnitude |
2X Powermate Magnification |
Limiting Magnitude |
||
|
26mm (Q 70) |
58x |
1.2 |
13.6 |
117x |
0.6 |
14.4 |
|
32mm (Q 70) |
48x |
1.5 |
13.4 |
95x |
0.7 |
14.1 |
|
38mm (Q 70) |
40x |
1.8 |
13.2 |
80x |
0.9 |
14.0 |
|
|
|
|
|
|
||
|
Lens Aperture |
X Magnification |
Limiting |
2X Powermate |
Limiting |
||
|
2” |
(82° AFOV) |
Magnitude |
Magnification |
Magnitude |
||
|
17mm TV |
89x |
0.9 |
14.1 |
179x |
0.5 |
14.8 |
|
|
(Nagler Type IV) |
|
|
|
||
|
Lens Aperture 2” |
X Magnification (82° AFOV) |
Limiting Magnitude |
2X Powermate Magnification |
Limiting Magnitude |
||
|
20mm (Meade) |
76x |
1.1 |
13.9 |
152x |
0.5 |
14.6 |
|
|
|
|
|
|
||
|
Lens Aperture |
X Magnification |
Limiting |
2X Powermate |
Limiting |
||
|
1.25” |
(76° AFOV) |
Magnitude |
Magnification |
Magnitude |
||
|
14mm Morph. |
109x |
0.7 |
14.3 |
217x |
0.4 |
15 |
|
8mm Hyperion |
190x |
0.4 |
14.9 |
380x |
0.2 |
15.2 |
|
|
(68° AFOV) |
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|
|
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- Jim7728, BarabinoSr, fate187 and 6 others like this
21 Comments
Taming of the slew(shrew) , no way . Learning to live with each other’s idiosyncrasies. Love what you two have done to live together. No weights on the backend but a chinstrap on the front . ; = )
Impressive project. I have always thought of getting a DOB. But, the ones I've seen weren't very good quality and having never learned star hoping, it would be quite a challenge. Your solution is very imaginative. Your wood-working is superb. Almost makes me want to run out and buy a DOB so I could build the mount like you have done. Congratulations on such a well documented project. Inspiring.
I merely combined my passion for wood woring with that of astronomy and modified the chassis. I marvel at folks who grind optics and build scopes from scratch - beyond my knowledge, skills, and abilities. As has been rightly said, 'a large Dob is the best bang for the buck,' providing you mitigate its two limiting factors: mobility and balance. If you are willing to apply home-made ingenuity to address these, then a large Dob is a good venture.
As with any modification, the formula = function over form, i.e. performance over beauty. If you can achieve both, then great. My setup is constrained to home use. Were I wanting to trasnport a large Dob to the field, I would absolutley go with a truss design.
Since this article I have replaced the outriggers with four each veneer presses with 7/8" dia screws with the large Acme threads and have largely completed the azimuth ring to be sammiched between the base plates and rotate around the lazy susan bearing. Whether wood working or any task, I thrive on self-discovery: what works, what doesn't.
m
Wow that is a nice setup-thanks for sharing this!
That is a non-traditional approach to "taming" your 12 inch Dob. Some interesting stuff.
I took the more traditional approach with my 12.5 inch Discovery Dob. In the 25 years I have owned it, it had gone through several transformations. It began as Sonotube Dob which was upgraded to a plywood base with Ebony Star-Teflon bearings. In 2007, I got lucky and I was able to acquire a truss conversion for a local builder.
It's a classic truss Dob with large diameter altitude bearings. It's compact, the footprint is 19" x 20" and it nests so the rocker box, mirror box and and upper cage are 28" high when disassembled. It takes up the seat space of one person.
Jon
Nice write up, thank you for sharing! I noticed your variety of lens, would you be willing to share which ones you use the most and under what circumstances?
Thanks again for the time and effort you put into the article.
Mike
Jon,
I admire your set up and parameters for a Dob that size. There are far worse passengers who could ride shotgun, rather than a beloved Dob. I have enteratained an 18" truss model for mobile deployment, but have so many irons in the fire I needn't add another now, as I also use a 6" SCT and 3 astro binos. I like your incremental improvements. Stars change in their evolution and proper motion in 25 years, so should your equipment. In the spirit of the New Mexico motto, "It Grows as it Goes." I am unorthodox in most all my approaches, which by no means indicates "smart," just different and labor intensive.
m
Mike,
After initial collimation I seem to always start with the 26mm (Q 70) 2" as a calibration EP to test tranparency/seeing, as a middle-of-the-road magnification. I use the 38mm (Q 70) 2" the least.
Caveat #1: while there is no disputing the merits of some of the top brand name EPs, I must say the Asian mfg 2" Q series and the (chinese) Celestron 1.25" X-cels are surprisingly good for price/performance ratio and are part of my regular ocualr retinue in all viewing sessions with the Dob and a 6" SCT. I bought all my EPs/X-cels pre-pandemic, and all the X-cels ran $60ish at the time - now circa $100 ea. I admittedly have more glass than necessary and would not claim it is necessary to invenst in that many EPs, especially at today's prices, to cover your needs with a Dob and have meaningful viewing sessions.
Caveat #2: I have 59 year old retinas and I wear glasses, but never when using telescopes or binos. I'll try to note the EPs that are particularly problematic with glasses.
Caveat #3: When I made my foray into amateur astronomy I made some mistakes not understanding the various applications of EPs and their compatability with particular scopes. Hence, I purcahsed some EPs that were superfluous, e.g. a Celestron X-Cel 2.3mm sitting new/unused in my closet. I recommend an ecclectic appraoch: pick and choose select EPs from a variety of brands upon researching and do not get into the collector mindset thinking you have to buy into every EP in a given series - not so. Strength is in variety, not continuity of a set.
I usually juggle both 2" and 1.25" EPs in most sessions. If my intended targets are open clusters, broad/general meandering, or macro navigating to known targets, I use the following in 2": 32mm, 26mm Q 70s (some times the 38mm) and the 20mm coke can Meade (I believe now discontinued and very problematic/nigh impossible for glasses, but offers a satisfyingly immersive view). I frequently use the TeleVue 2X Powermate with these EPs for DSOs and globular clusters for starters before increasing magnification. I like the graduated approach and go throiugh 3-4 EPs on a target requiring high(er) magnification. I prefer finding nuances with increased magnification rather than just jumping to high power. The Powermate takes both size EPs and I bought it after I purchased the X-cel Barlow, which I seldom use (even with the 6" SCT), much preferring the superior Powermate with the Dob. I highly recommend investing in a top quality Barlow/Powermate/Parracor, etc. over doubling up on EPs. My favorite general purpose EP to balance magnification and field of view is the TeleVue 17mm Nagler Type IV (now discontinued). Some nights after testing with the 26mm this is the only EP I use if I'm not going deep or planet hunting. In the 1.25" for this general use I am very fond of the 32mm TeleVue Plossl with a Baader Coma Corrector (another accouterment I would highly recommend for Dob use).
I am fond of hunting galaxies and multiple star systems (throw in all the sundry DSOs in this bin). I now gravitate toward the Baader 14mm, 8mm, sometimes the TeleVue Plossls (nigh impossible to use with glasses), and the 1.25" EPs in the 18mm - 9mm range. Bear in mind light intake diminshes with increased magnification. Often you can achieve a more satisfying view of some DSOs with a mid/upper-range magnification EP gathering more light, rather than a high-range one that is more occlusive, especially with filters (broad/narrow band, OIII, etc).
When I am looking at planets I rely on the Baader 8mm, 1.25" EPs in the 12mm - 5mm range and particularly the TeleVue 7mm DeLite (nigh impossible to use with glasses), providing transparency/seeing permits desired magnification. Summers in the South are problematic and often prelude max capabilities. The greatest challenge with a manual Dob at these very high powers is the rapid drift of the target across the EP's field of view and learning to manually track/adjust. (probably the greatest detriment of a Dob, whereas they excel at panoramic views). Guess I have to lump the moon in this category. I tend to use the 2" 26mm and/or Powermate with a 2" variable polarizer when the moon is half to full, and the 1.25" TeleVue Plossls and Celestron X-Cels in the 18mm-9mm range when half or less, with/without a 13% filter.
In summary, were I to distill my inventory to the bear necessities based on my preferences and historical use I'd keep the 32mm TeleVue Plossl, 26mm Q70, 17mm TeleVue Nagler, 14mm Baader Morpheus, 8mm Baader Hyperion and 1.25" X-Cels in the 12mm - 5mm range, and the TeleVue 2X Powermate and Baader Coma Corrector.
Hopefully I answered your question without digressing too much. If not, hit me again.
Thx,
m
Addendum to OTA
Several modifications not previously mentioned:
1. In 2022 I replaced the 1/4 wave OEM secondary mirror with a 1/15 wave Astrosytems version. I have read various positions about the efficacy of such upgrades due to limitations/capacity of the human eye (I'll leave the opining and pontificating to the opticians and astronomy mavens). The Astrosystems iteration is dimensionally a little different than the OEM at 2.6" long axis. I separated the OEM mirror from the stalk and sent in the stalk, which had to be somewhat shortened and the replacement mirror attached ($180 for mirror and $40 for modification/attachment at that time). I subjectively believe it resulted in some perceptible improvement. I heavily darkened the mirror edge with a Sharpie prior to installment. Two years in, the Sharpie pigment has held up well.
2. I wanted to flock the tube. However, when I removed the secondary mirror for upgrade and the primary mirror to clean it, I just heavily coated the OTA with ultra flat black camo spray paint. The OEM paint was markedly lighter, more of black/olive drab and not super flat. I subjectively believe it resulted in some perceptible improvement in contrast and reduced reflectivity.
3. I initially used the OEM cooling fan attached to the rear of the cell and secured the battery carriage to the OTA with industrial Velcro. Oddly, the mounting screws for the fan are only accessible from inside of the cell, requiring cell removal to remove the fan. The fan motor ceased working after I had removed the cell/cleaned the primary. It is now dead weight and I will remove it upon next primary cleaning. Because my rig is for home use only, I use a floor/box fan to expedite cooling, which is far more efficient. I raise the OTA to about 45 degrees and use a 20" fan on low.
m
I do this same thing with my 13.1 inch F/5.5 Starsplitter. It has a full thickness mirror so it's slow to cool and since it's also a backyard scope, I use a 2000 cfm drum fan to cool the mirror. I keep it running during the night so I have move it around.
If you decide to replace you old fan, I recommend the Floyd Blue design. It's a full baffle made from 1/16" ABS that's fitted to the mirror cell and mounted using Velcro. The Velcro provides vibration isolation.
Jon,
info much appreciated. I am not familiar with this fan assembly, will have to research. I see potential for DIY, as well based on your pic. I'm just an old school guy shuffling down the halls of the new school smiling at all the 'youngsters' who don't know there is nothing new under the sun. Always a good practice to begin the day shaving with Occam's Razor.
m
Here's a link for floating azimuth scale.
https://eastridingas...k/help-DIY.html
The benefits of this arrangement are that the setting circle can be adjusted, find a know star in the FOV and turn the setting circle until it matches the Az in your app.
I use a digital inclinometer for the Alt angle.
Addendum to upgraded outriggers:
The enclosed pics show the replacement of the 3/8" threaded rod/improvised lifters to the veneer presses (Fox Shop brand). The press screws are more robust and have a coarse pitch Acme thread facilitating quicker motion. The press is a male screw and female threaded cylinder receiver. It is intended for wood working clamping applications, but can function as a press/clamp, spreader or jack (merely a spreader separating and lifiting something from the earth against gravity).
The last pic shows one in original condition that I used to make a tail vise on a workbench I built. The handles and grip knobs were too long and obtrusive for the chassis of the scope. I drove out the roll pins and separated the handles from the screws, cut the handles down on a metal bandsaw (not hardened, hacksaw or elec handsaw with metal blade sufficient), softened the cut edges on a bench grinder and painted the handles and swivel feet with black enamel paint and reattached the handles to the screws. I removed the threaded T nuts I originally installed, enlargened the mortises in the base frame and installed the veneer cylinders. I dressed up the tops with cedar cover plates and notched the inner corners with a mildly curved radius to roughly match the radius of the OEM baseplate.
m
Attached Thumbnails
Leeseafish, thanks for the info/link from across the Pond. I'll check it out.
I am still experimenting with the azimuth circle build/design, though mostly complete. I went with making a plywood ring with tempered Masonite on the bottom with a circumfrential rabbet that rides upon four sassafrass bearings similarly rabbetted that I have already made and installed just outside the lazy susan bearing between the OEM baseplates. The height of the upgraded bearing permits such an install.
I had a local printer make the scale. I attached it to the ring with double-sided tape. However, I tried to attach it to the ring monolithically and put a wrinkle in it. I should have incised a cut through it perpendicularly to prevent this. Once I redo the scale sans wrinkles it will be ready for install.
In anticipation of the azimuth circle I previously built the holder for a Wixey brand elec angle finder complete with a spare AAA battery well actuated by a simple lift/plunger.
m
Attached Thumbnails
Can you please tell me which Lazy Suan bearing you used? I found this one on the website you recommended. 1000 pound capacity and 10 inches in diameter. Is this the one?
https://www.leevalle...gs?item=12K0104
I also found this one:
https://www.amazon.c...7ON2&gQT=1&th=1
Mariner 2
Lee Valley offers multiple diameters from 9" - 29.5". My base plates are circa 24" dia. I utilized the nearly 18" version which permitted circumfrential space for the azimuth ring. If you do not need this space I'd say going with the biggest possible bearing the best option:
https://www.leevalle...sicD0-OFQ&gQT=1
m
Also, the iteration of the Lee Valley bearing has good friction/tension, such an improvement in use over the OEM plastic needle sheet and metal plates. However, preventing swivel during transit is an issue with any bearing on a Dob of this design and size. I simply drilled a hole through both base plates into the frame and affixed with a walnut dowel and wooden head. I installed a short register pin to prevent the head from rotating.....little of which flourishment is necessary for an effective fix. Any bolt or metal pin with a head will suffice.
m
Attached Thumbnails
Thanks.
Collimation:
Veteran and seasoned users have established methods and preferred tools for collimation. However, if you are new to amateur astronomy or new to a reflector, collimation may be initially challenging, if not a consternation. I have come to favor the AstroSystems Light Pipe coupled with a laser collimator (separate device by another mfg).
https://www.astrosystems.biz/
Between the two I rely on the pipe far more than the laser. I made the mistake when I first began astronomy of over-working the secondary mirror and making too many adjustments too frequently, consequenty losing time and gaining frustration. Once the secondary is centered under the focuser and initially collimated it requires very little further adjustment, and just minute ones when necessary. I barely have to tweak it on a rare occasion. The primary mirror gets the most attention. Again, required adjustments should be small and not have you going all over the place, teetering on going gimble. Even with significant tranist of my Dob from the house to the driveway over a threshold and with a small drop/step, careful transport never causes significant misalignment.
I usually set up the Dob a couple hours prior to intended use. In the summer this is still during daylight or twilight hours1. In winter it is late twilight (Astronomical) or darkness. I let the box fan cool the OTA and purge the tube while I do other things. Obviously winter witnesses the greatest temperature variation from a warm house to a cold environment. Consequently, I learned collimating prior to fully cooling and allowing the primary mirror to acclimate is an exercise in futility. I do not collimate until I am ready to begin a viewing session.
Herein lies the beauty of the Light Pipe. It has a translucent head that pulls in sunlight and permits veiwing to make adjustments. Additionally, it works about as well under artificial light, even with a red light to preserve your night vision (see pics). This facilitates subsequent collimation throughout a viewing session, especially when temperatures vary significantly. It is helpful to rotate your Dob and raise/lower it in altiitude a couple times as well, prior to initially collimating. I never collimate in sunlight or white light.
1. Twilight: Civil = center of the sun 6 deg below the horizon, Nautical = center of the sun 12 deg below the horizon, Astronomical = center of the sun 18 deg below the horizon, neglible solar component of sky glow (Observer's Handbook 2025, Royal Astronomical Society of Canada, Marquis Book Printing, page 204).
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Accessorizing:
Familiarity and comfort with your Dob over time will permit you to modify it, even drilling into the OTA, etc. If you are not keen on this or have an SCT or refractor with a sealed OTA, one alternate option to attach optical accessories is to use a Telrad mounting base with 3M foam adhesive tape (supplied with base) and modifying the Telrad risers to receive the desired accessory.
I attched one to my Dob as well as one on a 6" SCT (see pics). The tape is very strong/efficient and long-lasting, resulting in a 'permanent' feature, so make sure you are happy with the exact placement prior to attaching. You may want to modify the riser and connect optical accessory to base and hold or temporarily attach it to the OTA while you view through it and determine desired placement prior to fully attaching with the adhesive tape.
I attacehd a Synta style shoe to a riser/base on my Dob to accept a red dot finder (I favor both a 'macro' red dot and 'micro' StellarVue 9x50 scope for navigation). Additionally, I can swap the red dot for a Telrad in under 60 seconds. On the SCT I bolted the scope mounting rings to the riser which mates with the base. Again, a swap of the scope with a Telrad is fast and efficient. The tape has held up with no issues on the SCT to support the StellarVue scope at all angles on a manual German Equatorial Mount.
On the Dob I modified a 2" riser by cutting down the front/back portions to reduce the size of the mounting surface to accept the shoe. The 2" elevation was necessary for visual clearance. On the SCT I cut off the vertical legs and top plate and bolted the rings to the base portion of a 2" riser which mates with the Telrad mounting base.
A current perusal of Agena seems to show the riser design has changed, which may change the approach. The older design appears to offer more latitude in modification than the new(er) design, if you can find them:
https://agenaastro.c...esult/?q=telrad
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Addendum to collimation and accessorizing:
I was remiss not to mention the following brief recommendations in the two previous posts
1. Collimation - one legitimate issue/complaint with many mass market laser collimators is the beam diameter and resultant dispersion of laser light on the primary mirror when attempting to center it on the mirror's donut for alignment. It usually obliterates a clear view of the donut's outer and inner ring and reduces accuracy of alignment. You can minimize this with an improvised insert in the end of the collimator's barrell with an exactly centered pin hole. More expedient yet, and counterintuitive is to shine a red lensed flashlight down the OTA on the primary mirror during collimation. It surpriisingly cleans up much of the light scatter and makes the laser beam more discernible within the donut for a more accurate alignment.
2. Accessorizing - should you pursue using a Telrad mounting base on your OTA (for optical devices other than a Telrad, or with a Telrad), you can accurately mark placement with blue painter's/masking tape to delineate position. Affix the desired optical device to the modified riser and mounting base, hold or temporarily affix it to the OTA and test placement and performance. Once satisfied, (place tape tightly around, but not under the edge of the base), place tape around the perimeter of the mounting base or just at the corners/ends as an index. Ensure the base is parallell to the long axis of your OTA and not cattywampus. Peel off tape backing and affix within marking tape. Once applied there is no readjustment. It will be stuck like........well, use your own analogy. The painter's tape is then easiy removed and will leave no adhesive residue or tackiness on your OTA.
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