Posts Made By: Matt Luttinen

Here's a closeup of the mount. Pointing is courtesy of Wildcard's Argo Navis.

Here's a closup of the bottom end.

heh, well, the OTA weighs ~90lb or so, but the counterweights (100lb) and the mount (80lb) add up. It is an extremely mobile scope, but it does take ~1 hr to set up (and take down). But it is definitely worth the effort.

Matt

Lee,

You are correct, the heaviest component is ~40lb.

The pier is ~7" schedule 40 steel pipe. The azimuth pivot is based on a 3" diameter aluminum shaft topped by a Timken tapered bearing with an Aluminum "cap" to provide for preloading the bearing via a center bolt into the shaft. The az encoder attaches to this center bolt. The az axis rides on ~1.5" O.D. common sealed ball bearings on a "race" (3/16" aluminum plate)with a diameter of 14". The motion is very smooth. The only problem I have is that the center bolt loosens over time so I have to watch it closely. I am thinking on a fix for this niggling little issue. I know it might be hard to visualize, but I welcome any ideas. I might take the thing apart and post an exploded view picture if it would help.

Matt

Lee and Chuck,

Thanks again for the complimentary words. I see from the wonderful scope pictures posted here that I am not alone in my love for scope making!

Lee, I would consider motorizing the scope, if only the ServoCat was a little less expensive. For now the excellent accuracy of the Argo Navis and my muscle power will have to do. I must admit, there is something special about pushing the scope myself, although tracking would sure be nice.

I definitely plan on placing the scope in an observatory setting some day on a massive EQ mount (of my own creation, of course). The only problem there is with focuser position, so a rotating OTA would be in order. Or perhaps I might dedicate the scope to CCD planetary work. By that time (who knows how far off this dream is), CCD cameras should be really awesome!

Chuck, I have no real balance issues. I do hold on to the scope when changing EPs, but the ~1 lb EP weight range is not enough to upset the balance.

In the initial design, I was very close on the OTA balance, purposely making the thing a bit bottom heavy. I now regret this, as I have had to hide some lead CW in the top end. I should have trusted my math . . .

Also, the mount has a bit of "twang" in altitude. It is nothing serious, and damps out in ~2-3 sec, but it is annoying. I will be adding a thrust face to the alt axis at some future date. That is why the alt/az head is still only primered . . .

Matt

Bart,

heh heh, thanks, but it's not for sale. And, there are no "plans" in a real sense--I drew things up "on the fly," sometimes right on the plywood. I did make a few life-size "sectional" drawings of some parts as construction proceeded, but they are in no way organized! I would build something, decide if it "looked right," and then move on.

I spent more time weighing things on my postal scale to nail the OTA balance than anything else. And painting it by hand, that was rather time consuming.

Building this scope was definitely a labor of love, and as my first large scope project, *really* educational as well.

I hope to top it some day by building a 30" f3.5 Newt based on a Stabilite mirror (a Paracorr will be needed for this one!). My main design parameter is that no scope be taller than my eye-height at the top of my 4-step Little Jumbo ladder (98"), and a 30" f3.5 is about the biggest aperture that meets this limitation. I imagine a 6-strut minimalist, motorized everything (including OTA rotation) monster that moves in and out of its transporter under servo/RC control--a 4-wheel-drive telescope. I don't need no stinking transport handles!

Oh, and a trailer is in the future, too. And bunches of $ (hopefully) to pay for it all.

Matt

Lee,

Nice scope! All black really looks wonderful. While stain shows wood grain and gives the fine furniture vibe, I like solid finishes. Also, you can hide "deviations from the blueprint" behind a few coats of enamel.

It is so great to get a look at everyone's work. It gives me ideas, ideas, ideas . . .

Keep 'em coming, everybody!

Matt

Hello everybody,

I am looking for a Synta 120mm f8.3 tube (only). . .

Anyone out there have this part? I would put up a wanted ad but it seems like a long shot.

Oh, and I need a dew shield for the same scope.

Matt

Mike,

Sorry Herb, but I have one on order; it is due at my door Wednesday Jan 7th. I am getting the OTA only so I will not be able to render an opinion on the base.

I will post a report ASAP. I am anxious to have a medium aperture scope that amounts to "grab-n-go" compared to my 14.25" f7 double-truss Newt.

Matt

Jack,

I purchased a DSH 12 OTA from Hardin optical in January. I did not buy the base so I will limit my comments to the tube and associated hardware.

The tube is 56.6" long and just under 14" diameter. The "clear" diameter of the primary is 11 7/8" and the secondary is 2.6". However, the surround on the all-plastic secondary holder adds ~0.2" to the obstruction for ~24% total. The holder and standard three-screw adjustment works OK but the screws dig into the plastic so it is the only real "fix" needed on this scope. Some users add a washer or replace the holder with something better. The spider is heavy enough with metal vanes of the right thickness. The inside of the tube is painted flat black. Down by the primary, the mirror support is 9-point with push-pull locking in an all-aluminum frame that bolts to the end of the tube via 6 machine screws. The mirror is secured by rubber L-brackets to the frame. Mine arrived with the L-brackets secured too tightly, so some adjustment was necessary but not difficult at all to do. The primary is center-dotted, and amazingly enough, the rather small doughnut is accurately placed.

Back at the top end, the focuser is OK (read: not a Feathertouch) with somewhat stiff action but it is good enough to leave alone for now.

Nice touches: compression-ring 2-to-1 1/4" adapter; fully threaded and blackened 2" focuser draw-tube; decent 9x50 finder.

Not-so-nice touches: plastic secondary holder; the tube seam is a little "loose" and as such the OTA is not quite round until sqeezed by tube rings; the included eyepiece set is of mediocre quality.

The net weight from the shipping box is 21kg or ~46lb.

The optical quality of the DSH 12 (for a sub-$1K scope) is nothing short of outstanding. Star testing shows ~1/8th wave overcorrection. In focus the views are contrasty and definitely limited by atmospheric conditions. I had a great view of Saturn last weekend and pushed the power to 450x with no sign of breakdown. At SAC's desert dark site last month M33 showed more detail with less mag than the view in my other scope, a 14 1/4" f7 truss Newt. I was more than a little surprised by this.

Needless to say, I am happy with my purchase. The scope arrived via truck without incident and while the OTA is large, it is just small enough to handle without too much difficulty.

Good luck on your new scope decision.

Matt
Saguaro Astronomy Club
Glendale, AZ