Discovery Truss 12.5" f5


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Brand and Model:Discovery Truss 12.5" f5
Price ($USD):$1999
Type:Newtonian
Attributes: un-checked Go-To un-checked PEC
Aperture:318mm (12.5")
f Ratio:f/5
Focal Length:1587mm
Finder:7x50
Electric Power:n/a
Mount:Dobsonian
Tripod:n/a
Weight (lbs):80
Dimensions (w/h/d):
Description:2" PL eyepiece, light shroud, 2" JMI focuser

Discovery's Truss Page

Ed Ting's Review

Vote Highlights Vote
Discovery Truss 12.5" f5
Wonderful optics in an affordable package. It is really a hard telescope to beat for what you are paying. The mirror quality far exceeds typical Chinese scopes, as does the hardware. Does not use cheap particle board, but instead uses real birch plywood construction. Movements are very smooth and easy. JMI focuser is excellent. My only complaint is that it is not balanced well when using 2" eyepieces.

Overall Rating: 9
Optics:9 Mount:8 Ease of Use:10 Value:10
Weight: 11 (Trustworthy Vote)
Date:
By: TelescopeFan
Link to this vote: http://www.excelsis.com/1.0/displayvote.php?voteid=419913


Discovery Truss 12.5" f5
This is my 11th scope, and I regularly observe at a place filled with big dobs, and I'd looked through others from Discovery, so I knew what to expect.
Delivery:
The web sites said I should expect an average of 4 months, and it took 3-1/2. The back-ordered DSC and fan took another couple weeks. Since I plan to have the scope for many years, this was not a problem.
Initial impression:
Favorable, and EZ to collimate. Balance was very front heavy with my heavy eyepieces, so I added a sliding weight system to the mirror box. and I can achieve balance anywhere from 0 to 90 degrees altitude. The scope is VERY smooth--1 finger on the front can steer the scope anywhere. Tracking at over 300X is easy.
Optics:
I had two initial problems--a big fingerprint on the secondary's optical surface and astigmatism in the star images during the last bit of focusing. The first problem was solved by carefully doing a distilled water wash (it came right off). The second problem was probably due to tightening the mirror clips while the silicone cement that holds the mirror in the cell was still drying. I returned the mirror to Discovery, and they re-cemented the mirror and left the clips off. I still do not use the scope with mirror clips, but to prevent the mirror from falling forward if the glue bond were to fail, I have two nylon straps glued to the edge of the mirror and attached to the cell.
Observations:
12.5" is a lot of aperture. I see color in a lot of DSO's and the star images are fine (close doubles can be easily separated). The full-thickness mirror takes a long time to cool, so I recommend a fan. When cooled, the images are astounding. A 35 Panoptic give a 1.5 degree field!

Improvements needed:
1) a light shield to extend the UTA upward at least another 10" on the side opposite the focuser to prevent stray light from entering the bottom of the eyepiece.
2) a tighter-fitting light shroud that doesn't flutter like the flags in a used-car lot when the breeze blows
3) felt pads between the mirror box and the rocker box to prevent the wood from scraping against wood.
4) An optional weight system for the mirror box to balance heavy eyepieces. A spring might work here, as well.
5) plastic washers under the mirror cell bolts so that tightening doesn't crush the wood of the mirror box.
6) Though the JMI NGF-DX3 focuser is a fine piece, with no play and straight action, it isn't silky smooth--an upgrade focuser offering would be nice (say, a Moonlite CR1/CR2 or FeatherTouch) for an upgrade price.
7) a full-size front panel to the rocker box. The 1/2 size panel keeps the rocker box light, but adds to the flexure of the rocker box's side panels. I added a stiffening plate across the front and dramatically stiffened the side panels.
8) The secondary collimation screws can be hand turned--if your fingers are pencil thin. I recommend replacing them with screws long enough to have the heads above the vanes instead of just below them. The heads are inconveniently located as they are, though usable.

I'm a tinkerer, and I will probably continue to tinker with the scope as long as I own it, so some of the mount-related issues I had to "solve" were only minor glitches to me. I think most people who buy a truss tube dob are already good collimators, but I have become better (I STRONGLY recommend the SightTube, Cheshire, and Autocollimator from Catseye Collimation) and more knowledgeable because collimation is necessary every time the scope is reassembled.

It transports easily in the back of a very small car, and assembles easily. Read my comments carefully (they are similar to remarks almost everyone makes about dobs), and I still recommend it as a "Good Buy" among telescopes.
Don Pensack
pensack1@excite.com

Overall Rating: 9
Optics:9 Mount:8 Ease of Use:10 Value:10
Weight: 5 (Veritable Vote)
Date:
By: Starman1
Link to this vote: http://www.excelsis.com/1.0/displayvote.php?voteid=416150


Discovery Truss 12.5" f5
This product is a very good value for the money. I've never looked through a Zambuto telescope, but this scope gives great views of Jupiter and Saturn (much better than a C9.25), most likely due to increased aperature. The light grasp is great compared to price. The scope breaks down quickly and easily, and stores in a relatively small package. The full size mirror (2.5") is extremely heavy. Collimation is very easy with a laser collimator-- all the adjustments can be made by hand. I'm very pleased. The woodworking isn't furniture quality, but I usually observe my furniture during the day while I operate my scope at night. This is my 6th telescope, and I'm not selling. I'm very pleased.

Overall Rating: 8
Optics:7 Mount:8 Ease of Use:6 Value:9
Weight: 4 (Unreliable Vote)
Date:
By: Anonymous (xxx.xxx.7.56)
Link to this vote: http://www.excelsis.com/1.0/displayvote.php?voteid=74472


Discovery Truss 12.5" f5
My first truss telescope. Light enough to use all the time and a good Price. (Discovery, 12.5 inch.)

Overall Rating: 10
Optics:8 Mount:8 Ease of Use:8 Value:9
Weight: 1 (Unreliable Vote)
Date:
By: Anonymous (xxx.xxx.2.1)
Link to this vote: http://www.excelsis.com/1.0/displayvote.php?voteid=355117


Discovery Truss 12.5" f5
Recieved telescope in good order. Took a while to get the Helix collimator. Once the Helix arrived collimation was easy. Was lucky enough to get break on price due to mine being a floor model. What a step up from my 8" coulter dob. Overall couldn't be happier. Easily fits in my Honda Civic trunk. Can't wait to see m13. Saw Saturn and the Orion Nebula so far, just amazing.

Overall Rating: 9
Optics:10 Mount:8 Ease of Use:8 Value:9
Weight: 1 (Unreliable Vote)
Date:
By: Anonymous (xxx.xxx.50.206)
Link to this vote: http://www.excelsis.com/1.0/displayvote.php?voteid=164319


Discovery Truss 12.5" f5
Very good optical perfomance once collimated. That can be a trick, however, since the low-end secondary is often difficult to lock-in. Weakest feature on the scope is the truss tube attachment design. This uses screwn-on knobs over flat end plates... tedious and imprecise.

Woodwork is very good. Secondary arrived covered with gunk (appeared sprayed-on).

Overall Rating: 7
Optics:8 Mount:8 Ease of Use:6 Value:7
Weight: 1 (Unreliable Vote)
Date:
By: Anonymous (xxx.xxx.54.137)
Link to this vote: http://www.excelsis.com/1.0/displayvote.php?voteid=101360


Discovery Truss 12.5" f5
The scope has an excellent combination of smooth mechanical movements and fine optics.It is well balanced with the telrad and has performed well when compared to refractors and schmidt-cassegrain units ranging in size of seven to fourteen inches on Mt Pinos California. It also breaks down quickly for easy portability.

Overall Rating: 9
Weight: 1 (Unreliable Vote)
Date:
By: Anonymous (xxx.xxx.46.109)
Link to this vote: http://www.excelsis.com/1.0/displayvote.php?voteid=40584


Discovery Truss 12.5" f5
The first thing you notice about Discovery telescopes is their poor customer service. They never seem to be sure what their production schedule is or when a product ships. This 'scope was over 3 months later than scheduled, despite claims during the remaining 2 months that the 'scope had been shipped, which wasn't true. At least they are easy to get a hold of, and want to be helpful.

The 'scope arrived VERY well packed. No way anything is going to happen to the 'scope during shipping. Everything is packed in oversized boxes and filled with expanding foam.

The really nasty surprise came when the primary and cell were opened. The primary is shipped in the cell, and there were several sheets of tissue paper taped over the mirror surface, with the tape going all the way around the mirror, isolating it from contaminants... you'd think. In the box was a large quantity of SAND. And upon removing the tissue from the primary, I discovered sand ON THE SURFACE OF THE PRIMARY. It was even stuck to the surface of the extememely dirty mirror. The whole mirror seemed to have been sprayed with Pam or some such oily substance. Some sand grains had to be picked off the surface of the mirror, most slid off. Total volume of sand on the surface was about 1/8 teaspoon. In the end, though, the mirror cleaned up fine, and, miraculously, showed no signs of sleeking or scratching. Amazing considering the amount of sand present! Discovery had little to say, other than that they figured the sand came from the inside of the steel tube cell, left over from sandblasting. Still, the fact that the sand was on the surface of the taped and sealed mirror indicates that it was present when the mirror was packed.

The mirror cell needed refinement to allow collimation. First, the collimating bolts hit the primary, and had to be filed to allow clearance. Second, there was no provision for centering and holding the mirror in the cell, unless the mirror clips were really tightened down, which could easily introduce astigmatism, even in the 2" thick mirror. The mirror is now held centered in the cell with globs of silicone. The cell is a 3 point non-floating suspension. Probably OK for a 2" thick mirror, but a flotation cell would be better. Lastly, the center dot on the mirror was 1/4" off center and had to be replaced.

The secondary spider assembly was not flat on the top and bottom. This is a pain if you wish to align the focusser axis with the spider axis by threading a bolt through the spider with the secondary removed, ala "the Dobsonian Telescope" by Kriege and Barry. If the secondary doesn't offer a flat surface, then the bolt will not follow the optical axis of the scope. It's fairly important to be able to do this to allow accurate collimation, which is very critical even at f5. This was fixed by filing the spider surface flat.

The scope otherwise went together fine. The hardware is not captive, meaning lots of parts to keep track of and not drop in the grass. No tools are needed.

The bearings are the classic ebony star and teflon. EXTREMELY smooth and VERY light touch, too much so for my taste; the scope would leave the target when changing eyepieces. The Azimuth bearings were way to light and a little tippy due to the too-tall center pad. This had to be sanded down to allow the 3 main pads to take more weight. Without this adjustment, the rocker tipped back and forth on the central pad.

The worst offense was that the 'scope turned out to be top heavy even without the finder attached. This is the worst case, as counterbalancing a top heavy 'scope requires 3 to 4 times the offending weight at the rear of the 'scope. So, adding the included 8 x 50 finder was out of the question. Normally, finder weights are considered when the 'scope is being built. This 'scope was ordered with the 8x50 finder, and should have balanced with it present, let alone without it. This issue was fixed with "virtual" counterweights; bungee cords rigged on the mirror box and rocker to take up the excess weight. A functional, though poor fix. Normally this shouldn't have to be done to a commercial Dob until you add the 8 x 50, Telrad, AND a Panoptic EP...

The 'scope is very stable, and well constructed and finished, though not furniture quality; the finish is rough to the touch and the parts are stapled and glued together. The staple holes are filled, at least.

Collimation is easy and tool free. The secondary has thumb screws.

The secondary is perfectly sized. Big enough to allow a 5/8" fully illuminated field, yet small enough to have only a 20% obstruction.

The mirror star-tests all right. Diffraction rings are not the same on either side of focus, indicating over or under correction, I can never remember which. However, images focus very well anyway. I've seen VERY few mirrors that have identical diffraction rings in and out of focus, so this mirror is par for the course. Things focus fine up to 250X. Past this, poor seeing has likely been the culprit in limiting further power. So, in the end, I can't speak very quantitatively about the mirror, other than it doesn't show any severe aberrations.

The focusser is a JMI Crayford, low profile, and smooth. Finder is functional though has significant coma, making all the edge of filed stars fuzzy and crescent shaped. This is bad enough to make star hopping difficult; especially if field stars are dim, and stars only focus near the very center of the field. I have much better luck with Celestron and Meade 8 x 50's. So, I'd get the 'scope with a Telrad and purchase the 8 x 50 from another company.

All said, the 'scope is very nice. Gave it a 7 for the modifications, out of balance, dirty mirrors and SAND, mediocre focusser, and delivery time.

Overall Rating: 7
Weight: 1 (Unreliable Vote)
Date:
By: Anonymous (xxx.xxx.160.184)
Link to this vote: http://www.excelsis.com/1.0/displayvote.php?voteid=40583


Discovery Truss 12.5" f5
Optics are very nice. Good contrast. Focuser workds smoothly. Lousy customer service-- They installed the DSC in a manner that would never have worked and never fixed the problems. Thank goodness for knowledgable friends willing to help! Still not able to obtain a working DSC cable long enough to fit properly. (This is Feb. and I bought the scope in Nov. 2000.) Calls for assistance to the factory have gone unanswered. Still, a nice scope for the price.

Overall Rating: 8
Weight: 1 (Unreliable Vote)
Date:
By: Anonymous (xxx.xxx.199.183)
Link to this vote: http://www.excelsis.com/1.0/displayvote.php?voteid=40582


Discovery Truss 12.5" f5
Am very pleased with the scope. Optics preform very well. Construction is good and neat. NOt as sharp as a Obsession so that it could pass ass furniture for storing in your living room but still very well made.

Came with a 2" 40mm orthor and not the 32mm plossol they advertised. Also the finder scope sucks. You get a choice of finder or telrad with it. Get the telrad and buy a good finder elsewhere!!

Otherwise easy to assemble and store and a joy to use!!! Recomded it!!

Overall Rating: 9
Weight: 1 (Unreliable Vote)
Date:
By: Anonymous (xxx.xxx.115.90)
Link to this vote: http://www.excelsis.com/1.0/displayvote.php?voteid=40581

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