For those of you who don’t know me, I build large Dobsonian telescopes as a hobby. My definition of large is 24” and up. I teach telescope building classes that emphasize the reasoning behind doing something a certain way, rather than just following a set of plans. I consider myself a more than competent woodworker. I am an AstroMart Moderator, and I currently use a 30” f/5.3 Dobsonian telescope that I designed and built myself. The largest telescope I have built is a 36”. I have owned or used almost every brand of Dob in the world, and then some.
I’ve come to believe that most, if not all, magazine reviews are puff pieces. When was the last time you saw a negative review in a major magazine? I understand the economics of it, if you anger the advertisers; you loose their money (that is why you never see ads for BOSE in Stereophile Magazine). I believe that if a manufacturer knows the unit they are sending is going to be reviewed, it will be cherry picked; so how representative of a review could it be? I have actually had manufacturers say “We want to be able to approve your review before you publish it”. Yeah, that’s going happen….
I have heard that I have a reputation for being tough in my reviews. My answer always is: Good. There once was a time in America where people were taught to question everything, and to assume everything commercial is a scam. A return to those times would probably not be too bad of an idea.
Scopes from the Far East are not designed by astronomers. I found this out when I was young and naïve. I called Orion Telescope one day and said “Hey, if you just change ….”, only to have the gentleman patiently explain to me that the scopes are designed in the Far East and that Orion has no input on anything. It suddenly all made sense to me why tube ends were sealed from air flow, why focusers were full of grease that turned to rock in the cold and why their eyepieces had chrome inside the barrels.
GETTING TO THE POINT
There was quite a bit of anticipation surrounding the Astro-Tech 16, it was supposed to be a souped up version of the Meade Lightbridge. Costing $400 more, it was going to have to be pretty special considering they are both made by the same company, GSO of Taiwan. I had borrowed a Meade 16” Lightbridge some time ago but it did not impress me. It almost seemed like the people who designed it went out of their way to make it not Astro friendly. White painted lips inside the tube, bearings that rode on felt, ALT bearings that were dished out to make it as difficult as possible to add encoders… I did not even bother with a review, I simply returned it.
I got the very first production unit from Great Red Spot. I told the owner, Jeff, that I wanted a sealed unit. That way no cherry picking of the optics could take place, and I could relate what the average user would encounter when purchasing this scope. He agreed and it went something like this:
The scope comes in 3 large boxes weighing in at 155 lbs total. My office scale says that the entire scope when unboxed weighs a mighty 141 lbs (That’s more than a 20” Obsession weighs). Now don’t assume that extra weight is always a bad thing. It can make a scope actually more stable. Most people who have used an “ultra light” telescope can relate to what I’m saying.
How can a smaller aperture scope weigh more than a larger one? Two reasons; the scope base is physically larger and it is made of particle board. The Ground Board of the scope is almost 32” across! That would be the size of a GB on a 25” truss scope. Again, a large GB gives the scope a wide stance (Larry Craig will want one), and that can equal stability. Particle Board can weigh twice as much as plywood, and can degrade in wet conditions, but the thousands of GSO Dobs out in the field shows their fused plastic coating does a good job repelling moisture.
Inside the largest box is the Ground Board, the Rocker Box, three Struts and a box of hardware. No instructions or diagrams were included with the scope. I’ll cover assembly a little more thoroughly than usual to help out the early adopters.
The bottom side of the GB (the side without the Teflon) gets the three feet using the three gold screws. You could even make this scope a tad more stable by placing the feet directly under the Teflon pads, or moving them all the way out to the edge. I did not want to drill any additional holes in a scope that was not mine, so I used the predrilled holes provided.
The Rocker Box rides on a hybrid system of both “lazy susan” rollers and Teflon pads. It looks like in this case that the Teflon functions as a speed control, keeping the scope from spinning too fast.
The rollers are sandwiched between two, thin metal discs. The plastic coating on the particle board would bee too rough to roll directly on. The GB was very dusty out of the box. I vacuumed up the debris to keep it from getting into the rollers before assembly.
At this point in the review I’m going to point out that the underside of the Rockerbox was damaged in shipping because the staples that hold the Teflon pads on were not set beneath the surface of the Teflon. So the metal staple scraped up the bottom plastic coating of the RB.
I always teach my telescope students that using screws, staples, or nails to hold the Teflon on to the scope is false economy. Sooner or later the soft Teflon will wear down to the metal fasteners and the screws will destroy the bearing surface. Always use “Acid-Etched” Teflon and GLUE it onto the telescope. Because you get to wear the entire thickness down, you get twice the service life out of the Teflon.
Using a standard screwdriver, I tapped all three of the staples halfway beneath the surface of the Teflon.
To repair the bottom of the RB, I simply shaved the rough plastic coating at a very low angle with a fresh razor knife blade. Testing the scope, I could not detect the point where the repair was made.
The Azimuth Tension Knob allows you to crank down the resistance of the GB. In practice, the best match for the resistance of the Altitude knobs was leaving the knob not cranked down at all. This “loose” resistance setting gave the best feel. Dobson’s Hole was easy to cruise through, but please be reminded that the scope and Teflon was new. It is possible that after the Teflon wears down a bit, more resistance will be required. Time will tell.
I usually paste wax the surfaces that ride against Teflon, but the scope moved so well, I did not bother. I would give the whole scope a waxing once a year to keep the rust away.
The Rocker Box sides are plastic coated particle board also. They accept the two carrying handles. If this was my own scope, I would move both the handles to the front board of the scope, because the way they are designed to be installed, they are too far apart for easy carrying.
The hardware box came with an Allen Wrench hex tool to screw everything together with. Please, save you fingers and use a hex bit in your cordless drill. Be careful to not over tighten the screws or they will easily strip out in the predrilled particle board holes. If you do strip a screw hole, drip a few drops of white glue down the hole and screw it in again in the morning.
Each side of the RB has a slot that accepts the LOTA (Lower Optical Tube Assembly). There is a piece of felt adhered to the leading edge of both slots so you don’t chew up the wood every time you slide it in; very clever. One piece was un-adhered as delivered, so I simply wiped clean any dust and stuck it back where it belonged. I’m glad one piece was already properly installed, because without directions, I would have never guessed where those pieces of felt belonged (and that they are applied over the leading lip).
Inside the LOTA Box we have the Finder Scope box, the LOTA and the mirror cover, also known as the “Trash Lid”. In the past year, many Meade owners discovered that the Trash Can Lid had worked itself loose in shipping and had destroyed the optics of their Lightbridge. Astro-Tech was wise to specify that the lid should be nowhere near the delicate mirror during shipping.
It may surprise some that the mirror is just sitting unprotected inside the LOTA. The LOTA is in a plastic bag, so it is protected from dust. This seems like a workable system and of course, far better than the Trash Lid damaging the optics.
There is no way on person can lift the LOTA out of the depths of the box. Better to cut the tape on the bottom of the box and just let the LOTA and the Styrofoam base slide out on to the floor.
The coolest and most innovative thing about this telescope is the Altitude bearings. Most telescopes are just copies of tired designs from 20 years ago, but this is something new and functional. The ALT bearing is a big hunk of machined aluminum that will impress any real man.
I took off one of the knobs to see how the system worked and I just had to heft the knob in my hand a few times and smile. One can easily imagine milling a 1 /4” hole into this knob and it being ready for encoders.
Under the knob are a few washers and a Needle Roller Thrust Bearing that make the whole system work so smoothly. Those of you who tried the sticky and jerky Starhopper Dob resistance system and expected more of the same are in for a pleasant surprise; the AT16 is smooth!
The second part of what makes these ALT bearings so great is that you can adjust the Center Of Gravity by moving the bearing center point back and forth. A scale is engraved (well, probably stamped, I could not tell) on the hub so you can adjust both sides identically. I’ve seen this feature before on expensive, semi-high end Dobs, but never engraved with any type of scale, and certainly never this precise. I’ll discuss more about this feature in the use section of the review.
The Upper Tube Assembly box held the UTA, Battery pack for the primary mirror fan, 30mm eyepiece, and a 9mm eyepiece. Although advertised as being included, there was no laser collimator or moon filter included with the scope.
It was nice to see a battery pack, jack and wiring included with the stock scope. I don’t know how many times I’ve seen people unpack their mega buck Obsession scope, only to discover that Obsession gives you a fan with just dangling bare wires, no battery pack or jack and no way to hook it up.
Mirror Cell – Yes, they left a gap between the mirror face and the safety clips.
The Mirror Cell was an odd contraption. The mirror was supposedly floating on an 18 point cell, but the mirror was glued in with big black globs of silicone, so the floating points could not be examined. There were three safety clips that would hold the mirror in place should the silicone fail (fat chance, they used a lot of silicone). The clips were mounted about a millimeter above the face of the mirror (as it should be). If the clips were to touch the mirror face, they would induce astigmatism into the image.
The mirror is actually 1/16” of an inch shy of being a full 16”. The center spot was measured and determined to be accurately placed.
Rear Cell - Don't use the white knobs.
On the rear of the cell there are three black collimation knobs and three white “lock” knobs. The lock knobs are too far away from the collimation knobs to act as locks, so they become collimation knobs themselves. Just ignore them. You have to collimate every time you set the scope up, so don’t bother trying to lock it down. If for some reason you are intent on using the locks, drill and tap new holes as close to the collimation knobs as possible, and move the knobs to their new homes.
Credit has to be given to AT for supplying knobs rather than screws that require tools to use. Whoever thought it was a good idea to need a screwdriver or coin to collimate those other Dobs every night, clearly was not an astronomer.
There are three feet on the rear of the cell so you can place the LOTA on the ground without scratching up the collimation knobs. Nice idea, the LOTA is heavy, so it’s going to be seeing plenty of time on the ground.
The LOTA when placed in the Rocker Box has plenty of clearance over the AZ pivot point for the mounting of some aftermarket digital encoders. One of the feet is in the worst possible location for clearance, but you can simply unscrew it and move it over a few inches, if you need additional room. Most modern encoders are so slim, they will not require this step, so it’s certainly not going to be a problem for most users.
SETUP FOR OBSERVING
To set the scope up, you place the Rocker Box on level ground (I always rock the scope a bit to seat it in the dirt). Then you place the LOTA into the Rocker Box by sliding it into the provided slots. The seam on the LOTA faces away from you so the front Strut will be on top of the assembled scope. The importance of this will be apparent latter on in the review.
Any decently strong person should have no problem lifting up the LOTA and getting it into the Rocker Box. If you have back problems, you better get another person’s assistance. My 95 lb. spinner girlfriend could not quite do it by herself. It is harder to get the LOTA out of the box during teardown than it is getting it in. So make sure you are not the last guy left out on the observing field if you had difficulty getting it together in the first place.
The Struts are held in place with 4 knobs each. DO NOT CALL THESE TRUSSES!!!! Trusses are triangles, and these Struts certainly do not form any type of structural triangle. The struts are made of extruded aluminum. You can just feel them deflect when you squeeze them, but they seem plenty stiff for the job at hand.
The shafts of the knobs and the receiving sockets were clearly painted after having their threads cut. The paint made them hard to assemble. I used a tap and cleaned up the holes and used a die to clean up the shafts. This made assembly much easier. If you don’t have a tap and die set, any real hardware store (not Home Depot) will perform this service for a few dollars. They might even do it for free, once you explain to the bewildered clerk that the parts form a telescope. Do not use any grease or WD-40 thinking that you are going to lube the threads up. This will just attract grit in the field and make things worse.
After attaching the three Struts to the LOTA you hold onto the UTA and get the knobs from the struts started. DO NOT LET GO OF THE UTA BEFORE HAND! There is no positive stop to lay the UTA onto during this process, so if you just set the UTA around the Struts, it can fall at any time. It is not secure until the knobs are in!
Go around and re-tighten all of the knobs now that the UTA is installed. The addition of the UTA changes the angle of the Struts, so they need the final tweak.
I checked the focuser for square-ness and it was almost perfectly square. A small tweak of the focuser screws fixed it nicely. The secondary positioning was only off by 1/8”, that’s the closest I’ve ever seen a Far East scope. Using the CatsEye sight tube, I corrected the offset.
The Secondary Holder was clearly a leftover from some other GSO scope. Most GSO scopes require an Allen Wrench to make the adjustments to the secondary. Scopes designed by astronomers have knobs to adjust the secondary, so that you don’t drop any tools onto the expensive primary while collimating. The AT16 requires a Philips screwdriver to make the adjustments. This is even worse than an Allen Wrench because if you drop a screwdriver on the mirror, you are likely to do much more damage than a little Allen. In addition, Philips screw heads will strip out from repeated torque (remember, you are going to make this adjustment EVERY time you observe).
And it gets worse. The Philips screws have sharp, circular ends that dig into a soft metal plate on the secondary holder. So instead of each adjustment screw deflecting the mirror in a predictable pattern, they make the mirror spin in a little circle! It was maddening.
I took out the screws and used a metal file to smooth off their ends. Then I placed a hard metal washer over the soft metal plate. This fixed the problem, but it’s something that really should have been done at the design stage.
If you buy this scope, be sure to replace the Philips screws with Socket Head Hex Screws, and place Knob Caps over the heads so you can use your fingers only for collimation. I’m sure you have a metal washer in the bottom of your tool box. Your blood pressure (and primary mirror) will thank you.
I like to collimate most Dobs at 45 degrees of elevation. That way you spit the difference if there is any deflection (there always seems to be a little bit) as you move the scope through its arc.
I was not prepared for the amount of movement I saw in the AT16. The above picture shows just how off the collimation became moving the scope just half way through its arc. I knew I had the spider centered and tightened as far as it would go, and I knew the Struts were tight, so my suspicions went to the mirror cell. Sure enough, the three springs in the bottom of the mirror cell are not strong enough to support the heavy 16” mirror. Playing with the springs, I would guess that they would be a good stiffness for a 10” mirror, maybe. I wedged some Styrofoam between the cell and frame to help the springs support the mirror, but if I was keeping this scope, the very first thing I would do would be replace those springs with some stiff ones from the hardware store. You really can’t use the scope without them.
A huge storm had just blown past, killing power to much of South East Michigan. And as it often happens, a nice patch of clear sky followed the storm. With the power out, the skies were darker than usual.
I was anxious to star test the optics because the only thing we could test on the club’s interferometer was the secondary (which was a little over 1 /4 wave – good). Due to the primary being glued into the cell, it was very front heavy. This caused the stepper motors on the testing stage to stall or jump track. Normally the mirror lies in a metal sling at the center of gravity. We tried to rig up some kind of counter balance, but we just did not have enough tools on hand to make it work. We sure did not want to risk the testing stage dumping the mirror on its face!
I used an 110v house fan to cool the mirror, as there was no telling how long our patch of clear sky would last. On the 16” Lightbridge I had borrowed, the included fan had usually taken 2 hours to equalize the mirror, and I was not going to wait that long. After 30 minutes of high speed fanning, the mirror was within 3 degrees of the ambient air temp (I tested it with a Laser Thermometer), so I figured that was close enough to start.
I wanted to test the scope as delivered, so I started with the included eyepieces and finder scope.
The finder scope is a Right Angle unit, with nice looking coatings throughout.
Spinning the knurled grip on the front lens brings the cross hairs into focus. The adjustment knobs on the holder work very smoothly; much smoother than the ones on my old XT10. The finder exhibited some astigmatism, but who cares in a finder? It’s not like you are going to be taking pictures through it.
Stand behind to “sight” the scope before homing in with the finder scope
I’ve been using a Telrad for so long that the RA finder was a bit of a switch for me; especially on such a large scope. You need to sight the scope like you would a gun, and then spiral around while looking through the finder scope until the object is centered in the view. The top Strut has a nice set of bright chrome screws to use just for this purpose.
I’m sure after a few nights of practice it would become second nature to use the RA finder, but like the good book says…He knows the time is short (Revelations 13:18), so I pulled the magnetic Telrad finder off my 10” scope and stuck it on the UTA. After a quick alignment I was in high speed star hop mode, without standing behind the scope or craning my neck.
M13 was at zenith, so I felt that would be a good target to try the included 30mm eyepiece with. The eyepiece was sharp in the center, but the outer 40% was almost useless. Trying the 9mm eyepiece on Saturn was about the same. As the planet drifted from one edge of the eyepiece to the other, you could see that the outer 30% of the eyepiece was a blur. The included eyepieces are not up to the caliber of the rest of this scope. They may work better on a scope with a longer focal length, but it’s just as likely they won’t. Plan on buying some better eyepieces to get your money’s worth out of this scope.
Switching over to Nagler eyepieces gave the scope a new life. At 60X with the 31mm Nagler, the scope delivered the wide, sharp views you expect. At 370X with a 5mm Nagler, the scope was near the limit of the seeing for the night. Sliding along the Moon’s terminator there were moments of clarity that showed nice, high contrast images.
The temperature kept dropping and clouds came in so no definitive star test ever occurred.
THE SCOPE ITSELF
The first thing you notice is that the scope is black. Why would anyone design a white scope that reflects any available ambient light into your unused eye? Who would want all that glare at the eyepiece? The only thing that could have made the color choice better is if it were flat black.
The AT16 has over a half inch of wobble in actual use. If you are accustomed to the super stiff, zero backlash movement of a well built truss Dob, you are going to need an hour or so to acclimate to the “feel” of the AT16. At high powers, I learned to slightly overshoot my target, so the image would snap back into the eyepiece. The OTA is stiff enough, but the base is too tall and thin, so the wood itself flexes side to side. If this were my scope, I would add two vertical “fins” perpendicular to the Rocker Box sides (there is plenty of room on the Ground Board) to stiffen the structure.
Looking through the empty focuser, you can see over the UTA into the sky. This means that the focuser is too close to the front of the scope and stray light will enter the eyepiece. Owners will want to add a lightweight plastic light baffle opposite the focuser for maximum contrast.
A sharp tap on the UTA results in a 3.5 second wait for the vibrations to dissipate.
I numbered the Struts, and then disassembled and reassembled the scope to see how closely it held collimation. It was way off every time. I think it’s because you can seemingly always turn each Strut knob a little more. They never just bottom out. It is no big deal; just remember you have to collimate the scope EVERY time you set up.
The Focuser was a very serviceable 2 speed unit. It moved quite smoothly. I’m not saying it is going to put Feathertouch out of business, but it is a great piece of hardware. The eyepieces are protected with a brass compression ring, so you won’t have a bunch of set screw marks all over your barrels.
CAUTION: don't ruin your filters!
Quite a few years ago Feathertouch started threading their 1.25” adapters so you could use standard 2” filters with your 1.25” eyepieces. This saved you lots of money buying redundant 1.25” and 2” filter sets.
The AT16 1.25” adapter is threaded for 2” filters, but they did not make the adapter deep enough to clear the base of an eyepiece. So if you actually try it, you will damage your 2” filter when the two collide. Again, no astronomer designed this “feature” before the adapter went into production. Most larger camera shops have 48mm extension rings, make sure you get one deep enough to clear ALL of your 1.25” eyepieces.
OK, I admit, I saved the best for last. The AT16 balances perfectly with no counterweights. Yep, you read that correctly. Go ahead and read it again.
Every Far East Dob usually has a bunch of magnets hanging off it, or gym weights or lead shot. Sometimes they don’t even balance with the lightest, included eyepiece. Not this baby. I could go from the 5mm Nagler all the way to the monster 31mm Nagler and all I had to do was crank down the ALT bearings. Cranking down the ALT bearings did not make the scope movement sticky at all. It was smooth and silky.
After I moved the adjustment back on the ALT bearing, I could even use the Denk II Binoviewers with no counterweight! To say I was impressed would be an understatement.
I know this was another of my lengthy reviews, so many of you just skipped down to the summary wanting to see if the scope is worth $400 more than the 16” Lightbridge. The answer to that would be – YES. The innovative ALT bearing resistance system is worth the money all by itself. To just simply observe without having to toy with counterweights every time you change eyepieces is one step closer to that elusive perfect scope.
BUT and this is a pretty big but; if you did not read the review, you need to know that the scope is not ready for starlight right out of the box. It is said that every Dob is a project, and this scope certainly will not dispel that truism.
What are you giving up with a $2500 16” scope that you would be getting with a $6000 16” scope? The premium scope would be lighter, smaller and come with wheels to move it about. It would also have a better spider you could really tighten down, a better secondary holder and a deeper UTA that would block out stray light. It would have a primary mirror that you could simply reach in and remove for cleaning or recoating. It would have a mirror cell that did not use springs to support the mirror. Finally, it would come with a light shroud and a neck saving Telrad finder.
Hopefully, some company will come out with a conversion kit that will have 2 plastic coated matching reinforcement fins for the base, 3 thumb screws and washer for the secondary, 3 heavy duty springs for the cell and a 48mm extension ring. A Light Shroud would be nice too. Of course, I would hope that Astro-Tech would simply include those necessary improvements with the next shipment of scopes, but I guess I know better.
Clear Dark Skies,
|All times are in (GMT-8:00) Pacific Standard Time Zone|
|Astronomy News | Telecope Classifieds | Telescope Auctions | Telescope Reviews | Telescopes | Telescope and Astronomy Forums | My Account | Help | RSS|