Webster Telescopes C-32: A review of the structure, optics, and functionality of my Webster Telescopes 32" F/3.6 truss style dobsonian.
By: Joe Wambo
My Observing Experience: I've been observing since I was around 8-10 years old with various small refractors and a Cave 10" reflector in my teen years. For the past 3.5 years with a 12.5" F/5 truss dobsonian with an excellent Ed Stevens primary. I have used the 32" F/3.6 that this review is based on since March 13, 2010 when I picked it up new from Eric Webster in Garden City, MI.
Ordering, wait, and completion: In late 2007, I decided to order the big dob that I had always dreamed of. At the time, it sounded like the bar of optical quality had been raised to the point where a large aperture mirror of excellent quality and fast F ratio could be attained. After extensive online and forum research into the major dob and optics companies, I decided to order a 28" telescope from Webster Telescopes. The excellent woodworking, structural stability, appearance, and low profile/streamlining won me over. I had not heard any negative reports about the quality of Kennedy mirrors, and in 2007, Steve Kennedy Optical had the best reputation for quality large aperture mirrors. I had not looked through a Kennedy mirrored scope personally. A very large part of me deciding to order from Webster was due to the review of a Webster C-28 F/4 telescope on Astromart that was written by Dave Bonandrini in mid 2006. Confident about the quality of the scope/optics, I took the leap of faith and placed the order with Eric Webster in early December 2007 for a C-28 F/3.6. My deposit check was received by Webster Telescopes on 12/17/2007. I was told the delivery time would be 12-14 months.
Fast forward 16 months to May 8th, 2009. A post on Cloudynights reported that Webster Telescopes would be finishing runs of 24" and 32" telescopes in the coming months, and then moving on to the 22" and 28" early next year. Being personally uninformed of this news frustrated me, as this would push my wait time beyond 2 years. I contacted Eric about it and he confirmed that the 32" telescopes would indeed be done before my 28". Knowing that this was a once in a lifetime purchase and growing impatient, I asked Eric if I could upgrade to a 32" if one was available. He confirmed that one was available, as they had intended on making an extra unit of each size. To avoid any extended wait, I decided to upgrade to the C-32 with a F/3.6 Kennedy mirror. Fast forward to March 13, 2010. Now at the 2 year 4 month mark, I picked the scope up from Eric Webster in Garden City, MI. Why the lengthy wait? Well, the last 7-8 months were chalked up to other vendors lag times. That is what I was told. I would have had to wait even longer for the 28" I originally ordered as described above. Final note: my mirror was dated April 2008(picture below).
Product description: This scope is the latest 32” aperture truss dobsonian offering from Webster Telescopes designated as their C series. The scope was ordered with a 32” F/3.6 mirror from Steve Kennedy Optics. The metal and wood structure is very substantial and solid which is a necessity for this aperture size/focal ratio. The assembled scope weight is @ 435 lbs. UTA weight is @ 30-35 lbs with secondary mirror installed. The connecting ring weighs 5-6 lbs. Rocker and mirror box (including mirror) combined weigh @ 380 lbs.
The current MSRP of this scope with options/tracking is @ $31,000 and is available from Webster Telescopes online website.
This scope is equipped with the following options:
ArgoNavis/Servocat tracking/goto system
Cooling fan package
12 volt integrated secondary heater
Included in the base purchase price are the following features:
transport wheels/jack system
2 inch Feathertouch Focuser 1.5 inch drawtube
light shroud made of Rip stop nylon
Focal Length 115 inches
Eyepiece height at zenith 108 inches
Secondary mirror minor axis 6 inches pyrex substrate(18.75%)
Secondary mirror thickness/weight 1.375 inches/5-6 lbs.
Bearing material Teflon on FRP board
Focuser Dual rate Feathertouch 1.5” drawtube
Primary mirror 32” F/3.6 pyrex 2.20 inch edge thickness Kennedy Optics Primary
Primary coating Flabeg standard aluminum with overcoat
Primary weight @119 lbs.
Transport weight @380 lbs. + transport wheels/jack system
Total assembled weight @ 430-440 lbs.
Ground board/Rocker Box/Mirror Box: The ground board of this scope is a “powered version” which has a single three prong audio plug mounted in one of the ground board feet to receive power from a 12 volt power source. The board is fitted with power contacts which relay current to the rocker box throughout the 360 degree azimuth movement of the scope eliminating the need for power cords or in “rocker box” batteries. This setup/hardware comes as an installation kit from Stellarcat.
The 37.5 inch x 37.5 inch rocker box of this scope is constructed of 1.5 inch width plywood with exception of the end boards which are ¾” thickness. The bottom of the rocker box has white FRP board glued on it to ride on the ground board Teflon pads. The remainder of the rocker box is covered in black Roadex (think of industrial grade felt) which is glued on. There are two slots cut out of the front of the rocker box to allow clearance for the truss poles when viewing at lower altitudes. This is a very low profile rocker box. All Servocat/power/encoder wiring is stapled firmly to the inside of the rocker and is loomed at certain critical points to avoid wear and possible shorts in the wiring due to repetitive movement. The hardware and electronics of the Servocat drive are nicely and cleanly installed in the rocker box.
The mirror box is very nicely executed, and is the centerpiece of the scope. The 35.5 inch x 35.5 inch box is constructed of ¾ inch 13 layer plywood with dovetail joints at the corners. The box surrounds the mirror cell and has a total of 12 ¼-20 stainless screws securing it to the cell plus two bolts that pass through both the ALT bearings and the mirror box. The mirror box is further braced with 2 large gussets per inside corner with a large hole in each gusset to prevent air from pooling beneath them. Braces are also present in each corner. The mirrorbox is capped with a circular baffle of ¼ inch plywood that is painted flat black. The mirror box interior is painted flat black throughout. All outer edges and corners of the box are either nicely routed or rounded. The poly finish texture appears to be hand rubbed. The 2 inch width, 42 inch diameter cast aluminum altitude bearings are bolted to the mirror box with 5 bolts per side and are anodized black. The altitude bearings have black FRP contact cemented to them for the bearing material. There is about 5/16 inch of lateral (side to side) movement between the rocker box and the mirror box.
Truss Poles/Clamps: The truss poles for this scope are made of aluminum 1.5 inch diameter tubing. The wall thickness of the aluminum tubing is 1/16 inch. The truss pole lengths are 72 7/16 inch are made of one continuous piece of aluminum tubing per pole. The poles are anodized black. The color of the anodization is very uniform and is actually black and not purple or some variation of black. The anodization is well done. The bottom truss clamps are bolted on the outside of the mirror box. The lower clamp assembly contains a positioning pin that correlates with a hole drilled in the truss pole (image 10). The clamps enable the trusses to be held securely in place, and they also ensure repeatability with assembly alignment and positioning. I marked the truss poles so each pair is put in the same position during reassembly.
UTA: The UTA rings are ¾ inch plywood that are spaced by six 1.5 inch diameter black anodized struts that are countersunk into the plywood rings and bolted from the top/bottom. The I.D. of the UTA is 33 ¼ inch with a height of 20 ¾ inch. The light baffle is made of thin sheet aluminum, not kydex, painted black on the outside and flat black on the inside of the UTA. The spider/secondary mirror holder is an Astrosystems model. The spider incorporates 1/32” thick steel vanes that have two mounting points at the end of each vane. The 6 inch m.a. secondary holder has ¾ inch offset built into it and is mounted on a 1/2 inch threaded stud. The Astrosystems secondary heater is powered by a thin conductive strip that runs down the side of one of the spider vanes, and is integrated into the 12 V system with an RCA style plug. The focuser board is made of ¾ inch thick plywood and holds the 2 speed Feathertouch and also has the Servocat hand pad and Argonavis mounted to it. I added the optical finder mounting board seen in the picture (image 14). The focuser was squared to the UTA during assembly.
Assembly and mirror maintenance: The assembly process of the scope is no different than any other truss dob with the exception of the use of a connecting ring. After rolling the scope out of the trailer, which is by far the hardest part of owning and transporting this scope, the truss poles are clamped onto the mirror box and the connecting ring is carried up the ladder and clamped to the upper truss clamps. From here the connecting ring is used to pull the scope down to a low altitude and can be strapped to a deep cycle battery which holds the scope in position. It takes about 35 lbs. of force to pull the scope down with the connecting ring to a lower altitude. The UTA is then positioned onto the connecting ring utilizing the three positioning pins and is clamped down. Assembly can easily be performed in 10 minutes with one person as the awkward 30# UTA doesn’t have to be carried up the ladder thanks to the connecting ring. I should note that the scope cannot be completely assembled when standing on the ground. A ladder or moderate step stool will be needed to place the connecting ring on top of the truss poles. No big deal, you are using a ladder anyway. It wouldn’t be hard to mount a couple of locking pins to keep the mirror box pointed at a lower altitude so you could put the trusses and connecting ring on while standing on the ground. I simply haven’t gotten around to implementing it. Securing, loading, and unloading of the scope from the trailer is the most time consuming part of the setup and must be added onto the 10 minute assembly time when traveling to a star party or observing site. I know for a fact that I would not use this scope nearly as much if I had to transport it to a site every time I observed.
Homecoming/Setup concerns/Troubleshooting: I slowly unloaded the trailer and brought the scope to rest in my garage. After 2+ years of waiting, I was ready to enjoy my investment. I unloaded the scope and assembled it, and immediately went about moving the scope around manually and attempted to test the Servocat drive, which was new to me. I had successfully built a working equatorial tracking platform for my 12.5” dob, and had experience with the Argo Navis setting circles, but I had no experience with the Servocat tracking system(although I had researched it thoroughly during my wait).
Here are some structural issues I had in the first week or two that had to be remedied before any serious observing could be enjoyed. With the scope unloaded and assembled sitting in my garage, I began to attempt to move the scope around manually and by using the Servocat handpad. The scope moved fine throughout the 360 degree azimuth range utilizing the Servocat slew/guide buttons, but the ALT motor repeatedly “seized” when attempting to perform ALT movements. Even moving the scope manually through the ALT range required up to 15-17 lbs. of force at some points secondary to the ALT bearings binding against the rocker box. The majority of the binding was traced to the ALT Servocat drive cable being pinched between the rocker box and the focuser side ALT bearing. This caused the ALT servo motor to shut off secondary to the amperage overload safety limit being breached (axis limit settings) on the Servocat drive. There was simply not enough clearance for the 1/16 inch diameter Servocat drive cable between the rocker box and altitude bearing. I removed the black Roadex covering (after talking to Webster about the issue) from this location and had to grind wood off of the rocker box in front of the Teflon bearing pad (image 17) until enough clearance was achieved to prevent the ALT drive cable from being pinched between the ALT bearing and the rocker box (picture below). The same procedure had to be performed on the opposite side of the scope but less wood had to be removed as there is no drive cable on that side therefore less clearance was necessary. When talking to Webster about the problem, they suggested that I remove the roadex carpeting from the locations that were pinching, which I did. It helped relieve some of the binding, but more wood had to be ground from the rocker box surface. They were stumped. I thought at the time that the radius that was cut out of the rocker box was possibly out of round. But that didn’t turn out to be the case.
Note: After tiring of grinding more and more wood from the rocker box, I revisited the issue recently. I discovered that 3/32 inch thick Teflon pads had been used for the altitude bearing pads. Considering that the Servocat drive cable is 1/16 inch diameter, this left only 1/32 inch of clearance between the rocker box and altitude bearing drive cable surface which is simply not enough as the rocker box bearing radius is rough cut, and the seam where the two ¾ inch sheets of plywood were glued together to make the 1.5 inch thick rocker box side, is raised upon its entire length. The cable was also being pinched by this raised seam at points between the ALT bearing and the rocker box. This issue would have worsened with use, as the thinner the bearing pad became with wear from use, the smaller the clearance would have been between the ALT bearing and the rocker box. I replaced all four 3/32” thick altitude bearing pads with 3/16” thick pads I cut and grooved (for the ALT drive cable) from Teflon I had leftover from another scope project (image 18). This permanently cured the issue and improved the scope ALT movement as I added about 3/4 inch of length to each of the 4 altitude bearing pads. I’m not sure if this was an design oversight, or simply trying to reduce every bit of height possible, but this should have been easily noticed in testing, as the binding of the Servocat ALT drive cable rendered the scope tracking/slewing inoperable upon pickup, and made manual use difficult and frustrating.
While examining the general mechanical alignment of the scope such as the mirror position, spider centering, squaring of the focuser to the UTA, etc…, I noticed the mirror was riding noticeable “low” in the mirror box sitting on the cable sling. Looking at the mirror down through the UTA, the spacing gap was much larger between the mirror edge and the top of the mirror box/corner braces than between the mirror edge and the bottom of the mirror box/corner gussets. This was simply fixed by adjusting the turnbuckle on the cable sling to shorten the cable length, thereby raising the mirror into the center of the mirror box. This is a picture of the cable sling adjustment and positioning assembly, gusset, and bracing.
Another noteworthy mechanical misalignment was the position of the cable where it contacted the mirror. For this mirror, the cable position should support the mirror .993 inches from the back surface. Three small cable positioning “channels” made of strips of Velcro had been placed along the mirror edge in three places along the lower third of the mirror edge. However, the cable was initially contacting the mirror edge substantially closer to the front of the mirror than the required .993 inches. The cable was initially contacting the mirror edge @1.6-1.7 inches from the back surface of the mirror. As you can imagine, this was causing some “potato chip” astigmatism of the mirror at lower altitudes. The sling positioning studs, which the cable runs through (image 19), had to be backed out .75 inches towards the rear of the mirror cell for the cable to achieve the correct position at its initial contact point on the mirror edge.
The other notable setup issue was concerning the mounting of the Servocat ALT drive motor. The ALT drive wheel/mounting plate was noticeably tilted/skewed with respect to the ALT bearing axis. The ALT servo motor box had a small piece of Teflon glued to it in an attempt to limit the lateral movement of the mirror box within the rocker box throughout the ALT range of motion (image 20). The mounting plate was actually bent away from the rocker box and the drive roller is visibly tilted relative to the ALT axis.
This caused two separate issues. First, the little Teflon piece was easily knocked off of the servo motor box during transport and allowed the ALT bearing to grind against the servo motor box at certain points in the ALT range of motion. This is not very handy when you arrive at a star party with darkness falling and find the Teflon piece missing. Metal on metal grinding is not a pleasant sound at 3:00 a.m. in the morning when slewing to objects.
The second issue was the Servocat auto-cal sequence repeatedly failed secondary to encoder count errors. I began troubleshooting and scouring the Servocat manual to figure out what the possible cause of the failure was. Due to the tilt of the drive spool with respect to the ALT axis, the movement of the motor was greater/farther than that of the encoder causing the auto-cal program to throw encoder count errors. After removing the mounting plate and straightening it, I spaced it 1/4” out from the rocker box and reinstalled. Instead of depending on the Teflon/Alt motor assembly to control the lateral mirror box movement, I added Teflon “bumpers” attached to the rocker box that ride against the ALT bearing and keep the mirror box positioned properly. The Servocat auto-cal program ran successfully on the first attempt after these modifications.
Secondary Collimation Shift: During my initial weeks of testing and observing I noticed a significant collimation shift in the autocollimator when the scope was moved from zenith to lower altitudes. I would not have been concerned about this if it was a minuscule amount of movement, but reflections were coming un-stacked to the point where visual effects present themselves at this F ratio. With a laser in the focuser and the scope positioned at zenith, as I moved the scope down toward down toward lower altitudes, the laser point moves(deflected) up and slightly to the right across the surface of the primary mirror if viewing from the front of the scope on the order of 1/8-3/16”. What would cause this repeatable collimation drift phenomenon? Well, after many frustrating sessions over 3-4 weeks eliminating causes, the only thing that I could envision causing this collimation shift was the rotation of the secondary holder around its center axis. In the end, this was the cause of the collimation drift from zenith to around 35-45 degrees at which point the drift/laser point stopped. Starting at zenith and moving to scope to lower altitudes, the laser dot moves up and slightly right on the surface of the primary which makes perfect sense once you think about it. Due to the ¾” offset built into the secondary holder, there is more mass/weight on the side opposite of the focuser. Gravity begins to “work” on the secondary holder at a fairly high altitude causing the secondary holder to rotate clockwise(and some slight lateral movement) if looking at it from the front of the scope. This rotational movement continues until the scope is around 35-45 degrees at which time gravity has maxed out its pull on the secondary holder. The spider just isn’t designed for rotational rigidity. This line of thought is confirmed by both the autocollimator reflections un-stacking and the laser dot movement. Further evidence of the lack of rotational rigidity is noticed by simply hanging 12 ounces of weight on the secondary collimation screw closest to the focuser. I was shocked when I saw the laser dot deflect down and slightly right about 3/16” and then return to its original position when the weight was removed.
I settled on the solution of weighting the secondary holder on the focuser side to counterbalance the increased weight on the opposite side due to the ¾” offset. I’m not sure why the offset was ¾”. I calculated the appropriate offset at .42”. Anyway, I ended up using 8 ounces of counterweights on the focuser side of the secondary holder. Amazingly, this instantly took care of 90% of the laser deflection and un-stacking of the autocollimator stack when the scope is moved from zenith to lower altitudes. The addition of a few more ounces onto the top (focuser side) of the secondary holder eliminated the remaining movement. At this point, the collimation stack held itself well with negligible movement or un-stacking noticed through the altitude motion which is a tribute to the rest of the structure. I painted the weights flat black to match. Isolating this collimation shift was quite a relief as now I did not have to collimate the scope at night when observing at 75 degrees altitude plus, and then re-collimate when observing lower altitude objects. This was intended to be a temporary solution until I could custom order a spider that had the proper offset built into it.
Optical Coating Quality: In the beginning, my initial impressions of the telescope structure were great (and after troubleshooting and fixing the setup issues listed above, the structure works very well), my initial impressions of the mirror and mirror coating were questionable. Soon after I picked the scope up from Webster in March, I was very concerned about the coating quality. Within weeks of pickup, I cleaned the very thick layer of dust off of the mirror and noticed several thin areas in the coating and a strange pattern that was visible in certain lighting/moisture conditions across the front of the mirror. I placed a couple of halogen work lights behind the mirror and noticed a very disturbing pattern of unevenness as seen in the pictures below. A multitude of large "pinholes" in the mirror coating were also visible. I expressed my concerns to Eric about the coating. While some very small pinholes spread across the surface of the mirror coating are normal, this was far beyond that. I suggested to Eric at that time that I might have to bring the telescope back for inspection, as fixing minor structural issues was one thing, but the optical coating being subpar is unacceptable.
Eric immediately gave me a call and assured me that the coating was fine as he had checked it with a halogen light from behind the mirror. I knew the coating on my smaller mirror had no visible pattern in it like the 32" coating did, but I trusted Eric’s judgment of the coating. I was disappointed. "Larger mirrors are just more difficult to coat", I thought. The coating was done by Flabeg, and was standard AL with overcoat. The second picture below is of the mirror with condensation present on the surface. The same coating inconsistency can be seen. Obviously this coating was a failure.
Optical performance and quality: In the following months of observing, the cell appeared to be supporting the mirror well, as there was no visible astigmatism in the star test or best focused images. Images were OK and star images were round. However, the images I was seeing with the 32" were not nearly as sharp or contrasted/crisp as I had seen with my older, smaller scope. At first, I was overwhelmed by the brightness and added color of the 32". The mirror was better than some of the astigmatic, terribly corrected large aperture train wrecks that I have looked through in the past. The more I observed, especially lunar and planetary, even with a 21mm Ethos, I could see that I could not find a definitive focus point. At first, I chalked it up to bad seeing. On many different nights, I found that the further inside of best focus I went, the sharper the image became, but I noticed a very noticeable veiling glare or scattered light that was present and masking the images. All along, I had been star testing the scope. I had become very comfortable with star testing over the last 4 years, but had learned that multiple tests over multiple nights must be compiled to be sure if a consistent aberration is present. Almost every time I observed, I noticed a repeated, consistently under corrected star test. Sometimes it was less or more under corrected, but it was consistent when the atmosphere supported star testing. Even while the mirror was cooling, the star test remained under corrected. The under correction symptoms were noticed even while observing more diffuse objects such as nebulae and galaxies, as intricate detail was amiss, and the stars in the field were round, but were bloated as if I was stuck in a perpetual loop of abysmal seeing. Globulars were “soft” and did not focus down to the fine dust that I was accustomed to seeing with my 12.5”. The level of increased intricate detail that was expected from this jump in aperture simply was not present and the increased detail that was present was veiled in glare when observing bright objects.
I tried to keep a positive attitude, and went about the business of blaming/eliminating thermals, seeing, or collimation for the visual symptoms of spherical aberration. I had mentioned the under corrected star tests to Eric in one or two phone conversations/email. Eric reinforced the idea that Kennedy leaves mirrors under corrected for figure changes during cooling and the mirror was fine, as he and others had observed with it before I picked it up. I thought to myself, "I must really be cooling the mirror efficiently to around ambient if I'm noticing such significant under correction so persistently." I found myself more often than not blaming the seeing. The problem was the star test showed significant (>1/2 wave) under correction during cooling on every night that was steady enough to get a decent star test. Some nights the under correction was so blatantly obvious in the star test (an undefined circular blob outside of focus, and very contrasted Fresnel rings on the inside of focus), that I couldn't believe it, and convinced myself it was some atmospheric disturbance. I was confused since during cooling, a mirror can typically show a bit of overcorrection.
Over and over on different nights, I tweaked cooling fans/shut off cooling fans, and checked and rechecked collimation. I repeatedly checked temperature of the mirror against ambient temperature and recorded data. All of this effort was poured into trying to understand why the images didn't live up to my expectations. "Why are the star images soft and bloated?", I wondered. The lack of sharpness/contrast of the images was always a concern, as was the lack of sharp “snap” focus, even at low magnification (160x /5mm exit pupil). The opinions of other observers were often about the amount of color or brightness, but never about the crispness/sharpness of the images. Observers at star parties were initially overwhelmed by the aperture (color/brightness) as I was originally. Don’t get me wrong, the scope showed much more brightness /color and obvious extra detail compared to my 12.5”, but the sharpness, definition, and contrast was not on the same level. The scope just did not deliver the image sharpness, contrast, and detail that I expected from this aperture. The extra detail was mired in glare and softness. Compared to scopes on the same field at multiple events the same magnifications/same objects, the optics simply underperformed. I remember a specific evening at Cherry Springs where a couple of experienced observers took a look at Saturn and were unimpressed due to lack of exact focus and softness of the image. They blamed it on the fast F ratio and walked away. What could I say? They were right about the images. Still in aberrated mirror denial mode and in self doubt of what my observations were telling me, I went to the Okie-Tex Star Party.
Okie-Tex came, and the under correction was once again glaringly obvious to me. After repeatedly star testing night after night and seeing more of the same significant UC, I slowly began to come to terms with the fact that my Kennedy mirror had some serious issues. My 133 LPI ronchi grating eyepiece also showed some under correction, as the band curvature at the edges of defocused stars indicated, but a Ronchi test is hard to quantify as to the amount of correction error that is present. Band curvature at this focal ratio is very concerning with the Ronchi eyepiece test, as the sensitivity of the test decreases with faster focal ratios. All I knew is there was consistent, significant under correction present. The most eye opening moments were when the scope was used alongside other scopes of known quality on the same objects/same nights. One night at Okie-tex, I directly compared views of M-27(and other objects including Jupiter) through the C-32 to views of the same objects through a 22" F3.3 and my 12.5" F/5. The images through both the 22" and the 12.5" scopes absolutely blew my 32" away when it came to sharpness and image contrast. Even intermittent observers, such as my father, with limited observing experience, commented about the superiority of the 12.5” and 22" scopes sharpness compared to the 32". Views through the 22" F 3.3 were awesome, easily exceeding image detail and far surpassing image sharpness/contrast of my big scope. I felt absolutely disheartened by the experience, but it wasn’t the first experience in which the scope was clearly outperformed by other, smaller aperture scopes. I had spent all summer blaming and eliminating all possible variables to come to this point. I was trying desperately not to accept that the mirror was poorly figured. All other variables had been eliminated. The views through the scope were very bright and colorful but they were simply soft with no crisp focus available.
Bench Testing: I returned home, and in late October, I transported my primary mirror and secondary mirror to a third party professional optician that is proficient with figuring large aperture very fast parabolic/hyperbolic optics. The plan was to bench test the primary and flat to finally quantify the under correction, and test for any other aberrations that might be present in the optical chain. I was present for the testing. I knew that my star testing/Ronchi testing/breakout testing and visual observations over six-seven months indicated equal to or greater than ½ wave of under correction. It was time to verify my observations and find out quality of optics I paid for. The results:
1) My 32" mirror had an undercorrection p/v wavefront error of 1/1.1 - 1/1.3 . (Foucault)
2) Mirror polish was fairly smooth.
3) No astigmatism was present as my star testing/visual observing had indicated.
4) The mirror had between 1/16” and 1/8” width TDE around the perimeter.
5) Secondary mirror deviation from perfect flat was > 1/4 wave when tested over the entire surface (reference flat interferometry).
Bummer! The wind had been completely taken out of my sails and I was left languishing in the doldrums. I finally had to face the reality of what all those nights of visual observing and star testing were indicating to me. I felt completely and utterly swindled and at the same time I felt vindicated as the testing results immediately validated and confirmed my star testing/Ronchi testing/breakout testing, and most important, my disappointing “best focus” visual observations. I wasn't crazy. I had been hanging onto reassurances from vendors and had been in denial of what my multiple, consistent observations were telling me. It’s not that I doubted my observations, I simply did not want to believe it. I was hoping that the mirror was better than 1/2 wave or greater under correction that my testing and observations indicated. With this magnitude of under correction, no wonder I had to wander around "best focus" to get the best “soft” images even at 160x/5mm exit pupil. Crisp focus could simply not be achieved due to the large area of longitudinal aberration created by the significant under correction. Magnification only increased the symptoms of the aberration.
Under correction can often mimic poor atmospheric seeing, nothing ever comes to crisp focus. Poor seeing becomes the excuse of choice for poor visual performance of large optics with correction errors. However, consistent, multi-session star testing results don’t lie. Everything clicked together as far as my observing experiences with the scope. I had been accustomed to observing with a 12.5 inch mirror that tests < 1/10 wave p/v. This mirror clearly did not perform to those same high standards with the crisp focus I was accustomed to. No more denial or excuses. Nobody wants to admit that their premium Kennedy Optical mirror that they paid big $$$ for is significantly spherically aberrated. The primary/secondary mirror set was not as advertised. Note: I did not receive any testing documentation in regard to mirror quality of either the Steve Kennedy primary or the secondary flat. There was only the assumption of exquisite quality drawn from statements of quality on Kennedy’s/Webster’s websites. The secondary is advertised to meet 1/8 wave spec on Webster’s website. Obviously, I expected at least diffraction limited optics, ¼ wave, 1/14 RMS, .8 strehl etc…. At least it was not astigmatic, as many large mirrors that I have observed through in the past have been. This mirror was a step above some of the large aperture trainwrecks I have seen. Astigmatism would have further complicated future refiguring concerns.
I was mad at myself for how long I "chased my tail" because of my blind faith in reputations. I simply did not want to jump to conclusions and gave the primary mirror the benefit of the doubt. After six-seven months with it, I had seen enough. At least I knew exactly where I stood as far as the amount of mirror correction error was concerned and could now make a plan to move forward. The experience absolutely wore me out. I spent an enormous amount of time testing/eliminating possible variables get to this point. And there was still more work to be done before the optics met my expectations and also met what level of accuracy that they were advertised to be. I informed Webster Telescopes and Steve Kennedy of my cumulative findings and my intention to have the mirror set refigured by another optician of my choice.
The offer to send the mirror back to Steve Kennedy was presented by Eric. Since this mirror, with its significant correction error, was deemed of sufficient quality to ship out of Steve’s optical shop originally, I chose to not send the mirror back. I felt I had invested enough time and money, almost three years at this point. I was ready to cut my losses and move forward. I did not have confidence that what I would get back would be any better quality than what I had, and I would have to go through the same process of testing again. I chose to pay to have the mirror and secondary flat refigured by another professional optician whose large optics I had observed through and was impressed with the results. He graciously fit the refigure into his schedule.
Note: During refiguring, the primary mirror anneal was checked and no significant strain was found in the glass. This finding negated any remote possibility that anneal changes after the original figuring may have cropped up somehow. Obviously, if the mirror was somehow re-annealed after the original figuring, the figure would have been completely and unevenly lost.
Exceptionally corrected large aperture optics can be procured. After observing the stunning visual results after having the mirror set refigured and recoated, I’m glad I trusted my observations and instincts. The refigured mirror set provides views every bit as sharp and contrasty as my aforementioned 12.5”, but with all the added intricate detail and vivid color that the aperture provides. Star diameters are radically decreased across the entire field of view. Focus now “snaps” as cleanly as any scope I have observed with, large or small aperture. It puts a smile on my face every time. The significant under correction of the primary mirror has been completely removed as my post refigure star testing has indicated. I am very pleased with the refigured telescope optics, but the specifics of the refigured optical quality will require another review independent of this one as I want to focus on what the scope came equipped with.
Function under the stars: I found the operation of the telescope to be excellent after the setup and mechanical issues listed above were addressed. The movements are smooth in both axes. I found the ALT axis movement to be a bit stiff. This was remedied by the larger ALT Teflon pads I put on the scope. An occasional waxing of the bearings is required when the movement begins to require increased effort. The azimuth movement is smooth but too stiff for my taste even after waxing. I may increase the contact surface area by increasing the AZ Teflon pad size.
After addressing the secondary holder collimation shift, the structure holds a respectable stack in the autocollimator when ranged from zenith to lower altitudes. The mirror cell and cable edge support do a good job as no astigmatism is present even at lower altitudes. Collimation with the fine threaded bolts in the mirror cell is painless, and the Catseye tools make precise collimation a snap. The scope is very well balanced with the Argo navis mounted on the UTA. Webster did a fine job of calculating the balance as the scope holds position with everything from a 5mm Nagler to binoviewers even with the ALT drive cable disengaged. The dual speed Feathertouch works beautifully, and is necessary at this focal ratio.
The Servocat/Argo combination works flawlessly and is infinitely programmable. The variable brightness red Argo display is very convenient and functional, with descriptions of each object available at the touch of a button. Dedicated reading of the exhaustive Servocat and Argo Navis manuals is recommended since many cool features and programs that are easily overlooked are explained in detail. It also helps to know these systems well in case issues arise out in the field. The Astrosystems secondary mirror dew guard failed to work adequately until I removed the secondary mirror and turned the rheostat on the dew guard up. After that, it has worked well without incident. The venerable Telrad works wonderfully even when centering objects near zenith while standing on the ground. An eight foot Strathmore orchard ladder, with eight inch spaced steps, is the perfect height for this scope, even for the shortest observers.
The scope’s stability is very good. Even in stiff breezes such as at the Winter Star Party this year, and Okie-Tex last year, the scope buffeted, but maintained its position and performed admirably considering the conditions. In fact, this was one of a select few large aperture scopes that I remember seeing still operating on some of the windy nights at the WSP. The stronger the breeze the more spider vibration is apparent depending on the angle of the wind. Obviously the shroud has to be taken off in breezy situations as it is made out of rip stop nylon. It is literally a parachute. After the modifications and troubleshooting listed in the setup section of this review, I am very pleased with the present structure, although I plan on replacing the spider assembly at some point with an offset version.
Summary: Here is a list of positives and negatives about the scope and optics.
Pros: 1) A very streamlined, low profile, stiff structure that holds acceptable collimation(after secondary counter weighting). The truss clamps and hardware are very well done and provide repeatable assembly position.
2) The mirror cell is properly designed and provides adequate edge support even at low altitudes as no astigmatism is present when observing at all altitudes.
3) The Stellarcat/Argo Navis tracking platform wiring and hardware was very cleanly and was properly installed with exception of the ALT motor mounting.
4) The transport jack and wheel system works very well for transporting the scope even when fully assembled. The system works great when rolling the scope out of the garage for a night of observing, or rolling the assembled scope around the observing field looking for a place to escape the wind. Not so great for loading
and unloading from a trailer.
5) The woodworking is beautiful and very well done, with good craftsmanship shown especially upon thorough examination of the mirror box structure and joinery.
6) Quality anodization of truss poles with a uniform black color.
Cons: 1) Severe lack of coating quality. To say the optics were a disappointment would be the understatement of the decade for me. The optics fell far below diffraction limited criteria, with the 32” Kennedy Optical primary being more severely than ½ wave p/v under corrected at the wavefront, with a thin TDE. The secondary also fell
below the advertised specs on the Webster Telescopes website of 1/8 wave.
2) The lack of field testing and mechanical set-up of the structure and optics before pickup was unfortunate. Attention to detail is important. Many of the small structural setup issues that I had to deal with
should have been remedied before I picked the scope up. At this price point, one does not expect to get a scope home and find that the tracking and goto is inoperable
secondary to the issue with the ALT tracking drive cable and bearing clearance detailed in the setup concerns portion of this review. Collimation shift was also an issue but was remedied with troubleshooting.
I did not expect to be a beta tester for this scope.
3) Being told that the wait would be 12-14 months and in actuality, it ended up being 2 years and 4 months. Eric always answers the phone and responds to email, but realistic delivery times are very important, as is builder transparency. I like to know exactly what I am waiting for.
Conclusion: After initially troubleshooting the structure and fixing overlooked setup issues, I found the Webster Telescopes C-32 to be a well engineered structure that possesses the stability, stiffness, balance and potential to be an excellent large aperture observing instrument. The tracking is well integrated and is almost a necessity when observing with a group. It’s been a long journey, but I feel the scope is now living up to its potential. Unfortunately, much time, money and effort after pickup was required to get the scope to this point primarily due to the optics. Obviously, the significantly under corrected optics that were the original heart of this scope were a disappointment as I was looking forward to the premium optics that were advertised. I was not willing to lower my expectations. After all, this was not a bargain basement light bucket I ordered. I paid a premium price, and expected a premium scope and optics to match.
I wouldn’t hesitate to recommend a Webster Telescopes structure to anyone IF the wait time was reasonable AND proper setup and testing were performed to the structure before delivery. I have done a fair amount of troubleshooting with this structure, and communicated my findings to Eric at Webster Telescopes, thus the setup and mechanical issues with my scope will hopefully not be present in future versions.
As far as optics, I cannot recommend Kennedy Optics for this aperture size based on my experience documented here. If I knew that I would have had to work through these optical and structural issues, I’m not sure I would order the scope again, but hindsight is 20/20. I ended up with an excellent scope. I simply could not have foreseen the path I would have to take to end up at this point. I hope someone else looking into purchasing a large aperture instrument can benefit from my experiences. It’s definitely a commitment that must be taken seriously and researched thoroughly. Quality cannot automatically be assumed. That being said, after I replace the spider assembly, the C-32 structure in its present state is a capable observing machine that I can now look forward to enjoying.
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