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About tonyowens_uk

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    Hillwalking, cycling, engineering, travel, wine, politics, telescope-making, model-making, invention, history
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    Wicklow, Ireland
  1. As a prominent Western prophet said "the truth will set you free". Objective eyepiece testing is far from straightforward and in any case is not the only criterion for value of an ocular. I had the chance to return the XW30 I had bought, following my own comparison (using my own preferred equipment). But though I intended to, I have not done so. 20 years ago I remember being blown away by the overall experience of using an XW10 compared with various commercially-available and privately developed high quality oculars - the ease of use, the lack of scatter, the ergonomics, even the smell. That memory was instrumental in my decision to buy a 6 element all-spherical design in 2020. The essential difference between the XW30 and the APM 30UFF (apart from superior tech performance and lower cost of the latter) is 'character'. We humans aren't the cold rational creatures assumed by most economic theory. As I've got older I've come to trust my non-rational judgements more and more...
  2. Here is a summary of the testing I carried out on these two oculars a month and a half ago after I received the APM 30mm UFF which was briefly out of stock at APM: Test of Pentax XW30 v APM UFF30 Date: 25/05/20 Setup: Intes-Micro MN86 Deluxe, collimated, F5.9, flatfield EQ8, tracking Visual use with and without glasses My vision is within 1 diopter of normal, negligible astigmatism, reduced accommodation Seeing: 7/10, traces of high cloud occasionally, 12 C, not truly dark. Various sky targets Targets M27 Dumbbell nebula NGC6960 Veil Nebula area C1399 asterism (altitude 44 deg) M8 Lagoon (v low) Saturn (v low) Altair (for veiling glare and polish assessment) APM 30 UFF NOTES 545 gms No chromatic aberration anywhere Sharp to within a couple of degrees of the edge Eyecup not as effective as the Pentax at excluding ambient light, but can be folded over quickly to accommodate wearers of glasses. Little veiling glare apparent on Saturn or Altair Folded down eyecup a bit more comfortable and suits non-varifocal glasses wearers Pentax 30 XW NOTES 680 gms Seemed slightly brighter - a little more spectacle Head positioning to the exit pupil a little easier Sharpness starts to suffer noticeably from ~60% of the field on, not bad until close to the edge, but noticeable deterioration Obvious chromatic aberration off-axis on brighter stars A bit harder to locate the eyeball to the exit pupil perfectly, due to size of barrel end Little veiling glare apparent on Altair centre-field A little warmer in colour transmission than the UFF Conclusions Overall, the UFF performs better due to tighter stars across the entire field and no chromatic aberration. The Pentax is inferior, most likely due to an ageing optical design which does not suit modern astronomical telescopes with image surfaces of low curvature. I was also able to confirm broadly identical behaviours using a Skywatcher 80mm F5 APO without its focal corrector/flattener fitted, in some quick testing the following night. In view of the poor off-axis performance of the Pentax I didn't bother rigging the APO with the field flattener and retesting. As the direction of image plane curvature is opposite between APO refractors and mirror scopes like the Mak-Newt, it was clear that the Pentax was not going to match the APM ocular regardless of the image curvature sign or magnitude.
  3. I have an APM 30mm UFF on backorder with APM. I plan to assess the Pentax XW30 v the APM UFF 30 when I get my hands on one. I'll do this with and without the field flattener fitted to the 80mm APO.
  4. Hi. I bought an 80 mm Skywatcher triplet scope a couple of years ago with portable imaging and occasional visual use in mind. Until recently it hasnt had much use. Debugging the imaging side of things is being attended to currently, but I had hoped to come up with a choice of quality eyepieces that allowed widefield sweeping of the Milky Way at one extreme, down to around 160x or so for lunar views while travelling. I have the Skywatcher fleld flattener by the way. So recently I replaced a Televue Panoptic 27 with a Pentax XW30, as I hadnt been happy with the edge of field performance of the Pan with or without the FF fitted. I find the XW30 is not a lot better. I'm interested in recommendations for oculars that can do justice to the razor sharp imagery that this triplet delivers (evident in the star shapes while imaging). I have no astigmatism or other eyesight defects other than the usual lack of accommodation that is appropriate to a man in his late 50's! I prefer to avoid anything wider than 80 degrees or so (Nagler territory), and I's like to use the scope by day as well as night, so avoidance of 'kidney bean' is also an issue. Mainly, I'm after razor sharp images over 95% of the field and great comfort, with this fast, short FL scope. Thanks Tony Owens
  5. I'm sure Bog Snorkelling is an important formative experience for Irish undergraduates: As for Green Swamp server (GSS) its been around for a while. Unlike EQMOD its in active development. Initially the target mount was just EQ8/HDI 110 but it now includes other Nantong Schmidt EQ mounts. There are several controls which extract better performance from EQ8's when autoguiding than EQMOD does. One, is homing that is far more reliable. But the key ones for imagers are motor current doubling during tracking and autoguiding, (which doubles stepper motor torque in small corrective moves to reduce following error) and use of short range GoTo commands while autoguiding using pulse guiding. These improve corrective move accuracy, reducing control loop dither around the target position. It is necessary to download a bugfix version for the EQ8 firmware to access the full feature set. There is a discussion groups here: groups.io/GSS/ Tony
  6. Hi Goran. Your point about the original EQ8 and the quality of guiding it provides is well made. I have modernised or refurbished a number of them and all provides around 0.5 arcsec RMS following error on each axis when they left. Neither revised nor original EQ8 offer antibacklash gearing. Also, the original EQ8 used a badly designed clutch that directly caused minute deformations of the mount that manifested as image shifts and (for Declination axis) binding and run-out. The Declination shaft bearings can make this problem worse, as can other constructional details. But all of this is soluble, and if done properly the mount is very dependable. The Freedom Find encoders were a piece of whimsy I believe. They can't be used during precision pointing such as imaging, and were aimed at casual visual users with a product mentality who stick with the Synscan control paddle. Those encoders never protected against pier crashes and contributed nothing to accuracy. Which given their tendency to deteriorate with moisture ingress into the Declination worm wheel shroud, was just as well! With proper sealing, updated clutches, steel shafts, precision bearings and an antibacklash Declination gear, an EQ8 controlled using Green Swamp server, (a modern alternative to EQMOD) will point and autoguide a 35 kg imaging payload for years, with excellent reliability.
  7. For those who have bought one of these but are not instrument design engineers, here are my thoughts. I happen to have designed and built very high resolution traction drives for special machines with similar accuracy requirements, though not for telescopes. In friction mounts the weaknesses are: 1. susceptibility to moisture and dust (affects the reduction ratio of the friction final drive 2. low output torque (this is limited by the maximum safe contact pressure at the friction final drive that does not result in indentation - I note the reference to ceramic material which is interesting). There is an implication for maximum out-of-balance torque that the instrument payload can present to the mount. 3. the 'biggie' is usually what happens when an overload occurs, e.g., bumping into the scope. Unless a very reliable overload clutch is incorporated into the drivetrain, the friction wheel and pinion will slip, creating a flat spot on the pinion and introducing periodic error. 4. if absolute encoders are used that are not on the axis of the instrument, then position accuracy will be good for short goto moves but there will be inaccuracy over long moves due to slip at the traction drive. So plate-solving and syncing may be required, adding to move time in application involving lots of point-to-point moves. The norm when buying a costly and complex instrument from a new supplier is to review the proposed design in detail before commissioning the project to proceed. In this case, as can be seen by scrutinising the various stages of mechanical R&D in phill76's post, all of these issues appear to have been visited. The concerns I would have are: 1. whether the promoter had any real knowledge and experience of friction mounts at the point when he started commercialising his project, and perhaps more importantly, is he now an expert and a 'safe pair of hands' in the art of friction mounts? 2. what performance and specification does the current incarnation of this mount offer? What is the proposed maximum payload? What is the lowest natural frequency of vibration under that payload, when mounted as recommended? Are there provisions to wipe the surfaces of the contacting friction components to remove wear detritus? How effective is the sealing? What are the overload clutch arrangements? What is the max slewing speed, and worst-case following error? How much backlash is there on each axis? (the motors use high reduction gearheads - what is their spec?) Is the mount documented? Does it come with the servomotors tuned? 3. what sort of ongoing maintenance is needed? How is that to be delivered? What are the warranty terms? For how long are custom parts going to be available as spares (e.g. pinions and wheels)? If I was in the market for one of these, I would be looking for a free evaluation unit (sale or return) so I could evaluate the answers to some of these questions - which I would be fairly confident are not currently available from the promoter. As for Louis Mesu and his designs - I have the impression that his mounts reflect a lifetime of obsessive development of friction mounts and precision instruments, not just for astronomers but also for large engineering businesses in NL. He is arguably the definitive 'safe pair of hands'. Tony Owens
  8. FWIW I'll add my own experience of getting stuck in the firmware update loop with an AZGTi and how it was resolved. My unit was on firmware rev. 3.12 and never updated. After a rebuild I tried to flash it to the current non-EQ version, which is 3.20, using the Synscan Pro app on an iPhone, across the wifi link to the AZGTi. The flash failed part-way through, and foolishly I cycled the power as instructed by the MCU update app, and tried again. The AZGTi would now only broadcast the ID "ESP_xxxxxx" instead of the ID "Synscan_5227" I had previously seen from my unit. The LED was cycling through three quick flashes, i.e., the MCU was still in update mode. I couldn't connect and further power cycling made no difference. I tried connecting using PC Direct Mode with my Synscan V4 handpad, but did not have either an RJ12 to RJ45 adapter or the time to make one up. So I bought the Skywatcher Wifi Adapter kit, which has one of these. After this arrived, I put the AZGTi on a 12VDC feed, connected the new wifi adapter using Skywatcher's RJ12 to RJ45 adapter and looked for a new Wifi connection. The only one available was still the one being broadcast be the AZGTi's MCU, i.e., ESP_xxxxxx. The Skywatcher wifi adapter was clearly getting power from the AZGTi but there was no 'heatbeat' LED. So I gave up on the new wifi adapter and just used the RJ12 to RJ45 adapter cable to connect my Synscan paddle to the AZGTi serial port, connected the paddle to a laptop using a serial-to-USB adapter (with FTDI chip), setup PC Direct Mode on the Synscan paddle, and tried to connect from the PC to the MCU using Skywatcher's MCFirmwareLoader.exe v 1.74_nonwifi. I selected PC Direct Mode on the app and manually selected the correct COM port to use on the PC. No dice. The app could not find an MCU. Finally, expecting to have to replace the AZGTi MCU with a new one, I decided to give the Skywatcher Synscan Relay Mode v4 a try. This turns the paddle into a simple transciever between an RS232 connection to a PC and the TTL level serial comms to the AZGTi MCU across its Hand Paddle port. So I first flashed my V4 paddle with SynscanRelay_V4_4.2 firmware, which was uneventful, then cycled the power on the mount (and thus the paddle) to boot up the transciever firmware. On trying to connect to the AZGTi with the MCU update app, the currently-loaded firmware could not be read, as before. But I linked the v3.20 firmware, and tried to update the MCU anyway. I was surprised to see this now went smoothly, and after power cycling the AZGTi on completion, restored to me a working mount. As a final step I re-flashed the paddle to the current version of Synscan firmware. I very rarely use the paddle for mount control but find it occasionally useful for verifying reliable comms to Skywatcher mounts where I doubt the health of the MCU board.
  9. Hi Andy and thanks for your most interesting post. Your Astro-related activity level over your life as you describe it is actually very typical for a professional person! The overall impression I got from your post was: ‘here is a chap who wants to “boil the ocean”, but do I really believe that is necessary? Ummm - no!’ ASCOM modularity allows even simple amateur telescope and instrument control to be simplified and maintained more easily. As TCS’s have bloated in the last two decades this modularity and ability to keep the bits that work and in which people have invested learning time is important. My suggestion would be to first look hard at what is wrong with other more developed telescope mount controller products and open source projects before doing anything more. I’d be particularly critical about conflating cost-driven Reprap technology from 3D printing with performance driven tech as needed in credible imaging mounts to be used in cold damp environments by elderly people of widely varying abilities! Cast a cold, critical eye on what you see. Some practical points: 1. You would be very brave to take this on, alone. But some of the finest engineers on this planet are involved with Open source astro engineering projects and getting their assistance would be wise 2. Be careful about stepper motor technology in telescope tracking applications where both position and rate control are critical. In the real world, microstepping a common bipolar step motor does not increase the positioning resolution of a motion system by anything like x256 times, due to low rotor stiffness, constructional and phase current tolerances, resonant effects and load torque variations. Trinamics impressive driver technology is great but won’t change the laws of physics. I recommend looking hard at low cost closed loop stepper-based motor/driver units from Chinese firms like Leadshine. They blur the distinctions between brushless servo and stepper technology very nicely, offering ‘real’ x64 microstepping capability out of 100 pole motor construction and smooth loop closure with step/dir interface. On the motion controller side, dont neglect the most recent Duet 3D print boards being introduced. These are provoking interest in the professional CNC world due to the safety engineering, embedded RTOS, and open source code base, and work well with a RPi front end. Another consideration is the emulation of common mounts. There is a huge installed base of Skywatcher/Orion amateur mounts globally, for example, but only one TCS project (EQDrive out of Ukraine) I’ve seen that exploits that ecosystem by adopting the SW mount controller command set (perhaps with extensions). By adopting a de facto standard like this, your users benefit from existing investments they’ve made in Skywatcher mounts and accessories. I’ve also found Skywatchrt Engineering to be professional and accommodating of people who can customise or extend their platforms. I hope my remarks don’t discourage you Andy. My experience over two decades has been that Astro engineering helped transform my professional engineering career from a stepping stone to boring old programme management and power politics to a far more satisfying one in technology consulting. I hope you are seeing that too! Tony Owens
  10. The whole area of heat flows in gas expansion is messy Vlad. First decide whether you want a practical engineering approach to refrigeration-in-a-box or a romp around the relevant thermodynamics. In my practice, the latter follows the former, not the reverse. Joule-Thompson cooling does not work with near-ideal gas mixtures except in close proximity to the discharging jet - where significant but very localised chilling is obtained. There are lots of other similar options to look at, one of which is the Rank-Hilsch vortex tube. They are actually used occasionally in controls enclosure cooling. Use of a low cost phase changing material e.g. propane/butane mix (AP30 aerosol propellant) is another possibility. But the cooling power of a discharging liquid AP30 jet which flashes from liquid to vapour during passage through a nozzle from 3 bar gauge to ambient is not a lot. And bloody dangerous if there are ignition sources around. There is steam jet refrigeration, possible using water/steam as a refrigerant too, and employing a steam-jet ejector to create near vacuum pressure to evaporate and chill a mass of liquid water. Lots of possibilities. But compressed air, in itself, isnt a good place to start when trying to create useful cooling within a fridge-sized enclosure!
  11. I think your design and design approach are fantastic Chris! Like you I had to change my whole thinking about pathways to structural stiffness as a result of commissioning 'cheap plastic' prototypes in SLS or FDM from service bureaus. The apparent stiffness and damping with the parts perplexed me until I discovered the routine use of low density infill to cut material use. Hey presto, cellular lightweight plastic 'castings', with resonant frequencies comparable to homogenous metal parts!. My emerging practice now is to use like you a mixture of materials and processes in which FDM and SLS fit. Where ultra-stable 'mechanical grounding' of parts in the face of temperature humudty and load variations is required (as in some optics and some grinding operations) I specify waterjetted granite or moulded polymer concrete. For thermal stability but lower stability requirements I use steel or Permali Wood. For general structures and parts without any special strength or stability aluminium in all its forms was what I used. There has been a developing problem over the last 25 years with the gradual disappearance of jobbing machine shops in Anglo countries, presumably linked to the financialisation of their economies and a wholesale shift to Asian sourcing for consumer goods. This has made both my professional and 'hobby' work more difficult. I have responded by investing in basic machining and printing capability. I'm seeing a gradual substitution of SLS and FDM printed parts, with critical surfaces machined if necessary. I also source gravity and pressure die casting parts from India and mouldings from many sources including Poland and Spain, where previously I would have turned to UK and German firms. The main reason I posted details of my 14" planetary Newt concept (I havent had time to start building one!) was to offer you a quantitative datapoint about gravitational sags and frequencies in a similar truss-type telescope structure for high resolution use. My concept used machined and extruded aluminium for most of the structure. I am not judging your structural concept about which I know little. FWIW given the cellular parts and super-light weight at the secondary end, I would be surprised if you were troubled by structural issues. There are some unique advantages that apply to 3D printed parts for telescopes too. One of those, is high levels of insulation. For things that are within or close to the optical beamline, where metal parts like tubes and spiders if made of metal tend to sub-cool during clear nights, there is far less of an issue if cellular dimensionally-stable resins are used. Another is relative freedom from the need for coatings and finishes. Finally there is the ease of incorpating things like brackets, reinforcements, pneumatics and wiring. As you say, our profession is having to reinvent again all the established design techniques, in a world where the West now struggles to manufacture things profitably and where additive technology is finally becoming reliable and good enough for first-class products. I'd be very interested in your progress on the Gregorian once the secondary is polished! Good luck with your endeavours! Tony Owens
  12. Hi Chris and my compliments on your unorthodox monorail Gregorian. This style of 'monorail' tubeless scope reminds me of the late Horace Dall's planetary Dall-Kirkham. I had a crack at designing a 14" F4 planetary prime focus Newt a couple of years ago. At the prime focus I could interchange various coma correctors, cameras and filters. I used ITEM alloy extrusions with screwed and epoxy-bonded joints and waterjet-cut pieces of 4mm and 10mm alloy plate to construct a goniometric primary mirror mount and various reinforcements to get the gravitational sag under control. For a Newt the max tolerable decentration of the 'true' axis of the primary mirror from the eyepiece or camera to maintain no more than a 0.20 drop in Strehl is given approx by DeC = 0.005 . FR^3 [mm]. For my optic I therefore needed to assure no more than around 0.32 mm decentration of the primary from the camera, for all possible poses of the OTA and for the heaviest imaging train payload at the prime focus. This number is somewhat simplistic and debatable and little more than a guideline for acceptable structural sags, but as a target it was fine. In designing a structure I actually worked to around 25% of this target and aimed for a lowest natural frequency of around 20Hz. The thinking here was that the EQ8 mount I was planning to mount this on is marginally capable of supporting a 20Kg payload/counterweight combination with a natural frequency of around this. The natural frequency not just of the mount but of the entire scope/camera system needs to be as high as possible to allow a good percentage of quality frames when lucky imaging Moon and Jupiter at 120 Hz especially with some wind. Here is what I ended up with: I used a CFRP flat plate secondary single-stalk design which is magnetically fixed to the OTA using a kinematic mount for interchangeability. The mirror is contained in a lightweight shroud. The structural deflections due to gravity (linear and tilt displacements) of the OTA at zenith pointing looked good. This was Horizon Pointing showing less than 100um of linear sag of the prime focus group: This was Zenith Pointing. Note how tilts of Primary and primae focus group matched: This was another Horizon Pointing scenario with the OTA rolled through 90 degrees w.r.t. the gravitation direction. It proved to be the worst case but still the linear sags fell not too far outside my target: This pic shows the lowest natural frequency of the OTA assuming a rigid circular saddle support of diameter 160mm is used. I call this 'Nodding Duck'. The frequency is 34 Hz which is perfectly acceptable: This is the second lowest vibration mode, at 38 Hz. I call this 'Secondary Stalk Waggle': Finally, this is the third lowest vibration mode which I named 'Primary Waggle'. It appears at 42 Hz so is not a concern: My experience was that structural FEA was of tremendous help in arriving at something that almost met my stiffness requriements under all possible poses and imaging payload configurations. It never occurred to me to 3D print structural parts in something like PET-G using lightweight cellular infill at that time because to be honest I did not take FDM printing seriously. I since revised that silly opinion and am now gradually learning the practice of large 3D printing with a large printer. I am very encouraged to see your project and hope your practical findings about collimation stability show my own analysis to be too conservative! best Tony Owens
  13. What I'm looking for doesnt exist yet! I want a mount that has no meridian flips, no worm gears (despite all my work on refining EQ8's) no microstepped stepper motors, has a weight and size low enough to be airline cabin baggage, maintenance-free, cable-free, backlash-free, counterweight-free, capable of being rained-on without ill effects, and with at least a 20 Kg imaging payload. Perhaps combine the wireless servo controls and GUI of the AZGTi, provide differential timing belt transmissions, reinforced phenolic casework, wire race bearings and a single arm fork design... Or maybe something with delta 3d printer kinematics plus a 4th axis for image derotation? One of the best resolved commercial designs I've seen recently is the Panther line of Goto mounts. Despite the counterweights!
  14. A good gloss of that period of hope and belief in the power of technology to effect change for the better. Spoiled a bit by the creaky voice (vocal fry) now fashionable among yuppie American women.
  15. All worm gear mounts of this class are pretty similar and better than 5 arcsecs peak-to-peak periodic error is typical. It doesn't make any real difference what the exact figure is, provided sensibly tuned autoguiding is being used. All will be reduced to 0.5" RMS on RA and a bit less on Dec, provided backlash is controlled. The EC mounts are a different animal, and essentially offer more linear RA or RA/Dec motion. But this is not a useful advance on open-loop tracking (no encoder/s) unless unguided imaging is a requirement and some mount modelling can be considered.
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