Oddsocks

From your description of the problem it seems that the contact area and limited compression range of a standard Viton or Nitrile rubber ‘O’ ring is just too small to accommodate the flex range of your casing when it is bolted together. How about a wide flat gasket cut from closed cell expanded neoprene rubber, with a large compression range and increased contact area it should cope easily with distortion of the casing when bolted together. As long as it is not over exposed to UV it should have a good few years of life. Fairly easy to cut from a flat sheet with a sharp craft knife or scalpel using a printed paper template as a guide. Might be a solution? I have a few offcuts of low density 6mm thick, self adhesive, expanded neoprene sheet here, left over from when I insulated my observatory’s glass fibre dome roof last year, I can put a couple of bits approx’ 300mmx300mm in a postal tube and mail them off to you .f.o.c. Just send me a pm with a suitable delivery address if wanted. Otherwise, here is a link to a set of closed cell neoprene foam sheet gasket material on eBay: https://www.ebay.co.uk/itm/Neoprene-Rubber-Sponge-Rubber-Nitrile-Cork-Sheet-GASKET-Material-Foam/191593795500?hash=item2c9be14fac:g:U1IAAMXQvTlRgzTV William.

What type of bearings are used on the worm shaft and worm block carriers Huw, plain ball or tapered roller with pre-load? In the original thread you had some engineers blue paste to check that worm-gear mesh was on the valley sides of the gear and not the valley floor, did you ever confirm with the blue paste that the worm-gear mesh was ok and not bottoming? My money would be on combined end and side float on the worm carrier and worm shaft bearings as a minuscule amount of both end and side float on both bearing sets working together with a worm gear translates to a large combined end play, or backlash under load so with a worm-gear lift, twist and end float in any of the worm carrier or worm shaft bearings will contribute to backlash. Having begun using a new mini-lathe earlier this year I found a surprising amount of end-play at the chuck with the standard plain ball bearings in the head stock, even with a large pre-load applied, and changing those to quality tapered rollers eliminated that. Of course, the magnitude of the loads involved between a lathe and a telescope mount are somewhat different but the principle is sound and if you are currently using plain ball bearings on the worm block carriers and worm shafts I think that would be my first place for a change to quality tapered rollers with a good bit of pre-load applied and see if that made a difference. Can’t think of anything else ATM but will come back to this if I do. William.

@PhotoGav , @Davey-T , @continuum, @Mathieu80, @Whirlwind, @ollypenrice Just a quick thanks to all who posted in this thread. I had this banding problem with my QSI683-8-WSG since new, can't believe that was back in 2012, but as it mostly calibrated out I wasn't that bothered until recently begun using scaled darks for asteroid and NEO studies with limited data in PixInsight, where it became more apparent. Also a big thanks to Andrew Kirby at QSI support who emailed me the new FPGA and version 7.1.1. firmware within an hour of requesting it, installed in a few minutes and problem fixed....? The banding in the bias master with the old FPGA and firmware is very subtle but can be seen, it is much more apparent in the darks and totally absent with the new FPGA and firmware. For reference below are four QSI master frames, bias and calibrated darks, showing the problem before and after upgrading the firmware. Unfortunately I did not make a note of the original FPGA version, only the original firmware which was v6.3.1, the new FPGA version is 0212 and firmware version 7.1.1. If Gav hadn't started the thread I would have been non-the-wiser so thanks again... William. Old firmware v6.3.1 and original FPGA, master bias, 999 frames bin 1x1, -15c, high image quality download mode: New firmware v7.1.1 and FPGA v0212, master bias, 1998 frames bin 1x1, -15c, high image quality download mode: Old firmware v6.3.1 and original FPGA, calibrated master dark, 100 frames bin 1x1, -15c, high image quality download mode: New firmware v7.1.1 and FPGA v0212, calibrated master dark, 100 frames bin 1x1, -15c, high image quality download mode:

Hi Tom Not having a MESU or Sitech here to play with I can’t help that much with the setup, the only thing that consistently appears in web discussions is the need to configure the Sitech, Encoders Config, set encoders to “Polite” mode, plus a fairly large tolerance of 10:00:00 degrees in the supervisory threshold window, otherwise the MESU’s motor encoders and shaft encoders may consistently argue with each other after a slew causing the mount to continually re-slew to the requested coordinates. ( I think this info originated in Steve Richards quick-start guide but has been referenced several times in other web pages ) William.

Hi David. POTH (Plain Old Telescope Handset) is more of a developer tool, think of it as a mail sorting office with the added benefit that you can read and rifle through the incoming and outgoing messages and only choose to deliver the messages you think fit. With logging enabled it is a great resource to help with ASCOM driver development etc. There is no reason for you not to use POTH it is just more difficult to set up when presented with all the capabilities that POTH has. You will find a help document for POTH under All Programs > ASCOM Platform 6 > Scope-Dome-Hubs > POTH Help. To use it for your purposes you make no changes to the options in the POTH control window, all settings should be left at default but rather, in the client program(s) APT, Stellarium etc you have to choose in setup POTH as the Telescope, and optionally, POTH as the Focuser, & Dome. Each time you make a selection of POTH in the client program as the device being connected to, the POTH setup window will open where you choose the actual telescope driver, EQMOD in your case, and optionally focuser and dome drivers if used. You only need to set up the actual device hardware drivers in POTH once, so if you open APT and choose POTH, set up POTH for the EQMOD driver, focuser driver and dome driver, if applicable, then in Stellarium Scope just set POTH as the "Telescope" there is no need to repeat the actual device driver selection again as once selected in POTH it will be the same for all client software connecting to it. To use POTH you do nothing other than connect to the "Telescope" plus "Focuser" & "Dome" if used, in the client software which will then connect to POTH and POTH will relay the messages back and forth between hardware device and client software. Do not try to manually connect to the Telescope, Focuser or Dome from within POTH unless you want to actively test the ASCOM drivers etc. When used for actual mount control, when you connect to the "Telescope" (POTH) from inside APT and Stellarium Scope the POTH window will launch, you need to minimise this to the bottom tool bar on the desktop, or hide it out of the way on the desktop and do not interact with it at all, however the program, must remain "open" otherwise POTH will not work and your client programs will have nothing to connect to. As an alternative, the ASCOM "Generic Hub" does all the above but without the developer tools and log tracing that are included with POTH. Setup and use of the "Generic Hub" is exactly the same as it was for POTH and you will probably find it does everything you need with less user "options" to get in the way. HTH William.

Probably best to ask Ollie to give the IEC power connection cables to the UPS a once over, they never seem to fit tightly in the sockets and can be easily dislodged, it could be the mains input cable has worked loose, equally, it could just be a temporary reduction in mains input voltage that triggered the UPS into action, depending which model UPS you have and what thresholds have been set up a reduction of just ten Volts or so below nominal mains input may be enough to trigger the UPS while not being noticeable to the residents on site. Farnell do have the occasional glitch with their payments system and I find it best to give their order line a call when having problems though normally once your account is set up and the CC registered then ordering is quite straight forward. I'll keep watching the thread to see how things pan out. William.

Has all the hall marks of an earth leakage / ground loop, Tom. Just a small nick in the jacket insulation of your old USB cable to the Sitech can introduce an unwanted ground point, conversely, a broken shield on the USB cable would introduce noise on the USB signal lines. When you tested the RS232 adaptor with the Eagle were you using the original USB cable as a connection beween the Eagle and the RS232 adaptor or bypassing the old cable completely? Leaving the old USB cable in situ or disconnecting both ends while testing the RS232 adaptor etc.....? I meant to ask earlier whether your UPS was an on-line / line interactive or off-line / standby model. I have had problems with several makes of the on-line / line interactive types over the years where the output AC is not symmetric around earth and this can lead to small differences between the DC 0V levels of your connected AC/DC step down convertors and true ground. We used opto or magneto galvanic isolators quite extensively for both USB and serial interconnections on medical equipment to prevent earth loops, though more to do with connecting between equipment on different mains phases in three phase environments we also found them necessary on systems using a UPS (the isolators we used, being medical rated, cost several hundred Euros each). Having the UPS run through an operating cycle, mainly the off-line types, is something we did every three months on maintenance inspections as this is important to help keep the UPS’s internal change-over contactor contact-set clean, if the UPS was left for many months always in the standby mode then the change-over contactor became electrically noisy due to contact tarnishing which introduces high frequency noise and spikes on the output side. While you wait for the USB isolator, if the problem occurs again on mains supply ask Ollie to temporarily take the UPS out of circuit, if the UPS uses standard IEC leads just shut it down, pull the input and output leads and plug them together. It would be another possible problem source eliminated. William.

Hello Tom. Most likely a multimeter wouldn't help, leakage currents are typically too small to measure sensibly, an oscilloscope is the best method, and that is what I would have used for this kind of problem when I used to work on these sorts of problems for a living. The UPS provides smooth 220/230 AC to the Eagle, and I have an APC UPS in my own observatory to protect the equipment and shut down the computer correctly in the case of a power interruption, the problem then is what the Eagle does with that clean supply. The step-down power convertor, AC/DC, that is used in general electronics, switch mode PSU's, can leak a small amount of incoming mains 220/230VAC to the 0V rail of the DC output via internal interference suppression capacitors. The current is very small, just a few milliamps, but if this current finds a route to earth via USB or RS232 leads it 'can' interfere with comms. If you have an iPad, or a similar device with a metallic case you will often feel a tingle when running your fingers over the device when it is connected to an AC/DC charger, this is quite safe, and is caused by the leakage current from the AC/DC convertors suppression capacitors as described above, but it 'can' be the source of comms issues when connecting lots of different devices together. I think the MESU/Sitech combination maybe prone to these sorts of issues because the Sitech control unit is solidly bolted to the MESU and the MESU is bolted to the pier, which is grounded, so it is the last link in the chain for a leakage current to flow to earth. If leakage currents are the issue then there are several possible approaches to the problem. First, all separate pieces of equipment can be connected to a single earth point, but this means the MESU has to be installed on the pier using isolator washers, or an insulating sheet between the MESU and the pier, with isolator washers also used under the bolt heads that bolt the MESU to the pier and isolation ferrules or plastic tape around the parts of the bolts that pass through the MESU that bolt the MESU to the pier. If this is done then there can be no leakage currents flowing between the Eagle - Sitech - Pier - Earth, so long as the MESU and pier remain dry, in an observatory this is easy to control but out in the open, if the MESU and pier become damp through frost and condensation etc then the isolation may break down leading to intermittent comms issues that are difficult to trace. With the Sitech/MESU isolated from ground and all devices connected to a single earth point then earth loops and leakage currents can be controlled. The second way is to use galvanic isolators between the different components of the system. As a point of reference, I have a Paramount MX and it has had two failed MKS5000 control boards in five years, at $800 a time this is not funny. The problem is the USB UART on the MKS5000 is totally unprotected against voltage spikes, if an active thunderstorm passes close by the observatory, the induced voltage spikes generated in the long USB leads by the lightning destroys the USB UART. After the second MKS5000 failure I fitted a USB opto-isolator, that was three years ago and I haven't had any further failures since then, I also bought a few spare USB UART chips, just in case, as the cost of buying the replacement boards from Software Bisque was not justifiable, especially since they could have chosen to fit rapid spike suppression diodes on the USB inputs that would have given a degree of protection. The type of isolator I have on the MX is one of these: https://uk.farnell.com/olimex/usb-iso/usb-isolator-1000vdc-for-pc-laptop/dp/1795095?st=usb isolator It gets it's power from the host USB socket (Eagle), via a built-in isolation supply, but if this proves insufficient you can plug in a +8V to +15V external supply. This isolator is connected via a very short USB lead ~15cm long, to the USB input of the Paramount with a long 3mtr USB cable from the isolator back to the host computer. These isolators are built for use in the dry, so if the Sitech/MESU gets to be damp then put it in a box. As mentioned before, I wouldn't jump to a conclusion that a leakage current is to blame and rush out to buy one without proving that this is the problem first and powering from a battery would be the simplest way. I will be away from the internet now till the weekend, probably Sunday, or early next week, but I'll look back in when I get a chance. William.

Hello Tom. Away travelling at the moment so access to SGL very limited..... I don’t know the Eagle other than seeing a few pictures and reading the occasional user posts here on SGL and other forums so this response is not specific to the Eagle, only generic. From your tests it does sound as though the Eagle is possibly suspect. Although you have tested with USB and RS232 on the Eagle, both communication methods still rely on and use the Eagles USB ports, the only real difference is that using RS232 forces a slower communication rate, which is generally more robust than straight USB to USB, Eagle to Sitech. From an engineers stand point the next test I would do, just to eliminate the possibility, would be to check for ground loops and power supply noise using an oscilloscope. Although your Eagle power supply might have enough amps to power all the kit connected to the Eagle, if the supply is electrically ‘leaky’ or noisy then it’s possible that an earth leakage route can exist that flows from the Eagle’s USB ports, and RS232 adaptor if used, across the connection to the Sitech, and via the Sitechs 0V common down to ground via the mount and pier. If the power supply is leaking to earth across this route it will cause communication issues. By using the Alienware instead of the Eagle as the connection to the Sitech you effectively broke any possible power supply leakage route via the Sitech’s com ports. Appreciating that you probably don’t have access to an oscilloscope for testing for ground loops and noise on the power supply, and that travelling back and forth between home and Ollies is not really an option can you arrange for Ollie to try a different power supply? preferably a clean source for the Eagle such as a big leisure battery, or, if this is not possible and you are using some kind of AC to DC convertor try powering the AC-DC convertor via a site safety isolating transformer as this removes ground leakage route. Ollie may have one already at his site since he has done so much work outside over the years. Although a site safety transformer is not suitable for full time usage, they usually only have a ~25% duty cycle and aren’t designed for continuous use or they overheat, but can be used in short periods of twenty minutes or so for testing. If running on battery, an isolating transformer or a different AC to DC convertor cures the problem then the simplest solution is to prevent possible earth leakage routes via the Eagle-Sitech in the first place, a galvanic (opto) isolator for either the USB - USB or USB to RS232 convertor that is used between Eagle and Sitech would do that but I would hesitate to suggest you thow more money at the problem without proving that a ground loop is to blame first. Try battery power first for testing, if possible, for the Eagle - Sitech and see how that pans out, if the problem is cured then a galvanic (opto) isolator on the Eagle to Sitech USB-USB or USB-RS232 may be all that is required. BTW, port # retention on the USB to RS232 adaptor isn’t between computers, only on the same computer, the fact is was the same port # on both the Eagle and the Alienware is just ‘chance’. HTH. William.

For architectural drawings with FreeCAD a good starting place are the tutorials for ARCH and BIM. https://www.freecadweb.org/wiki/Tutorials You will find many Youtube videos also though it can be time consuming sorting the most informative.

I'm 90% sure that the 2018 free version was when they first migrated to the online web-based model. I did try 2018 on-line but it (or I) managed to lose some CNC router work that I had been designing over several weeks and gave up. Have been using TurboCad for Mac and MeshCam for Mac since then as I still do a lot of engineering designs for CNC lathes and routers, plus some 3D printing that I'm just getting into but neither TurboCad or MeshCam are freeware. I used TurboCad for my listed building re-roof planning application last year and since I saved several thousand that I had been quoted to have the plans drawn professionally I considered TurboCad money well spent. Have a look at FreeCAD, that might be all you need for architectural observatory plans, it does mean learning a new program though, there are not that many similarities with Sketchup Make. https://www.freecadweb.org William.

https://help.sketchup.com/en/downloading-older-versions Any help?

Host is the PC, client is the mount. At the host end (computer) 9-pin D-plug, pin 2 is received data, pin 3 is transmitted data and pin 5 is ground. At the Sitech end, with the locking tab of the RJ plug uppermost, the furthest right side pin is transmitted data leaving the mount, XMT, this goes to pin 2, received data at the computer end. The second pin from the right side at the Sitech end is data into the mount, received data, RCV, and this is connected to pin 3 at the computer end, transmitted data. Lastly, the third pin from the right at the Sitech end is 0v and this goes to pin 5 at the computer end. According to the colours you added to the Sitech drawing for the RJ socket, you have the correct wiring so all should be good and you won't need a cross-over adaptor. The confusing thing, as mentioned before is that Sitech have shown the outline drawing of the hand-pad connector in their documentation and not the RJ socket that they use for the RS232 connector but as long as the pinouts for the socket are shown in the correct sequence that all should be well. If you want to double check drop @harry page a PM and ask him to confirm your appended image as I know he is running his MESU via the RS232 connector. William.

Looks good Tom. Regarding the Sitech manual RS232 info, it has not been drawn/written that clearly and is open to interpretation, they could really do with a minor revision and clarification. In the line drawing of the RJ plug wiring, the text of the furthest right connection, “From Host RCV <- XMT” should really say “To Host RCV <- XMT” , and in the diagram of the RS232 RJ socket on the front panel of the Sitech they show a latch-notch top and bottom of the socket, which could lead to some confusion regarding which way up the plug slides into the socket. The drawing, assuming I’ve read it right, should show the latch-notch at the top and a flat base line across the bottom where the connector pins should be. You seem to have read it right though. You don't need to add any extra jumpers in the D plug, just the three wires to Rx, Tx and 0v are all that are needed normally for basic RS232 protocol. William.

Hello Dave. I have the ODK 10, just along the coast, a bit east of you. A long reply, took some time to write with a lot to cover, hope it proves useful. I have the OO heater kit for the 10” ODK here ready to fit, had it for five years but never got around to fitting it. When I ordered the kit from OO they were having problems obtaining the secondary heater pad and were only able to supply the primary heater, they suggested I bought the secondary heater directly from Kendrik in Canada. OO recommended that the full-width heater pad was best as it provides direct contact between heater pad and the mirror while the ‘C’ shaped external heater pad that wraps around the outside of the mirror support did not work so well because there is no direct contact between the mirror and the mirror support plate, the two are separated by thick blobs of silicone rubber and the screw-on baffle shroud. Partly, the reason for not fitting the kit so far is that even though I’m an experienced engineer the prospect of having to unglue the secondary from the secondary support plate to install the full-width heater pad across the back of the mirror is not something to be taken lightly even though OO told me it’s just a matter of cutting the silicone rubber at the join between the secondary support plate and the mirror with a hobbyists scalpel, levering off the mirror from the back plate and refixing with acid free silicone on both sides of the heater pad. My hands (and nerves) are just not steady enough for that these days! I might abandon the idea of fitting the full width pad and buy and fit the external ‘C’ type heater ring, for now I’m using a quadruplet refractor in the observatory and have no plans to begin using the ODK again any time soon. The vanes of the ODK 10 OTA are thick cast/machined aluminium, much wider than the secondary heater wires, so it’s relatively easy to attach the wires to the top or bottom of the vanes with silicone, or little blobs of hot glue and hide them within the width of the vane, they would not intrude into the light path. Once the secondary heater pad is attached it will be much more difficult to carry out occasional mirror cleaning as the heater wires are supplied as a one piece kit, one length of continual wire that runs from the heater pad, down inside the OTA tube and back to a pre-wired audio type jack socket that you have to mount on the OTA backplate. As it stands, to remove the secondary for cleaning once the heater is installed requires that the heater wires are unglued from the vanes and the wires and socket removed from the backplate. If you hot-glue or tape the wires to the inside if the OTA to prevent them straying into the light path on the run from the secondary vanes down to the backplate then obviously you can’t remove the wires and can’t detach the secondary from the vanes/OTA so the wires need to have an inline joiner of some sort at the juction of the secondary support and the vanes so that you can detach the wires and remove the secondary. Mini spade terminals and shrouded receptacles would probably do. There is a tight, close-tolerance fit between the circular secondary mirror, the threaded secondary baffle shroud and the threaded secondary support plate. In order to bring the secondary heater wires of a full-width heater pad around the edge of the secondary support and refit the baffle-shroud it would be necessary to file or grind a notch into the edge of the secondary support plate to take the wires. Of course, this would not apply to the ‘C’ type, external, secondary heater as the wires are routed around the outside of the secondary support and baffle-shroud. The OO supplied primary heater is not attached directly to the mirror, this is a semi rigid wrap-around collar that sits against the OTA wall and radiates heat towards the mirror, there is no direct contact betwen primary heater and mirror, which makes regular cleaning a lot easier. The heater collar has to be siliconed or hot-glued against the OTA wall to hold it in place. Even with careful handling, removing the primary heater from it’s packaging causes large patches of the anti-reflective black paint to flake off the GRP base, leaving the yellow-green (shiny) GRP base showing through, it will need repainting after fixing in place next to the mirror (with the mirror removed). Unless OO have changed the design of the OTA backplate since mine was supplied, two extra holes have to be drilled in the backplate to accept the pre-wired audio-jack sockets that are attached to the ends of the supplied heater wires. My ODK 10 was last used inside a domed observatory and there was very little dewing. When dew did appear it occurred on the primary first and I found that keeping the OTA fans running largely prevented dewing except for a handfull of occasions. Before having a domed observatory I had a Skyshed Pod that fully exposed the OTA to the sky. I had continual problems with dewing and icing on both mirrors at that time which was why I bought the heater kit but before getting around to fitting it I had issues with condensation forming inside, between the lenses, of the ODK’s built-in corrector assembly. I was able to use a heater tape wrapped around the corrector where it projects beyond the rear of the OTA back plate to evaporate the moisture but it would reform within a day if the heater was switched off. In the end I brought the OTA inside the house to dry out but even after a month indoors the condensation reappeared inside the corrector after a few days back in the Pod and eventually I had to remove the corrector, unscrew the lens retainer ring at one end, remove and clean the lens groups of water marks, reassemble the corrector and leave it in a sealed plastic box with silica gel for a few weeks before refitting. For the remainder of that winter season I had a heater tape around the corrector that was switched on permanently. As you are probably aware, collimating an ODK is not an easy task. The distance between the primary, secondary and corrector are critical to achieving specified spot sizes and optimum optical correction. I believe OO now provide a collimation tool which comprises a calibrated distance tube and Ronchi eyepiece which is used on a bright star to set the distance between primary and secondary, the tolerance is small, a fraction of a mm away from the correct distance results in star bloat and under/over correction. When I bought my ODK 10 the distance tube and Ronchi eyepiece were not supplied and had to be obtained separately. You need these tools for accurate re-collimation whenever you take the mirrors out for cleaning. If you have to remove the corrector, as I did for drying out, there are no optical tools provided to ensure it is refitted at the correct distance from the secondary and I used a vernier to measure the distance between the centre of the rear corrector lens and backplate before removing the corrector assembly for drying, setting the same distance after cleaning and refitting. If you lost this corrector distance I think it might be really difficult to set it back again empirically given that ODK correction seems to be wavelength dependent, i.e, best compromise of spot size for the full optical bandwidth, and most likely this might need an optical bench to set up, this is just a guess though and it would be best to talk to OO regarding cleaning/drying of the corrector if the same internal corrector condensation issue that I experienced happened to you. So, if you want to want to fit the full size, full-width secondary heater be aware that collimating afterwards requires the special distance tube and Ronchi eyepiece to get the distance between secondary and primary correct since you now have a thick heater pad between mirror and mirror support thus changing the distance between the two mirrors. Using the Ronchi on a bright star, making small adjustments to the secondary distance, refocussing, recentering on the star, evaluating the Ronchi pattern and repeating takes a long time. Don’t be suprised to have to spend a few nights on this after mirror cleaning or fitting a full width secondary heater. For many reasons I have not used the ODK for the last couple of years. Partly, the observatory is used remotely and unattended for much of the observing season and an open tube OTA required too much maintenance. The observatory is adjacent a mixed arrable and dairy farm with ploughing/tilling dust, flies, spiders eating the flies and pollen a constant problem. A smaller refractor with an electric remote opening dew shield flap to keep the dust, flies and spiders away was needed and there just is not the space between a 10” OTA and the roof of the dome to fit one. A long dew shield extending from the OTA would probably be enough, together with the OTA fans to prevent, or reduce, dewing but again in my observatory there is no room. To sum up: If you are in a domed observatory most likely you woudn’t need heaters at all. If the OO kit uses the ‘C’ type secondary heater it is relatively easy to fit yourself but not as effective as the full width heater pad that requires major surgery to install. Both primary and secondary heaters are wired to sockets on the back plate. You may need to drill holes in the back plate to mount the sockets if OO do not now provide the back plate pre-drilled. After fitting the primary heater, you most likely will need to touch up the black paint on the heater (unless OO now prime and paint the GRP base with a suitable flexible paint and not with a single coat of some water? based paint that doesn’t stick to GRP as was the case with the one they sent me. If you change the distance between the primary and secondary of an ODK, even by a fraction of a mm, you need to collimate using the calibrated distance tube and Ronchi eyepiece that I think OO now supply as standard with the telescope, when mine was supplied you had to obtain these separately. If your ODK 10 is to be kept outside permanently watch out for condensation forming between the lenses of the back plate mounted corrector, consider fitting a wrap-around heater tape where the corrector protrudes from the back plate and apply a liitle heat right through the winter to mitigate against this. Unless you have some experience of dissasembilng lens assemblies, and the tools to do so, then preventing condensation forming inside the corrector in the first place is a whole lot better than dealing with the problem and cleaning up residual water marks afterwards. If OO are supplying the full width secondary heater pad and have not ‘notched’ the secondary backplate to accept the wires that allow the baffle-shroud to be refitted once the heater is glued in place then it might be best to pay to have them fit the kit. If OO are supplying the ‘C’ type external heater pad then you can fit this relatively easily yourself, provided that the OTA backplate is pre-drilled for the heater wiring sockets otherwise you will need to attack this with a drill yourself. If not supplied, obtain a couple of mini in-line spade terminals and shrouded receptacles, cut the wires for the secondary heater close to the secondary stalk and fit the terminals there so that you can easily remove the secondary for routine cleaning without having to unglue the wires from the vanes. William.

Glad that the DIY ‘photometer’ method worked out for you, looks like a good build! I’m not a great fan of dimmer controls for LED panels, most of the models at the lower price end of the market use PWM (Pulse Width Modulation) to vary the light output and at very low light levels used in flat boxes this means the LEDs are only lit for very short periods in each clock cycle, in effect they become high frequency strobe lights. PWM controllers are ok for tungsten filament / Halogen lamps because the filament does not react quickly enough to the strobing for it to affect the quality of the captured flat frame but with LEDs they do switch on/off very quickly and although your eye does not see this strobing the camera can. LED strobing can manifest itself as horizontal, vertical or diagonal bars of various thickness in the flat frame. It can not be predicted which cameras and sensors will be affected, it depends on things such as whether the camera has a mechanical shutter or uses a global or rolling electronic shutter, exposure time, frequency of the PWM brightness control and it’s pulse-to-space ratio etc. For LED lights in a flats source a linear brightness controller is best but these are more expensive, generally bulkier and heavier, inefficient and run quite hot. To avoid strobing artefacts run the LEDs at full brightness, preferably with no brightness control at all, and use several layers of neutral density photographic gel filter to dim the output of the flats source. Linked below is a UK source of neutral density gel filters, 1 sheet, 1.22m x 0.53m @ £7.00 would be enough to give you three or four thicknesses of filtration, each layer of 1.2 density reducing the light by 4 stops. https://www.sblite.co.uk/neutral-density/265-409-rosco-299-12-neutral-density.html#/23-sheet_roll-sheet These gel filters are surface coated polyester and though tough the surface coating can be scratched so its best to place them behind a sheet of clear acrylic if you intend to place the light box over the OTA aperture so that there is some contact beween the output diffuser and the front of the telescope. Technical specs for the linked gel filters supplied by sblite of sheffield are found at the manufacturers web site, Rosco, (e-colour+ series) here: https://emea.rosco.com/en/product/e-colour William.

Hi Tom. Not quite sure what you are doing here, you can't cut the end off a standard USB cable and connect it directly via a RG11 to the RS232 port on the MESU. Windows will never recognise the MESU as a RS232 port, the USB port hardware on the host computer will only recognise and configure standard USB devices. You must use a USB-to-RS232 port emulator/adaptor and connect the emulator/adaptor to the MESU. Something like this, preferably using a FTDI UART chip with COM retention, USB-to-RS232 emulator: https://www.amazon.co.uk/StarTech-com-USB-Serial-Adapter-Powered/dp/B004ZMYTYC/ref=sr_1_1?ie=UTF8&amp;qid=1549930141&amp;sr=8-1&amp;keywords=1+port+ftdi+usb+to+serial+rs232+adapter+cable+with+com+retention You will also need a re-wireable DB9 connector, with shrouds, to connect the RS232 emulator/adaptor cable to the RJ11 plug. https://www.amazon.co.uk/Serial-Connector-Removable-Plastic-Housing/dp/B00KDBXD3W/ref=sr_1_fkmr1_1?ie=UTF8&amp;qid=1549930766&amp;sr=8-1-fkmr1&amp;keywords=rewireable+db9+female I've linked to a Startech RS232 emulator/adaptor above as these were the make I used to use at work and proved reliable, though expensive. You can find cheaper makes that use FTDI UART's but avoid Prolific UART's there are so many fake Prolific UART chipped devices out there and many prove unreliable. The latest FTDI UARTS use COM port retention so once Windows has recognised it and registered the COM port even if you move the USB plug to a different USB socket on the computer the port number in software does not change. HTH William. *EDIT* Note, see appendix D of the Sitech manual (page 47) for wiring diagram of the RS232 port DB9 plug to Sitech RJ11 plug, also, you do not require or connect the 5V pin, only RX, TX and 0v are used.

Thank you for the kind comments Alan. I think you can probably tell I spent too much of my youth watching Blue Peter! ?

Hello Jamie. As described above in Alans reply, @symmetal, the contour maps are produced by specialist software however this would not be of much use to you in this case because they map the entire optical chain of the telescope as well as the light source and with a large aperture OTA such as the C9.25 you won’t be able to move the entire OTA over the face of the light box to determine the evenness of light distribution without overlapping the edge of the light box and producing an inaccurate result. Happily there is a simple solution using your ZWO ASI 1600 camera by converting it into a temporary photometer. Remove the camera from the telescope and if not already fitted then attach the standard camera 2” nosepiece. Using a piece of aluminium kitchen foil, temporarily wrap the foil over the nosepiece so that it lies flat across the nosepiece aperture. Make a 1mm diameter pin hole in the foil in the centre of the nosepiece aperture. Carefully slide the foil off the nosepiece then cut a couple of pieces of white printer paper into small disks or squares for use as a diffuser/attenuator, approx 1cm x 1cm, shape doesn’t really matter, and glue or tape the paper disks (or squares) across the pinhole on the inside of the foil as a double thickness. Reattach the foil to the nosepiece and secure with tape or rubber bands. Reinforce the foil with a couple of strips of transparent sticky tape across the face ensuring that the pin hole is roughly centred to a piece of the tape and not lying across the edge of the tape (to avoid diffraction effects). The camera can now be used as a crude but accurate and effective photometer. Place the camera nosepiece in close, direct contact with the surface diffuser of the flat panel, somewhere near the centre of the panel, ensure the flat panel has been switched on for at least fifteen minutes to allow it to stabilise, darken the room to avoid stray light affecting the measurements and then take an image with the camera. Adjust the camera exposure time to achieve an average ADU for the entire image of approximately half max value (saturation) then using the same exposure time simply move the camera across the face of the flat panel in a rough grid pattern, 1cm steps would be sufficient, make a note of the camera average ADU reading at each sample grid point as you move the camera over the flat panel and then plot the resulting readings. What you have constructed could be described as a 'spot' photometer and it's sample area is very small, dictated by the size of the pinhole in the foil. Measurements made with a spot photometer can be adversely affected by small defects in the surface of the flat panel diffuser which, when used as a light source for the telescope would not be noticeable as the light source is so far out of focus. You could enlarge the size of the pinhole and add additional paper attenuators to the inside of the foil to increase the sample area size however you would achieve better results by converting the 'spot' photometer into an 'area' photometer by moving the surface of the foil/camera away from the face of the flat panel diffuser. To do this simply measure the length of the camera nosepiece and cut a cardboard tube approximately 1cm longer from the inside of a roll of toilet paper or kitchen paper (or simply 'roll your own') and slide it over the nosepiece so that the foil face and pinhole is now sitting inside the tube to a depth of 1cm. Now when you hold the camera against the flat panel the pinhole being further from the panel will be sampling a larger area, depending on the geometry of the camera probably ~5mm to ~10mm diameter, which will even out the small imperfections in the flat panel diffuser and give you a more meaningful measurement. When used as an area photometer it would be good practice to blacken the face of the aluminium foil that looks towards the flat panel to prevent over illumination due to internal reflections between the face of the flat panel diffuser and the foil, it probably won't make a lot of difference when used for this task as the inaccuracies due to the reflections will be the same across all the measurements however if you wanted to improve the accuracy of the photometer you could blacken the foil, or place a blackened cardboard aperture mask across the face of the foil, use a different material for the foil such as thick opaque black plastic etc, just depends what materials you have to hand. Your capture program should be able to display image stats like max/min and average ADU pixel values and using the camera as a photometer in this way the average ADU would be sufficient. If your capture program does not display image stats then there are several free image processsing programs and FITS viewers available that can show this information. A well made EL panel would typically show a variation of less than ~1% average ADU across it’s illuminated surface, a LED draughting panel rather more, up to 5% is not unusual, even for a very well made panel. If your flat panel shows a variation of less than 5% ADU across the field then it should be adequate. HTH. William.

Tom. If I remember correctly RS485 uses differential amplifiers in the transceivers for the RX and TX signals so Rx has it’s own separate 0v and Tx has it own 0v, they can’t share a common 0v on the signal pairs. The Sitech is RS232 and RS232 uses end-to-end cabling and doesn’t use differential amps so you only need three wires, Rx, Tx and a common 0v (and maybe +5v if the receiver amp in the device is not host powered). Besides the above, the logic levels are different with RS232 working at either 5v or 15v and RS485 working at 6v, finally, RS232 uses simplex or full duplex modes and RS485 only uses simplex or half duplex. Bottom line is that in very few cases can RS485 be directly substituted for RS232 unless the port hardware is either user or auto detect configurable and the full set of cabling is provided. Looking at the Sitech drawings and manual this appears to be an RS232 only device. HTH. William.

The EPDM is certainly easier James. The flat, low-profile corrugated steel panels look better and probably last longer but installation on a ridged roof is complicated unless you can get all the components needed from the same manufacturer. We re-roofed the scout hut with metal panels two years ago, previously it was felted but vandals set the roof on fire and we thought metal was less of a liability. We had to cancel the TP order though when we found they didn't stock the ridge caps and barge boards. One of the scout assistants knew somebody in the trade and we bought enough 1.6mm thick sheets in blue to cover the 4m x 6m hut, with matching barge boards, ridge caps, and corrugation meshes, and got free delivery, from a company in the Midlands. I seem to recall the final bill was around £500 though. My neighbour has re-roofed his garage with TP panels in grey but that is a flat roof with just a six degree fall so no need for ridge caps and the barge boards are all treated timber plus he didn't need to cut any of the panels so a much easier job. William.

Hello James. There are ~five Travis Perkins depots within twelve miles of you that can deliver plastic-coated galvanised-steel low profile sheet roofing panels in two colours, grey or green, and three lengths, i’ve linked below to the shortest length they do in green. https://www.travisperkins.co.uk/Steel-Roof-Sheet-BS12B29-Juniper-Green-Plastic-Coated-Sheet-6ft-(1825mm)/p/766965 The only issue with TP is they don't stock and are unable to supply the matching ridge cap and barge board panels so you have to find a solution that works for you for the ridge cap, I don’t know why TP don’t supply these, we did email them several times but answer came there none! No wonder TP are always in some kind of financial mess. Things they don’t tell you in the technical specs: The panels expand and contract a large amount with temperature change and when the panels are nailed or screwed to the roof only the first fixing hole at the top of the sheet should be a tight fit on the shank of the fixing, all the holes below it should be drilled oversize, at least twice the diameter of the fixing shank, so that the panel can move as it heats up, otherwise the thin panel will warp and lift and never sit flat on the roof. If you have to cut the panels to length the cut ends should be painted with a flexible sealant, such as bitumen or a silicone rubber as even though the steel is galvanised before coating it will gradually rust inwards from the cut and delaminate, the cut ends should be hidden under the ridge cap or under overlapping sheets when used on long spans. When used on a battened roof you can’t walk across the panels, the TP ones are too thin and will crease, the panels used in commmercial builds are much thicker and stronger. The TP panels are ok to walk on when laid directly on a supporting board. The open ends of the corrugations at the eaves and at the ridge need closing with a mesh so that wasps can’t set up home in the corrugation voids but there is still some ventilation under the panels. The grey coloured panels are better at keeping cool, the green ones look good but get very hot, both are better than black rubber or felt though for helping keep the inside of the building cool, especially if you use mesh guards at the corrugation openings rather than foam inserts to maintain airflow. HTH William.

Even worse this morning Grant. Unable to load any page on iMac from home fast fibre, takes around four minutes to load on an iPad if Safari doesn’t give up and time out first. William

A European alternative to Precise Parts is TS in Germany, they offer a range of adaptors to your specification, Sonder65 to Sonder125 ~65 EUR to 125 EUR (Sonder in German = Special in English). https://www.teleskop-express.de/shop/index.php/cat/c123_Adapter-to-other-Threads.html Less expensive than the Precise Parts equivalent as there are no import duties though you would probably have to finish the TS adaptor by hand painting internally, the Precise Parts adaptors are both black anodised and painted internally with anti-reflective matt-black paint, the TS adaptors are only black anodised and therefore remain quite reflective to certain wavelengths of light. If you email a sketch drawing of the adaptor you want built, including thread diameters, length of thread and thread pitch to TS they will quote you a price.

Depends how much you are willing to pay and what length of focal path you have to play with Mark. The shortest length that I found possible uses 8.8mm of focal path and that would be a custom adaptor from Precise Parts in the USA. I have used them in the past and they are well made and fairly quick to ship, usually three to five weeks from order to delivery. A suitable custom adaptor would be ~$112, plus shipping, plus VAT, and plus duty when it lands in the UK. If you use their 'Build-an-Adaptor' service on their web site you will see a 3d representation of the part and it's cost. I don't know the make of OAG you have so in the 'Build-an-Adaptor' I used Skywatcher Esprit 120/150ED flattener for the M62 Female side and Hotech 2" M48 Field flattener for the male side to give the m48 male thread (obviously you wouldn't be connecting two flatteners together but this generates an adaptor with the right threads and minimum focal path). If you know the make and model of OAG you have you might find it is already listed in the Precise Parts 'Build-an-Adaptor" database, if not, there are many other possibilities to try that have 2" M48 threads. https://www.preciseparts.com/ppmain/adapter.html Otherwise, I think FLO have, or did have, an engineer that could make adaptors and other engineering parts to order. William.