Got out to the observatory early last night which was lucky as the clouds rolled in by 8:30 pm, after setting up I ran an auto focus run in MaxIm DL and got a full-width half-maximum measurement of 2.8 on the focus star, so it must have been better "seeing" than the previous night I guess, I then set about doing a new pointing model but this time I started on the eastern side of the sky, unfortunately every time the mount pointed towards the south eastern part of the sky the mount would become confused and want to point towards the ground, so I'm now thinking this it's not a mirror flop issue at all, it only seems to happen in this part of the sky, once it happens the mount will not point to anything accurately again until it has been homed again, which I know you can't home the mount while doing a t-point model as this will change the parameters, so this is an issue that will need to resolved if we ever plan on capturing a dense full sky pointing model, I'm really perplexed as to what could be causing this problem, it's the same problem that stopped my previous nights pointing model run after already capturing 56 sample points!
After attempting a pointing model on the eastern side a few times with the same result the clouds came rolling in and put an end to any further attempts, so I just re-loaded the previous nights pointing model and slewed the telescope around a bit with the dome slaved to see if I could refine the parameters so that the telescope would be pointing in the middle of the shutter every time as Steve had shown me how to do that, before I could make any adjustments though, the dome started to inexplicably stop stopping where the telescope was pointing, it would just continue around and around doing full rotations until aborted in the Lesve Dome control, so it was being a bad slave to say the very least! I homed the dome but then found the dome would no longer park either, so being a bit frustrated and having no idea how to fix the problem I just closed up up the observatory and headed home.
Clouded out with barely a star to point at, I headed home early ^
Got out to Kumeu Observatory a bit late last night but ended up working until 5:30 am so it was a pretty productive night, first thing I did after setting up was to loosen the shipping bolts in the C14 so I could move the primary mirror, once that was done I attempted to do an auto focus run in MaxIum DL but for some reason it would focus on a hot pixel and not the stars on the frame, so guessing that I needed to get it closer to focus manually I proceeded to focus the telescope as best I could, after getting the stars as focused as best I could I then selected a star and attempted another auto focus run but again it would just take loads of images and then fail due to too many exposures even though I had entered the parameters that Grant Christie had suggested, feeling a bit frustrated and thinking that the focus was probably good enough for a pointing model I switched the camera control over to the Sky X and attempted to do an automated calibration run, the newly slaved dome couldn't keep up with the randomized pointing model so I ended up manually moving the dome which worked fine, the problem I run into was that after 20 or so pointing samples it would stop astrometricaly solving the images, after a couple of attempts I noticed that the temperature compensating focuser was not tracking the changes in temperature and I knew this was a problem, so I figured I better try resolve the focusing issue before attempting another pointing model, after attempting a few more auto-focus runs I noticed that the focal ratio in the focus setup was in error so after entering the correct focal ratio I was overjoyed to see a lovely V curve and got my 1st auto focus successfully completed, I measured the full-width half-maximum of the focus star at 3.548 which isn't that bad considering we haven't collimated the telescope yet.
With the focus looking better than ever I proceeded to do another pointing model, this time I got the entire western side of the sky successfully with 53 sample points I then got through 3 sample points on the eastern side before running into trouble, I'm not sure why but it could be due to mirror flop seeing as the focuser was tracking the changes in temperature at this point, what would happen is that the mount would become confused and want to point to the ground and the only way to fix that problem was to re-home the mount, knowing that you really can't continue a pointing model after homing the mount I just finished and saved the pointing model at 56 points, hopefully if the sky is clear tonight I'll try another pointing model but start on the eastern side this time and see if I run into the same problem, it was getting late by the time I finished the 56 point model but I couldn't resist testing the pointing model, at 1st the model was saying we needed to make an adjustment in Altitude but after converting the model into a super model it was saying not to make any adjustments to the polar alignment at all, so this is looking hopeful and seeing as my test images at 200 seconds were showing only the slightest of drift I figure our polar alignment must be pretty good, so I slewed to a few objects and was happy to see each object on the frame although each object was a bit off to the right of center, probably due to the pointing model not being completed perfectly and without hardly any pointing samples on the eastern side of the sky, below are two images from my pointing tests, vignetting is worse than normal due to the gibbous Moon and the calibration still needs to be re-done, I was really happy to see the SBIG CCD get down to -19.5 though, so I think as we move into Winter we should have no problems getting down to -20.
M27 The Dumbbell Nebula was a pointing test low to the horizon ^
Lenticular galaxy IC 5122 was a pointing test high in the sky ^
Last night I headed out to Kumeu Observatory even though the sky was fairly cloudy, I figured there were enough gaps around so I couldn't resist testing out the repaired Paramount GT-1100s, I'm very happy to report that the slewing and tracking sounds very smooth now, in fact I've never heard it sound this good before! I did manage to take some images although I had trouble with the focus, predictably the focus was out after having the OTA off the mount, so I manually got the focus close again, I then attempted to do an auto focus with Maxim DL but it failed as it wanted to go past 7000 which is the maximum amount of steps the TCF can go to, I'm not sure why this was the case perhaps we don't have enough back focus or the primary mirror might need to have the shipping bolts loosened.
Seeing more dense clouds coming in I decided to make use of the sucker holes while they were still there and took some exposures testing the tracking in different areas of the sky, I'd say the results were very promising with the tracking being even better than before the repair, I took 100 sec and 200 second exposures without any noticeable movement in the stars, although I didn't get to test all parts of the sky due to the clouds so I may have just been in "sweet" spots, we could never get 200 second exposures without star drift before the repair so this is all looking very hopeful, once we get the auto guider working we should be able to get up to 500 seconds without too much issue.
I've included some images from last night but note that after the failed auto focus runs I just manually got the focus back to being close so it definitely wasn't anywhere near perfect focus, also there was significant vignetting due to the gibbous Moon being up and the image calibration doesn't really work anymore due to the camera being taken off the OTA during repairs so no doubt we will need to re-do all our calibration files again, one thing I did notice was that the SBIG-ST10 CCD was still unable to reach -20, it did seem like a hot night but it's a bit of a concern that it still can't get down to -20 at this stage of the year.
Finally after a brief break due to the mount needing repairs Kumeu Observatory is back in action, thanks to help and advice from Graham Beazley, Grant Christie, Marc Bos and Tim Natusch. Steve Hennerley was able to reinstall the repaired declination worm assembly successfully with assistance from Jonathan Green on Saturday the 9th of April, then last Friday night Jonathan Green and Steve Hennerley put the "Nustrini" Celestron 14' SCT back on the mount, with the S-BIG CCD camera re-attached and after spending a fair bit of time getting the balance correct they are confident that the setup is ready for action again, so bring on those clear skies!
The newly repaired and re- installed declination worm assembly ^
Steve Hennerley adds the finishing touches to the Paramount GT-1100S ^
On the Friday night we also used a Howie Glatter laser collimator which fires concentric laser circles to do a preliminary test of the "Nustrini" Celestron 14' SCT's collimation, we were happy to note that the C14 isn't too far out of collimation, so hopefully it will only need some slight tweaking to get the telescope back into perfect collimation. ^
So after a careful examination of the dec drive assembly from the paramount, Auckland Astronomical Society's engineering wiz, Graham Beazley removed the bearings from the assembly, and after a quick trip to Saeco had new bearings for just $17+GST.
Graham reassembled and adjusted the tension and it looks like the assembly is now back in business.
Hopefully we'll get this reinstalled in the mount in the next few days and will then be ready to get the system backup and running again !
Sorry for the lack of updates... the "unhealthy noise" reported by Jonathan has been the main focus of the observatory for the last few weeks...
Shortly after Jonathan's last post, I headed out there with him to listen to the noise (which I hadn't heard until then) and see if I could work anything out. It didn't take too long before it became pretty obvious that something wasn't right.. .
We managed to narrow down the "noise" - which was really more like a "clunk" sound - to the declination axis - it only seemed to happen when the scope was slewing in dec. The clink noise didn't really seem to happen at the same point in the slew (which I theorised might indicate an issue with the ring gear), nor did it seem periodic enough to happen on every turn of the worm.
What was slightly worrying though is that the OTA was being visibly deflected every time there was a clunk, and you could certainly "feel" the roughness in the motion by putting a light touch on the OTA when it was moving. As you might imagine, we didn't so this for long. My thoughts were firmly that this was a more "mechanical" issue, than any variation in the sound of the slewing caused by software/pointing model adjustments.
I really wanted to isolate there being a gear meshing issue, so I disengaged the dec worm assembly from the gear (the same process used when balancing the OTA) and commanded the mount to slew in declination again. I recorded a video of this (not for the visuals so much as to record the sound of the issue to demonstrate to the AAS/Stardome team - so please forgive the iphone camera work!)
This was both a good and a bad result.... the good news being that it couldn't be any problem with the worm or gear as the noise still happened when these were disengaged - the bad news being that it was now even more obvious that we have a mechanical problem to solve.
The old "mechanics stethoscope' trick (using a screwdriver handle held to the ear and the "blade" touched to various parts of the mechanism) seemed to narrow down the source of the clunking sound to be the region of the dec drive assembly close to the pulley on the end of the worm shaft. This led to a working theory of a possible bearing issue.
We didn't proceed with any more troubleshooting that night but did seek help and advice from both Grant Christie and Marc Bos (Stardome Curator of Instruments), and also to assess what options we might start looking into to find parts and repair if it does end up being a failed bearing.
Another visit to Kumeu with Marc seemed to lead towards a general agreement that possibly a bearing may be the issue - but confirmation would require removal of the assembly for closer examination to narrow down exactly what the cause might be, also eliminating other possibilities such as the servo motor. Permission was to be sought from Stardome (who own the mount on loan to Kumeu) for this investigative work to proceed.
After agreement that the dec assembly really should be removed and examined with the aim of repair (either locally, or by sending back to the manufacturer) - Jonathan and I again headed up to Kumeu to remove the OTA from the mount again and remove the offending assembly as previously discussed with Marc.
The paramount worm shaft -there is a bearing at each end
at least one of which seems to be causing the problems
It didn't take too long to carefully remove the dec assembly from the mount. Once on the desk, loosening and removing the belts (well one of them - the other had already had to be removed with the motor to remove screws bolting the assembly to the mount) - it became obvious that whilst the motor and pulley shafts were both very smooth to move - the worm shaft was anything but... The rotation of the worm shaft was very rough, even "binding" occasionally - certainly not the feel that precision rotating parts should have.
Next steps will be to have Marc, and our other engineering experts take a look and see if we think this is something that we can have repaired and set up locally, or whether we package it up and send it off to the US.
In other news - you might recall a few blog posts back that I had been having trouble getting a response from the dome rotation "azimuth" sensor. Well, whilst the scope has been out of action, we took the opportunity to get electronics wizard, and dome rotation expert Tony Burns out to the site to have a look and give us his valued opinion. We ended up removing the sensor and the board and he took it away to check.
Turns out there were a few problems with the system - so it was a good thing we did. Firstly there was actually a problem with the USB board itself - at some point in history a short circuit or similar had caused some damage on the board (lifting some of the copper "track"). Also - and probably unrelated - there was an issue with at least one of the input channels that needed investigation.
Tony replaced the control ICs on the board and repaired the broken track - effectively returning the interface board to "good as new" condition.
The Azimuth sensor however was not quite a simple. The postion of the sensor (as I've mentioned before) is very close to the dome slot in the open position. This means that there's a very good chance that any moisture may find its way into that area (as the dome is opened, or closed, usually in that position). Add to this Auckland's very humid climate - and there is a very good chance that corrosion might at some point give some trouble.
Looks like the connections to the photosensor and IR LEDs has corroded away - meaning there was no chance of this working!. Tony has fabricated a new set of optoelectronics for the encoder wheel using much more robust connections that will hopefully last many years to come.
All that remains is for this all to be reinstalled and tested - and hopefully the "break" we've just been forced to have will give us the opportunity to do this over the next few weeks.
Phew... that was a big post - and that'll teach me for waiting so long between updates. I will post more when we know what is happening with our dec assembly and hopefully when we will be back up and running....
I went out to Kumeu last night determined to figure out the T - Point automated calibration run, I was setting up when I was pleasantly surprised to see Allister had turned up to set up his giant binocular Dobsonian for some observational fun, there was a few clouds about but there were also plenty of big gaps so after getting the C14 focused, I started an automated calibration run, this time I just paused the run after each image was taken of the first six sample points that were all in the start region, I then right clicked the images and astrometrically solved them via the image link feature of the Sky X, this seemed to do the trick, as every sample point after these six would automatically solve and add the sample points, needless to say I was elated to have finally got the automated process working, I then proceeded to capture 61 sample points covering one half of the sky, Grant Christie had advised me to do half the sky at a time to avoid mirror flop issues, so once this was done I then proceeded to capture sample points on the eastern side of the sky, unfortunately the first row of points was below the level of the dome so I just skipped these points, I had captured about 17 points on the eastern side when clouds put a stop to any further efforts, so I took a break and went outside to hang out with Allister who by this point was packing up his equipment, by the time Allister left the sky had cleared up again so I continued the automated calibration run but after just a few sample points the slewing of the telescope started making the same unhealthy noise that I had reported after doing my manual pointing model, knowing that the solution to this problem was clearing the pointing model and being happy that I could now easily do a new automated pointing model, I deleted the pointing model that I had spent all night capturing, I then re-homed the telescope and turned off the Paramount thinking that this would solve the problem but when I restarted the mount and gave it a test slew it was still making the same unhealthy noise, so again I re-homed the telescope turned off the mount and this time turned the Sky X off, I then took a good half an hour break before restarting the Sky X and the Paramount but again the mount was making the same unhealthy slewing noise, I'm starting to think the problem may not have had anything to do with the pointing model after all because this was happening with no pointing model at all, not wanting to cause any damage to the Paramount I just re-homed the mount and turned it off, the next clear night I will head out and try the automated calibration run again but if the mount is still making the unhealthy slewing noise I will have to just wait until someone can come out and take a look at it as I have no idea why it would still be making this unhealthy noise when there is no pointing model, heading home I was elated that I had finally figured out how to do the T -Point automated calibration run but this feeling was tempered by the concern I have for the unhealthy slewing noise the mount was making, hopefully it's nothing too serious.
^ T - Point sample plot screen shot.
^ Allister's giant binocular Dobsonian ( built by David Moorhouse )
We had a clear night out at Kumeu last night, so I went out there with the plan of doing the automated T- point calibration, after taking a few images manually with the Sky X and astrometrically solving the images via the image link feature, I started an automated calibration run, I quickly became frustrated though as none of the automated images would solve, I found this to be inexplicable as I could pause the calibration run, right click on an image that was captured via the automated calibration run and open it up in the image link feature and successfully solve the same image that failed to solve during the calibration run, it wasn't like it was taking a long time to solve the image either, so after trying this more than a few times, I then decided I would just slew to each mapping point of the calibration run, take an image and manually solve each image, this would work up to at most 11 sample points but then after that I couldn't solve anymore images, it was like the image link would just start to fail to recognise the stars anymore even though to my eye the images looked the same from start to finish, I remember Grant Christie telling me that you could run into problems if the temperature compensating focuser (TCF) wasn't correctly tracking the temperature, I was controlling the TCF using Maxim DL as the Sky X still can't connect to the TCF since we had the power cut that I reported a few weeks back, so this might be the issue, although I'm really unsure about it, I did have the temperature tracking turned on in Maxim DL and I was watching the TCF and I could see it was making adjustments over the night so I really am quite perplexed, after attempting different exposure lengths and different binning modes without any luck, I really felt at a loss to why the images captured during the automated calibration run wouldn't astrometrically solve, maybe I need to adjust the detection threshold in the image link or something? I kept at it until 4 am in the morning becoming even more frustrated as the hours went by, clouds rolled in around 4 am putting an end to my efforts so I closed down the dome and called it a night heading home in frustration, I think I'm going to need some help with this as I re-read the T-Point manual today and could find nothing that would help me resolve the problem, hopefully once we get the TCF working with the Sky X again this will help although I'm still at a loss to explain why none of the automated calibration images would astrometrically solve.
I rang Grant Christie today to let him know about the unhealthy noise the mount has been making when slewing, he let me know that the problem was probably due to me having to home the scope during the T - Point calibration run, apparently doing so changes two of the parameters of the pointing model and can cause problems, so I went out to Kumeu tonight to clear the pointing model to see if this would fix the slewing problem and I'm very happy to report that the slewing of the mount is now back to sounding healthy again, I also finally figured out how to connect the CCD to the Sky X, the reason I was getting error messages was that you can't have the camera connected to Maxim DL and the Sky X at the same time, up until now the first thing I used to do when I arrived at the observatory was to connect the camera to Maxim DL so I can turn on the camera's coolers as it takes a while for the camera to cool down, I know now this was the reason why I was getting no response from the camera when attempting to connect to it through the Sky X, I'm feeling a little bit sheepish that it took me so long to figure this out but I guess it's all part of the learning process to have a bit of trial and error.
Unfortunately the sky was pretty cloudy out at Kumeu tonight, I did take a few images using the Sky X to control the CCD but I failed to astrometrically solve the images, this was probably due to the images being affected by clouds, hopefully the next time it's clear I will be able to do a new pointing model using an automated calibration run, I plan to take two to three hundred samples of the sky so we will end up with a very robust pointing model, I stayed out at Kumeu until 10:30 but the sky seemed to be getting worse and with the internet not working ( another problem that needs to be addressed soon ) I had no way to know if it was worth waiting around to see if it would clear up, so heading home a bit frustrated that I couldn't get more done tonight I had to console myself that at least when the next opportunity presents itself the telescope and mount are ready for action again.
On Friday night I spent the entire night working on making a new pointing model, I scrapped the last one after reading the T - Point user manual and finding out that it was not advisable to take samples down near the horizon due to atmospheric refraction that causes offsets between the actual position of an object and it's observed position, I started collecting samples around 9:30 and only stopped collecting samples early in the morning due to the mount making an inexplicably unhealthy noise when it was slewing, I couldn't see any obvious reason why the mount was suddenly making the noise ( sounds like a rattle with clicking or cracking type noises ) so I just put the mount back in the home position and called it a night, by the time this had happened I had collected 82 sample points, the new model showed that we are only off by 2 arc-minutes in azimuth while the altitude was still excellent and we don't need any more adjustments in that area.
After attending the Auckland Astronomical Society council meeting at Andrew's house on Saturday, I thought I'd head out to Kumeu and see if the Slewing was still making that same noise and to also test the new pointing model, The first ten or so slews sounded healthy but then again inexplicably the unhealthy noise started up again, so again I just put the mount back into the home position and called it a night, I've talked to Steve about the problem and he is at a loss to explain it as well so we might need Grant Christie or Tim Natusch to come out and take a look at it, hopefully it's nothing too serious, before this happened I was quite happy with the accuracy of the new pointing model, objects were always just a few arc-seconds from the center of the frame although I didn't get a chance to slew all over the sky so some areas may be worse than others, I still had the same problem with the mount in the area of sky to the South East that I had the first time I attempted a pointing model so I couldn't take samples around Centaurus, Crux or Carina, below is an example image of the Galaxy NGC 1532, the image was a 100 sec long exposure and I was quite happy with how close the galaxy was to the center of the frame, the image exhibits some pretty bad vignetting but I think this was due to the Moon being almost full and very bright.
Last night the waxing gibbous Moon was up and more than a few clouds were about as well but seeing that there were plenty of large gaps in the clouds I thought it would be a perfect night to get the new pointing model done using T - Point, when I arrived at the observatory I noticed that the computer was off and the temperature compensating focuser was flashing, I'm guessing that there was a power cut during the storm we had earlier on in the week, I booted up the computer and connected to both the telescope and camera without issue but when I tried to connect to the focuser it would not connect and came back with an error message from both Maxim DL and the Sky X, after ringing steve for help I switched the focuser back to manual mode and manually set the focuser back to the last known good focus, this worked well enough for me to be able to do the pointing model, the next issue was aligning the finder scope again which must have been knocked fairly far out of alignment at some point, this took me a while to get right but once I was happy that the finder scope and the field of view of the CCD were aligned again I got started on the pointing model, at first I had wanted to do an automatic calibration run but unfortunately the Sky X would not connect to the camera and I got error messages, I also noticed that it will be quite hard to keep up with an automated calibration due to the dome being fairly slow, not wanting to waste a good opportunity to get a pointing model done, I set about doing a manual pointing model using stars that I knew and that I could confirm through the finder scope, by the time the clouds really rolled in at 2:30 am, I had captured 57 samples, one problem I noticed when I was capturing the samples was that I couldn't take any samples from around Carina and Crux any attempt to jog the telescope in this area of the sky caused the mount to become confused and try to point the telescope at the floor, each time this happened I had to re-home the telescope before it would accurately point and track again.
The new pointing model confirmed that the altitude of the mount is correct but that the azimuth still needed to be adjusted ( by about 3 arc minutes ), I then enabled the Pro Track so that the new pointing model can make minor adjustments to improve the sidereal tracking rate of the Paramount GT - 1100S, at this stage the clouds had become so thick that trying to test the new pointing model's accuracy was pointless, so at 3:30 am I closed up the dome and called it a night, I'm looking forward to the next clear night when we can test out the adjusted tracking rate and also the accuracy of the new pointing model.
Last week we had a one good clear night and few nights with sporadic clouds, Thuesday night was the one clear night and on that night I took images of two pairs of galaxies that are in the catalog of interacting galaxies of Dr. Halton C Arp, one pair was NGC 1253 & NGC 1253A, collectively known as ARP 279 they are located in the constellation Eridanus and are thought to be lie around 75 million light years away, the other pair is NGC 1888 & NGC 1889 which are collectively known as Arp 123, they can be found in the constellation Lepus, after doing some research I've found that NGC 1888 is thought to lie 33.5 megaparsecs away which is over 109 million light years! for now this is the most distant object I have ever imaged, I'm looking forward to breaking that record soon hopefully, the image below is of Arp 123, image data was captured by Jonathan Green and then processed by Amit Kamble.
On the Thursday I also collected more image data on Arp 279 but not long after the Moon set clouds started to roll in, there were still gaps in the clouds so I attempted to image a couple of comets, I imaged both 81P/Wild and 203P/Linear but finding them took some effort, I realised after finding the 1st comet that our pointing model was off by about 13 arc minutes, this was due to our refinement of the polar alignment on a previous night.
On the Friday night the sky looked nice and clear and the satellite image data also looked promising so I rang Steve to see if he was free to head out to Kumeu to work on the Polar alignment and to create a new pointing model with T-Point, we also had a couple of Auckland Astronomical Society members show up with their Dobsonian telescopes looking to take advantage of the clear skies, unfortunately the clear skies did not last long so the nights observing was a bit of a bust, fortunately we could still detect stars through the cloud so we ended up spending the night until 2 am in the morning refining the polar alignment again, now all we need is some clear skies to do a new pointing model.
