Thursday, April 28, 2016

Pointing Model Issues in the South East & Dome Slave Issues

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 ^

Posted by Jonathan Green

Wednesday, April 27, 2016

Auto Focus Issues Resolved and New Pointing Model

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 ^

Posted by Jonathan Green

Wednesday, April 20, 2016

Initial Tracking and Slewing Tests

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.

100 second exposure tracking test ^

200 second exposure tracking test ^

Posted by Jonathan Green

Sunday, April 17, 2016

Back In Action

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. ^

Posted by Jonathan Green

Wednesday, April 6, 2016

New Bearings!

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 !


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