PaulE54

I use an RC, with the CCDT67 reducer and an ASI294MC Pro. Focal length is 1004mm with the reducer. I have upgraded to a Baader Diamond Steeltrack focuser with a home made stepper motor focuser kit. I autofocus using APT and this works well. I mount the guide scope (280mm ZWO scope with an ASI290mini guide cam) on the top rail of the main scope. This way I don't get any balance issues. The 290 guidecam has smaller pixels than the 294 main cam, so pixel ratio is around 2.5:1, which works well. I've avoided OAGs because I have enough tech to struggle with already! Total weight is around 9kg. I mount the main and guide scopes on a CEM40, and on nights of low wind this combination will guide at below 0.5arcsec RMS for extended periods. I have no experience of the HEM27 but would expect it to work equally well. Clear skies Paul

I'd be wary of tilting tripod legs since it may bring the Centre of Gravity of the whole assembly worryingly close to tipping over. Keep the tripod level, keep the CoG of the whole assembly central within the area of the tripod legs, and tilt the mount attachment to the tripod using shims as described above. Safer! Paul

Hi Herman. Sorry not checked the forums for a few days. I've been having similar but intermittent problems with my CEM40 and PHD2. In my case it looks like it was an intermittent problem with the USB cable to the mount. So PHD2 was sending lots of corrections to the mount but none of them were being received and the mount was getting more and more off target. Hopefully an easy fix. We're not going to learn a lot from the logs of the combination that was working. I don't I'm afraid know much about the guiding software in ASIAIR - I think it may be a variant of PHD2? A quick google re location of guide log files for ASIAIR says "look in the usb drive under log folder, use the phd2 log viewer to examine the log file." From what you say it sounds like the mount may not be responding to guiding? Paul

OK here are a few questions to try to get a clearer view. Did you try the EQ80 / lodestar with ASIAIR? If not what guiding software and hardware did you use when things were "working well"? It would be useful to see some sample guide graphs so we can see exactly what kind of "disastrous" we're talking about. Does the guiding software in ASIAIR produces logs like PHD2 does? If so the logs may give clues. Good luck Paul

Just to add my support to David's suggestions, I collimated my RC6 using the plastic disc method, very happy with the results. I did final tweaks using real stars and metaguide, which is very easy to use if your camera is one of the ones that works with metaguide (my ZWOs do, you just need the video driver). Paul

Nice capture Francis. How are you finding the NB1? Paul

I use APT on a windows 10/64 machine to talk to my CEM40 and never had a problem. Central to the software stack is the iOptron commander software, which you need to install. This makes the mount appear as an ASCOM mount to APT, CdC, PHD2 and anything else that needs to talk to the mount. In terms of hardware, I use a single USB3 active cable from the Windows machine inside the house, out to the mount via a powered USB3 hub next to the mount. The USB3 hub takes leads from the camera, the mount and the iPolar. The USB cable to talk to the mount plugs into the socket labelled USB on the side of the mount opposite to the on/off switch, next to the socket marked iPort. Page 8 of the manual. The other socket marked USB (on the end of the mount, underneath the iPolar socket) does NOT control the mount - that links to whatever you have plugged into the USB socket on the saddle. Hope this helps but shout if you need more. Paul E

Well I said I'd report back. This is a CCD Inspector plot for my RC6 - I've just collimated with David's method, I've not done anything else yet. FWHMs are a bit high, but I think that's just focus being a bit off. Basically these figures are better than it was before I took it apart to clean the primary. I have an artificial star, so I'm going to check mirror spacing tomorrow, and then recollimate if it needs adjustment. Many thanks to David (and Nicholas) for your advice, really pleased with progress so far. Paul

Thanks David, that's very helpful. Photographing the primary collimation (as you did in your PDF doc) is useful, - I found choice of lens to be critical. With my cropped sensor DSLR, my weapon of choice was a 100mm f2.8 macro at 3 feet distance and F25 for sufficient depth of field. Tripod mandatory of course. I'm waiting for clear skies to do a star test, so I'll report back in a few months... Paul

Hi Nicolàs Many thanks for this prompt reply. I had seen reference to your article but had not switched on google translate to read it. I'm going to to do that now! Best wishes Paul

Apologies for resurrecting an old thread – but it is an extremely useful thread - many thanks to David for his detailed explanations of his method. I’ve downloaded and am working through the PDF. I have a 6 inch RC. I bought it used, it was well collimated by the previous owner and held collimation well. However after 3 years heavy use, the primary had been getting more and more dusty to the point where I eventually had to clean it. Turned out to be sticky pollen – water and detergent wouldn’t get it all off, eventually needed pure IPA. Nice and clean now, no scratches. I measure collimation using Metaguide and CCD Inspector. I took some metrics before starting so I have a baseline. When I reassembled the scope after cleaning I checked collimation before touching anything and it was well out. 1st iteration of the disc method and it halved all the errors, but I still have double the error before I touched it, so more work to do. Haven’t done a star test yet – just measuring star fields with CCDI. I have a few problems – 1. I’ve checked the native FL by plate solving and it is 1366mm, spec 1370. However I want to check mirror spacing using a Ronchi eyepiece, which I have. Can someone (David if you see this?) please confirm the meaning of barrel distortion inside focus? David’s post of 12/06/20 on this thread says “A barrel-shaped Ronchi pattern inside focus = overcorrected scope, too short focal length, mirrors too far apart.” On this old Cloudy Nights thread https://www.cloudynights.com/topic/423163-precise-rc-mirror-spacing/ post 24 says “a barrel pattern inside focus means mirrors too close together”. I’m now officially confused. Doesn’t take much….:-) 2. Because the gaps between the spider vanes of the RC6 are so narrow, I can’t get my hands in to reach the primary baffle tube or hold the secondary when I loosen the centre screw. This means that to use the “hole in disc” method I have to take the complete secondary end cap off the scope after I have collimated it, thus disturbing the fine adjustments I have just made. David, again if you read this - you mention calibrating RC6s using your method. How did you get round this? 3. Finally, once I have collimated the scope using the hole in disc method, I need to star test it. Once I attach extension tubes, a focuser and an eyepiece or camera, I am at risk of the scope optical axis being misaligned with the focuser / camera / eyepiece axis, so is there a risk of chasing my tail here, how do I mitigate that? I have a Cheshire if it helps. Any and all suggestions gratefully received…. Paul

That's really astonishingly good. Looking forward to seeing more from this setup. Paul E

Well you learn something every day...i never knew PHD2 log viewer could do that. 🙂 If it helps, I've just done the frequency analysis for one of my guide logs and mine is worse than yours! I've got a 200sec peak of 1 arcsec, a 400sec peak of 1.7 arcsec, and a 600sec peak of 2 arcsec. However if you expand the X axis at the bottom of the plot, each peak is many 10s of seconds wide, with quite a gentle rise and fall, so I think guiding is just sorting them out. Hope this helps - clear skies! Paul

One thought - you do have the scope and counterweights fitted, and the mount in balance in RA and Dec, don't you? A badly unbalanced mount might do that...otherwise, I'd be phoning the dealer. Hope you get it sorted. Paul

The magnitude of the 200sec and 400sec spikes you are getting is tiny compared to the magnitude of your dithers. When I look at your log in PHD log viewer I can't see the spikes as they're dwarfed by the dither spikes. What software are you using to produce the first graph? If it's something free I'll process some of my old guide logs from my CEM40 through it, to see if I have similar spikes. I believe 400 secs is the RA worm period for the CEM40. Overall your guide RMS as reported by PHD log viewer (which ignores the dither moves) looks about the same as I would get on an average night. I do see overall guide RMS of around 0.5RMS from my CEM40 with a 9kg load on (rare) nights of good seeing. I think in typical UK suburban locations you'll find the skies not the mount are the limiting factor. Cheers Paul