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As a new CEM70 (not G) owner and my first proper mount I can say I'm very happy with it so far. I've imaged successfully unguided upto 3 min subs at 600mm focal length and had guiding working for the first time on Xmas Eve which was succesful. Polar alignment is quick and accurate with iPolar, the only issue I have is one of the altitude clamps (see pic) is too stiff to tighten to lock, any tips on loosening this are welcome. 20201224_153708 (1).jpg Clear skies |
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If I recall there's just a nut on the back side. You might back it all the way out, and back in? A drop of grease in the nut? Or is something not aligned? Those need to tighten smoothly as they hold the whole assembly down. If they are loose it rocks back and forth. |
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Linwood Ferguson: Thanks Linwood, You're absolutely right, there is just a nut on the inside so I'll try backing it out and greasing it, hopefully it's not cross threaded. Thanks and clear skies. |
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Hello, i've been using my new CEM70g mount for the last two weeks. This is a big improvement from my old Celestron AVX mount. It also requires to learn some new things (like using the iPolar software) o realearning others (like the way to do a proper balance). At the very start, i had guiding issues caused by a loose RA gear, but i corrected most of it by adjusting the gear mesh, following the procedure described in the manual. The iGuider camera works fine, but for some reason, PHD does not save the parameters of the camera (brightness, gain, exposure, etc), so i have to configure them at the start of every session. Also, I've also having some connection issues (my mount loses connection with SGP about two hours after starting the sequence) but i hope the next version of the iOptron Commander can fix that. Besides that, i am happy with my mount, because the guiding is much more precise than my old AVX, and i hope to resolve all this little problems in the near future. Regards, Diego. |
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Diego Cartes: I’m currently using an AVX (rebuilt/tuned), but have been looking into upgrading to the CEM70G to carry my ES N208CF (23lbs, 0.94 arcsec/px). My concern with this mount though are reports of high-frequency oscillation in the RA, most noticeable as star elongation with long exposure at longer focal lengths, or when planetary imaging. Wondering what focal length you’re using, and what the payload weight and dimensions are. Thanks, Nikko |
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My payload is 26 pounds. 115mm Orion Eon. Focal length is 805mm. Pixel scale is 1.54". Below is my guide graph from tonight. Guiding with a 240mm focal length guider (60mm helical guide scope from Orion) |
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Nikkolai Davenport:Diego Cartes: Wow, that's a very interesting thread. I'll post my experience as soon as i catch up with all 34 pages of posts...  I didn't know about this issue. I am also having some elongated stars in my 900s frames, but i thought they were caused by unbalance or errors in alignment. I'm using a Televue TV76 with focal reducer, and that's about 380mm f/5.0. I believe the payload is about 4 kg/9 lbs, and the dimensions of the tube with the camera and focuser are 60cms x 10 cms. (23,6 x 3,9 inches). Attached are some images of my telescope/mount configuration, my guiding log and some 900s subs taken using a SII filter of the Rosette Nebula. They are higly magnified and all show some elongation in the stars.     |
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I am one trying to resolve RA vibration.Diego Cartes: What I and most others I have corresponded with are seeing a very small, relatively fast (a bit over once a second) vibration. If you have them you can see the elongation in 1s exposures and 900s equally. Even moreso, significant bloom from long exposure will hide it, i.e. in long exposures my large stars may be round while medium and dim are oval. If you are seeing elongation only in longer exposures you must likely have guiding errors instead (or some other issue). My vibrations are in the 1" range. This also means you cannot see them at shorter focal length, or at least they are unnoticeable if not unmeasurable (they start falling under a pixel). The earliest reports I saw were from people with barlows doing video of planetary objects, where the frame rate was high enough to see the motion. Yes, before some object, this is under seeing -- but a consistent motion gets added statistically and is visible despite random motion that is larger. Some suggested approaches: - Do a 20s or so exposure with tracking off to get a sample showing clearly the RA axis in the camera, save it - Expose a series of shots, like 1s, 2s, 10s, 100s and look for oval shapes - Rotate the camera 30 degrees, and repeat (including the star trails) - Do this through 90 degrees at least Now go through these, with blink or something. The star trails provide a good visual clue. The vibration issue will show as a consistent angle, aligned with the star trails in each one regardless of camera orientation, and be able the same amount of oval-ness regardless of exposure in non-blooming stars. One good way to analyze the images is with pixinsight's Dynamic PSF routine. Take repeated images (short and long exposures) and select a dozen or so of the same stars in each; compare theta (angle of the oval) and FWHMx and FWHMy differences (amount of the oval in pixel) averages. Vibration will have similar differences regardless of exposure and similar angles, and the angles will be aligned with the RA axis. Same idea as above visually but more quantitative. One other thing to try that's giving me issues that mask this: Do all the above with, and without the cooler fan on for your camera. I found fan vibration was giving me a similar scale vibration but at a different angle. These added to the RA vibration statistically but at different angles to make the result more messy (e.g. often not aligned with RA) and made this look more like seeing than a consistent direction vibration. At least on my ASI camera (ASI6200MM) if you turn off the cooler the fan turns off. Another way to see this vibration is in Metaguide -- pretend you are planning to use it for collimation and get all set up with a good star, and turn it on and off (you can do it from within metaguide). Watch the star shape. Mine goes from nice and round to a messy, shape changing oval. At long focal lengths (or more precisely pixel scales of fractional arc seconds per pixel, which many people avoid as over-sampling). |
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Linwood Ferguson: Thank you! I think if the vibration is in the 1'' range, then you're right and i will probably not be able to see it, as is inferior to the resolution of my imaging rig (2.03 arcsecs/pixel). Still, i will run these tests as soon as possible. Diego. |
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Diego Cartes: Also, does your mount "tick" a bit faster than once a second? If you lightly lay a hand on it, do you feel the ticks? I just think that whole "tick" is wrong, and the cause of these; they may be more or less strong on different instances of the mount, but so far everyone hears the "tick". |
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Linwood Ferguson:Diego Cartes: Are you referring to this sound? The one that sounds like a metronome? I recorded it a couple days ago with my phone. I still don't know what causes it. Tick sound |
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Diego Cartes: That's it. If you lightly put your hand on some places on the mount while it happens you can feel it. If you can feel it, it's moving the mount. It is not the guiding per se, since that's much faster, though it's been speculated that guiding is microsteps (between actual stops on the stepper) and that these are actual steps on the stepper motor. But regardless, anything that you can feel moving the mount like that is not a good thing for smooth tracking. |
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2 months in I now have a problem with mine. It is no longer tracking properly. One night it ran flawless and I got my most recent image, the next night same setup I go out to get more data it no longer tracks proper and because of that it can't guide. I spent 2 nights and about 11 hours disassembling and reassembling every single component using different computers new firmware etc. My RA is constantly driving but it seems to be too much because the stars run off the image in a few minutes of sitting there watching it live. Moves faster than guide can correct and you hear a battle of wills back and forth. This had nothing to do with guide rate as tracking rate is dictated by the SIDEREAL which is the mode it is in. I will be sending this mount back to iOptron but will probably sell it and never buy another iOptron @Matt Proulx we are on the same boat, all we hear about this mount is 'la vie en rose', but a few are struggling with not a single reply from iOptron support. Those with long FL will notice the most and things are a mess on my RC8. CEM70 has been making me pull my hair since the day I bought it. One night it functions properly with 0.6 RMS, followed by 20 nights of 1.5 RMS (even with the same settings). This glimpse of hope has been keeping me outside in the cold wasting clear nights, just testing and fiddling with settings. I adjusted spacing, tightened belts, 3D balanced, PPEC, PEC, guiding rates. Later to notice that the major issue comes from the RA. It just doesn't track well anymore, guiding assistant shows a much different periodic error than before: instead of one period spread across 348s, it is now split into several periods of 50s (give or take), seems like RA is not moving constantly but rather fast and slow rates within each sub-period. Those periods are almost random and impossible to correct with any type PEC. It's obvious that this mount is robust with a great potential, and while we probably got bad copies, I wish support can answer and provides solution at least. Attached are two Phd2 Guiding assistant graphs, separated by 2 months, respectively with 100 and 400 views (guiding with disabled corrections).   |
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Linwood Ferguson:Diego Cartes: Mine ticks 90% of the time while tracking, tracking is better when it doesn't tick, and that's only times when guiding goes down to 0.6rms (of course, that's according to experience until now) |
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| You can do it through PHD2, if I recall, but it's a separate setting that has to be coordinated. I no longer have my CEM70G so thats an old memory, hopefully someone can clarify if I have it wrong. |
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Maroun Habib:2 months in I now have a problem with mine. It is no longer tracking properly. One night it ran flawless and I got my most recent image, the next night same setup I go out to get more data it no longer tracks proper and because of that it can't guide. I spent 2 nights and about 11 hours disassembling and reassembling every single component using different computers new firmware etc. My RA is constantly driving but it seems to be too much because the stars run off the image in a few minutes of sitting there watching it live. Moves faster than guide can correct and you hear a battle of wills back and forth. This had nothing to do with guide rate as tracking rate is dictated by the SIDEREAL which is the mode it is in. I will be sending this mount back to iOptron but will probably sell it and never buy another iOptron I have my mount working flawless now, I had a few problems. One, the wifi card wasn’t fully seated and was sending a signal but was not able to connect, I am sure this was causing problems somewhere. Another problem is that, when not having the hand controller plugged in the date and time would always revert to default and even when I did update it the built in ipolar would put me in the wrong place. This made me unable to plate solve and my tracking was very bad. But even to this day when I use ipolar it is many degrees off from where sharpcap puts me so I just use sharpcap now. I guide on average between .34” and .5” |
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| I guide around 0.9" and it's irregular. I've since switched to OAG and that's helped a lot, but overall still get some bigger swings. My stars look pretty crisp, so I chalk it up to wind and bad seeing, but wondering if I should be raising my expectations... |
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I have found my CEM70G (Using the iguider) to respond best to some unconventional looking RA guide settings. I am running hysteresis algo, 115% aggression and about 5% hysteresis and using 0.5 second guide exposures, guide rate on the mount set to 0.9 X. It needs a little care to ensure the min move amounts keep it from chasing the seeing but prior to using those settings it would slowly oscillate in RA all night. I am typically seeing around 0.7 to 0.8" total RMS using those settings, before it was more like 1.0 to 1.2" total RMS and the RA was the culprit, it would typically be nearly double the Dec RMS error. I still have a few niggles, I connect via the commander software and don't even plug in the hand controller (Though these issues happened with it plugged in too) but I often find my time offset has changed to 480 minutes not the 600 it should be, and every time that resets to 480 minutes the angle past the meridian before it stops the mount has changed back to 0 degrees my park setting has been lost and the guide rate goes back to the 0.5 X default. The time setting is not too great an issue (Though it it was operated properly remotely it would be) and the park setting being lost is just an inconvenience (It defaults to what in the southern hemisphere is a stupid, but safe position, so long as the home position has not been lost) but the tracking limit going back to 0 degrees instead of tracking through the meridian would cause me an issue. The imaging software I use images through the meridian before flipping, so the mount needs to track at least far enough past the meridian to accommodate the longest sub length plus a bit of fat. Voyager would probably recover and keep going, but it would be annoying to loose a good 900 second sub at the 850 second mark because the target passed the meridian! My only other real gripe is I wish they used a different camera in the iguider, one that PHD2 can directly control the gain and exposure time on and that retains settings through a power cycle. Focusing the guider was a bit of a pain, but I have only needed to do that once. |
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115% agression and 5% hysterisis basically is all reactive, at 0.5s intervals and fast guide rate. That's almost like a slow metaguide.  I never got an answer from anyone, but my mount shipped (at least to me) with a 0.9x guide rate on both axes. I used it, except for one brief attempt, at 0.5x. I did not see a real difference at 0.9x, but one would expect it could react a bit faster. Does it? |
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| The biggest struggle I have is I'm using the guiding in ASIAir which is pretty limited in guiding features. I can't pick algorithms, can only set max move and aggressiveness, etc. Since I went OAG it's started to "lose" stars even when I can see them clearly, and I could really use the full PHD for optimizing the centroid algorithms. |
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I could not say if it makes a real difference (0.9 X rate) I am hoping to set up this weekend for some testing of various bits during the full moon so I can try going back to 0.5 X rate. I went to 0.9 X when I was having the slow RA oscillations (As it would drift east then have multiple west corrections, increasing in size before it reacted, then it would drift west and the multiple, increasing east corrections would happen) but I believe the really aggressive guide settings did most of the work to tame it. I reckon if everything was working nicely, the 0.9 X rate would mostly contribute to faster recentering after dithers. at 0.9 X rate PHD2 can move the scope about 7.5" per second. I certainly can't be bothered trying to write something myself but the ex tech in me wonders how mounts would react to a PID control scheme, some of the PHD2 algos sort of emulate PID but not really directly. |
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I received my CEM70G mount in mid December and have so far not been able to get decent guiding. First off PHD2 reported a backlash of over 4000ms consistently. I adjusted the gears and tensioned the belt with no change. The best I can get on a good night of seeing is 1.2RMS. For a start I don’t see how a belt driven system can have 4sec of backlash. When I look at the belt and change directions the response is instantaneous. There must be another underlying issue. irregardless this backlash issue should not be up to the consumer to resolve. These are new mounts and should be fully tested and function properly out of the box. I previously had a CEM60 for 4 years and was totally satisfied with it, not tinkering much I could easily get consistent guiding in the .5RMS range. I have contacted iOptron as well as my retailer but am still waiting on them to give me a solution. Not impressed so far! |
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Lorenzo Siciliano: Hi, I heard about it, but it seems to be adressed by tightening a screw. Don't know if you've done it, but it would be a good lead to start with. It's a shame a new mount need to be tweaked, but otherwise, I heard really good things about this one. The cem70 is a bit too big for me, I'm looking for a cem40 which is from their same new serie of mounts if I'm correct (CEM26, 40, 70). Hope you'll get around this issue. |
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| I found it very difficult to adjust the backlash with the DEC belt, there is inadequate room in the oval holes for adjustment. I managed by trying over and over and prying with a big flathead, others I have read removed the motor and put a spacer in. But ultimately that appears to be the solution for the DEC backlash. I got mine down to about 400-600ms from over 2000ms. |
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I bought a CEM70 last September and initially used it with a C8, but then moved to a refractor in February : SVX130T F7 with an OAG, filter wheel and ZWO camera. Overall I am quite happy with it. Guiding with the C8 and guide camera was around 1" but improved greatly with the refractor setup. Last week I imaged NGC-2903 for 4 hours at 0.35" RMS, using PHD2 and multiple star guiding. More often I am in the range of 0.5 to 0.7" RMS but the mount is capable of sub .5" guiding if the seeing is good. My seeing conditions vary quite a lot. I guide at 2.5 second intervals. My CEM70 seems to have a fair amount of RA error, possibly more than iOptron's spec of +-3.5", but PHD2 corrects for it. For anyone with this problem, I suggest trying the Predictive PEC algorithm for RA guiding. My DEC backlash has not caused any guiding problems. But for some reason it changes from one session to another. PHD2 GA says 400ms one session, then maybe 130ms the next. I am keeping a session log to record the GA results and see if there is a pattern for this other doing the test in bad seeing conditions. I discovered that the mount GPS does not connect if a computer is close to the mount. After I mounted a NUC on top of my OTA, the GPS refused to connect. I thought the problem was the GPS module, so I sent it back to iOptron who tested it and said it was fine. So after some indoor analysis I found that if a computer is within 6' of the mount it interferes with the GPS. Easy solution: power the mount first and let the GPS connect (takes 1 min), then power up the rest of the equipment. This completely solved the issue. I use a two-outlet internet switch to separately control the 110v power for the mount and for everything else. The NUC gives me USB3 speed for the camera. The other devices are fine with USB2. Images are saved on the NUC SSD drive and it connects to my network with its wifi. I control it all with NINA on the NUC, and RDP to a computer inside the house to stay warm. I highly recommend it. The mount is not perfect but I guess no mount is. Since it is providing good results, I'm happy and I would recommend it. |
