Hi Guys, I have a double encoder mount CEM70EC2 which I have been imaging with for a few months now and have wanted to find out what settings etc others are using with an ASIAIR for autoguiding.

There has been many discussions on this subject before with varying opinions about these mounts, but personally I believe that they are the same as ordinary non encoder mounts but with much less periodic error, so less autoguiding corrections are needed. I am usually using 5 second exposures for guiding and on good nights 7 second exposures with 15 to 25% aggressiveness on RA & DEC and get good guiding results. I always do a calibration first near the meridian at 30-40 degrees or so and then slew to the target etc...

I was wanting to know if there are any settings/thoughts/recommendations from others that may be helpful for autoguiding with encoder mounts using an ASIAIR Plus.

cheers
Nick

  • w7ay replied to this.

    SFn8CieR I was wanting to know if there are any settings/thoughts/recommendations from others that may be helpful for autoguiding with encoder mounts using an ASIAIR Plus.

    If the mount was designed properly, you can just treat a mount with an encoder just as any mount.

    Unfortunately, not all mounts with encoders are properly designed. The encoder loop with these bad mounts would fight against the autoguiding loop.

    The proper mounts will let the autoguiding loop move the OTA away from the encoder's own absolute position.

    Ask the mount manufacturer if their encoded mount can be autoguided. It is not an ASIAIR issue.

    FWIW, my RST-135E (RST-135 with a Renishaw encoder) works fine when autoguided with the current ASIAIR version -- around 0.35" total RMS error, using 0.1pix MinMo multistar guiding, a 180mm focal length, f/4.5 guide scope with a flattener (it is essential for a flat field when using multi-star guiding), and ASI178MM guide camera at gain 270 with a Baader Neodymium filter).

    Your settings will depend on your guide scope/camera; don't use my settings. With ASIAIR multi-star autoguiding, you want to increase the gain until you see 12 stars being used -- and then add at least another 10 dB gain (100 ZWO gain units) -- this will remove one or two brightest stars, otherwise they will skew the centroid averaging (the ASIAIR uses SNR weighted centroids), causing guiding with the equivalent of only one or two star autoguiding even though 12 stars are selected.

    If you don't have a nice flat field from the guide scope, you might be better off with using single star guiding, and depending on longer exposures to fight "seeing," instead of depending on the average centroid of multiple stars to fight "seeing."

    Chen

      Hi Chen, I have contacted ioptron to see if my CEM70EC2 mount is able to be autoguided. I will let you know the outcome.
      So if it not, then I take it you have to take unguided exposures and depending on the seeing, will determine the maximum exposure time. I can get round stars using my 30mm 120FL guidescope with ASI120mm mini on a good night up to 3 minute unguided exposures, which is pretty good. I have also had many successful nights of guided exposures, but as I mentioned, sometimes the guiding is good for a while then it goes nuts.. So I think my mount can be autoguided using ASIAIR but lets see what ioptron have to say.

      How did you set the 0.1pix MinMo on an ASIAIR?
      It is also interesting that you say you need a field flattener for the guidescope to successfully multiguide. I have just setup my 130PHQ scope with a 60mm SVBony Guidescope and a ASI174mm Guiding Camera so I will try to get 12 stars by increasing the gain + extra 10db. Aslo how would I know if I need a FF?

      thanks again Nick

      • w7ay replied to this.

        SFn8CieR How did you set the 0.1pix MinMo on an ASIAIR?

        Guide Camera Settings > Guiding Advanced Settings. ZWO tries to hide the fact that they are stealing IP from PHD2 by calling MinMo "Corrected Trigger Accuracy." With the joke of an ASIAIR, you can also only choose between 0.1 pixel and 0.2 pixel.

        People keep reminding ZWO that the license to use PHD2 requires them to publish any changes to the PHD2 source code. Which ZWO has never done. Out and out IP theft, and making money from it.

        Aslo how would I know if I need a FF?

        If the stars that you see in the guide window don't all have have pinpoint shape. The shape of the stars changes their crentroids, and as stars scintillate, the signal to noise ratio of the stars changes, and ZWO uses SNR to weight the centroids. So the averaged centroid would actually itslef move around. This is not a problem with single star guiding - you are not switching from the centroid of one star to the centroid of a second star.

        Shorter answer -- you need a field flattener to get the best from multi-star guiding.

        Chen

          Hi Chen,
          Yes that makes total sense, thanks. I need to sharpen the focus a little better to see if I have pinpoint stars in the guide window. I have searched for a FF for my SVBony SV106 60mm Guidescope but I cannot find one. Do you know where I can get one and also you mentioned a Baader Neodymium filter for your guiding camera. This is a skyglow filter that increases contrast without losing brightness - brilliant!

          • w7ay replied to this.

            SFn8CieR Do you know where I can get one

            Sorry,I don't. I stay away from brands like SVBONY.

            Baader Neodymium filter for your guiding camera

            Yeah, I use that in an ASI178MM that I have been using for guiding with the visible spectrum. I just bought the monochrome version of the ASI678, and will be using that instead, going forwards.

            The 678 is quite sensitive in the near-IR spectrum, and I want to play again with near-IR guiding, using 685nm pass and 750nm pass filters. The atmospheric turbulence has a inverse wavelength relationship, and IR guiding should be more reistant to turbulence if there are enough stars for multi star guiding, and if the camera is sensitive enough. In the past, I have seen 25% type smaller errors when using near-IR guiding. Not a huge deal, but it is fun to look into.

            increases contrast without losing brightness

            By the way, in the last two releases of ASIAIR, ZWO finally added dark frame subtraction for guiding. Check the Guide window for that option. It can make quite a big difference.

            Chen

              Hi Chen,
              So what guidescope would you recommend for my Askar 130-PHQ scope? I thought the SVBony would be fine for guiding? Maybe not?

              I use the ASI174 MM Mini for guiding. I originally bought that camera for an OAG but ended up going for a guidescope instead. Infra red guiding sounds amazing. never thought about it but sounds like you are ahead of your time!

              Last night I had clear steady skies and I calibrated west of the equator and meridian and the red and blue lines were indeed at 90 deg. I then went to an object in the east, flipped the guiding, and started imaging. My guiding started off well at 0.5 -0.6 arc secs then after a few minutes it shot up to 1.2 -1.4 etc. I was taking 5 sec exposures, gain at 280 for multistar guiding, RA & DEC agressiveness I tried low and high values, calibration step at 1450 (from PHD2 for my guidescope and camera) and I could not guide my CEM70EC2 mount properly at all. I tried 10 sec exposures and 3 sec exposures all with varying agressiveness values but still no good. I got frustrated and finally gave up. I dont know what else to do?

              • w7ay replied to this.

                SFn8CieR So what guidescope would you recommend for my Askar 130-PHQ scope?

                I don't recommend products. But I can tell you what I use, to give you an idea of what to look for. I am guiding an RST-135E to the region of 0.35" total RMS error.

                The guide scope is an FMA180 pro (the pro version comes with a flattener). The camera is an ASI178MM (but switching to ASI678MM soon). I have a 1-1/4" Neodymium filter in the ASI178MM's flange. The gain of the ASI178MM is set to 27dB (in ZWOs term "270"), and using dark frame subtraction for guiding. I use 0.5 second guide exposure to get 2 FPS (you won't need that high speed for a non-strain wave mount).

                My mount requires RA and declination step sizes of around 150 (yours will probably be smaller, since it is smoother than a strain wave mount). The loop gain is set very low, I set my aggressiveness setting to less than 30%. Usually around 25%. Note that I set the autoguiding to make very gentle corrections, even though it is a strain wave mount. Lots of people use huge step size and aggressiveness, and the strain wave mounts just corrects and overcorrects (they have very small backlash) all over the place. With a legacy (worm gear) mount, you should be able to use even smaller correction step sizes and smaller aggressiveness. Just remember to adjust everything to just be enough to correct for mount errors. Don't try to correct for winds, etc (an encoded mount does not correct for wind either).

                You can see the guide scope here on a dual saddle plate (under the FSQ-85), with its own EAF:

                My other quide scope (longer focal length of 250mm) is based on the Borg 55FL objective and the TS-Optics TSFLAT flattener. But so far the 180mm focal length, with a 2.4µm pixel camera, appears to be good enough (0.35" total RMS) for my lightweight setups with ASIAIR (75 years old, and the Baby Q is the heaviest OTA that I can handle).

                Only recommendation I have is to never, ever use the ZWO guide scope. Stay away from that trash if you want to use the multi-star approach to reduce effects of atmospheric turbulence. I use the multi-star approach because I need 2 FPS update rate with strainwave mounts (I use two RST-135E and two RST-135) -- if not for that, I would probably pick single star guiding with 3 second exposures with smooth legacy mounts. My EM-11 mount is very smooth, but too much weight and hassle for an old man; so I haven't brought it outdoors for 3 or 4 years now.

                Chen

                  Hi Chen,
                  Nice setup you have there. I looked into the FMA180 pro with a FL=180 and it is very well built and great optics but may be too small for my 130-FSQ with FL=1000. That is a 5.55 focal ratio so may need a guidescope with longer FL=250 like the Vixen scope you have. Which model is that? Does it take a 2" TS Optics 1x FF?

                  I am lucky that I have an observatory with a roll off roof so I dont have to carry stuff out all the time, but changing scopes on the mount is becoming a 2 man job for me. My Askar 130-PHQ is heavy and when fully loaded with all the other stuff it is quite cumbersome and awkward to handle. I am feeling my age too.

                  I am considering buying a GSO 10"RC one day down the track. Some good and bad reviews but also some stunning pics too. Do you have any thoughts here?

                  Anyway, back on the subject, you say my RA & DEC Step size for my CEM70EC2 mount should be less than 150 and my Aggressiveness less than 25%. I calculated that my Calibration Step size should be 1650 (using PHD2) @ 0,5 Siderial guiding rate for my 60mm Guidescope FL=240 and ASI174mm Pro camera with 5.86x5.86 pixels. Does that look about right? So next time I get a chance to image (rain is here now) I will try these figures to see how I go. I will also calibrate properly and flip the guiding as required....thanks to you I know this now.. BTW my calibration the other night was really good with orthogonal red and blue lines and 13 steps to move 25 pixels, so thats good.

                  You also mentioned that the gain on my guide camera should be set to 100 units above the recommended gain of 189 for this camera so I can remove any really bright stars from my multi-star guiding, which I have tried and it did work. So what I want to know is what exposure length would you recommend for guiding? I know that for RA and DEC Duration if you use short exposures you need longer duration and for longer exposures you need shorter duration, but you say that they should be less than 150, so I will try that.
                  many many thanks
                  Nick

                  • w7ay replied to this.

                    SFn8CieR I looked into the FMA180 pro with a FL=180 and it is very well built and great optics but may be too small for my 130-FSQ with FL=1000.

                    You have been listening to too many YouTube shills.

                    What is important is not ratio of the focal lengths (that is such a stupid myth). What is important is the actual guiding error in arc seconds.

                    Compare that with your plate scale. I will bet that 0.4" to 0.5" of error is smaller than other errors in your imaging system.

                    Chen

                      SFn8CieR Which model is that? Does it take a 2" TS Optics 1x FF?

                      Vixen has its own custom flattener. The TS Optics flattener I have is used in a Borg 55mm fluorite guide scope. Ever since being able to get better than 0.4" total RMS guiding error with the FMA180p, I haven't had to bring put the bigger Borg scope.

                      My Askar 130-PHQ is heavy and when fully loaded with all the other stuff it is quite cumbersome and awkward to handle.

                      I am 5' 2" and well over 70 years old. The Baby Q is the heaviest OTA I can handle, otherwise, I would be using a real Q (FSQ-106). I may be able to just handle the FSQ106 by removing the camera and filter wheels, but that is such a hassle. Currently, I have the RST-135E on a William Optics Mortar, together with electronics in an ASB box at the base of the tripier. The mount, tripier, and ABS box are outdoors 24x7x360, under a large dry bag. Setting up is just bring out the main OTA in one trip, the guide scope in a second trip, and that's it. Polar Alignment is done about once a year. Focusing does involve walking out to install a Bahtinov mask.

                      I am considering buying a GSO 10"RC one day down the track.

                      My largest scope (not really that heavy) is the 180mm Mewlon . Not an RC, but a Dall-Kirkham.

                      Anyway, back on the subject, you say my RA & DEC Step size for my CEM70EC2 mount should be less than 150.

                      No, I am just guessing, since it is a nice legacy mount. If the periodic error is sinusoidal, then the slope of the worse case correction is easy to figure out (derivative of sine is cosine). The worst case slope is what determines the step size.

                      BTW my calibration the other night was really good with orthogonal red and blue lines and 13 steps to move 25 pixels, so thats good.

                      There you go. Legacy mounts are really very nice in that respect. You should how flakey some Chinese strain wave mounts are like. Yeah, the 13 steps is perfect -- tells you that you have the Calibration step size perfected.

                      So what I want to know is what exposure length would you recommend for guiding?

                      Again, you have a legacy mount that is smooth. You probably can use 1 to 2 second guide exposures (guide updates once per second to once per two seconds) without the mount going anywhere before the next guide pulse is issue. Strain wave mounts (even the RainbowAstro ones that use the real Harmonic Drives, instead of Chinese copycats) hve irregular and large error slopes, and need to be guided rapidly. I use 0.5 second exposure and picked a guide camera that can achieve 2 frames per second guiding. The guide error goes above 0.5" when I use 1 second guiding (1 guide update per second). You should not have this problem.

                      Good luck.

                      Chen

                          w7ay
                          Hi there Chen,
                          I am glad I have the correct value for calibration step 12-13 steps for 25 pixel movement.
                          I am surprised you say 1 to 2 sec guide exposure time as I would have thought that a mount with encoders could handle longer times between corrections since they have the encoders and are very low periodic error.

                          I did not really understand this comment from you. Can you explain this in laymans terms if you can please.
                          "No, I am just guessing (that RA & DEC Step size should be <150), since it is a nice legacy mount. If the periodic error is sinusoidal, then the slope of the worse case correction is easy to figure out (derivative of sine is cosine). The worst case slope is what determines the step size" I got totally lost here.

                          I am starting to understand how you think and how all this stuff fits together. I had no idea, and from what I have read, many other too do not know what to do. ZWO do not provided any instructions on what to do and so many people are left in the dark...so to speak, like me. As you mentioned before, ZWO should do this for you via the ASIAIR as they know the FL, camera, pixel size, tracking rate etc, but for whatever reason they do not do this as they say it is user friendly and simple to use?

                          As we say in Greek, Yiasou !
                          Nick

                          • w7ay replied to this.

                              SFn8CieR Can you explain this in laymans terms if you can please.

                              Unfortunately, no, if you do not know what a derivative is, then it is impossible to explain.

                              The crudest way to explain autoguiding is this: lets say you update the loop once every three seconds, i.e., take a 3 second exposure and then depending upon where the star has moved, send a correction to the mount to move the same amount in the opposite direction.

                              The autoguider tells the mount the amount to move by initially setting up the guide rate. The rate the mount moves is usually given as rate relative to the rate the stars move ("sidereal rate"). Stars move 360 degrees in 23 hours 56 seconds. Or about 15 degrees per hour of time, or about 0.25 degrees (15 arc minutes) per minute of time, or 15 arc seconds per second of time.

                              For example, a guide rate of 0.5x sidereal would correspond to moving the mount by 15*0.5 = 7.5 arc seconds per second of time.

                              To move the mount by a certain amount, the computer basically tells the mount to start moving (at this rate), wait N seconds, and then then tell the mount to stop moving. This is known as a pulse that is N seconds long. If you want to move the mount by 1 arc second, and if your guide rate is 1x sidereal rate, then, you would send a pulse to the mount that is 1/15 second, or 66 milliseconds long. if your guide rate is 0.5x sidereal rate (the most common guide rate for reason you need to buy a good book to find out;I really don't have time to explain everything) then you would need to send a pulse that is 132 milliseconds long to the mount.

                              Thus, for the most common rate of 0.5x sidereal rate, if your mount has drifted by no more than 1 arc second between the sampling rate (3 seconds in our example), then the pulse would never need to be more than 132 milliseconds long. This is the max rate parameter. The previous couple of paragraphs explains why max guide duration is in units of time, not angle.

                              How much your mount moves every 3 seconds is the max derivative of the periodic error of your mount multiplied by 3. This is where the derivative comes in. The periodic error itself is only useful for visual astronomy. For autoguiding, it is the derivative of the periodic error is the important parameter. I can't explain derivatives to you if you do not know calculus. You need to read a book on it.

                              The periodic error curve of a good mount looks very much like a sine wave. Therefore the derivative is a cosine waveform.

                              To determine the max pulse duration (132 milliseconds in our example above), you simply need to know the largest derivative of the periodic error curve. And with a good legacy mount the largest derivative of the periodic error curve is likely going to be less than 1 arc second (angle) per second (time); and that implies that the max pulse duration need not be more than 132 milliseconds when using 3 second exposure time.

                              ZWO should do this for you via the ASIAIR as they know the FL, camera, pixel size, tracking rate etc, but for whatever reason

                              ZWO just wants to make money, not help you understand how things really work. I recommend some other manufacturer if you want decent documentation. A large part is that ZWO employees do not understand anything themselves, and just use open sourced software that is written by others.

                              Chen

                                Hi Chen,

                                Thank you for a great explanation!

                                I do know what a derivative is, I am a recently retired Civil Engineer but I could not relate it to periodic error curves as a derivative for me is just a mathematical expression without any real meaning apart from a basic understanding that it is a measurement of a rate of change from a known fixed point. So there you go, it does now make sense what you are saying when considering PE as a wave. Never thought of it that way.

                                My mount has a factory supposed periodic error of <0.3 arc seconds rms, so if that is the fact, then the max pulse duration of 132 milliseconds in your example for a 3 sec exposure will be less - as 0.3 RMS is root mean squared equates to 0.547 arc sec PE, so 0.547x 132=72.2 milliseconds if I am right.

                                I did astrophotography many many moons ago with AP1200 mount, RCOS 12" RC Scope, ST11000XM Camera, AOL adaptive optics, Rotator etc etc and sold everything due to family problems, it was hard back then to control everything but now with ASIAIR it is too easy.
                                I must admit ZWO are really innovative and opened up astrophotography for the masses. U understand a lot of people say they have a monopoly because asiair only uses ZWO products but also they would be shooting themselves in the foot if they allowed other brands of equipment. A shrewd business decision for them but not for us. It is easy to use and I can go to sleep at night rather than staying up till 3 or 4am like I used to. I dont want to go back to the old (even though I had the best equipment) and I am now (as an old man) enjoying the ease of use of the new gear.

                                • w7ay replied to this.

                                  SFn8CieR ST11000XM Camera

                                  I still have my ST8300 :-). But pretty much obsolete at this point, but was the best thing since sliced bread when it came out. Notice ZWO is now copycatting the ST7 by adding a guide sensor with the main sensor.

                                  I am now (as an old man) enjoying the ease of use of the new gear.

                                  I am over 75 years old now. I started when I was about 16 in high school in Kuala Lumpur. Ground my first 5" Newtonian mirror then.

                                    Yes Chen, life changes and you get old. technology has moved a long way. We are lucky to have seen it change but sometimes I feel it is going too fast. My friend had the ST8300 (colour I think?) I was well versed on the AOL with its moving mirrors doing the guiding. Amazing tech for that time. I am surprised no one is doing it now? Active Optics is here but not really that good, but adaptive Optics well, that is something else. Maybe I need to whisper in ZWOs ear about that and a rotator too. I had an ST7 back then with a dual sensor, but the AOL was next level. It only moved the mount when it ran out of mirror movement and that usually took a while if it was running right.

                                    When I was 2 or 3, as my mum tells me, I would hold her hand and take her outside at night and point to the stars and say what are those? She would say stars. I asked but what are they and why cant we see them during the day...
                                    I am still inquisitive about the universe, it still fascinates me. Anyway, thank you Chen and I wish you well with a happy life and good health!

                                    yiasou Nick

                                    I am now waiting for a good night to try out everything you have taught me. Cant wait.

                                    • w7ay replied to this.

                                      Hi Chen,
                                      I finally heard back from Ioptron roday asking whether my CEM70EC2 is able to be autoguided. Her is their response.

                                      Hi Nick,
                                      Yes, the CEM70EC is good for autoguiding. Try a little long exposure time, such as 2000ms or 3000ms. Try send less pulse by using timelapse. You may also using multistar guiding.

                                      Clear Skies!

                                      Kevin (Tech2
                                      Your Tech Support Team

                                      Not sure what he means by using timelapse?? but it is able to be autoguided using 2 to 3 sec exposures with less pulse which is what you are saying.

                                      I had a look at the A08 which looks promising but limited to only a few cameras atm. I used an A0L back in the day and never had to worry about autoguiding as we are doing today. No wonder I had no idea of what to do. again thank you...
                                      Nick

                                      • w7ay replied to this.

                                        SFn8CieR Not sure what he means by using timelapse?? but it is able to be autoguided using 2 to 3 sec exposures with less pulse which is what you are saying.

                                        He also needs to learn the difference between "less" and "fewer" :-). In math, we knew it as countable vs uncountable sets :-).

                                        Like you, I have no idea what he means by timelapse. My guess is he wants you to use 2 to 3 second exposures, but do not talk to the mount that often. Perhaps talk to the mount every two exposures.

                                        Yeah, he is claiming that the mount is good enough that you only need to now and then give it a kick. Good, large legacy mounts are like that. You only need to occasionally steer it just a little in case a polar misalignment is causing the mount to drift away over time. Encoders don't track the sky, it tracks a little glass plate :-).

                                        I have been telling people exactly this when they ask about encoders. Both cases uses some feedback from a known source. In the case of an encoded mount, it is coming from something local in the mount, and in the autoguiding case, the feedback is coming from the stars. The latter is actually far superior (much higher resolution than any encoder man can build) if only there is no atmospheric turbulence. Multistar is an effort to reduce the effect of atmospheric turbulence by averaging the centroid of many stars to reduce the variance of the error (with equal weights, the average of two stars (since the are acctected by different pockets of turbulence) reduces the variance by two, etc. So, given enough stars, there is no affect from turbulence.

                                        The problem with something like ASIAIR multi-star is they use Signal-to-Noise ratio weighting -- so the autmospheric turbulence on brighter stars have a bigger influence on the error than dimmer stars (lower SNR). This is why I recommend lots of gain for the guide camera. That would clip the brightest stars and they get dropped from being used. The remaining stars have a more uniform SNR distribution.

                                        If you don't do this (adding an extra 10 dB of gain), what appears as 12 stars is only equivalent to using 1 to 3 stars -- you might as well use single star guiding. Once the brightest two or three stars are removed, 12 star multiguiding is probably equivalent to something like using 6 stars on ASIAIR. Much better, but it would be even better if they had not use SNR-weighted centroid averages.

                                        Chen