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PEC training
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First of all, I'm aware this is a dumb and basic question. But for the life of me I can't find a definitive answer online.
Now that I am using multi star guiding which reduces the effects of transient seeing effects, I can see what appears to be a couple arcseconds peak of what certainly looks like periodic error. I have done several PEC training sessions (training with PHD2 / pulse guiding) but if anything, my (assumed) PE gets worse. So I have a couple questions. 1. If you train more than once, does the G2 store / average more than one PEC curve, or does each new training session overwrite / replace any previous sessions? 2. Is there a way to erase the PEC curve? Only necessary I guess if it averages multiple sessions. TIA, Paul -- Paul Goelz Rochester Hills, MI USA pgoelz@... www.pgoelz.com |
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Hi Paul >>> I have done several PEC training sessions (training with PHD2 / pulse guiding) but if anything, my (assumed) PE gets worse.??For high quality astro imaging, you need a high quality PEC. this approach is not high quality enough. you really need to be using PEMPro for PEC? the gemini II built-in pec is really more designed for visual - one cycle, no multiple passes, no averaging.? you also have a lag there between observed movement and reaction so you will always be a tiny bit behind i really recommend you save yourself grief and give PEMPro a shot - they have something like a 45 or 60 day trial period B On Thu, Dec 10, 2020 at 7:21 PM Paul Goelz <pgoelz@...> wrote: First of all, I'm aware this is a dumb and basic question.? But for the --
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PS i should have also mentioned you can deactive/ delete PEC from inside the Gemini Telescope.net application the PEC checkbox to enable/disable is right there on the soft hand controller The ability to autoload pec on startup or clear PEC is under Setup menu->PEC settings On Thu, Dec 10, 2020 at 7:26 PM Brian Valente via <bvalente=[email protected]> wrote:
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On 12/10/2020 10:25 PM, Brian Valente wrote:
the gemini II built-in pec is really more designed for visual - one cycle, no multiple passes, no averaging.Thanks Brian, that makes sense. Too bad the G2 does not average multiple sessions though. I can certainly try PemPro on a trial basis but I'm afraid that I find the purchase cost of $149 excessive. On a side note.... if guiding is working correctly, should periodic error beyond fractional arcseconds even be visible? As an experiment, I increased the RA aggressiveness from 70% to 90% and things got better. Again, it is not excessive at all and tonight was the only time I have actually had oval stars. Mostly it does not seem to be affecting my images. Paul -- Paul Goelz Rochester Hills, MI USA pgoelz@... www.pgoelz.com |
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On 12/10/2020 10:29 PM, Brian Valente wrote:
PS i should have also mentioned you can deactive/ delete PEC from inside the Gemini Telescope.net applicationYe, I am aware of those checkboxes and functions. While I can see how to turn PEC on and off, I don't see a way to ERASE it. Again, not an issue if it only stores one curve. Paul -- Paul Goelz Rochester Hills, MI USA pgoelz@... www.pgoelz.com |
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?if guiding is working correctly, should periodic error beyond fractional arcseconds even be visible?? As an experiment, I increased the RA aggressiveness from 70% to 90% and things got better.? >>
?tonight was the only time I have actually had oval stars.??? Eccentricity (star roundness) really depends on how close RA and DEC RMS are, not necessarily how high is your RMS low RMS = small stars RA and DEC RMS close in value = round stars On Thu, Dec 10, 2020 at 7:36 PM Paul Goelz <pgoelz@...> wrote: On 12/10/2020 10:25 PM, Brian Valente wrote: --
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On 12/10/2020 10:41 PM, Brian Valente wrote:
Eccentricity (star roundness) really depends on how close RA and DEC RMS are, not necessarily how high is your RMSYes, I agree. The oval stars tonight were because the P-P RA error at about 2-3" was noticeably higher than the DEC (which was VERY smooth and <1"). Usually they are roughly equivalent and the stars are round. I would not have even mentioned it except that there was a noticeable periodic component to the RA guide graph that I was assuming is PE. Maybe not? Paul -- Paul Goelz Rochester Hills, MI USA pgoelz@... www.pgoelz.com |
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On 12/10/2020 10:41 PM, Brian Valente wrote:
Eccentricity (star roundness) really depends on how close RA and DEC RMS are, not necessarily how high is your RMSI should also add that although seeing seemed OK, transparency was awful due to high humidity and (I think) thin high cirrus. Bands of high cirrus passing through could have I guess caused asymmetrical guide star movement.... even with multi star guiding enabled? Paul -- Paul Goelz Rochester Hills, MI USA pgoelz@... www.pgoelz.com |
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Any of the things you mentioned could contribute to that. a bad PEC could certainly create havoc too best way is to upload your guidelogs and we can do some analysis On Thu, Dec 10, 2020 at 7:51 PM Paul Goelz <pgoelz@...> wrote: On 12/10/2020 10:41 PM, Brian Valente wrote: --
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On 12/10/2020 10:55 PM, Brian Valente wrote:
Any of the things you mentioned could contribute to that. a bad PEC could certainly create havoc tooIts bedtime for Bonzo here.... I'll upload tomorrow and see what you can see. Paul -- Paul Goelz Rochester Hills, MI USA pgoelz@... www.pgoelz.com |
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On 12/10/2020 10:55 PM, Brian Valente wrote:
Any of the things you mentioned could contribute to that. a bad PEC could certainly create havoc tooOK, I have uploaded the log from this session. You should see a couple short guiding runs as I played around with it before starting an imaging run. Then there should be a long 100 minute guiding run while I imaged. During that 100 minute imaging run I did a PEC train, watched it for a bit, then turned PEC off and left it off. Some time later (still during that 100 minute run) I changed RA aggressiveness from 70 to 90, then to 100 and then back to 90 (as I recall). Except for the RA aggressiveness, all other settings are per the last guiding assistant run. Note that DEC backlash started around 1000mS but drifted upwards from there to a little north of 2000mS as I recall. DEC guiding looked near perfect to me. RA looked pretty good as well aside from the occasional vaguely periodic swings +/- 2" or thereabouts. I'll be interested to hear what you find. Paul -- Paul Goelz Rochester Hills, MI USA pgoelz@... www.pgoelz.com |
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On 12/11/2020 3:07 AM, Paul Goelz wrote:
On 12/10/2020 10:55 PM, Brian Valente wrote:Guys,Any of the things you mentioned could contribute to that. a bad PEC could certainly create havoc tooOK, I have uploaded the log from this session. After a night of reflection I realized that since the orientation of my oval stars was not coincident with RA or DEC, it is likely it was not caused by a guiding issue. So this morning I had a look at my subs and found the following: 1. My subs are not perfectly in focus. 2. My collimation (this is an 8" SCT) is just a touch off. I may have a small amount of sensor tilt as well.... not sure. But coupled with the fact that I was not perfectly in focus, that caused the aggregate star image during the 10 minute subs to be oval in an 11:00 / 5:00 orientation. That matches the oval in the final stack. 3. The ten 10 minute subs do show creep along the RA axis (12:00 / 6:00) from one sub to the next that could be tracking issues or flexure or mirror flop..... or some combination of all three. So I still have questions about the tracking / PE and am interested in what you see in my log. But I am not sure how responsible any RA issue are for my oval stars. Paul -- Paul Goelz Rochester Hills, MI USA pgoelz@... www.pgoelz.com |
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Arun Hegde
"Eccentricity (star roundness) really depends on how close RA and DEC RMS are, not necessarily how high is your RMS
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low RMS = small stars
RA and DEC RMS close in value = round stars"
True - but I'd think that if both were less than your image scale, whether one is greater than the other would not matter; you'd get round stars because your pixels would be too large to resolve the difference. And if both were larger than your image scale and close to each other, you'd have round stars but they'd be larger than they could be from optical effects alone, plus you'd lose feature resolution. So a desirable end point is to have both as well as your total RMS smaller than your image scale. On Thu, Dec 10, 2020 at 10:42 PM, Brian Valente wrote:
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¿ªÔÆÌåÓýHi I am interested in this discussion. Can someone explain the statements that the closer RA and Dec are in RMS the more round the star. What is the underlying explanation. ? Thanks. ? Aubrey ? Sent from for Windows 10 ? From: Arun Hegde
Sent: Friday, December 11, 2020 12:20 PM To: [email protected] Subject: Re: [Losmandy_users_io] PEC training ? "Eccentricity (star roundness) really depends on how close RA and DEC RMS are, not necessarily how high is your RMS ? low RMS = small stars RA and DEC RMS close in value = round stars"
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Arun Hegde
RMS stands for Root Mean Square. It is a measure of, on average, how large the deviations are from the baseline. An RMS value of zero means a perfectly flat graph.
In the context of autoguiding, we are concerned with how far the centroid of the guide star deviates from the point where it should be (or we want it to be). These deviations are measured in two directions which are at right angles to each other - Right Ascension and Declination (RA and DEC), Now think of your star as a circle with two diameter lines at right angles to each other. If the deviation in the direction of RA is greater that in DEC, the diameter of the circle is greater in the RA direction than in DEC. The circle is "stretched", it is no longer a circle, but an oval or ellipse, longer in the RA direction than DEC.? If the RA and DEC RMS are close to each other, then the circle remains a circle. Now you can also think about the case where the deviations in RA and DEC are both close to each other, but both very large. That's still a circle, but a rather bloated one. Your images will have round stars, but large ones. Fine features of your image will be smeared. The ideal case is when both deviations are much smaller than one pixel in your image. At that point, all the deviations are "contained" within one pixel, and your guiding no longer limits the size and roundness of your stars, nor feature resolution. The finer your image scale, the more demanding your guiding becomes, and the more you'll be able to see faults in your guiding. Many people consider that a value of lower than 0.8 " RMS to be a good number to aim for. Because at point, under most conditions, deviations caused by things like atmospheric seeing become more critical. With proper polar alignment, balancing, appropriate clutch tightening, etc., you should be able to guide consistently under this value with good mounts. That has certainly been the case for me (with some work) with the GM811G and a small (80mm) refractor. |
¿ªÔÆÌåÓýVery good Arun, I have never heard that before. So if you move from an STT 8300 with the Kodak Chip 5.6 Pixels to a Starlight Express 814 with 3.6 pixels, on an 2000 mm f/9 scope what effect would you expect to see? ? Aubrey ? Sent from for Windows 10 ? From: Arun Hegde
Sent: Friday, December 11, 2020 1:16 PM To: [email protected] Subject: Re: [Losmandy_users_io] PEC training ? RMS stands for Root Mean Square. It is a measure of, on average, how large the deviations are from the baseline. An RMS value of zero means a perfectly flat graph. ? |
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Hi Aubrey Aurun pretty much nailed the answer.? the relationship depends on the image scale from your guiding setup and the image scale on your imaging setup if you can supply this info i can give you a better answer Imaging camera (make/model, pixel size, sensor size in x-y pixels) imaging scope (make/model, focal length f-number) any reducers same for guiding setup On Fri, Dec 11, 2020 at 11:58 AM Aubrey Brickhouse <abrickhouse1@...> wrote:
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>>>
True - but I'd think that if both were less than your image scale, whether one is greater than the other would not matter; you'd get round stars because your pixels would be too large to resolve the difference. yes i generally agree, but i often see things at or above the image scale.? also it's the image scale of the imaging setup, not the guide setup. Often the guider is at a more coarse scale, so arcsec is preferred to make that assessment.? i see a fair number of people saying their guiding is sub-pixel, but it's the much larger image scale of the guiding setup! On Fri, Dec 11, 2020 at 10:20 AM Arun Hegde <arun.k.hegde@...> wrote: "Eccentricity (star roundness) really depends on how close RA and DEC RMS are, not necessarily how high is your RMS --
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Arun Hegde
Hi Brian,
I was referring to the main image scale, not the guiding image scale. Yes, that is why I pay attention to the arc second number in PHD2, since it the more meaningful number in translating whether my guiding is good enough. Depending on the night and position in the sky, my guiding varies between 0.5 and 0.7" RMS. That's much lower than my image scale for 1.6"/px on my main camera and scope. Whether or not I am sub pixel as measured by my guide camera pixels is interesting but less material.? For many people that use a separate guide scope, their guide camera image scale is most likely coarser than their main image scale, but not necessarily if you are using an off axis guider. For example, I use an ASI290MM as my guide cam, and an ASI1600 as my main cam. This makes my guide camera scale finer than my main camera scale, since both use my main OTA (the 290MM has 2.9 micron pixels, the 1600 has 3.8 micron pixels). What makes autoguiding work at a scale smaller than the image scale of your guide camera is that it is possible to calculate the position of the centroid of the guide star to an accuracy much greater than a single pixel. Because of this, star motions under 1 guide camera pixel can be detected and corrected for. In the case of Aubrey's question - assuming he has changed nothing else (i.e., his guiding camera and guide scope and OTA are the same, seeing and mount is the same), going to the Starlight Express 814 would show guiding and any other imperfections better if he looks closely enough, or uses software to measure things like star eccentricity. A simple way to think about it is the following: the guide camera, guide scope, responsiveness and quality of your mount, weight of your setup, seeing, etc. determine what kind of deviations from perfection you get. All your main camera does is record these deviations. Going to a finer image scale (smaller pixels) means that you can measure or record these deviations better, which is not always a good thing. Sometimes, it is best to not look too closely! Arun |
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Hi Arun yes, you and I are on the same page. Having done a lot of PHD support over the years, there are many people who only relate to what they see in PHD graphs and statistics, without knowing how it relates to the image scale of their imaging setup. I know *you* know this, but i have a tendency to spell out the obvious because there are beginners who may not know this On Fri, Dec 11, 2020 at 1:26 PM Arun Hegde <arun.k.hegde@...> wrote: Hi Brian, --
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