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Showing results for tags 'periodic error'.
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Hi Guys Since we lost Jupiter, Saturn and Mars from easy viewing I've been getting into photographing deep-sky-objects, initially I wasn't really interested but since seeing what other people have done and getting a glimpse of a couple of objects myself I've been inspired! I recently bought an EQ3-2 dual axis motor drive system and have been reading up on polar alignment. I've attached my best efforts to date on M42, orders of magnitude away from the majestic images I've seen on here but I've been seeing a steady improvement as I've used the motors and improved my technique. I'd like to highlight the star trailing evident in the oblong appearance of the stars in the image. I don't think I'm imaging long enough for periodic error to creep in (please correct me if I'm wrong!) and the drift seems to not be in the RA axis so I'm guessing it's DEC drift? I'm aware that the EQ3-2 is not really adequate for long exposures of DSOs but the most I've been able to achieve without considerable trailing is an 8 second sub, when I feel like I should be able to achieve a stable frame for maybe up to 20-30 seconds. I've been polar aligning by eye as I don't have a polarscope and I've been having trouble getting my mount fully aligned before I begin a polar alignment as I'm not 100% sure that I've got the mount fully straightened before aligning. The DEC axis has an arrow that allows me get it lined up nicely at 90º, however the the scale for the RA axis (shown in the other attached image) moves as I move the RA axis unless I lock it in place, so I don't know whether I'm completely straight or not, which I'm assuming can affect the quality of my alignment. Any advice or comments would be much appreciated! Thanks, Roysten
I'm a complete noob with imaging but am really methodical in approaching any hobby I pick up so I'm hoping that with a little practice I can someday take some amazing images for my own enjoyment. Currently I'm having no end of trouble with my scope setup and was hoping someone could shed some light on what MIGHT be going on here. I have a Nexstar 6se which uses spur gears I realize, but it's what I have. I'm using a celestron 6/8se wedge on a cpc 1100 tripod which makes for a rock solid platform for this modest scope. Movement calms down with this setup in under a second so I'm confident it's not the mount. The problem though, when I get my camera on the scope, get things focused as well as I can without a mask (i'm working on getting one 3d printed), I'm getting trails no matter what I do! I'm polar aligned, making very sure to use a high power eyepiece and really spend the time to line up my mount. Any image longer than about 20 seconds however exhibit trails! I've adjusted the backlash controls from 0 to 50 in 5 unit increments with no discernible results. I've used A/C power as well as a 12 volt 20amp/hr battery so I don't believe it to be power related. This setup, with the heavy tripod, the wedge, a decent computerized mount should allow me to image for a couple of minutes at least in my mind, but I cannot get it to work properly for even super short exposures! I'm wondering if this is something that can be adjusted with the mounts clutch or some other trick to get things working how they should. The images I've attached show an extreme amount of error in tracking and I'm beginning to wonder if my particular mount is just not going to work no matter what! The "trailing 3" image is of Albireo and you can see that the stars below this double are doubled themselves, meaning to me that the mount is skipping or jumping partway through the exposure (45 seconds in this case) Any help would be awesome.
Hi all first post here! I've been reading your forum's post for a long time and I have found really instructive and educational information. Last year, I bought my first telescope to fulfil my dream! A combination of a Skywatcher Black Diamond 120ED and an AQ-EZ6 GT mount. Last year I tried the visual part, to learn the basics and take some photographs (with mediocre results). This year I tried to improve my photographic skills. The first thing I noticed was that I could not take a photo without extreme star trailing. As I've read, a bad polar alignment would be the cause. So I tried carefully to improve it through the PA scope of the mount, or with the 3-star alignment of the mount with no good results. The strange thing I noticed looking through the eyepiece, was that sometimes the stars were drifting, after I had released the keypad button during the alignment. Last month I bought a QHY5L-II camera to use it as a guiding camera. I connected the mount to my laptop using a custom made adapter (cost me 14€) and with the very good EQMOD drivers, I start using software solutions for Polar Alignment, including PHD2 and EQAlign (more accurate and friendly but a little bit buggy). For guiding I tried also the MetaGuide (the only one that allowed me to take a photo of 30 secs!! without trailing). I soon realized that the mount should have significant Periodic Error on the RA axis. Using PHD2 and these instructions http://eq-mod.sourceforge.net/docs/eqmod_vs-pec.pdf (appendix A), I measured the PE curve of the mount and imported the measurements into the PECPrep for evaluation. The peak to peak value is extreme: 130arcsecs Strange thing is that the period of the PE is not the period of the worm but a quarter of it: It is worm's fourth harmonic or Stepper motor's period (119.67 secs). A harmonic cannot have larger amplitude than the base frequency, so I guess something is wrong with the stepper motor or the motor pulley or the motor driver circuitry or maybe the belt. I changed the belt with a new one (a Contitech Syncroflex) and repeated the measurement but the results where similar. The contribution of the 116.67secs error is 3 to 4 times more than the error from the worm. The resulting PE is really difficult to be handled by the PHD which after 5 to 10 secs fails to follow the movement. Even at the calibration phase it prompt errors regarding the orthogonality error. Drift align is almost impossible with PHD (target circle never gets steady but keeps growing and then shrinking and back again). Any suggestions? Thanks in advance, Panayiotis