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I’ve been struggling with elongated stars for the past few months now and have tried numerous things and read through similar threads here and on other forums with no success. This is really starting to get to me as I’ve lost track of the number of clear nights wasted so far. The elongation direction is not consistent at all and varies over different parts of the sky. The kit: Mesu 200, Celestron RASA, 60mm StarGuider guidescope, QHY5L-II guidecam, Atik 414EX main imaging camera, Baader UFC, Baader F2 High Speed narrowband filters. Things tried so far: Tested for cable drag and recently started routing all cables coming off the scope at the back of the dovetail. Both RA and DEC balance is spot on. This was performed several times with a digital fishing scale and the balance points marked. I’ve always used SharpCap for PA but also tried several runs of PHD static and drift alignment with the same results. Read the entire SiTech Operations manual for the Mesu as at one point I was getting elongation mostly in Ra and though the mount may not be tracking at a correct sidereal rate. There’s a method of calculating the proper track rate and have spent a couple of imaging sessions doing this with limited success. The method involves measuring the drift of a star in Ra in an interval of 10 minutes. Then after some clever math, one can change the Ra motor ticks in the ServoConfig configuration for the mount. This worked, but only for the position in the sky where the drift was measured and as soon as the mount was pointed to another part of the sky, the issue would immediately reappear. What’s worse is that the same tracking rate would no longer give round stars on a different night in the same position in the sky it did for the night before. Short exposures of a minute or shorter in any position in the sky give perfectly round stars. This eliminates collimation, issues with the camera or any other optical element in the light path as I see it. Differential flexure between the main scope and the guide scope is a non-factor as I get elongation during unguided exposures. Tried tweaking the settings in PHD2 thinking I might be able to guide it out. Results, again, vary depending on the night and position the scope is in. Sometimes guiding would give almost acceptable stars and some improvement over unguided and other times it would simply make matters worse. Additionally, rotating the camera 90 degrees results in the direction of elongation being rotated as well. The camera is coupled to the front corrector plate via screw adapters which I simply can’t see flexing. The only time I can get round stars is with the scope pointing near the Zenith. I’m at a point now that the only thing making sense is flexure within the RASA or imaging train. I know the camera is tightly fixed to the corrector plate so there can’t be any play there. The only place where flexure could occur would be at the main RASA Losmandy mounting plate. The plate is screwed in to the front and back aluminium holders by four M5 screws I believe. Thought these might have loosened over time but after checking, they’re as tight as they’d go. Not sure how solid a RASA should be and I didn’t really test or look at this when I got the scope as there was no need, but when fully mounted, the scope can be easily rocked by applying light pressure to the top mounting plate. This is not an issue with the Mesu head as it’s simply rock solid and can’t move it at all regardless of the force applied. At this point it’s all pointing to the scope/mounting plate flexing due to gravity as the scope is not exactly light. This could explain the odd behaviour throughout different parts of the sky as the scope is flexing in different directions. Trying to determine if it is indeed the scope flexing, I’ve done some testing yesterday. Setup everything as usual during the day and focused on a brick wall roughly 30 meters away on a day with no wind. Mount was off and both axes were locked with the mount hooks, so mount tracking errors or movement would be eliminated this way. Started with 5 short consecutive exposures, then at 10 minute intervals another 5 exposures were taken until 40 minutes elapsed. Each set of 5 exposures were integrated in PI using an average combination with no normalisation or any pixel rejection algorithms. This was done with the scope on both the East and West side of the pier pointing at the same brick wall and with the mirror both locked and unlocked. Combining these integrated images into GIFs and plotting the Ra and Dec orientation clearly shows considerable drift over the course of 40 minutes. As can be seen the drift is not purely in Ra or Dec, but a combination of both. Mirror locked. Scope on East side of pier. Mirror unlocked. Scope on East side of pier. Mirror locked. Scope on West side of pier. Mirror unlocked. Scope on West side of pier. These next four GIFs show the result of pushing on the scope’s top mounting bar. The direction of movement when applying pressure on the scope is very similar to the direction of drift in the first two GIFs. If I’m not mistaken this would indicate that the RASA is indeed flexing/sagging due to gravity. The scope was purchased from FLO about two years ago. Would this be considered normal behaviour or am I just barking up the wrong tree here? Mirror locked. Scope on East side of pier. Before and after pressure applied on scope mounting bar. Mirror unlocked. Scope on East side of pier. Before and after pressure applied on scope mounting bar. Mirror locked. Scope on West side of pier. Before and after pressure applied on scope mounting bar. Mirror unlocked. Scope on West side of pier. Before and after pressure applied on scope mounting bar. I find it hard to believe that the image should drift this much over the course of 40 mins, but then again, I may be wrong and this isn’t out of the ordinary??? Any help with this from the awesome and knowledgeable SGL comunity would be greatly appreciated as I’m simply out of ideas and things to try.
Hi all! Yesterday good weather, so had my first go at drift alignment with my new reticulated eyepiece. I took my time to figure out well the various steps in the right order, etc... At one time, pointing a star in the east, I think I overdid the correction on the Altitude, because the star started drifting a lot, so I started again from the beginning... As always a learning curve! :-) But I had fun doing it. It took me a lot of time, but finally I got to shooting some subs, and these are the results: M57 @ 38 second subs: M13 @ 63 second subs: The usual coma problem is visible, but I am nevertheless quite satisfied with this first try... The stars look pretty good, if not enlarged too much ;-) Opins? Any feedback would be appreciated! Gerhard.
I bought a new CEM25P and just spend two nights trying to get it to track. I've had many GEM mounts over the last 30 years, so I thought this would easy. But it seems that either I have a problem with the mount, or I am getting old. I leveled, balanced, and polar aligned the mount well. Then I attached a guide scope. I did NOT attach the cable from the guidescope to mount. I also did not attach the mount to my computer. This way I could watch stars drift and get an idea of was going on with just the mount. I checked the CEM25's tracking rate, and it is set to sidereal. LAT/LONG and perfect. Time accurate. Next, I watched stars drift on my laptop using PHD. When the mount is turned on, and tracking turned ON - the stars move somewhat quickly in RA. Like they are slewing slowly. When I turn OFF the tracking (zero key) they still drift, but a little slower. When I turn off the power to the mount, of course the stars drift, but at slower rate still - normal sidereal rate. When I turn the power back on the stars drift a little faster. Turn the tracking back on, and they drift faster still. But when I set the slew speed to 2x, and press and hold down the left arrow key, and the stars STOP drifting. Perfect tracking. Thanks for any advice! CF
After a 2 month wait, we finally got some clear slies last night so I had a chance to finally try out the Orion Starshoot autoguider. Sadly, I spent a long and very frustrating night just trying to get the darn thing to guide properly, but wihout success. I was getting great tracking results from my HEQ5pro mount on its own, round stars on any exposures up to about 30 seconds, but as soon as I engaged the tracking scope, it was driving it all over the place (see attached pics). I'm using the 50mm guidescope that comes in the "Orion Magnificent Mini" kit, and I made sure to enter the correct focal length (which I believe is 162mm) into the PHD2 software (not 50mm as I've read others have accidentally done ). There was zero wind last night, so I can't really blame that. Everything seemed to be done-up tight, although I have just started using the HEQ5pro extension tube to avoid tripod leg collisions, which together with the Explore Scientific AR152 refractor scope, does make for a very tall setup, but I think I can discount that because it still tracks really well without the autoguider engaged. A lot of the PHD2 tools and controls are a bit of an alien language to me, but I spent most of the night trying various settings and running some of the built in tools and following the reccomendataion, but to no avail, not even a slight improvement. Does anyone have any ideas how to get this autoguider to work? Would really apprciate any pointers - ideally without abbreviations, as they'll just make my brain hurt even more that it already does Much thanks in advance.
Hi all, just posting some new pics I took the other night in Saint Barthélemy, at 1633 meters above sea level (very good seeing): M27: M31: IC1396: The usual problems arise: guiding, coma, and noise from the camera (especially visible in the M31, I think). These are pics from 30 73secs exposures at 800 ISO with darks and bias. I did not take flats... Do you think that would improve the noise problem? I'm hoping to construct a flatbox some time... And maybe acquiring a laptop to use for serious guiding. A guide scope would already be available from my astro club... Any thoughts, suggestions would be very welcome! :-) Gerhard.
Hi all, I was just wondering... I've been looking for eyepieces to do drift alignment with, and as per this video: http://www.andysshot...tAlignment.html and after trying out with my own 5mm eyepiece (without reticle), I wanted a 5mm reticle eyepiece. But searching it turns out there are practically only 12,5mm illuminated reticle eyepieces... The 5mm Orion seems to have been discontinued... Anybody have any idea why this is? Did the 5mm cost too much? As I see it a 5 mm would do nicely, because one easily sees the direction a star goes, when turning off the motor drive, and I'm guessing it would also be better for detecting the drift. More so than with a 12,5mm... Thanks for any ideas, thoughts! Gerhard.