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Review of iPolar hardware and software for polar alignment
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Review of iPolar hardware and software for polar alignment
By: Stephen Andrew Kennedy
From: Strawn, Texas (Near Fort Worth, TX)
Experience: Relatively New (but I have an old soul…)
Executive Summary: iOptron’s iPolar upgrade, which replaces the optical scope on the iOptron SkyGuider Pro, does not accurately provide polar alignment when compared to results measured using identical equipment operating Sharpcap Pro and the specified guide camera and scope. Data was collected while simultaneously running both the iPolar alignment software and SharcapPro on the same equipment. The deficiency is consistent with an issue in the iPolar system’s calculation of altitude parameters in polar alignment after plate solving.
Equipment and software:
Tripod: Robus RC-5570 Vantage Series 3 Carbon Fiber Tripod
Mount: SkyGuider Pro Mount with factory-installed iPolar alignment hardware
Base: William Optics replacement base for SkyGuider Pro
Scope: William Optics RedCat 51
Guide scope: ZWO 30mm f/4 MiniScope
Guide camera: ZWO ASI 120 mm mono
Camera: Canon EOS Ra
Software: iOpton iPolar Software version 2.41 (current version at time of review)
Software: SharpCap Pro version 3.2.6448 (current at time of review)
Software: PHD2 2.6.9dev1
Issue Presented: After several months of operating factory-installed iPolar alignment equipment on the iOptron Skyguider Pro, the author observed consistent unsatisfactory polar alignment results with light exposures greater than 90s. Specifically, the author observed alignment degradation that was measurably constant over time beginning within minutes of achieving polar alignment even when a guide scope was applied with PHD2 tracking software. As discussed below, because PHD2 tracking software cannot adjust declination axis parameters of the SkyGuider Pro, the author hypothesizes that the flaw in the iPolar alignment system likely resides in altitude calculations after plate solving, but the author cannot completely rule out other inaccuracies in measurement, especially given the quantification calculations described below as registered by SharpCap Pro. The author acknowledges that the best practice to determine the exact issue would require inspection of iPolar software source code, which is not available to the author.
Discussion: The author observed that the iPolar alignment system could not maintain polar alignment for more than a few minutes when collecting exposures greater than 90 seconds. The author employed a guide scope and PHD2 software to correct observed deficiencies for exposures of more than 90s but found no significant improvement. At the suggestion of a cloudynights subscriber, the author compared SharpCap Pro polar alignment capabilities with the iPolar system. The author ran both polar alignment systems simultaneously over three consecutive evenings with identical errors observed in iPolar alignment during each test.
The experiment parameters included a routine of first achieving polar alignment with the iPolar alignment system, which uses a camera embedded in the SkyGuider Pro mount, and iPolar software version 2.41. Upon achieving polar alignment with the iPolar system, the author then checked polar alignment using SharpCap Pro version 3.2.6448 and the ZWO 30mm f/4 MiniScope and ZWO ASI 120 mm mono camera. SharpCap evaluates polar alignment as “poor,” “fair,” “good,” and “excellent” and provides specific numeric calculations on whether the alignment requires “up/down” and “right/left” adjustments, which the author understands to be altitude and azimuth calculations, respectively. On each test, after polar alignment had been achieved according to the iPolar system, SharpCap rated the polar alignment to be “poor” with both the up/down and right/left alignment errors to be greater than 1.00.00 while the iPolar alignment system software, running in the background, registered polar alignment to be on target. The author then captured 240 second duration exposures of the Rosette nebula and observed star trails after the second exposure even when using the PHD2 system and guide camera. Within approximately three to four minutes, the PHD2 guiding graph registered right declination corrections being sent to the mount which exceeded 4 on the graph and never corrected to less than 4 thereafter.
After one hour of guiding with the iPolar system, the author changed the test parameters and conducted polar alignment using SharpCap Pro and the referenced guide camera. Upon achieving polar alignment with SharpCap, the author then compared the polar alignment parameters with the iPolar alignment system, which was still running in the background. The iPolar system immediately indicated that Polar alignment was off target. However, because the iPolar alignment system does not provide numerical measurements of alignment, but instead includes an image of the alignment, the calculated deficiency per iPolar is unknown. For reference purposes, the author includes images of the polar alignment measurement of SharpCap (showing “good” quality alignment) versus the simultaneous off-target measurement registered by the iPolar system in figures one and two below. The author then proceeded to collect 240 second exposures of the Rosette nebula over one hour using the PHD2 guiding software. The author observed no star trails in any of the images, and the guiding graph registered right declination corrections in the range of 1 to 3 during the hour long test period. An example of a 240 second exposure of the Rosette nebula at 1600 ISO using SharpCap as the polar alignment system during the test period is provided in figure 3.
Conclusion: Unless there is an equipment-specific anomaly unique to the author, which seems unlikely given the successful results in operating the SharpCap Pro polar alignment system with the same equipment, the author concludes that the iOptron iPolar alignment system is not reliable and cannot recommend using the iPolar system for polar alignment.
Stephen Andrew Kennedy
Attorney at Law