I suspect that I might have a continuing problem with an RA oscillation in the movement of my Ioptron CEM70? It can be an explanation for Eccentric star shapes elongated along the RA axis direction. Interested to know if others have experienced or detected anything similar in their mounts?
Previously ....in an earlier-model CEM70 mount - now returned - at about 1s intervals there was a regular rapid ~ 1.5-2 arcsec detour in RA that then quickly settled back to the mean until the next cycle on the following second. This appeared to distribute some of the light along the RA axis making stars appear elliptical. The problem did not show up in PHD2 guiding because that only resolves movement on a 2-3s timescale .
I only discovered this RA oscillation after carrying out quite a few experiments a couple of years ago with the first CEM70 mount that I had before it was replaced (much to their credit and without any fuss by First Light Optics) - the problem with the first being 1.5-2 arcsec oscilations accompanied by a faint clicking sound.
When imaging 'normally' at resolutions above 1.0 arcsec / pixel the problem was hardly visible in terms of its effect upon star shape. However down at 0.4-0.5 arcsec pixel the problem became more obvious with star shape Eccentricities averaging at 0.5 - 0.6 and r of PSFs ~ 0.8- 0.85 across the field.
Interested to know if this second-scale oscillation in RA movement was just a freak occurence with my particular set up -- or something that others have seen too
Tim
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I thought it might possibly also be useful to append some parts of a presentation I did on the original diagnosis of the problem? The set up was a PDS200 (f=1000 mm) on the original CEM70 mount and movements monitored with an ASI294 MM camera at 2.315 u pixel size. Hopefully it is self explanatory ... I used the grid of sensor pixels to track what the scope and mount were doing every 100ms over a 60s period.
Previously ....in an earlier-model CEM70 mount - now returned - at about 1s intervals there was a regular rapid ~ 1.5-2 arcsec detour in RA that then quickly settled back to the mean until the next cycle on the following second. This appeared to distribute some of the light along the RA axis making stars appear elliptical. The problem did not show up in PHD2 guiding because that only resolves movement on a 2-3s timescale .
I only discovered this RA oscillation after carrying out quite a few experiments a couple of years ago with the first CEM70 mount that I had before it was replaced (much to their credit and without any fuss by First Light Optics) - the problem with the first being 1.5-2 arcsec oscilations accompanied by a faint clicking sound.
When imaging 'normally' at resolutions above 1.0 arcsec / pixel the problem was hardly visible in terms of its effect upon star shape. However down at 0.4-0.5 arcsec pixel the problem became more obvious with star shape Eccentricities averaging at 0.5 - 0.6 and r of PSFs ~ 0.8- 0.85 across the field.
Interested to know if this second-scale oscillation in RA movement was just a freak occurence with my particular set up -- or something that others have seen too
Tim
------------------------------------
I thought it might possibly also be useful to append some parts of a presentation I did on the original diagnosis of the problem? The set up was a PDS200 (f=1000 mm) on the original CEM70 mount and movements monitored with an ASI294 MM camera at 2.315 u pixel size. Hopefully it is self explanatory ... I used the grid of sensor pixels to track what the scope and mount were doing every 100ms over a 60s period.