I'm an observer of asteroid occultations, and for years we've typically used monochrome analog video cameras, with external GPS-based video overlay timing devices to provide precise timing. However, with analog cameras becoming rare, and with the improvements in CMOS planetary cameras, several of us are starting to use cameras like the ASI290MM, and particularly the new ASI462MM to record and measure occultations. For timing, we're using GPS-based LED flashers that flood the sensor field at precise times with light at a level that doesn't saturate the detector. We can then interpolate between frame illumination levels to determine accurate frame times. It works, but there are limitations, and it requires setting LED flash levels correctly.
There is some ongoing development work using industrial machine-vision cameras with frame strobe or frame trigger functions, with the intention of using a custom GPS-based timing device to measure frame times accurately. This approach eliminates the issues with flash timing, but limits observers to "special" cameras, when many potential observers already have or would be willing to buy a planetary camera.
It occurred to me that for most imaging uses, the ST-4 guiding port is unused, and might be available to implement a start-of-exposure strobe pulse. Obviously I'm making assumptions about the suitability of the port hardware, which appear to be simple open-drain switches to ground, and implementing a strobe may not be feasible. If it is possible, however, that would provide a new capability for accurate timing of occultation and other time-sensitive observations. I'm presuming this might be done in firmware alone with no hardware changes, since hardware changes are clearly not going to happen.
In the ideal case, the firmware might support both guiding or strobe functions, with a switch in the camera driver to select one or the other. Alternatively, there might just be a special firmware that users might load into their cameras to disable guiding functions in favor of a frame strobe. In the best possible case, such firmware might allow retrofitting timing capability onto existing cameras already in the hands of users. If it could be done for the ASI290MM and ASI462MM cameras, there would suddenly be a lot of cameras already in the field that would be excellent occultation cameras. Obviously it's not something that would be practical to do for an entire camera line.
There have been special cameras developed to allow precise timing (e.g. the QHY174 GPS) but they are expensive and require involved development such that it's not practical to keep up with new sensors. If a frame strobe could be implemented on the ST-4 port, that would allow precise timing with no onboard GPS needed, and would allow the groups doing specialized projects to implement the external timing equipment specific to their needs.
Thanks for considering this request!
Bob Jones
