I'm struggling to understand why I have so much drift when photographing using my piggybacked Megrez 90.
Mounted on a paramount ME the primary OTA (12" SCT) has no drift in 5 minute exposures and slight in 10 minute exposures. However the piggybacked Megrez has noticeable drift in 5 minutes and significant drift in 10 minutes.
The drift is mostly dec but not pure 100%, some RA.
The drift is ongoing not cyclical (the FOV shifts increasingly one direction)
The drift is there even when the primary OTA is autoguiding with good accuracy.
The drift appears to INCREASE over time from one exposure to the next, the stars become more and more illongated (see example attached).
Surely it has to be flexure if the primary OTA is known to be tracking OK? But how could it be so consistent and ongoing?
Confused.
Regards,
Roger.