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Two minutes @ 250mm is definitely too long for consistent results with this
mount [you might get some usable subs], but obviously this is not your primary problem. Assuming that the elongation is in the R.A. tracking direction, it is most likely that it exposes correctly for a period of time, the
driven mass then slips quite quickly to a new fixed position, and continues exposing correctly at the new position for the rest of the duration of the exposure. If this is the case, then most likely something is not properly
firmly locked, such as the scope to the mount, or the drive clutch if the adventurer has one.
The other possibility is that you have not set the scope up so that it is slightly unbalanced against the direction of the drive, thereby eliminating the backlash that all gear trains have. This can frequently happen when imaging is commenced not long before the scope becomes vertical, and then flops forward a tiny bit when the scope passes through the vertical position.
raymo
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