Images elongated or show jumps

• The JKT is very sensitive to imbalance. Ensure the black bag is fitted (and not fallen off) around the bottom of the mirror cell. Another cause of imbalance is oil accumulation in the Dec axis, if the oil scavenging system is not working properly.
• If autoguiding, the star could be too faint to centroid properly.
• Is it windshake?
• It's also possible that the mirror support system is oscillating.
• Especially for sources that are in the west at a zenith distance of more than 50 degrees, we have observed double images due to mirror jumps. These jumps are typically a few to 15 arcsec long. If this is the case, move to a different object (closer to zenith).
• The JKT secondary is mounted in a way that allows it to flop when the telescope goes through the meridian. If you are observing on the meridian you might experience this; the images are affected by a jump of about half an arcminute.