One of the primary goals of ESI is to minimize the effects of flexure. A number of tools are provided to this end.

An example of flexure in all three modes is given below, in animated GIFs which show data taken at different elevations and different rotator angles. Starting at elevation of 90°, the first nine frames are taken at rotator position angles from -270° to +90° in 45° increments. The next nine frames are at elevation 60°, with the rotator moving in the opposite direction (+90° to -270°), followed by elevation 30° and elevation 0°, again switching directions at each new elevation. (At the lower elevations it is fairly easy to tell when a new elevation loop has started because of this change in direction.)

Note that you may need to hit RELOAD to view the movies! This will loop three times through the animations.

The top panel shows the raw, uncompensated image motion. The bottom panels show the motion with the FCS (Flexure Compensation System) activated. This system provides an open-loop correction derived from fits to measured flexure.

Note that the flexure is greatest at horizon, as expected and that the amount of flexure is quite comparable in all three modes. With the FCS on, the image motion is greatly reduced.

Also remember that these movies represent the worst-case scenario. Any real observations will cover a much smaller part of the (elevation, rotator angle) parameter space, hence will suffer significantly less image motion.

	Echellette	Low-Dispersion	Imaging
FCS off
FCS on