Tilt Series Scheduled Changes Dialog

This dialog box allows you to specify changes in several parameters during a series: Record exposure time, Record drift settling, target defocus, energy filter settings, and the frame time for Dose Fractionation mode in a K2/K3 camera. Each change is entered independently and appears as a separate line in the table at the bottom of the dialog. The upper section of the dialog contains controls for adjusting the change on the currently selected line of the table. The middle section has controls for adding or removing changes. The dialog may be resized to see more of the table.

Changes can be scheduled to happen on only one side of the tilt series, or a single entry can be used for a change that is to happen at both positive and negative angles. Changes can occur in either discrete steps or continuously, by changing linearly from one specified angle to another.

When changes are in discrete steps, they apply at and above the specified tilt angle. In this case, the value before the tilt series starts is applied below the lowest angle for a scheduled change. For example, suppose two changes are entered for the defocus target,one to set it to -3 at 40° and one to set it to -2 at 20°, both to occur at positive and negative angles. If the target is -1 before the tilt series starts, and the tilt increment is 1°, then the target would have the following values during the series: -3 above and at 40°, -2 from -39° to -20°, -1 from -19° to 19°, -2 from 20° to 39°, and -3 at and above 40°.

When a parameter is set to change linearly in a particular entry, the situation is more complex:

1. If there is a change set to occur at a higher angle, then the parameter will be changed linearly from the value at the given entry's angle to the value at the higher angle.
2. If there is no change set to occur at a higher angle, the parameter will be fixed at the value for the given entry. If you want a linear change, you must specify a change at a higher angle, such as the highest angle of the series.
3. If there is no change specified at a lower angle, the parameter will change linearly from its value before the tilt series starts at 0° to the value at the given entry's angle. If you do not want a linear change, you must specify an entry for 0° with a fixed value.

To apply this to the example, suppose that the defocus target is scheduled to be -3 at 40° and -2 at 20°, but with linear changes in each case. Then the target will be fixed at -3 above 40°, change linearly from -3 to -2 between 40° and 20°, respectively, and change linearly from -2 to -1 from 20° to 0°.

For dose-symmetric tilt series, all changes are imposed at angles relative to the starting angle of the tilt series, under the assumption that this angle is where the specimen itself is near zero tilt.  Thus, if the starting angle is 12°, a change scheduled to occur at 20° will actually occur at -8° and 32°.  For such series, all changes should be marked as occurring at plus and minus angles.

Setting the properties of a change

The currently selected itme in the table can be modified by entering a tilt angle and a value in the respective text boxes, selecting Change at both plus and minus angles to have the change occur at positive and negative angles, selecting a 'Set' radio button to set the type of parameter to change, and selecting Use fixed value or Change linearly depending on which is desired.