K2 Summit and K2 Base Direct Detection Camera User's Guide
33
Binning and Subareas
Binning is performed post-acquisition which means that it doesn’t increase readout speed by
itself in the way that binning does on a CCD. However, it does allow a large increase in
dynamic range in exchange for the associated loss in spatial resolution. Because of the very
low read noise of the camera, the noise floor remains low. Perhaps the biggest benefit,
however, is the possibility of imaging in Counted mode with large signal levels. As an
example, Counting mode binned by 6 allows 360 electrons per pixel per second instead of the
binned x 1 level of 10 electrons per pixel per second. This is very useful for microscope
alignment and stigmation with live diffractograms.
Dose Fractionation
Dose Fractionation mode provides straight-to-disk capture at 40 fps (0.025s per frame) in
Summit mode, and approximately 10 fps in Base. Dose Fractionation mode is accessed as an
alternate to the standard Record mode available in the camera palette. Selecting Dose
Fractionation mode in the camera palette switches the system from acquiring single images to
acquire a series of images.
Dose Fractionation mode splits the total electron dose that would normally be used to acquire
a single image into a number of separate frames. For instance a 20 e
-
/pixel dose in 1 second
can be distributed over twenty 50 ms images each with 1 e
-
/pixel.
These frames can be viewed independently and used for different options such as frame
alignment and drift correction or in some cases advanced usages such local drift correction
within regions of a single frame.
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