NICMOS cameras can be operated in parallel with each other. However, doing so may require serial dumps of the memory buffer which will cost on target time. Also, due to the NICMOS dewar anomaly, the three cameras are not parfocual -- that is, they are not in focus at a common PAM position. The focus positions for Cameras 1 and 2 are very close to each other, and when operated in parallel with each other, Cameras 1 and 2 will produce acceptable images. The intermediate PAM position provides a compromise focus position for Cameras 1 and 2, optional parameter CAMERA-FOCUS = 1-2.
The focus position for Camera 3 is far from the focus position for Cameras 1 and 2. When Camera 3 is operated in parallel to Cameras 1 and 2, star images in Camera 3 will look like donuts, and vice versa. The following is an example of specifying "PARallel" observations on the Phase II exposure line. For this example, Camera 1 is prime and Camera 2 is operated in parallel. It is recommended that the exposure times of parallel observations be shorter than the primary science observation.
Note: Since Cycle 7 and 7N, the NICMOS commanding has been changed so that a camera not used in parallel with a prime camera will be set into mode that will not produce "Electronic Bars."