LBC Overheads

Commissioning of the Large Binocular Cameras Overheads affecting observations with LBT+LBC are reported individually in the table below. It should be noted that some of them are superimposed so that, for example, telescope dithering, filter preset and rotator preset and executed at the same time, and thus the total overhead is not the bare sum of all the overheads from single subsystems.
From the point of view of the observer, the execution of a single OB, after image analysis, has the following global overheads:
• ~45s : from "play" command to the first shutter opening
• 45s-65s : from shutter closing to shutter reopening of OB ending

To these, the following "fixed" overheads should be added:
• 60s-180s : initial telescope preset (consider 120s as a mean value)
• ~120s : complete cycle of image analysis (on average, two are needed)

In total, there are therefore 120s for the initial preset + 240s for IA + 45s at the start of the OB + 60s for each image.
From these numbers it is clear that the longer the single exposure time, the smaller the impact of overheads, although the single exp. time depends, of course, on specific scientific requirements. If real-time image analysis is implemented, it will be possibile to reduce or eliminate the IA cycles before OB execution, thus remarkably reducing global overheads. Real-time IA is currently in a testing phase.
The first image analysis (4-5 cycles) is done at the beginning of the night during nautical twilight and does not affect scientific time. When possible, also photometric standards are observed during twilight, both evening and morning.



Subsystem	LBC Blue	LBC Red
Preset Telescope	90 / 180 sec	90 / 180 sec
Dithering Step	~30 sec	~30 sec
Rotator	~25 sec	~25 sec
Filters	0-22 sec	0-25 sec
Mirrors	5-20 sec	5-20 sec
Camera	10 sec	8 sec
Readout	26-27 sec	22-23 sec

commissioning: back