Merge pull request #115 from spacetelescope/bugfix/exposure_time_calc…

…ulator

add exposure time formula for science cam

catkit2/services/zwo_camera/zwo_camera.py

@@ -126,6 +126,9 @@ def open(self):
         self.offset_y = offset_y
 
         self.gain = self.config.get('gain', 0)
+        self.exposure_time_step_size = self.config.get('exposure_time_step_size', 1)
+        self.exposure_time_offset_correction = self.config.get('exposure_time_offset_correction', 0)
+        self.exposure_time_base_step = self.config.get('exposure_time_base_step', 1)
         self.exposure_time = self.config.get('exposure_time', 1000)
 
         # Create datastreams
@@ -220,10 +223,15 @@ def end_acquisition(self):
     @property
     def exposure_time(self):
         exposure_time, auto = self.camera.get_control_value(zwoasi.ASI_EXPOSURE)
-        return exposure_time
+        return exposure_time - self.exposure_time_offset_correction
 
     @exposure_time.setter
     def exposure_time(self, exposure_time):
+        exposure_time += self.exposure_time_offset_correction
+        exposure_time = np.round((exposure_time - self.exposure_time_base_step) / self.exposure_time_step_size)
+        exposure_time = np.maximum(exposure_time, 0)
+        exposure_time = exposure_time * self.exposure_time_step_size + self.exposure_time_base_step
+
         self.camera.set_control_value(zwoasi.ASI_EXPOSURE, int(exposure_time))
 
     @property