Correct focus distance (#693)

Fixes #691

Author: sonnyp

device-backend/control/planktoscopehat/planktoscope/focus.py

@@ -16,7 +16,8 @@
 
 
 class FocusProcess(multiprocessing.Process):
-    focus_steps_per_mm = 40
+    # https://github.com/PlanktoScope/PlanktoScope/issues/691
+    focus_steps_per_mm = 27
     # focus max speed is in mm/sec and is limited by the maximum number of pulses per second the PlanktoScope can send
     focus_max_speed = 5
 

device-backend/default-configs/fairscope-latest.hardware.json

@@ -1,6 +1,6 @@
 {
   "microsteps": 256,
-  "focus_steps_per_mm": 40,
+  "focus_steps_per_mm": 27,
   "pump_steps_per_ml": 2045,
   "focus_max_speed": 5,
   "pump_max_speed": 50,

device-backend/default-configs/planktoscopehat-latest.hardware.json

@@ -1,6 +1,6 @@
 {
   "microsteps": 256,
-  "focus_steps_per_mm": 40,
+  "focus_steps_per_mm": 27,
   "pump_steps_per_ml": 2045,
   "focus_max_speed": 5,
   "pump_max_speed": 50,