Adding a basic script for taking a bias frame.

* Adding a basic script for taking a bias frame.

This script takes the usb port (as reported by gphoto2) as the first
parameter and an optional second parameter for a filename. Default
filename is timestamped file prefixed with the word `bias-` that is
saved in current directory.

Changes camera settings to fastest possible shutter speed (1/4000s on
the EOS 100D), takes five exposures, then returns the camera to the
bulb setting.

scripts/take_bias.sh

@@ -0,0 +1,48 @@
+#!/bin/bash -e
+
+usage() {
+  echo -n "##################################################
+# Take a series of bias frame images.
+# 
+# This will change the camera setting to the quickest
+# exposure possible and then take a number of photos
+# before changing camera back to bulb setting.
+##################################################
+
+ $ $(basename $0) PORT [OUTFILE] [NUM_FRAMES] [SHUTTER_INDEX]
+ 
+ Options:
+  PORT              USB port as reported by gphoto2 --auto-detect, e.g. usb:001,004.
+  OUTFILE           Output filename, defaults to bias-YMD-HMS.cr2.
+  NUM_FRAMES        Number of exposures to take, defaults to 1.
+  SHUTTER_INDEX     The camera shutter index to use, defaults to 52 (1/4000s) on
+                    EOS100D.
+"
+}
+
+if [ $# -eq 0 ]; then
+    usage
+    exit 1
+fi
+
+P=$1
+
+SAVE_FILE=${2:-"bias-%Y%m%d-%H%M%S.cr2"}
+echo "Taking bias frames on port ${P}: ${SAVE_FILE}"
+
+NUM_FRAMES=${4:-1}
+SHUTTER_INDEX=${3:-52} # 1/4000s on EOS 100D
+
+# Set to fast speed
+gphoto2 --port=${P} --set-config-index shutterspeed=${SHUTTER_INDEX}
+
+COUNTER=0
+until [[ ${COUNTER} -eq ${NUM_FRAMES} ]]; do
+    gphoto2 --port=${P} --filename=${SAVE_FILE} --capture-image-and-download
+    let COUNTER+=1
+done
+
+# Set back to bulb
+gphoto2 --port=${P} --set-config-index shutterspeed=0
+
+echo "Done with bias"