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video_autofocus [2016/09/07 15:26]
asiadmin ↷ Page moved from documentation:video_autofocus to video_autofocus
video_autofocus [2016/10/04 15:13] (current)
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 The ASI auto-focus system uses an electronic circuit to detect the high spatial frequency information present in a video signal coming from an analog camera, and converts it to a focus value for each frame – the better the focus, the larger the focus value. ​ Depending on the sample and the type and power of the objective, the conditions to achieve the best focus value may change. ​ To compensate, the system incorporates an auto-calibration routine that automatically sets various internal parameters to get a good focus value. ​ The system also allows you to highlight any subset of the video field and focus on an object in it.  The ASI auto-focus system uses an electronic circuit to detect the high spatial frequency information present in a video signal coming from an analog camera, and converts it to a focus value for each frame – the better the focus, the larger the focus value. ​ Depending on the sample and the type and power of the objective, the conditions to achieve the best focus value may change. ​ To compensate, the system incorporates an auto-calibration routine that automatically sets various internal parameters to get a good focus value. ​ The system also allows you to highlight any subset of the video field and focus on an object in it. 
  
-[{{ :​documentation:​autofocus_connectors.png?​direct&​300 |Relevant Auto-focus Connections ​ }}]+[{{ autofocus_connectors.png?​direct&​300 |Relevant Auto-focus Connections ​ }}]
  
-[{{ :​documentation:​autofocus_video.png?​direct&​300 |Screenshot of Video Monitor signal from the Auto Focus controller showing Sampled/​Highlighted Area}}]+[{{ autofocus_video.png?​direct&​300 |Screenshot of Video Monitor signal from the Auto Focus controller showing Sampled/​Highlighted Area}}]
  
 When the controller is given an auto-focus command, it moves from a starting position to a stop position, constantly checking the focus signal. ​ The focus signal goes through a filtering process to remove unwanted false focuses caused by noise and other disturbances. ​ In //"​Normal"//​ mode, the controller takes the filtered signal and watches for the maximum value. ​ When a new maximum value is detected, the controller keeps track of the position where it was found. ​ When the end of the scan is reached, the controller goes back to the position that had the highest value. When the controller is given an auto-focus command, it moves from a starting position to a stop position, constantly checking the focus signal. ​ The focus signal goes through a filtering process to remove unwanted false focuses caused by noise and other disturbances. ​ In //"​Normal"//​ mode, the controller takes the filtered signal and watches for the maximum value. ​ When a new maximum value is detected, the controller keeps track of the position where it was found. ​ When the end of the scan is reached, the controller goes back to the position that had the highest value.
  
-[{{ :​documentation:​autofocus_scan.png?​direct&​300 |Fig 2: A "​Normal"​ auto-focus scan showing a stage’s focus-axis position in tenths of microns, and the focus signal and filtered focus signal (focus-value) extracted from input video signal.}}]+[{{ autofocus_scan.png?​direct&​300 |Fig 2: A "​Normal"​ auto-focus scan showing a stage’s focus-axis position in tenths of microns, and the focus signal and filtered focus signal (focus-value) extracted from input video signal.}}]
  
 There is also a //"​Hill Detect"//​ mode available. ​ In this mode, the auto-focus controller watches for the focus value to increase in value and then start to decrease, thus detecting a hill.  At this point, the auto-focus controller stops the scan and goes back to the position that had the highest focus value found on the hill.  This is somewhat subject to false focusing and should be used only on high contrast single-layer samples with sharp edges. There is also a //"​Hill Detect"//​ mode available. ​ In this mode, the auto-focus controller watches for the focus value to increase in value and then start to decrease, thus detecting a hill.  At this point, the auto-focus controller stops the scan and goes back to the position that had the highest focus value found on the hill.  This is somewhat subject to false focusing and should be used only on high contrast single-layer samples with sharp edges.
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 **Normal:​** ​ Enabled when ''​AF Z=0''​. ​ In this mode, the controller moves down 1/2 the //travel distance//, scans up the full //travel distance//, and then returns to the position that had the peak //focus value//​. ​ This is the Default mode. **Normal:​** ​ Enabled when ''​AF Z=0''​. ​ In this mode, the controller moves down 1/2 the //travel distance//, scans up the full //travel distance//, and then returns to the position that had the peak //focus value//​. ​ This is the Default mode.
  
-{{ :​documentation:​autofocus_normal_scan.png?​direct&​300 |}}+{{ autofocus_normal_scan.png?​direct&​300 |}}
  
 **Hill Detection:​** ​ Enabled when ''​AF Z=1''​. ​ In this mode, the controller moves down 1/2 the travel distance, then starts to scan up until the focus value rises from its lowest value to a peak then begins to decrease back to a lower value again. ​ When this hill is detected, the controller will return to the position that had that maximum focus value at the top of the hill.  This search is generally used to find the first focus point. ​ Note that if no hill is found, the controller will return to the highest focus value detected after reaching the end of the full //travel distance//. **Hill Detection:​** ​ Enabled when ''​AF Z=1''​. ​ In this mode, the controller moves down 1/2 the travel distance, then starts to scan up until the focus value rises from its lowest value to a peak then begins to decrease back to a lower value again. ​ When this hill is detected, the controller will return to the position that had that maximum focus value at the top of the hill.  This search is generally used to find the first focus point. ​ Note that if no hill is found, the controller will return to the highest focus value detected after reaching the end of the full //travel distance//.
  
-{{ :​documentation:​autofocus_hill.png?​direct&​300 |}}+{{ autofocus_hill.png?​direct&​300 |}}
  
 The **Hill Offset** value is the percentage that the //focus value// must decrease from its recent maximum before the scan is satisfied that a hill has been detected. The **Hill Offset** value is the percentage that the //focus value// must decrease from its recent maximum before the scan is satisfied that a hill has been detected.
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 1.Focus the sample manually and then press the ZERO button on the controller. ​ When correctly configured, the controller will never auto-focus to a position greater than 200 µm in the negative direction from the 0000 positioned. ​ (This safety feature may be disabled by the ''​AFLIM''​ (or ''​AL''​) command )  By zeroing the controller at a typical focus location, you should have a reasonable range for the auto-focus to operate yet still protect an objective from crashing into the sample (Fig 3).  You can also use the ''​HERE Z=0''​ command to zero the Z-axis position with software, if Z is the focus axis. 1.Focus the sample manually and then press the ZERO button on the controller. ​ When correctly configured, the controller will never auto-focus to a position greater than 200 µm in the negative direction from the 0000 positioned. ​ (This safety feature may be disabled by the ''​AFLIM''​ (or ''​AL''​) command )  By zeroing the controller at a typical focus location, you should have a reasonable range for the auto-focus to operate yet still protect an objective from crashing into the sample (Fig 3).  You can also use the ''​HERE Z=0''​ command to zero the Z-axis position with software, if Z is the focus axis.
  
-[{{ :​documentation:​autofocus_microscope_limits.png?​direct&​300 |Fig 3:  Set objective farther than 200 microns from the sample, then set the focus drive’s position to ZERO.}}]+[{{ autofocus_microscope_limits.png?​direct&​300 |Fig 3:  Set objective farther than 200 microns from the sample, then set the focus drive’s position to ZERO.}}]
  
 2.Insure that **DIP Switch 2** on the back of your controller to UP position (Fig. 4). Your LCD will now display the //focus value// marked as ''​F:####''​ on its bottom line.  This number will always be between ''​0000 and 2047''​. ​ 0000 indicates that little or no video signal is getting to the auto-focus card; check your connections. ​ If the //focus value// reads ''​2047'',​ then the system is saturated with too much signal; try adjusting the Video Gain, Brightness, and Contrast controls on your camera if available. If this does not help, then go to step 4. 2.Insure that **DIP Switch 2** on the back of your controller to UP position (Fig. 4). Your LCD will now display the //focus value// marked as ''​F:####''​ on its bottom line.  This number will always be between ''​0000 and 2047''​. ​ 0000 indicates that little or no video signal is getting to the auto-focus card; check your connections. ​ If the //focus value// reads ''​2047'',​ then the system is saturated with too much signal; try adjusting the Video Gain, Brightness, and Contrast controls on your camera if available. If this does not help, then go to step 4.
  
-[{{ :​documentation:​autofocus_display.png?​direct&​300 |Fig 4:  Shows the focus value as F:1696 on a two-line LCD display (a) and as F:1904 on a three-line LCD display (b).  Dip Switch 2 on the back of a controller in the UP position (c).}}]+[{{ autofocus_display.png?​direct&​300 |Fig 4:  Shows the focus value as F:1696 on a two-line LCD display (a) and as F:1904 on a three-line LCD display (b).  Dip Switch 2 on the back of a controller in the UP position (c).}}]
  
 3.By focusing through your sample, you can watch the focus value change on the LCD screen. ​ When the sample is held steady, the //focus value// on the LCD should remain steady; ideally, only the last digit should fluctuate by one or two counts. ​ This is due to slight noise in the system and is tolerable. ​ If the fluctuations are bigger, check the connections for any problems. 3.By focusing through your sample, you can watch the focus value change on the LCD screen. ​ When the sample is held steady, the //focus value// on the LCD should remain steady; ideally, only the last digit should fluctuate by one or two counts. ​ This is due to slight noise in the system and is tolerable. ​ If the fluctuations are bigger, check the connections for any problems.
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 == Focus value on the LCD ramps up and saturates when the sample is motionless and the focus controller is quiescent == == Focus value on the LCD ramps up and saturates when the sample is motionless and the focus controller is quiescent ==
  
-This problem occurs when the //Zero Potentiometer//​ (set by **X** argument of ''​AFADJ''​) is incorrectly set.  This can be corrected by running the Auto Calibration routine (''​AFCALIB''​ or ''​AFC''​) or by performing Step 2 of [[documentation:​video_autofocus#​Manual Calibration|Manual Calibration]] .+This problem occurs when the //Zero Potentiometer//​ (set by **X** argument of ''​AFADJ''​) is incorrectly set.  This can be corrected by running the Auto Calibration routine (''​AFCALIB''​ or ''​AFC''​) or by performing Step 2 of [[video_autofocus#​Manual Calibration|Manual Calibration]] .
  
 == Hill Detect does not work well. == == Hill Detect does not work well. ==
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 ===== AUTO-FOCUS CONTROLLER’S VIDEO PROCESSING SEQUENCE ===== ===== AUTO-FOCUS CONTROLLER’S VIDEO PROCESSING SEQUENCE =====
-{{ :​documentation:​autofocus_processing_sketch.png?​direct |}}+{{ autofocus_processing_sketch.png?​direct |}}
  
 {{tag>​manual autofocus ms2000 }} {{tag>​manual autofocus ms2000 }}
    
video_autofocus.txt · Last modified: 2016/10/04 15:13 (external edit)