ASI's video auto-focus provides a simple microscope focus control solution when using an analog video camera and any of ASI’s products with Focus Control including standard and piezo XYZ stage systems, linear and gantry stage systems, and stand-alone MFC-2000 focus controllers.

The auto-focus system uses the spatial information present in the analog video signal to determine a focus value. Firmware algorithms then maximize this focus value by adjusting the focal position with an ASI focus drive. The auto-focus option requires a standard NTSC/RS170, PAL/CCIR, or S-Video analog video signal from a camera. Auto-focus with a digital camera is possible with a dual-output camera (see video below), or by incorporating ASI’s Photoport Beam Splitter.

ASI's auto-focus system has improved sensitivity and stability, 8X higher resolution, and incorporates an auto-calibration routine that automatically accommodates for diverse lighting conditions, specimen characteristics, and different objective powers.

Auto-Focus Features

  • Fast Focusing - A typical accurate focus operation takes about one second, and can be configured for even faster operation.
  • Accurate Focusing - Where there is a "best focus" plane, ASI's auto-focus will find it as well as any human operator.
  • Objective Lens Protection - Once zeroed, auto-focus will not move more than 0.2 mm closer to the sample for safety.
  • Focus Value Readout - The focus value is always displayed on the LCD readout so you can easily verify correct operation.
  • Video Region Select - A rectangular subsection of the video frame may be selected as the active focus region. Selection is highlighted on monitor output.
  • Auto Calibration - Performs a series of scans and selects various internal parameters to achieve optimal focusing.
  • Focus Algorithms to fit your need - Auto-focusing can be accomplished via push-button on the controller or with commands from the host computer.
    • Full Range
    • Hill Detect

Auto-Focus in Action

The following is a two-second mpeg video (368KB) of typical auto-focus operation with prepared skin cells under a 40X objective. The camera was DVC's standard DVC-710M. This versatile camera has both RS170 analog video output routed to the auto-focus circuit of an ASI Z-drive controller, and simultaneous 784x484 digital video output which was recorded with DVCView™ software. The original monochromic video was later colorized with ImageJ image processing software for clarity.

The actual time to perform this auto-focus was 0.8 seconds, and used these configuration settings:

  • 100 µm Range
  • Hill Detect
  • Z-Drive Rate is 20% of Maximum Velocity
  • 16 ms Interlaced Video Sample Rate (RS170)
What you are seeing in the video:
Frame   Description   Time
1   In-Focus Frame (for reference after video rewind)   33 ms
2 - 28   Specimen Out-of-Focus   900 ms
(29)   (Auto-Focus is initiated)  
29 - 33   Drive down 50 µm   167 ms
34 - 50   Scan up (#46 is the actual in-focus frame)   567 ms
51 - 52   Drive back to In-Focus Position   67 ms
53 - 60   Specimen In-Focus   267 ms