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 attempt to maximize this "focus value" by adjusting the focal position with an ASI Z-drive. The auto-focus option requires a standard (NTSC/RS 170 or PAL/CCIR) video signal from an analog CCD 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.
Auto-Focus Features
- Fast Focusing - Typical focus operation takes ~1-2 second, or less.
- 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 0.2mm closer to the slide.
- Focus Value Readout - The focus value is always displayed on the LCD readout so you can easily verify correct operation.
- Video Region Select - Rectangular subsection of the video frame may be selected as the active focus region. Selection highlighted on monitor output.
- Focus Algorithms to fit your need - Auto-focusing can be accomplished via push-button on the controller or with commands from the host computer.
- Scan Up, Down, or Split
- Coarse or Fine Speed
- Hill Detect or Full Range
Auto-Focus in Action
The following is a two-second video (368KB MPG) 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 RS-170 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, Split Scan Algorithm
- Coarse Speed, Hill Detect
- Z-Drive Rate is 20% of Maximum Velocity
- 16 ms Interlaced Video Sample Rate (RS-170)
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 50 µm down |
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 |
