1. It’s All a Bit Blurry – The Importance of Focus and Focal Distance
Avid photographers are familiar with the importance of focus and focal distance. Much like a photographer’s camera, the lenses of industrial smart cameras and barcode imagers must be adjusted to focus light that enters the camera in a way that creates a sharp image.
An image is in focus when the edges of the object appear sharp. If the object is out of focus, the image becomes blurred. A longer focal length results in larger magnification of distant objects, and a narrower field of view (that is, the device can see things farther away, but the area in focus is relatively small). On the other hand, shorter focal length is associated with a wider field of view (that is, the device can see things closer up, and capture a larger area in focus). Focal length determines how much a lens will be able to capture in focus, but the more a camera zooms, the narrower the field of view becomes.
Lenses for consumer photography often have autofocus, whereas lenses for industrial barcode reading and machine vision either have fixed focus, manually-adjustable focus, or autofocus. Autofocus can be either mechanical or liquid lens autofocus based on the lens design. Here, we’ll focus on two common types of focus: fixed focus and liquid lens autofocus.
Focus Schmocus! What is Autofocus? An autofocus optical system uses a sensor, a control system, and a motor or optical element to focus on an automatically- or manually-selected point or area. Liquid lens autofocus technology has been featured in Microscan technology since the release of the company’s high-performance QX Hawk barcode imager in 2009. This technology uses electrostatic pressure to create electrical currents that react with the two liquids inside the lens to produce the appropriate lens curvature.
This enables barcode imagers to decode symbols at any distance and speed in any environment, from high-density 3.3 mil Data Matrix symbols on complex PCBs, to very large linear barcodes on packages, to low-contrast direct part mark (DPM) symbols on machined parts. Compared to mechanical autofocus, which uses a motor, liquid lens autofocus has no moving parts that can degrade or fail over time, making it a durable choice.
Manual vs. Truly Automatic Autofocus: While many autofocus devices must be adjusted using remote software commands (an operator tells a device where to refocus if a part or barcode can’t be found), some devices are able to self-adjust focus after several failed results to seek a barcode automatically at an unexpected distance or location. The imagers in the MicroHAWK product family can auto-adjust focus after five “no-read” results.
3. Total Access – How Easily Can You Access Settings and Results of Barcode Readers or Smart Cameras on the Production Line?
If your barcode readers or smart cameras are hard to reach on the production line, or if they’re embedded inside of equipment, making manual adjustments to devices can be practically impossible. In these cases, autofocus functionality provides a major benefit. Liquid lens autofocus technology eliminates the need to touch the lens of the camera to make manual adjustments, and simplifies installation, setup, and maintenance of cameras over time. It is the ideal choice when flexible positioning within machines is required, and for applications in which reading distances change from part to part or during changeovers but access to devices is limited or not possible.
Integrated autofocus technology makes the setup of devices far less complicated. Devices can adapt to change without the engineer or operator needing to predict the parameters that each change on the line will bring, from barcode location to part position, placement, or color. With liquid lens autofocus, automation engineers do not need to research multiple devices or configuration options before choosing an imager for an application.
Knowing that autofocus devices can adapt to change, operators do not need to be present on the line at all times to ensure that devices will function appropriately during a job. And, during line changeovers, pre-programmed inspection profiles can be loaded for new parts on the line, adjusting the autofocus lens to the focal distance that was saved for that particular part.
4. The Need for Speed
In fast-moving applications, it is necessary to “freeze” barcodes or other parts in order to achieve a crisp image. This can be achieved with a fast external strobe light that flashes as the part passes in front of the camera, or a with very short exposure time on the camera itself.
When using built-in lights in autofocus and fixed focus imagers, there is a limit to how short the exposure time can be while still capturing the correct amount of light. This is ultimately dictated by the aperture of the lens, (that is, how big the hole is in the camera lens that is letting light through to the sensor). If the fixed focus and autofocus lenses have the same aperture, both will have the same light gathering capability, making them equivalent for moving applications.
5. Time is Money – and Other Budget Considerations
The main benefit of autofocus imagers is flexibility. Does the cost of an autofocus device – often higher than that of a fixed focus device – justify the savings you will achieve in time and complexity? We’ve outlined a number of ways that autofocus devices streamline both the setup and control of imaging in applications that involve high degrees of part and process variability. However, if this is not the kind of application you’re running, the benefits of autofocus may in fact not be ideal from a cost standpoint.
Another consideration to make is the number of unique focal distances that you expect in your application. More focal distances may mean more devices, and more devices may mean a greater investment and more part numbers to manage in your inventory. If you are aiming to standardize on just a couple of part numbers in your imaging device, then autofocus makes the most sense, as fixed focus devices will require a unique part number or model for each pre-configured focal distance.
For OEM integrators, autofocus makes machines easier to use at the end customer, allowing operators to inspect a wider variety of parts without errors or specialized training. This is the benefit of the autofocus device’s ability to accommodate a greater number of variables. The last thing your end customer wants to worry about is making adjustments to a turnkey system so it will function correctly in their application.
A true solution shouldn’t require end user customization. For production line manufacturers, autofocus offers easier initial application setup with greater plug-and-play capability. Vision inspection jobs, for instance, can be set up just once and then operated continuously. When no manual adjustments to the camera and its focus settings are needed, hundreds of working hours can be saved in reduced equipment downtime.
The benefits of autofocus do come with a not-insignificant price tag. If you’ve gotten this far and the points above have you fairly convinced that a fixed focus imager is a sufficient choice for your project, and you don’t expect many application changes in the future, fixed focus could be your most cost-effective solution. But if your application involves any of the complex variables described above, an autofocus device can solve multiple application pain points simultaneously.
The Latest Developments in Autofocus from Microscan
Microscan builds its liquid lens autofocus technology directly into all-in-one imagers and smart cameras rather than requiring add-on optical accessories. For the manufacturer, this design optimizes cost, device size, and integration complexity when integrating new imaging technology. While fixed focus devices are factory-configured to decode at preconfigured focal distances, Microscan’s newest autofocus camera models offer both true autofocus (automatic, continuous symbol location and decoding) and software-programmable focus, which allows users to set fixed focal distances for autofocus devices from remote or browser-based user interfaces.
Click here to watch a demonstration of the various autofocus settings available in the browser-based WebLink interface for Microscan’s MicroHAWK Barcode Readers.
Quick Reference – The Benefits of Liquid Lens Autofocus:
• Read codes or inspect parts at varying distances, sizes, and locations
• Greatest range of possible focal distances in a single device
• Long-lasting and rugged – no moving parts (compared to mechanical autofocus cameras that use a motor)
• Fastest focus change response
• Superior optical quality
• Low power consumption
• Reduced device size – fully-integrated autofocus within camera lens (compared to add-on optical accessories)
All Barcodes Need a Little Love: Both fixed focus and autofocus readers from Microscan are able to read damaged and distorted codes, as well as DPM codes, in an array of colors. Regardless of the challenging code, marking method, or surface substrate, we have a decoding solution that just works.