What Do I Look for When Selecting a System Type?
A Wide Range of Magnification is Important
Many companies have a wide variety of parts to me measured or inspected. In some cases higher magnification is required however higher magnification provides a smaller field-of-view. This in turn allows the operator to see less of the part at one time.
Zoom Lenses Provide Flexibility for Magnification and is Easily Upgradeable
A Zoom lens can provide an image which can change magnification easily, is par-focal, and on a manual system can be par-central. Detents (click stops) can be used by operators to repeat back to predefined magnification positions. Auxiliary lenses can be added to increase or decrease.
The Optical Path and Camera must be square to the column to obtain accurate measurements
Fundamentals of machine design incorporate adjustments to be able to square all traveling components to one another (X, Y, and Z). If camera/optics are not square to the X, Y axis on a part that is situated on an angle, you will induce what is known as measurement error or cosign error.
Not all lenses are created equal: Locate companies that understand the importance of coatings on optics which allow more light to pass into the camera.
Glass by itself is not 100% translucent and there is no such thing as 100% reflectance. With those two principles in mind you can utilize coatings to refract light back into the objectives, keep out diffused light, minimize ghosting that occurs. Coatings applied at a certain wavelength and certain layers allow the "good light (part image)" to go back to the camera and keep the "bad light (reflectivity)" out.
What is a Par-Focal Optical System?
After the optics are focused on a specimen at the highest magnification, the image will remain in focus throughout the entire magnification range (highest to lowest).
What is a Par-Central Optical System?
Having a zoom system which is par-central means that as you zoom, the optical system stays on axis. For example: If you chose a single point on a stage at the center of a crosshair at low magnification and zoom to high magnification while viewing the same spot, the cross-hair will remain at the exact same point as when started. This can be useful in taking advantage of a zoom when trying to measure and having the ability to zoom back to seem more of the part at one time and then zoom up for high accuracy measurements.
What is the difference between a 6:1 Zoom Lens or a 12:1 Zoom?
Basically Price! The 12 to 1 Zoom lens will give you a higher magnification range, but will cost more. Be sure to evaluate your requirements to determine the magnification and field of view requirements.
How do Auxiliary Adapters provide flexibility?
Auxiliary lenses can be easily screwed on the bottom of the zoom lens to increase or decrease magnification ranges of the lens.
Cameras may have the same pixel array but not the same configuration capabilities
Be sure to select a video measurement system which provides the ability to manually adjust the parameters and settings. This allows a system to be configured to take advantage of the optical path, the lighting, and the customers parts.
Cameras are not simply "Plug and Play" for the Industrial Market
Most cameras and monitors are supplied with setting that are "auto everything" right out of the box. This is not good for the industrial market. While a decent image can be achieved, One must calibrate the gains, the white balance, and the color spectrum to industry color standards and experiences in the types of lighting being used.
S-Video Monitors with 720 lines produces a more realistic Image than LCD
CCD monitors resolution is defined by TV lines and not pixel array. While monitor technology is always changing, Vendors must stay up with technology by continually evaluating depth, color, saturation, and sharpness of the image. Most people go by what it says on the box which is standard 480 TV lines to 520 TV lines. The higher the TV resolution, the better the image. Video systems should be provided with a minimum of 720 lines of resolution.
What kind of Visual Repeatability can I get with 720 TV Lines?
If we have a 12x lens with a 2x auxiliary adapter and 720 TV lines, you will have about .50 millionths manually. If you need a finer resolution than one will require higher magnification objectives etc.
The Trade off between LCD and CRT is Space/Eye Fatigue Vs. Image Quality
When considering an LCD for your video system and the objective being the optimum image quality, one must evaluate contrast ratio, and the amount of illumination that comes out of the monitor. The higher the contrast ratio, the better the image quality you are going to get.
With LCD's the Larger the Monitor the smaller the Contrast Ratio
And not all monitors are created equal. If you buy 20 different nineteen inch monitors, each one will have a different contrast ratio and illumination output.
Don't Use the Monitor on your office computer for a Video Measurement System!
Work with a company that matches the right Monitor for your optical configuration. Most customers and vendors want to purchase or use the lowest cost LCD available. In the world of LCD's you get what you pay for! Check the contrast ratio. High quality monitors may have between 700 to 800 to 1 contrast ratio's, while many video systems are supplied with low cost LCD's with a contrast ratio of 400 to 1.
Ask what the Contrast Ratio is for the LCD you are thinking about purchasing!