Lens Selection Machine vision systems are installed in environments ranging from factory manufacturing lines to dedicated inspection equipment and automatic manufacturing robots, and their objects vary from fine-pitch IC patterns of a few μ to cars of a few square meters. It is important to select the optimal lens and lighting method to accurately capture the target object with the camera according to various environments. VST offers a system that matches the needs of customers with a product lineup based on its unique know-how specialized in machine vision.
We have narrowed down the lens that we need to some extend. So what kind of lens are there specifically ? Lens type and characteristics In general, machine vision optics are classified into Macro lens-based lenses and infinity FFL lenses. There are telecentric and non-telecentric lenses in the Macro lenses. The majority of Macro lenses are designed to provide maximum performance at close range (WD 300mm and below). We classify telecentric lenses as one type of lens, and classify lenses with large image circles such as digital cameras as line scan lenses.
Obtain the optical magnification from the FOV of the work to be imaged and the (planned) camera to be used.
FOV
Large Format・Line Scan Lenses
Telecentric Lenses
Macro Lenses
Fixed Focal Length Lenses
Opt. Mag =
How many times the FOV of the work can be captured into the camera.
Feature
Advantages
Disadvantages
Camera(V) or (H) Filed of View(V) or (H)
Opt. Mag =
High dimensional accuracy in the DOF direction. The view does not change between the center and the corner. Suitable for dimension measurement.
Telecentric Lenses
The chief ray is parallel to its optical axis. Required for co-axial illumination.
Big in dimensions. Expensive.
*Camera dimensions are calculated by pixel size x number of effective pixels.
Once the Opt. Mag is obtained, the conditions will be narrowed down based on the equipment space, camera installation distance, lens WD, etc.
Small TV distortions. Compact, lightweight. High vibration resistance.
Specially designed for short working distance.
Focusing only at a certain WD. Limited FOV (magnification) range.
Macro Lenses
Fixed Focal Length Lenses
Focuses to infinity. Adjustable focus and iris.
Flexible with FOV and WD. Low cost. Ideal for large FOV.
Large corner distortions in short WD, causing dimensional inaccuracy.
Long working distance with small difference in relative illuminance intensity.
Large Format・ Line Scan Lenses
A lens with a large image circle of the above lens.
Big in size and heavy weight.
Lens WD Flange WD O/I Space
❶Telecentric Lenses This is a lens where the primary beam is parallel to the optical axis of the lens. Object-side telecentric lenses are useful when coaxial illumination is required. It is advantageous for receiving regular reflected light from illumination perpendicular to the object. Measurement of dimensions in the direction of depth of field shows little variation in values and almost no corner distortion [Refer Figure 1-1(a)&(b)], making it suitable for high-precision measurements. It comes with a unique feature where the distance from the lens to the object (WD) is not affected by the size of the optical image of the object at the image positions. Note that as the FOV expands, the lens dimension will increase, and the price will rise accordingly.
❷ How to obtain the image range from the focal length
❶ How to obtain the lens focal length
FOV(V or H) = WD x Sensor size(V or H) / f (Focal Length)
f=WD x Opt. Mag (Sensor size (V or H) / FOV (V or H))
Sensor size 4.8
Sensor size 4.8
FOV200mm
FOV ｘ mm
f = 50mm
Lens WD＝2000mm
Lens WD=1500mm
f
Normal Lenses
Image side telecentric lenses
FOV = 1500 x 4.8 / 50 = 144 mm
f = 2000mm × Opt. Mag ( = Sensor size (4.8mm) /FOV (200mm)) f = 48mm
*Please be reminded to use the approximate formula as a guide only. Specifically when imaging in the near range (WD 300 mm or less), the calculated value may shift significantly. Please refer to our sales department or HP for details.
If WD is fixed, FOV will be larger when using a shorter "f(focal length)" lens, and smaller when using a longer "f" lens. If FOV is fixed, WD will be shorter when using shorter "f" lens, and longer when using a longer "f" lens.
Object side telecentric lens
Both-side telecentric lenses
Chief ray
180
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