This time, I would like to talk about special industrial lenses, especially lenses for capturing small objects. Camera lenses are basically used to image objects that are larger than the size of the image sensor, but this time, with the image sensor. Introducing a special lens used to image an object of the same size or smaller.

Objective lens and macro lens

The objective lens is a lens used for microscopic imaging, and an adapter that converts it to an industrial camera mount is provided. The feature is suitable for ultra-high magnification imaging like a microscope. The depth of field is shallow, making it difficult to adjust the focus. Another point is that objective lenses are expensive. A shallow depth of field may be advantageous when separating by distance, as it indicates that the in-focus and out-of-focus areas are at different distances. AF (autofocus) may be used when shooting while moving over a wide area. If you want to focus the entire image, use multiple focus stacking. Macro lenses have a lower magnification than objective lenses, but because of their simple structure and relatively low cost, they are the most used lenses for capturing small objects. However, since the depth of field is also shallow here, focus adjustment is severe. In addition, the size of a distant object and that of a near object differ greatly, and there is lens distortion, so calibration processing is required when using it for length measurement.

Telecentric lens

A telecentric lens is used to take an image of the same size as the image sensor mounted on the camera. The feature is that it is a lens with a mechanism that images only parallel light from an object, so it is not affected by incident light from the surroundings, and it is possible to focus on both distant and near objects of the same size with the same size. You can take an image in the correct state. This is especially suitable for image measurement, measurement, and shape recognition because it can capture images of the same size both in the distance and in the vicinity. High-magnification lenses that capture objects larger than the size of the image sensor are also available. Telecentric lenses use coaxial epi-illumination, in which illumination is incident from the side of the lens and reflected by a mirror for imaging.

Types of telecentric lenses

Variable magnification telecentric lens
A telecentric lens that maintains high telecentric performance over the entire range due to the variable magnification.

Here, we will introduce an example of a captured image using a telecentric lens (manufactured by DZOptics) as an example. Since only coaxial light is imaged, stable imaging can be performed without causing halation and being affected by ambient light.

You can see that the upper part of the dice and the measure of the background are both in focus, but even if you image dice of different heights, the dice are in focus at any height, regardless of the distance, and the size of the dice is , The image is taken at the correct ratio.