Computar TEC-55 Lens

The Computar TEC-55 is a wonderful lens that has some of the best features of telecentric lenses and macro lenses at a lower price. As a macro lens, the TEC-55 will focus at a working distance of 140mm; much closer than other lenses in this price category. The TEC-55 also exhibits telecentric performance at some magnifications; a telecentric lens has never been this affordable.

The Computar TEC-55 is ideal for your experiments to determine whether you need a custom made telecentric lens for your application.

Computer Optics Inc. also designs and manufactures custom telecentric lenses. Fill out our lens requirements form for more information.

* The lens data on this page provided with permission of Computar.

The Computar TEC-55 is a 55 mm f/2.8 lens which reduces or eliminates viewing angle error and magnification error while providing high resolution and contrast with low distortion when used in telecentric mode. This compact, light weight lens is competitively priced and can be used with 2/3", 1/2" and 1/3" format cameras. Options include O.75X converter and 2X extender.

Machine vision has made telecentric lenses popular because a conventional lens cannot accurately portray objects which are off axis to the lens, or at different distances from the lens. Viewing angle error and magnification error are inherent in conventional lenses, and these perspective distortions can create significant interpretation problems for machine vision software.

A true telecentric lens, however, maintains a constant viewing angle at any point across the clear aperture of the objective lens. This characteristic of the telecentric lens enables the machine vision system to generate images of objects which appear dimensionally accurate regardless of viewing angle or proximity to the lens. By eliminating perspective distortion, the telecentric lens produces a dimensionally accurate image which is simple for software to interpret.

Figure 1 shows an exaggerated top view of nine identical cylindrical objects as viewed by a conventional lens. Whether these objects are stationary or moving on a conveyor belt, the conventional lens will see each cylinder as dimensionally different, depending on its location relative to the axis of the lens. This viewing angle error is difficult for software to interpret.

Figure 2 shows the same top view of the same nine objects as seen by a Telecentric lens, which eliminates viewing angle error. Note that each cylinder appears to have the same shape and dimensions, regardless of viewing angle.

Figure 3 shows an exaggerated lateral view of three identical boxes which are positioned at different distances from a conventional lens. Note that the box located closest to the lens appears larger, while the box farthest from the lens appears to be smaller, while the two objects off axis to the lens also exhibit viewing angle error.

Figure 4 shows the same boxes as seen by a telecentric lens. Note that all three boxes now appear to have the same shape and dimensions. That's the Telecentric Advantage, and it's available now from the Computar TEC-55 at Computer Optics Inc.

Features

• Telecentric at selected magnification.
• Useable from infinity to 0.5X plus 1:1 with Extension tube.
• High resolution and contrast.
• One-touch locking focus and iris.
• Compact and lightweight.
• Competitive price.

Computar TEC-55 tolerates up to 700% more object movement than a conventional lens, with an error of less than 1%. The Computar TEC-55 lens tolerates +/- 12.4mm object movement at O.50X magnification in order to generate a 1% error in image scale. This amount of object motion compares very favorably with the +/- 1.7mm object motion permitted by a conventional lens at the same magnification. At a magnification of O.20X, the Telecentric lens still tolerates 9mm of object motion, or 29% more than a conventional lens.

Object Displacement vs. Image Size

An important problem with the conventional lens is that image scale magnification changes as a function of distance between object and lens. As the distance to a conventional lens increases, image size decreases. As this distance decreases, image size increases. Using a telecentric lens, however, there is little or no apparent change in image size as an object dithers within given boundaries.

One of the most important benefits to be derived from the telecentric lens is a reduction or elimination of magnification error or change in image size associated with variable distance between object and lens. But it is important to understand that there are inherent technical constraints to the application of this proven technology.

First, this discussion assumes that dithering movement remains within the optical depth of field. Second, the lens will be truly telecentric or display no image movement only at close working distances and for objects which are smaller than the diameter of the first element in the lens.

The Computar TEC-55 is truly telecentric when used at magnifications Of O.4X to 1:1. A field of view larger than the objective lens diameter will not yield true telecentricity, but will yield substantially less error than a conventional lens.

The 2x & 0.75x adaptors increase the flexibility by extending the focal range.

Model No.	Mount	Format	Focal Length	Aperture
TEC-55	C	2/3"	55mm	F2.8 - 32C

TEC-55	Size L=95mm x diameter = 53mm
0.75x Adaptor	Size L=15mm x diameter = 23mm
2x Adaptor	Size L=20mm x diameter = 30mm

Our price for this lens is $284.29 Please click here to go to our products page. Once on the page, please look under the heading STOCK LENSES and in the left hand column under FIXED FOCAL choose the 2/3" format. The TEC-55 can be found about halfway down the column. Follow the instructions being sure to include your e-mail. If you have any problems ordering from our website, please call us directly at (603) 889-2116.

* The lens data on this page provided with permission of Computar.