PEAK TELECENTRIC LUPE 7X

This is a special purpose loupe with a magnifying power of 7 times. It belongs to the category of scale-loupes with an affixed transparent glass scale which can be placed in contact with the object under examination, so that you can measure the length of the object very easily and accurately. However, the magnifying optical system of this loupe is not conventional, but is telecentric, i.e. characterized by a small opening fixed at the focal point of the lens system, through which you can measure the length or width of not only flat objects, but also three-dimensional ones such as small spheres, cylinders etc. without the error caused by parallax. This handy instrument is equivalent in its principle to expensive profile projectors. The lens system, composed of three elements in two groups, has been specially designed for the present purpose.

To use the loupe, first adjust the distance between the glass scale and the lens system by turning the knurled outer barrel until the scale can be sharply observed by your own eye through the opening with the largest diameter (3 mm), which can be selected simply by turning the turret ring at the top of the loupe. Then place the loupe upon the object to be measured so that the scale plate is in contact with it, and read its length by the scale. The scale is engraved 20 mm in total length at every 0.1 mm interval, so you can measure the length of objects with an error of less than 0.03 mm.

When measuring three-dimensional objects. the opening with the minimum diameter (1 mm), or preferably the one with a slit of 0.5 mm in width should be used; and the orientation of the slit should kept perpendicular to the direction along which the length of the object is to be measured. Even in these cases, the portions of the object that are not in contact with the scale plate may be fuzzy because they are out of focus. However, no error can occur in the measured length, as long as you measure the centre-to-centre distance of blurred images, thanks to the characteristic of the "tele­centric" system. The low brightness of the image due to the small openings can be compensated for by higher illumination of the object.

This loupe can be applied very effectively as a reading aid for mercury thermometers. By putting the end surface of the transparent tube of the loupe (the scale plate of which should, preferably, be taken off) correctly against the thermometer tube, you can read the temperature extremely accurately and without any parallax, even if the mercury thread and the temperature scale are not in the same plane. The slit-form opening is used very effectively in this case, with its orientation kept parallel to the engraved lines of the ther­mometer scale. (Care should be taken that your body temperature does not affect the temperature to be measured.) Also, by replacing the transparent tube of the loupe with a tube of the proper length and by putting its end surface squarely on the window of voltmeters etc., you can read the indication of the meter needle very accurately and without any parallax.