Page 63 - PowerPoint 演示文稿
P. 63
Prisms 53
Lensometer can also be used to detect the prism dioptre. To check this
get the best focus point of the target image and read the prismatic power.
In most of the lensometer, each circle of the scale indicate one prism dioptre,
as shown in the Figure 5.15. An additional accessory called ‘prism
compensator’ is to be attached to the lensometer for higher dioptre of prism.
Figure 5.15 shows 2.5 prism dioptre towards 90° in PENTAX OLH-1
lensometer.
SUMMARY
The optics of ophthalmic prism is still nightmare to many optical students
but in day-to-day practice, there is little complicated about them. Prisms, if
used with care, can be used to improve the appearance of spectacles.
