11. The first portrait objective lenses were rather small and had a diameter of 2.6 cm. 12. Reflected in the mirror is the image from the second objective lens ( C ). 13. Where is the width of the pixel and is the f-number of the objective lens . 14. An oil immersion objective is an objective lens specially designed to be used in this way. 15. A high power objective lens is typically used. 16. German optics companies ( T�pfer, Voigtl�nderkorrigie, Zeiss ) produced the Petzval objective lens until the 1940s. 17. These and other considerations are major factors influencing the choice of magnification and objective lens diameter. 18. An "'oil immersion objective "'is an objective lens specially designed to be used in this way. 19. In 1873 they built the objective lens for the refractor at the United States Naval Observatory. 20. The measurement arm 140 contains an objective lens 141 for imaging the surface to be studied 152.
