This was especially true in refracting telescopes, before the invention of achromatic objective lenses.
2.
The telescope features an achromatic objective, as well as an adjustable brass cap over the objective.
3.
Adopting a hypothetical law of the dispersion of differently colored rays of light, he proved analytically the possibility of constructing an achromatic objective composed of lenses of glass and water.
4.
"' Charles A . Spencer "'was an American scientific pioneer and inventor, who is widely believed to have developed the first American-made achromatic objective microscope.
5.
Petzval's portrait objective lens ( " Petzval Portr�tobjektiv " ) was an almost distortionless " Anachromatischer vierlinser " ( double achromatic objective lens, with four lenses in three groups ).
6.
This is easily confirmed by using a 40x achromatic objective with an NA = 0.9 and with a correction collar which is adjusted until the image is crisp-with the aperture diaphragm wide open to keep the NA at 0.9 . The effective cover-glass thickness can be read off the scale next to the correction collar . 40x objectives with achromatic and fluorite corrections have NA's less than 0.7 and are more tolerant to deviations from the optimal thickness of 0.17 mm " cover glasses ".
मोबाइल