Histotechnology I- Miscellaneous
Question No. 9. The Answer is: (A) 1, 2, and 3 are true.
1. Limited by the numerical aperture of the objective.
2. Affected by the condenser diaphragm.
3. Limited by the refractive index of the medium of the optical pathway.
Question: The resolution of an optical microscope is limited by the numerical aperture. The higher the numerical aperture the higher the resolution. The numerical aperture of the optical system is limited by the numerical aperture of the objective and also by the numerical aperture of the condenser. The numerical aperture can be further reduced by closing down the diaphragm of the condenser. The numerical aperture is also limited by the refractive index of the medium of the optical pathway between the condenser and the slide, and between the slide and the objective. Air has a refractive that is very close to 1.00 and therefore no dry objectives can exceed this numerical aperture. On the other hand, numerical aperture of oil or other fluid immersion objectives can exceed 1.00 because the refractive index of the oil and the fluid can exceed 1.00. It is important to note that oil or the immersion fluid has to be applied in between the glass slide and the objective and also the glass slide and the condenser to achieve the maximum numerical aperture and therefore the highest resolution. The light source does not affect the numerical aperture.