Polarizing Light Microscopy

Question

Abbe’s proved his theory of image formation in microscopy using a variety of experiments to show how diffraction was an integral function of how magnified images were formed in a microscope.

a. (15 pts) Define angular aperture and numerical aperture. Explain why numerical aperture is a better measure of resolution than angular aperture.

b. (16 pts) Describe two experiments that Abbe used to prove his theory of image formation with respect to resolution of image detail in microscopy.

c. (24 pts) You are examining a diatom sample using a BH2 polarizing light microscope with the 0.40 numerical aperture 20X magnification objective lens in air, but you’re not able to resolve the fine details of the sample with these settings. Describe three different specific methods that you can use to improve the resolution of detail of this sample. Explain in detail how each of these methods works to improve resolution of detail. (You can assume that the microscope has already been set up for Köhler illumination.)

d. (20 pts) You have placed a hexagonal grating on the stage of your polarizing light microscope and examine the grating using a 10X magnification binocular lens system and a 40X

magnification objective lens with a 0.70 numerical aperture; white light from the 6V tungsten lamp is used to illuminate the grating. You open the substage aperture diaphragm to a NA of 0.70. You pull out the left side ocular lens to look down the head of the microscope to observe the back focal plane of the objective. (i) Describe the diffraction pattern at the back focal plane of the objective lens for this hexagonal grating. (ii) If a horizontal spatial filter were placed at the back focal plane of the objective, blocking out all but the central horizontal diffraction pattern, how would this affect the image of the sample?

Answer 1

Guadalupe H.,

These are obviously test or exam questions -- you even left their numerical scoring values on the text. That's not what Wyzant is there for, answering such content is even forbidden.

Look like you really must have covered a lot of technical microscopy optics theory in your course. I'm impressed with the depth of the questions. Study your notes, and come back when you have some tentative answers. But you probably have already done that, and turned it in, already.

-- Cheers, --Mr. d.