Compound Microscopes and Refracting and Reflecting Telescopes

All flashcards

Objective lens in a compound microscope

The short-focal-length convex lens near the specimen; it forms the real intermediate image.

Eyepiece magnification at the near point

For relaxed conventions with the final image at the near point, its angular magnification is $1+25\text{ cm}/f_{eye}$ when $f_{eye}$ is in centimeters.

Refracting telescope angular magnification

For a simple two-lens telescope, $M=-f_{obj}/f_{eye}$; the minus sign indicates inversion.

Newtonian reflecting telescope

A concave primary mirror focuses light onto a small secondary mirror, which redirects it sideways to the eyepiece.

Chromatic aberration

Color fringing and image blur caused by different colors refracting by different amounts through a lens.

Quiz questions

1. In many microscopes described by the standard tube-length convention, what distance is called the tube length?Answer: The distance between the objective's image-side focal point and the eyepiece's object-side focal point.
2. For a simple two-lens refracting telescope, which expression gives angular magnification?Answer: $M=-f_{obj}/f_{eye}$
3. In a Newtonian reflecting telescope, what does the small secondary mirror do?Answer: It redirects light from the primary mirror sideways to the eyepiece.
4. Why can a reflecting telescope avoid chromatic aberration from its primary light-gathering element?Answer: Reflection does not refract different colors by different amounts.
5. What distinguishes the secondary-mirror arrangement of a Cassegrain telescope?Answer: A convex secondary sends light back through a hole in the primary mirror.