9.1 Telescopes Flashcards
What is the lens equation?
What do the letters represent in this equation?
What is the equation for power of a lens?
What do the letters represent in this equation?
What is the axis of symmetry called?
Principal axis.
What is the principal focus?
- A point on the axis which is the same distance from the optical centre as the focal length.
- Where light rays travelling parallel to the principal axis prior to refraction converge.
What is the focal length?
Distance between the centre of the lens and the principal focus.
What is the role of the objective lens?
To collext as much light as possible.
What is the purpose of the eyepiece lens?
To magnify the image produced by the objective lens.
What is normal adjustment?
When the distance between the objective and eyepiece lenses is equal to the sum of their focal lengths.
Draw a lens diagram of normal adjustment.
What is the equation for angular magnification in normal adjustment?
What is the equation for angular magnification in terms of focal lengths and what is the condition it can be used?
When both angle are less than 10o
What do the letters represent in this equation?
Draw an annoted ray diagram for a Cassegrain telescope.
What is chromatic aberration?
- When a lens refracts white light into different colours due to their wavelengths.
- Causing the image for each colour to form in different positions, resulting in coloured fringes around the image.
What is spherical aberration?
- Light is focused in different places due to the curvature of a lens or mirror, causing image blurring.
- Can be resolved in reflecting telescopes by using a parabolic mirror.
Describe a solution to chromatic and spherical aberration in lenses.
Using an achromatic doublet brings all rays of light into focus in the same position by using a convex lens and a concave lens of different types of glass cemented together.
Define collecting power.
A measure of the ability of a lens or mirror to collect incident EM radiation.
What is collecting power proportional to?
The square of the objective diameter.
Define resolving power.
The ability of a telelscope to produce separate images of close-together objects.
State the Rayleigh Criterion.
Two objects will not be resolved if any part of the central maximum of either of the images falls within the first minimum diffraction ring of the other.
What is the equation for the minimum angular separation?
What do the letters represent in this equation?
What are the advantages of large diameter telescopes?
Greater collecting power (brighter) and resolving power (clearer).
What is a CCD?
An array of light-sensitive pixels which become charged when they are exposed to light (by the photoelectric effect).
