astrophysics: optical telescopes

what is a refracting telescope made up of?

refracting telescopes are made of 2 converging lenses

what type of image does the objective lens create and where?

the objective lens creates a real image inside the telescope

what type of image does the eyepiece lens create and where?

the eyepiece lens creates a virtual image at infinity

does the eyepiece lens magnify or diminish the image?

the eyepiece lens magnifies the real image created by the objective lens

what does it mean when a telescope is in normal adjustment?

when a telescope is in normal adjustment, the principle focus of the objective lens and the eyepiece lens are at the same point.

draw a diagram for a telescope in normal adjustment.

i did it

what is the equation for angular magnification?

M = angle subtended by image at eye/angle subtended by object at unaided eye

how else can angular magnification be calculated? whats the equation for it?

using focal lengths. M = focal length of objective lens/focal length of eyepiece lens

how do you find the length of a telescope?

to find the length of a telescope, add the focal lengths of the objective lens and the eyepiece lens together.

light rays that are [] to the principle axis converge [] [] [] [].

parallel, at the principle focus

light rays that pass through the [] [] will emerge [] to the principle axis

principle focus, parallel

what is a reflecting telescope made up of?

a reflecting telescope is made up of a parabolic concave mirror, a convex secondary mirror and an eyepiece lens.

what is the purpose of the parabolic concave primary mirror?

the purpose of the parabolic mirror is to reflect and focus incoming light rays

what is the purpose of the convex secondary mirror?

to reflect the reflected rays again through a hole in the primary mirror to form a real image behind the primary mirror so that the image can be viewed without blocking the light source.

what is the purpose of the eyepiece lens in a reflecting telescope?

to refract the light rays forming the real image creating a viewable virtual image at infinity

what adjustment are reflecting telescopes normally in?

cassegrain adjustment

what does CCD stand for?

charged couple device

what do CCDs do?

CCDs capture images digitally

how do CCDs work?

CCDs are made of a grid of pixels. photons hit the silicon in a pixel, causing free electrons to be formed. these electrons are confined to that pixel, causing it to accumulate charge. this charge is then measured and used to create a digital signal.

does light intensity get measured using CCDs?

light intensity does get measured using CCDs. the charge on each pixel varies depending on the number of photons that hit it.

name 4 ways CCDs and the eye differ.

the quantum efficiency of a CCD is around 80%, while the eye has as quantum efficiency of 1%. CCDs can detect a wider spectrum of light than the eye. the resolving power of a CCD is better than the eye. CCDs are less convenient to set up, but can produce digital images that can be stored, copied and shared.

what is quantum efficiency?

the percentage of incident photons detected by a sensor