Telescopes Flashcards
What is chromatic aberration?
> Refraction by a lens splits white light into it’s multiple wavelengths (dispersion)
The objective lens focuses these different wavelengths over different focal points along the telescopes optical axis
The aberration is where images will, as an effect, have coloured edges/fringes to them
What is spherical aberration?
> Curvature of the lens means light rays in a parallel beam are focused at different focal points of the optical axis
The aberration is where the image, as an effect, becomes blurred
What is Rayleighs’ Criterion?
The principle that two objects can be resolved if their angular seperation (θ) is at least: θ = λ/D This would be the 'critical' angle λ = Wavelength of light D = Diameter of lens used
What are 2 advantages of reflecting telescopes over refracting telescopes?
> Unlike large lenses, larger mirrors are light and easily supported in larger telescopic structures
Does not suffer chromatic aberration (parabolic reflectors eliminate spherical aberration)
What are 2 disadvantages of refracting telescopes over reflecting telescopes?
> Heavier, therefore difficult to move around
> Large glass of sufficient clarity and cleanliness requires tedious and difficult maintenance
How is magnification calculated?
M = fₒ / fₑ
M = maginfication fₒ = focal length of objective lens fₑ = focal length of eyepiece lens
What is an achromatic doublet?
> The combination of a concave lens compensated by a convex lens serving as one objective lens to re-align the wavelengths of light to the same focal point
This reduces both chromatic and spherical aberration in refracting telescopes
Explain the use of parabolic reflectors:
The parabolic shape focuses all received parallel light rays to a single point perfectly
What is the resolving power of a lens?
The power of a lens to produce separate images of closely spaced objects
What are non-optical telescopes for?
> Detecting space objects of non-visible wavelengths
> Usually set in space
How do objective lenses and eyepiece lenses work together?
> The objective lens is convex, meaning it can gather the light from distant objects
The eyepiece lens is concave, meaning it can focus the gathered light in such a way that our eyes can receive it
What is collecting power?
> The amount of photons (of any wavelength) a telescope can collect in a given area
How do you calculate collecting power?
> Power ∝ Area
How do you calculate collecting power?
> Power ∝ Area
> Power = Intensity of source * Gathering Area
