Basics of Telescopes Quiz

What determines the amount of magnification in a telescope?

The focal length of the eyepiece.

What is the basis of telescopic images in the absence of an atmosphere?

Plane wavefronts diffract upon encountering the circular aperture, and focus as an Airy disk.

What happens to the wavefront distortions caused by the atmosphere in a short exposure?

They produce interfering Airy patterns.

How is the effect of atmospheric turbulence on a long exposure described?

It moves the individual maxima around the image plane to produce a large seeing disk. Signup and view all the answers

How is the Earth's atmosphere approximated in the context of atmospheric refraction?

As a series of plane-parallel plates, and the surface as an infinite plane. Signup and view all the answers

What is the effect of refraction in the limit of a large number of thin atmospheric layers?

It curves the path of the incident ray. Signup and view all the answers

What is the relationship between the focus and the primary mirror in a Cassegrain reflector?

In a Cassegrain reflector, the focus is behind the primary mirror ($\beta$ is positive). Signup and view all the answers

How do the values of $m$ and $k$ differ between Cassegrain and Gregorian reflectors?

For a Cassegrain reflector, $m$ and $k$ are both positive, while for a Gregorian reflector, they are both negative. Signup and view all the answers

What is the key difference between the classical Cassegrain/Gregorian reflectors and the aplanatic two-mirror telescopes?

The classical Cassegrain and Gregorian reflectors assume the primary mirror must be a paraboloid, resulting in coma and astigmatism, while the aplanatic two-mirror telescopes can use any conic constant for the primary and find a secondary shape that preserves freedom from spherical aberration. Signup and view all the answers

What type of aplanatic two-mirror telescope is called the Ritchey–Chretien (R–C) design?

The aplanatic Cassegrain is called the Ritchey–Chretien (R–C) design, and consists of a hyperbolic primary and hyperbolic secondary mirror. Signup and view all the answers

How does the tube length of a Cassegrain reflector compare to a Newtonian reflector of the same focal length?

The tube of the Cassegrain reflector will be much shorter than a Newtonian reflector of the same focal length. Signup and view all the answers

What is the relationship between the overall focal length and the mirror configurations in Cassegrain and Gregorian reflectors?

The overall focal length, $f$, is positive for a Cassegrain reflector and negative for a Gregorian reflector. Signup and view all the answers

What is the purpose of a tertiary flat in the Nasmyth configuration of reflecting telescopes?

Redirect light from the secondary mirror along the hollow altitude axis Signup and view all the answers

In the coude configuration of reflecting telescopes, how is the light from the secondary mirror redirected?

By a series of flats to bring the beam to the polar axis Signup and view all the answers

What is the main advantage of a Schmidt telescope over other telescope designs in terms of field of view?

Produces good images over a much larger field (6 to 8 degrees) Signup and view all the answers

How does a Schmidt telescope avoid off-axis aberrations?

By exploiting the symmetry of a spherical mirror Signup and view all the answers

What are the three main elements of a Schmidt telescope?

Spherical primary mirror, aperture stop, refracting corrector plate Signup and view all the answers

What is the field of view for the Schmidt telescope in terms of degrees?

6 to 8 degrees Signup and view all the answers

What is the main purpose of adaptive optics in telescopes?

To remove wavefront distortions caused by atmospheric turbulence. Signup and view all the answers

Where are the adjustable optical elements typically located in an adaptive optics system?

Near the telescope focal plane. Signup and view all the answers

What type of optical elements are commonly used as the adjustable elements in adaptive optics?

Reflective elements. Signup and view all the answers

How is the shape of the reflecting surface adjusted in adaptive optics?

To exactly cancel the distortions generated by atmospheric turbulence. Signup and view all the answers

What is wavefront reconstruction in the context of adaptive optics?

Determining the wavefront distortions to apply corrections. Signup and view all the answers

What is the purpose of the note at the end of the text?

It is a disclaimer about the usage and distribution of the presentation. Signup and view all the answers

What is the formula for the wavefront aberration of coma?

The wavefront aberration of coma depends on the formula $\rho^3 b \cos \phi$. Signup and view all the answers

What is the relationship between coma and spherical aberration?

Like spherical aberration, coma is particularly a problem of large apertures. Signup and view all the answers

What is an aplanatic optical system?

An aplanatic optical system is one with neither spherical aberration nor coma. Signup and view all the answers

Is it possible to have a single-element aplanatic telescope?

No, a single-element aplanatic telescope, either in a refractor or reflector, is not possible. Signup and view all the answers

How can coma be minimized in refracting systems?

Minimizing coma in refracting systems requires a system of lenses, and achromatic doublet or triplet designs that minimize spherical aberration also reduce coma. Signup and view all the answers

What is the formula for the wavefront distortion of astigmatism?

The wavefront distortion of astigmatism depends on the formula $\rho^3 b^2 \cos^2 \phi$. Signup and view all the answers