What is the physical diameter of the first optical element in the telescope?

Field of view

Optical aperture

Light detector

Effective focal length

Correct Answer : Optical aperture

Explanation : Each design of a telescope is characterized by an optical aperture, an effective focal length, and a field of view. The optical aperture is the physical diameter of the first element in the telescope.

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Anti reflection coated optics reduce ________

Refraction

Reflection angle

Intensity of star image

Optical transmission losses

Correct Answer : Option (D) : Optical transmission losses

Explanation : For anti-reflection coated optics, the optical transmission losses may be 1% or 2% at each air to glass or glass to air optical control surface within the telescope, including windows or sensor covers or surfaces. For uncoated optics, the loss per surface is about 4% to 5%.

The ratio of the focal length to aperture is called the ________

Focal number

f/ number

Critical aperture

Effective aperture

Correct Answer : Option (B) : f/ number

Explanation : The ratio of focal length to aperture is called the f/ number. For example, an f/10 telescope may have a 30 in. focal length and a 3 in. aperture.

The physical size of the star depends upon _____

Shape of image

Colour of image

Angular size of image

Intensity of image

Correct Answer : Option (C) : Angular size of image