Reflecting telescope calculation

In summary, for a reflecting telescope with a radius of curvature of 3.0m for its objective mirror and a radius of curvature of -1.50m for its eyepiece mirror, and a distance of 0.90m between the two mirrors, the photographic film should be placed 3m in front of the eyepiece to record the image of a star.
  • #1
tommy128268
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Homework Statement



A reflecting telescope has a radius of curvature of 3.0m for its objective mirror and a radius of curvature of -1.50m for its eyepiece mirror. If the distance between the two mirrors is 0.90m, how far in front of the eyepiece should you place the photographic film to record the image of a star?

Homework Equations


I could only find out the focal length of both objective mirror and eyepiece mirror.

f=radius of curvature / 2 ...(1)
1/f = 1/di + 1/do ...(2)

The Attempt at a Solution



For now, I got fo=1.5 and fe=-0.75
as the object are from infinity , by using equation 2, di=fo=1.5
Since the distance between the two mirrors is 0.90m , and 1.5-0.9=0.6
0.6 is the object distance of the eyepiece.

1/-0.75 = 1/di + 1/0.6
di is -0.3333
I haven't taught reflecting telescope in my class. I just find a similar solution in yahoo answer.
But I feel the ans is totally wrong. Can anyone help me?
 
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  • #2
You can always "unfold" a system with mirrors, replacing the mirror with a lens of equal focal length (at least for the purposes of geometric optics). So your approach is basically correct, and I agree that the image distance for the first mirror is 1.5m. But the distance to the second mirror is only 0.9m - so the image (the object for the second mirror) is beyond it. So in the second calculation ##d_o=-0.6##m. Then$$\begin {eqnarray*}\frac 1 {d_i}&=&\frac 1 {0.6}-\frac 1 {0.75}\\
&=&\frac 13\end {eqnarray*} $$and the answer you are looking for is 3m.
 

What is a reflecting telescope?

A reflecting telescope is a type of telescope that uses mirrors to gather and focus light, instead of lenses like in a refracting telescope. It was first invented by Sir Isaac Newton in the 17th century.

How do you calculate the magnification of a reflecting telescope?

The magnification of a reflecting telescope can be calculated by dividing the focal length of the telescope's primary mirror by the focal length of the eyepiece. For example, if the primary mirror has a focal length of 1000mm and the eyepiece has a focal length of 10mm, the magnification would be 100x.

What is the resolution of a reflecting telescope?

The resolution of a reflecting telescope is determined by its aperture, or the diameter of its primary mirror. The larger the aperture, the higher the resolution and the more detail the telescope can capture.

How do you determine the focal length of a reflecting telescope?

The focal length of a reflecting telescope can be determined by measuring the distance from the primary mirror to the focal point. This can be done by using a laser collimator or by projecting an image of the primary mirror onto a screen.

What are the advantages of using a reflecting telescope?

Reflecting telescopes have several advantages over refracting telescopes, including a larger aperture for better resolution, a shorter and more compact design, and the ability to use different types of mirrors to correct for lens aberrations.

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