Telescope geometric optics problem

In summary, the conversation revolved around a homework problem involving an astronomical telescope with a 32 cm focal-length objective lens. The objective of the problem was to find the distance to the nearer objects after moving the eyepiece 1.0 cm farther away from the objective. The conversation also touched on the principles of geometrical optics and using binoculars to view objects at different distances. The solution involved using the lensmaker's formula to calculate the object distance, which was found to be 33 cm. The original poster has not been active on the forum for more than 12 years.
  • #1
ryan11
1
0
Ok I'm working on my geometric optics homework and this is the last problem and I can't seem to get it right.

An 6 astronomical telescope has a 32 cm focal-length objective lens. After looking at stars, an astronomer moves the eyepiece 1.0 cm farther away from the objective to focus on nearer objects. What is the distance to the nearer objects?

I'm not really sure how to set this up. I know that magnification=fo/fe but I don't know how to find the distance of the nearer object. Thanks for any help.
 
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  • #2
I can't imagine, telescope is used to see stars which are so far away that we always take theirs distance to objective len infinite in formulae. How can it change @@.
 
  • #3
Maidien said:
I can't imagine, telescope is used to see stars which are so far away that we always take theirs distance to objective len infinite in formulae. How can it change @@.

Easy. Just move the eyepiece back and forth. That will change the focus. This is just like using binoculars to view wildlife, sporting events, or something else where the objects in view are at many different distances. You have to adjust the focus if the change in distance is large, such as viewing a bird on a limb where the background is miles away. You can focus on the bird and perhaps the tree at the same time, but the distant mountains will most likely be blurry, and vice-versa. The details of why this is so would require you to delve into geometrical optics.
 
  • #4
I'm hoping I'm not giving more info. than I should, but hints on this one are hard to give without giving almost the complete solution. For a telescope viewing at infinity, the focal point of the eyepiece is at the focal point of the objective lens which is where the image forms. ## 1/f=1/s+1/m ##. When ## s=+\infty ##, ## \ ##, ## m=f =32 ## cm. If the eyepiece needs to be moved 1 cm, it means the object focused (made a real image)from the objective lens at m=33 cm. Use the lensmaker's formula ## 1/f=1/s +1/m ## . ## f ## =32 cm and ## m ## =33 cm. Solve for ## s ## =object distance.
 
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  • #5
Charles Link said:
I'm hoping I'm not giving more info. than I should, but hints on this one are hard to give without giving almost the complete solution.

You're fine with posting complete solutions here in this forum. Just don't do it in the homework forums. See the post stickied at the top.
 
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  • #6
The last time the original poster logged on was more than 12 years ago, which was when the homework was due..
 
  • #7
George Jones said:
The last time the original poster logged on was more than 12 years ago, which was when the homework was due..
It was fun solving the homework problem. This one was one of the easier ones.
 

1. How do I calculate the magnification of a telescope?

To calculate the magnification of a telescope, you need to know the focal length of the objective lens or mirror (Fobj) and the focal length of the eyepiece (Feye). You can then use the formula M = Fobj / Feye to determine the magnification. For example, if the objective lens has a focal length of 1000mm and the eyepiece has a focal length of 25mm, the magnification would be 40x (1000/25).

2. What is the difference between a refracting and reflecting telescope?

A refracting telescope uses lenses to gather and focus light, while a reflecting telescope uses mirrors. Refracting telescopes have a long tube with lenses at both ends, while reflecting telescopes have a shorter tube with a large concave mirror at one end and a smaller flat mirror at the other end.

3. How does the diameter of the objective lens or mirror affect the image quality in a telescope?

The diameter of the objective lens or mirror, also known as the aperture, affects the amount of light that can enter the telescope. A larger aperture allows for more light to be collected, resulting in a brighter and sharper image. It also increases the resolving power of the telescope, allowing for finer details to be seen.

4. Can I use a telescope during the day?

Yes, you can use a telescope during the day. However, it is recommended to use a solar filter to protect your eyes and the telescope's optics from the intense sunlight. Without a solar filter, looking at the sun through a telescope can cause permanent eye damage.

5. How do I determine the exit pupil of a telescope?

The exit pupil of a telescope is calculated by dividing the diameter of the objective lens or mirror by the magnification. For example, if the objective lens has a diameter of 100mm and the magnification is 50x, the exit pupil would be 2mm (100/50). The exit pupil is important for determining the amount of light that reaches your eye, as it should match the size of your eye's pupil for optimal viewing conditions.

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