Why can this telescope only focus on very near objects?

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Discussion Overview

The discussion revolves around a theodolite's telescope that can only focus on objects within a short range of 3 to 7 feet. Participants explore potential causes for this limitation, including mechanical issues and optical misalignments, while considering the device's refractor design.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant suggests that the eyepiece optics may have been scrambled, possibly due to mishandling by a student.
  • Another participant questions whether the focus knob is functioning properly and considers the possibility of the eyepiece being removed and reassembled incorrectly.
  • A different participant, unfamiliar with theodolites but experienced with telescopes, proposes that misalignment of internal components, such as mirrors, could affect focusing on distant objects, although the device in question is a refractor.
  • One participant confirms that the focus knob works and emphasizes that the device is a refractor, ruling out mirror-related issues.
  • Another participant recommends a thorough inspection for loose lenses or physical damage but does not provide further insights.
  • A later reply reiterates the functioning of the focus knob and suggests that mechanical interference might be preventing the lens from moving appropriately to focus on distant objects, proposing careful disassembly as a potential solution.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the exact cause of the focusing issue, with multiple competing hypotheses presented regarding mechanical and optical problems.

Contextual Notes

Participants express uncertainty about the internal workings of the theodolite and the potential impact of previous handling on its functionality. There are unresolved questions regarding the specific nature of the mechanical or optical issues affecting the telescope.

Who May Find This Useful

This discussion may be of interest to individuals involved in optics, telescope maintenance, or those seeking to troubleshoot similar focusing issues in refractor telescopes.

Harlan
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OK - Here's a challenge. Our school has a theodolite; its telescope worked in the past. Now it suddenly won't focus beyond 7', though it gives a great image of objects between roughly 3'-7' away. The focus knob seems to move freely.

My thought is that the eyepiece optics somehow got scrambled, perhaps by a curious student...but what would cause this?
 
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Does the focus knob function? In other words, can you manipulate the focus between 3'-7', or could the focus knob be somehow disengaged from the lens?

Another thought- was the eyepiece ever removed? It's possible some of the elements inside fell out and were re-inserted wrong.

Take it in for repairs?
 
I don't know anything about a theodolite, but I do own a telescope. If it uses mirrors it is possible that a sudden jarring could misalign the mirrors. This might not have any noticeable effect on focusing on short range objects, but long range objects could get distinctly blurry depending on the severity of the misalignment.
 
Yes, the focus knob still works, and it is a refractor, so no mirrors.
 
All I can say is do a thorough check of the telescope and check for any loose lenses, dents, cracks, or any other damage. Other than that I can't say.
 
Harlan said:
Yes, the focus knob still works, and it is a refractor, so no mirrors.

In order to focus on distant objects, the lens must move closer to the eyepiece. There could be mechanical interference between the lens and eyepiece preventing movement (which you may be able to feel).

Depending on your comfort level, you could find a clean surface and carefully disassemble the device to see if there's an obvious problem.
 

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