Stargazing Why can this telescope only focus on very near objects?

[Harlan]

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?

 

[Andy Resnick]

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?

 

[Drakkith]

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.

 

[Harlan]

Yes, the focus knob still works, and it is a refractor, so no mirrors.

 

[Drakkith]

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.

 

[Andy Resnick]

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.