Solving Telescope Optics Homework Question Involving Five Lenses

  • Thread starter Thread starter chemphys1
  • Start date Start date
  • Tags Tags
    Optics Telescope
AI Thread Summary
The discussion revolves around a homework question involving the tracing of a ray through a telescope constructed with five lenses of varying focal lengths. The participant expresses confusion about the optical principles, particularly regarding the lens types and ray tracing. Key points include the importance of the lens equation and understanding that only one ray needs to be traced, entering parallel to the optical axis. Clarifications are provided about the focal lengths and how to correctly depict the ray's path after passing through the lenses. The conversation emphasizes the need for a clear understanding of optics to solve the problem effectively.
chemphys1
Messages
27
Reaction score
0

Homework Statement



*The diagram of the telescope is attached*

Question states

A telescope is constructed from five thin lenses of Diameter D and focal lengths 2F, F, F,F,2F
located at x = 0,2F,4F,6F,8F
Trace the path of a ray entering the system parallel to the optical axis


The Attempt at a Solution



This is undergraduate lab in chemistry but I haven't done physics before, I understand the middle line is the optical axis, but not much more. I've tried to do some reading but nothing seems to relate back to this question as it has little information about the type of lense/telescope and I seem to just be confusing myself completely

Any help really appreciated, quite confused!
 

Attachments

  • Untitled.png
    Untitled.png
    2.9 KB · Views: 579
Physics news on Phys.org
No tilts uninteresting
 
Sorry I don't follow?
 
Vespa71 said:
No tilts uninteresting

chemphys1 said:
Sorry I don't follow?

Disregard his reply. He is saying that the problem is fairly easy as stated, but it's an intro course so there is nothing wrong with starting with straightforward questions.

I'll post a reply to your OP in a sec...
 
chemphys1 said:

Homework Statement



*The diagram of the telescope is attached*

Question states

A telescope is constructed from five thin lenses of Diameter D and focal lengths 2F, F, F,F,2F
located at x = 0,2F,4F,6F,8F
Trace the path of a ray entering the system parallel to the optical axis


The Attempt at a Solution



This is undergraduate lab in chemistry but I haven't done physics before, I understand the middle line is the optical axis, but not much more. I've tried to do some reading but nothing seems to relate back to this question as it has little information about the type of lense/telescope and I seem to just be confusing myself completely

Any help really appreciated, quite confused!

One Relevant Equation that you should have posted is the "Lens Equation". Can you post it? And show a diagram demonstrating what it means for ray tracing through a single thin lens?
 
berkeman said:
One Relevant Equation that you should have posted is the "Lens Equation". Can you post it? And show a diagram demonstrating what it means for ray tracing through a single thin lens?

Ok thanks

Lens equation for a thin lens is 1/f = 1/d1 + 1/d2 ?

where f is the focal length of lens, d1 is image to lens distance, d2 object to lens distance

https://www.google.co.uk/search?q=l...ork-help%2Foptics%2Flens-formula.aspx;254;112

Not too sure about the lens, how do I know if the lens is concave or convex in this question?
 
chemphys1 said:
Ok thanks

Lens equation for a thin lens is 1/f = 1/d1 + 1/d2 ?

where f is the focal length of lens, d1 is image to lens distance, d2 object to lens distance

https://www.google.co.uk/search?q=l...ork-help%2Foptics%2Flens-formula.aspx;254;112

Not too sure about the lens, how do I know if the lens is concave or convex in this question?

If the focul length is positive, it is convex (focuses a real image). Are you sure the problem statement is complete, and all of the focul lengths are positive as shown in your OP?
 
berkeman said:
If the focul length is positive, it is convex (focuses a real image). Are you sure the problem statement is complete, and all of the focul lengths are positive as shown in your OP?

Yes all the focal lengths are positive,
the only difference between the question and my diagram is the diagram has arrows pointing up and down on the lenses, does that indicate convex too?
 
  • #10
chemphys1 said:
Yes all the focal lengths are positive,
the only difference between the question and my diagram is the diagram has arrows pointing up and down on the lenses, does that indicate convex too?

I don't think so. As you can see in the Google Images, arrows are sometimes used to show when an image is inverted or not. Can you post a scan of the actual problem image?
 
  • #11
attached
 

Attachments

  • photo (20).JPG
    photo (20).JPG
    26.4 KB · Views: 515
  • #12
Oh, double arrows. Yes, that might also imply convex/converging lenses.

So can you draw the first ray, coming in from the left about half-way up the first lens? Where does it cross the centeral axis?
 
  • #13
Like that? crossing at focal point F after the lens?
 

Attachments

  • Untitled 2.png
    Untitled 2.png
    2.7 KB · Views: 504
  • #14
is the whole pathway of the ray this? keeps going back through the next focal point?
 

Attachments

  • Untitled 3.png
    Untitled 3.png
    4 KB · Views: 545
  • #15
The first lens has a focul length of 2F, not F.
 
  • #16
berkeman said:
The first lens has a focul length of 2F, not F.

How does that affect the ray, does it not converge to the focal point at 3f?

would it hit the optical axis at 2F on the x axis, through the centre of the 2nd mirror?
 
  • #17
this?
 

Attachments

  • Untitled 4.png
    Untitled 4.png
    4.1 KB · Views: 484
  • #18
chemphys1 said:

Homework Statement



*The diagram of the telescope is attached*

Question states

A telescope is constructed from five thin lenses of Diameter D and focal lengths 2F, F, F,F,2F
located at x = 0,2F,4F,6F,8F
Trace the path of a ray entering the system parallel to the optical axis


The Attempt at a Solution



This is undergraduate lab in chemistry but I haven't done physics before, I understand the middle line is the optical axis, but not much more. I've tried to do some reading but nothing seems to relate back to this question as it has little information about the type of lense/telescope and I seem to just be confusing myself completely

Any help really appreciated, quite confused!

This may help you. Here you can see the ray paths.
convex-lens-ray-real.gif


http://mcat-review.org/light-geometrical-optics.php
 
  • #19
Sorry thank you for all the help but I'm really not understanding

The question says trace a ray, will I have 1 line like I did in my diagram or 3 lines like these images?
I literally knew nothing on optics before this question and my google searches were getting me more confused, including all these diagrams with lines going everywhere, multiple focal points etc.

Is my attempted diagrams completely wrong?
 
  • #20
chemphys1 said:
Sorry thank you for all the help but I'm really not understanding

The question says trace a ray, will I have 1 line like I did in my diagram or 3 lines like these images?
I literally knew nothing on optics before this question and my google searches were getting me more confused, including all these diagrams with lines going everywhere, multiple focal points etc.

Is my attempted diagrams completely wrong?

That is your problem statement:

Trace the path of a ray entering the system parallel to the optical axis

So you have to trace only the parallel ray, but you will need all 3 cases to draw it to the end.
 
  • #21
berkeman said:
The first lens has a focul length of 2F, not F.
chemphys1 said:
would it hit the optical axis at 2F on the x axis, through the centre of the 2nd mirror?
Yes. But in the figure you posted, it did not do that.

chemphys1 said:
Is my attempted diagrams completely wrong?
You just need 1 ray, as you have been doing. You started correctly with the parallel-to-the-axis ray, but things went wrong after the 1st lens -- hopefully what I posted above helps with that.
 
Back
Top