Solving Telescope Optics Homework Question Involving Five Lenses

[chemphys1]

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!

 

[Vespa71]

No tilts uninteresting

 

[chemphys1]

Sorry I don't follow?

 

[berkeman]

No tilts uninteresting

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...

 

[berkeman]

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?

 

[chemphys1]

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?

 

[berkeman]

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]

BTW, here is your Google search, but including multiple lenses now...

https://www.google.com/search?q=len...t6cFonjoATV3IJI&ved=0CDwQsAQ&biw=1182&bih=790

.

 

[chemphys1]

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?

 

[berkeman]

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?

 

[chemphys1]

attached

 

[berkeman]

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?

 

[chemphys1]

Like that? crossing at focal point F after the lens?

 

[chemphys1]

is the whole pathway of the ray this? keeps going back through the next focal point?

 

[berkeman]

The first lens has a focul length of 2F, not F.

 

[chemphys1]

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?

 

[chemphys1]

this?

 

[Malverin]

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.

http://mcat-review.org/light-geometrical-optics.php

 

[chemphys1]

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?

 

[Malverin]

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.

 

[Redbelly98]

The first lens has a focul length of 2F, not F.

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.

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.