What Determines the Size of an Image Formed at Infinity in Magnifiers?

[kent davidge]

I was reading my physics book and I didnt understand how can a image formed at infinity does not appear to us as infinitely large. The book says that lateral magnification is not valid in this case. So what really defines how large a image is?

 

[Suraj M]

First when we say infinity, it's not exactly "infinity"
It's a large distance from the pole, your object won't be exactly at the focus (practically)
so you won't have " infinitely large".
Infinitely large"- what does that actually mean?
What defines? It's the position and focal length of the mirror.

 

[kent davidge]

Yes, but I'm still trying to understand what in our eye determines how large an image will be. I'm showing you a image of the situation that caused my doubt. (sorry my bad english)

 

[Andy Resnick]

I was reading my physics book and I didnt understand how can a image formed at infinity does not appear to us as infinitely large. The book says that lateral magnification is not valid in this case. So what really defines how large a image is?

In this case (distant objects and/or distant images), it's conceptually easier to use angular magnification rather than linear magnification to characterize the system:

http://physics.ucsd.edu/students/courses/winter2008/physics1c/documents/5.2OpticalInstruments.notes.pdf .

Does this help?

 

[Drakkith]

Yes, but I'm still trying to understand what in our eye determines how large an image will be. I'm showing you a image of the situation that caused my doubt. (sorry my bad english)

Look at the picture on the right. The rays from the top of the inchworm enter the eye at angle θ. The eye then focuses the rays down onto the retina. The size of the image of the inchworm on the retina is determined by the angle at which the rays enter your eye and the focal length of your eye.

 

[kent davidge]

Oh thanks Andy Resnick and Drakkith. I understood it now.