Type of image from an afocal optical system

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An afocal optical system produces real images when the object is close enough, as diverging rays can enter the system. While parallel rays emerge from an afocal system, the human eye is necessary to focus these rays onto the retina, forming a real image. Telescopes are a common example of afocal systems, requiring an eyepiece to create an image. The transverse magnification remains constant regardless of the object's position along the axis. Ultimately, an image from an afocal system is always real, with variations depending on the lens configuration used.
fisico30
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Hello Forum,

what type of image does an afocal system produce if the object is an extended object? A real or virtual image?
Any example? Say a car is located 30 meters away...
Thanks
fisico30
 
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I just found a book chapter, AFOCAL SYSTEMS, by William B. Wetherell...

It seems that afocal system can form real images...but how, if the emerging rays are parallel?

fisico30
 
I guess this systems always imply that the human eye is there...that is the only way an image will form: each point on the object will have parallel rays emerging from the system.
The eye optical system will focus those bundles of rays on the retina and form a real image...
 
The only afocal systems I am familiar with are telescopes; an eyepiece is required to form an image.
 
Well, I was wrong in what I said.

If the object is very far, the input rays are parallel and the output rays are parallel too.
But if the object is close by, the rays entering the afocal system are diverging. Real images are possible. Moving the object along the axis does not change the transverse magnification, i.e. the image size...

See figure 1D at http://www.mntp.pitt.edu/Workshop/MNTP_Prtcp_res_2010/teaching/Optics_Chapter_95_LanniKeller.pdf

thanks,
fisico30
 
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An image from afocal system always is real. 2 types afocal; Keppler with 2 positive lens and Lagruerre with 1 positive len + 1 negative len, but f of positive always > f of negative.
 

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