Eyepiece - Huygens versus Ramsden

[thedy]

eyepiece -- Huygens versus Ramsden

Hi,can someone explain me this picture? : http://www.accessscience.com/search.aspx?rootID=792797
I don't understand,what it means,Im reading the description,but it doesn t help me.It looks,like if I use Huygens eyepiece we get virtual image,and if I use Ramsden,we get real image.But we know,that microscope resulting image is always real,isn it?
Thanks for clarifying

 

[Drakkith]

Both eyepieces cause the light rays to exit parallel to one another. (When focused correctly) This allows you to use your eye and focus at infinity, which requires no flexing of your lens and doesn't tire your eye out.

In A) the eyepiece is a Ramsden. The light comes to focus at the focal point of the objective, then begins to spread out again until it enters the first element of the eyepiece. The element bends the light towards the 2nd element and after exiting the eyepiece the light is now collimated and ready to enter your eye.

In B) the eyepiece is a Huygens. The converging light cone doesn't come to focus before entering the first element of the eyepiece. However the end result is the same. The light exits the eyepiece collimated and ready for viewing with your eye.

 

[Andy Resnick]

Interesting question- both eyepieces consist of 2 convex lenses and are the next step in complication from a singlet. In this context, the Huyghens eyepiece is similar to a Galilean telescope while the Ramsden is similar to a Keplerian telescope. The only (thin-lens) difference appears to the spacing between elements.

Both eyepiece designs are poorly corrected- meaning the design does not have enough 'degrees of freedom' to correct more than a couple aberrations. Here, the two designs are more distinct- the Ramsden eyepiece is better corrected than the Huyghens because the lens is reversed, allowing both optical surfaces to more equally contribute to the optical power.

http://spie.org/Images/Graphics/Publications/TT82_Fig8.6Big.jpg
http://spie.org/x33112.xml

Splitting the rear element allows additional aberration correction (Kellner eyepiece)

http://spie.org/x33129.xml

As for 'real' or 'virtual' images, Drakkith is spot-on.

 

[thedy]

Thanks for answers,so if my opinion is correct,does it mean,that resulting image is virtual and it is created by eye lens,not by field lens.So in picture,which I put here is not drawn the virtual image created by eye lens...?Correct,or not?
Thanks