# MICROSCOPY: Imaging a field of radiated light and it's source

by einfall
Tags: lens, light, magnification, microscopy, optics
 P: 11 I have a question about observing a field of radiated light (and it's source) through a microscope, specifically vis magnification and the scale of the final image observed (the field, and also the source). I have a slice of field intensity at the plane of a microscope's numerical aperture (i.e. all light entering the appropriate half-cone angle of 20 degrees). It's an accurate map of the intensity — it looks as expected. The objective is 75x, and the aperture sits about 1mm from a light source (a particle) with well-known dimensions. WHAT I AM CONFUSED ABOUT: Since the particle sits 1mm below the plane of the field I've calculated, how do I apply the 75x magnification to both the field and the particle to reform an image with appropriate dimensions (i.e. what I see when I look through the microscope)? The most obvious approach to me is to take the objective's focal-length, and then ray trace the field and the particle independently to the same image observation-point. Then put them back together. But this isn't giving the result I expected (particle location/dimensions don't make sense relative to the field). A reminder of the basic optics here would be highly appreciated, as this has me irritatingly confused.
 P: 11 *its
P: 5,539
 Quote by einfall this has me irritatingly confused.
I'm confused by your question. Specifically:

1) What do you mean by 'I have a slice of field intensity at the plane of a microscope's numerical aperture'? The numerical aperture is a measure of angle, not a plane.
2) What do you mean by 'the aperture sits about 1mm from a light source'? Which aperture?
3) What do you mean by 'how do I apply the 75x magnification to both the field and the particle to reform an image with appropriate dimensions'? Why are you distinguishing between the object (the particle) and 'the field' (whatever that means...)
4) Is this a compound or simple magnifier- a compound microscope has a secondary magnifier either/both in the eyepiece and in the main optical path (e.g. Zeiss Optivar)
5) What do you mean by 'ray trace the field and the particle independently to the same image observation-point'? Again, why are you separating the object and the emitted field?

 P: 11 MICROSCOPY: Imaging a field of radiated light and it's source Thanks very much for your response - you're right, my previous question was quite unclear. I have a micron-scale particle under lamp illumination which is also scattering laser light. I want to compute what the scattered field and particle "look like" with a specific numerical aperture under 75x magnification. I can calculate the scattered field for any point/plane in space, so my current solution is to compute the field for a plane sitting tangentially on the particle. I'm confusing myself because the lamp light and the scattered light both need to expand up through the solid-cone angle defined by the numerical aperture, but the scattered field is radially dependent and diverges while the lamp light is effectively collimated over this length-scale (at least I think this follows). How to go about replicating what would be "seen" on a CCD camera is the problem that's bugging me, especially because it seems like it ought to be the straightforward bit. I know this doesn't specifically address all your questions, but I hope it clarifies the issue. Also note: right now I'm completely ignoring the fact that the field is viewed through an aperture about 1mm above the particle, and for now I'm ignoring diffraction effects (nice Airy rings etc.)