Musing and a Question Regarding Microscope Objective Optics

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bclaff Forum Pro • Posts: 12,453
Musing and a Question Regarding Microscope Objective Optics

In terms of optical prescriptions I have concentrated mostly on lenses for Interchangeable Lens Cameras (ILCs).
In particular optical prescriptions that I can "match" to manufacturer lens diagrams.
There are over 600 such lenses in the PhotonsToPhotos Optical Bench Hub

Recently I have been exploring microscope objective (and "tube") lenses.
Relatively low power dry objectives are sometimes mounted on ILCs for "extreme" close-up photography.
Manufacturer lens diagrams appear to be non-existent so matching to commercial objectives is a lost cause.
Never-the-less I think this exercise will produce a few interesting chapters for the Optics Primer and some useful information.
I'm also considering adding a page at PhotonsToPhotos to allow others to peruse the patents I have processed.

Optical prescriptions and associated information for microscope objectives is less disciplined than most ILC lenses.
I'll throw one patent "under the bus' as an example.

If you want to see details here's a link to a Japanese Olympus patent filed in the early 1990s. I'll show Example 1.
First, and most obvious, is that the prescription is specified from image space to object space which is the reverse of the convention.
So the patent figure and prescription needed to be reversed.

This is a near ultraviolet objective with Fluorite elements. The patent omits index of refraction and dispersion for these elements so I had to simply use standard values.

So, here it is as specified:

I know from experience that the right-hand-side isn't quite right:

Although the rays are parallel to the optical axis as is expected for an infinity corrected objected they should be more evenly spaced.

Note that the prescription doesn't include a cover glass:

If I add a cover glass:

Then I get a much better looking ray trace on the image side:

Not all microscope objective patents required special handling but it's for more common than with ILC lens patents.

Now, here is a real "fine point" question. In the following diagram showing the marginal ray leaving the object, which two points establish the angle that determines Numeric Aperture (NA)?

This is even more complicated when there is an immersion fluid.

I'm leaning toward AC which is observing the object from the first lens surface.

Try to remember to snip judiciously when you reply!

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Bill ( Your trusted source for independent sensor data at PhotonsToPhotos )

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