Monochromatic Microscopes?

[mneium]

After reading about monochromatic photomicrography and its benefits, I wondered why there don't seem to be any microscopes designed from the ground up for monochromatic usage?
If you only have to make a flat field for one single wavelength, and you don't need to worry about chromatic aberration at all, can't you make vastly better (wider & flatter field) objectives for vastly less money?

[Hobbyst46]

At least because such an instrument, even if it could be made, would not answer the requirements of present research, clinical and other medical and biological analysis. Note that "monochromatic" means a single narrow wavelength. However, it is important to study specimens with different wavelengths, for example, because the variety of colors of a stained specimen will disappear. The light source can be monochromatic, like a red light laser or green light laser or other, but the microscope must be compatible with many wavelengths, so by definition it cannot be "monochromatic". Resolution and flatness of field are not all. In specific cases a grayscale is chosen, but for general use, the microscope should not be so limited.

[mneium]

I think there are surely professional situations where it would make sense. Not every application is "color-sensitive." For example, in some hematology applications, field width is more desired than anything else.
If there was a monochromatic microscope with 2x the field width of usual offerings, I bet it would attract a lot of buyers, even if just as a specialist tool for certain applications where a lot of dishes need to be scanned (for, as example, abnormal cells)

I think perhaps one reason this hasn't happened (an ultra-widefield monochromatic microscope system) is that such a system would produce an equally ultra-wide exit pupil. And in professional microscopy use-cases, most users are 40-60+ years old. The human capacity for pupil dilation decreases with age, so you effectively lose the ability to make use of an ultra-widefield system at some point.

[MichaelG.]

The ultimate ‘monochromatic’ microscope must surely be the Electron Microscope
... ‘though I admit that its wavelength is not what we normally describe as chromatic.

MichaelG.

[Tom Jones]

I'm curious to know in what hematology applications field width is prized over all else, including color?

[mneium]

I'm curious to know in what hematology applications field width is prized over all else, including color?

Counting lymphocytes and things like that. Is it really hard to envision a use case for monochromatically-driven wider fields etc. when there are certain applications of microscopes where you're scanning dishes for hours per day? A wider field makes that a certain % faster.

Maybe staining would be less effective with monochromatic objectives, but then again, you could stain for opacity rather than color. Easy to discriminate between an opaque cell and a transparent one in monochrome.
If you're designing the objective to the application, you could even design it around a tight spectrum (not necessarily monochromatic but less than the full visible color gamut) that includes the chosen stain and the usual subject color. So you would still get all of the benefits of color for that specific use-case, with the benefits associated with not having to compensate all the other spectra in the same objective.

[Scarodactyl]

I am not sure what niche this would serve. If you need to look at a wider field than standard there are specialty low mag compound objectives, stereomicroscopes and macroscopes. Wider field numbers at a given magnification have diminishing returns, and Nikon actually went down from 26.5mm to 25mm max for biological objectives. I would guess that having one wavelength blasted into your eyes all day wouldn't be pleasant either. There are machine vision applications that are monochrome but those are a bit more specialized all around.

[Tom Jones]

Color provides contrast among other things. Without color, you will need to find some other way to increase contrast enough to tell one thing from the other. It also provides more specific clues as to what you are looking at by way of differential staining. Think of the difficulty in distinguishing monocytes from atypical lymphocytes, or many blasts, without the color differences the staining brings to the cytoplasm and nuclei. How about eosinophils vs basophils? Sure there are generally differences in nuclear shape and cytoplasmic granule size, but it's a hell of a lot easier, faster, and more accurate to see one blue and the other red/orange.

Microscopists have been struggling for years trying to find ways to add distinguishing contrast to their specimens. Differential stains, dark field, oblique contrast, phase contrast, DIC, and various antibody bound fluorochromes. I seriously doubt anyone will go back. Resolution without contrast is useless.

[BramHuntingNematodes]

I mean they had phase scopes with a green filter that was basically the idea. Colorless subjects and a way to turn phase differences into amplitude differences. What else would be different?

[Greg Howald]

These days a mono system would probably be out of a reasonable price range as it would fall into specialty characteristics. It is right to think that a solid filter could restrict the image within a given wave length and that might be the easiest solution.
Using a camera can you get a useable mono image by adjusting camera settings?
Greg

[mneium]

Wider field numbers at a given magnification have diminishing returns, and Nikon actually went down from 26.5mm to 25mm max for biological objectives.

The perimeter of the eye is lower-detail, sure, but if you can handle the exit pupil I don't see how a larger field isn't significantly better (esp. for scanning lots of sample surface area)
Besides exit pupil size and it being cheaper to correct polychromatic aberrations in a smaller field, I would guess one other reason manufacturers settle on 26.5mm/25mm is that it's hard to accommodate eyeglasses wearers with ultra-widefield eyepieces, because eye relief won't be very far.

I find these reasons kind of lame in the face of how useful a wider field is. If you make the image diameter 2x larger, it doesn't convey 2x the amount of information, it conveys 4x more. And if an older user can't dilate to the size of the larger exit pupil, it's not like he won't be able to use the system, he just won't get the full field.

-

Regarding exit pupils, I think the exit pupil of microscope eyepieces can be obtained by dividing the field number (eg. 26.5) by the magnification (eg. 10, creating a 2.65mm exit pupil)

According to https://en.wikipedia.org/wiki/Exit_pupil the maximum pupil diameter of humans is like so:

pupil size
age - day - night
20 4.7 8
30 4.3 7
40 3.9 6
50 3.5 5
60 3.1 4.1
70 2.7 3.2
80 2.3 2.5

So a young user could use a 47mm field number, or in low-light (maybe darkfield) conditions, 80mm.

If I can deploy a pun, I think microscope manufacturers are narrowsighted on this matter. Imagine a specialized ultrawide monochromatic darkfield microscope with a 70mm field number. That's an amazing tool for hematology, or lyme disease diagnosis.

As a point of industry comparison, binoculars manufacturers produce ultra-widefield systems with exit pupils up to 7.1mm!
https://www.nikon.com/news/2017/0403_wx_01.htm

[hans]

I think you are mixing up aperture stops and field stops. From the Wikipedia article you linked:

The exit pupil is the image of the aperture stop in the optics that follow it.

[Scarodactyl]

Have you used ultra widefield eyepieces before? In my experience they're really nice but it's more of a luxury than a necessity, with the main utility being more accurate framing of pictures when I am doing direct projection onto aps-c. Generally you want to move the slide rather than your eyes whwn looking through a scope. If your goal is maximizing the field you can see visually it's a lot less complicated to just use a lower magnification. Big field numbwrs are great for larger sensoe cameras but your eyes will likely not get the same advantages.

[mneium]

(...)

I do have superwide eyepieces. They're amazing and totally ruined normal eyepieces for me. They almost suck you in onto the slide. But still - not big enough!
For all of my talk of professional applications (and those really do exist IMO,) my argument ultimately comes from my amateur desire to look into a microscope and see nothing but specimen from edge to edge.

[Scarodactyl]

How wide do you have? The widest field number that exists as far as I know are mitutoyo ultra widefield eyepieces with a 30mm FN (their objectives can all cover full frame, and some can even cover medium format decently with a good tube lens). I've nevwr gotten to try those, though bausch and lomb 15x uwfs have an apparent field number of about 30mm as well. I don't notice a huge difference between the 15x uwfs and nikon 26.5mm uwf eyepieces, the view is great in both.
Of course you can get a projection head like on a comparator or one of the vision engineering ones if you want to cheat.