Understanding Microscope Patents

Everything relating to microscopy hardware: Objectives, eyepieces, lamps and more.
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BrianBurnes
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Understanding Microscope Patents

#1 Post by BrianBurnes » Thu Oct 15, 2020 7:32 pm

Hi all,

I'm in the process of building some custom optics for my Microstar IV and I've been going through old Reichert and Cambridge patents to understand the intent of the original illuminating optics. However, a problem I've run into is that few of their patents actually seem to work. As a simple example, this patent seems to closely match the diascopic illuminator in my Microstar IV (the actual spacing/sizes are different in the real thing of course, but the same lens elements in the same arrangement are present), so this is a fairly simple system that is known to work.

However, when I take their suggested spacings/lens radii (from Table II) and plug them into spectral simulation software, I get an image like this:

Image

The beam emerges roughly collimated out of the first lens group as it should, but the focal point of the second lens falls short of the suggested condenser aperture F2 (marked by the white line on the right in the image). Doing the math by hand, the focal length of lens group II should be around 90mm, but they suggest the distance to the condenser to be 123mm instead, which is quite a bit beyond the focal point (as in the simulation). In other words, the filament is not actually imaged at the condenser pupil.

I'm not too used to reading optical patents, so I could use the help of someone more familiar in these matters: Is it to be expected that parameters listed in a patent don't lead to a working implementation (to keep the "secret sauce" away from the public), or am I completely misunderstanding how a microscope illuminator is supposed to work?

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Re: Understanding Microscope Patents

#2 Post by hans » Thu Oct 15, 2020 8:27 pm

I have also been trying to better understand the 410 illumination system, a few thoughts:
BrianBurnes wrote:
Thu Oct 15, 2020 7:32 pm
As a simple example, this patent seems to closely match the diascopic illuminator in my Microstar IV (the actual spacing/sizes are different in the real thing of course, but the same lens elements in the same arrangement are present), so this is a fairly simple system that is known to work.
The filing date 1975 is quite a bit earlier vs. 1985 for US4660942 and US4715697 which more obviously correspond to the 410. Perhaps that patent is for the 110?
BrianBurnes wrote:
Thu Oct 15, 2020 7:32 pm
...but the focal point of the second lens falls short of the suggested condenser aperture F2 (marked by the white line on the right in the image). Doing the math by hand, the focal length of lens group II should be around 90mm, but they suggest the distance to the condenser to be 123mm instead, which is quite a bit beyond the focal point (as in the simulation). In other words, the filament is not actually imaged at the condenser pupil.
I'm not sure the filament is expected to be exactly conjugate with the condenser diaphragm since the illumination is "modified" Koehler with the first lens surface facing the bulb frosted? I have not read the patent you linked carefully, does it mention the frosted surface?
BrianBurnes wrote:
Thu Oct 15, 2020 7:32 pm
Is it to be expected that parameters listed in a patent don't lead to a working implementation (to keep the "secret sauce" away from the public)...
Not a lawyer but roughly speaking the disclosure has to be detailed enough for someone "skilled in the art" to make a working implementation, otherwise the patent is not valid. However the implementation in the patent does not have to be very close to what ends up being manufactured, could be based on some early prototype, for example. The optical parameters in 410 "body" (aka head) patent do appear to match closely though.

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Re: Understanding Microscope Patents

#3 Post by BrianBurnes » Thu Oct 15, 2020 8:57 pm

Having dug through most of Reichert's and Camridge's patents, I have not found any other ones so far that describe a diascopic illumination system similar to the one found in the Microstar (though there is one describing the fluorescence attachment). It may be that subsequent iterations were deemed too derivative to be worthy of their own patent.
hans wrote:
Thu Oct 15, 2020 8:27 pm
I'm not sure the filament is expected to be exactly conjugate with the condenser diaphragm since the illumination is "modified" Koehler with the first lens surface facing the bulb frosted? I have not read the patent you linked carefully, does it mention the frosted surface?
The patent does not refer to modified Kohler or a frosted surface, but it does say this: "The collimator II reimages the filament in the region of condenser front pupil plane F2. At the same time, collimator II provides an image of field iris F1 at infinity". I just checked, and the field iris is indeed imaged at infinity by collimator II; however, the filament is not imaged in the correct place. Or perhaps "in the region of" is patent speak for "ballpark"?

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Re: Understanding Microscope Patents

#4 Post by hans » Thu Oct 15, 2020 9:23 pm

BrianBurnes wrote:
Thu Oct 15, 2020 8:57 pm
It may be that subsequent iterations were deemed too derivative to be worthy of their own patent.
Could be, I do have a couple beater 110s now that I was going to try to mix-and-match into a good one but have not looked at them closely yet. When I get a chance I will take one apart and see how well it matches the patent.
BrianBurnes wrote:
Thu Oct 15, 2020 8:57 pm
Or perhaps "in the region of" is patent speak for "ballpark"?
Seems likely.

Another thing I forgot to mention in my previous post... have you looked at the two elements of the collector lens assembly individually? I have one where the first, frosted lens is missing (looks like the adhesive failed, heat maybe, and it just fell out at some point) and looking through the second lens I thought it was aspheric. I will dig it out and try to get a photo later today. I have not looked at the first element alone yet because I do not want to take apart one of my good assemblies. In the patent drawing surface R4 actually does look somewhat aspheric, did you see anything about that in the description?

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Re: Understanding Microscope Patents

#5 Post by BrianBurnes » Thu Oct 15, 2020 10:02 pm

hans wrote:
Thu Oct 15, 2020 9:23 pm
Another thing I forgot to mention in my previous post... have you looked at the two elements of the collector lens assembly individually?
I have a broken Microstar IV that I have been stripping for parts, and from what I recall that lens did look aspheric. According to the patent it is intended to be, but a lot less dramatically so than the drawing makes it look - according to the text and the lens surface equation they give it's simply a parabola, though the drawing shows negative curvature at the rim.

This may just be a standard way of indicating an aspheric lens, but I vaguely recall the lens from the Microstar to also have that curvature. The simulation I did models the aspheric lens using the aspheric equation they give, but of course this just results in a parabola. I should dig out that lens and try to do some measurements.

That being said, the first lens group performs roughly as advertised and collimates the light coming from the filament fine. On the other hand, lens II performs differently than expected. It may just be that imaging the filament exactly at the condenser pupil is not hugely critical, since the condenser is on a moving rack anyway (though 30mm off the focal point seems like a large difference).

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Re: Understanding Microscope Patents

#6 Post by apochronaut » Thu Oct 15, 2020 10:14 pm

Patents include only enough information to secure the patent. There can be a lot hidden and a lot changed when production takes place. No company is bound by a patent except those other than the patent holder.
In looking at AO's and other patents I have found that many of them are filed for well after they are in production rather than before. I haven't looked at the patent that you are profiling here but given the date of 1975, I wouldn't think it was for the 410. Possibly the 110.

I am thinking too that the mirror and illuminator window/collimating lens aren't being factored in.

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Re: Understanding Microscope Patents

#7 Post by hans » Thu Oct 15, 2020 11:34 pm

The way it bends straight lines, looks more extreme than just parabolic to me, but hard to get much of a sense of shape looking at the lens itself.
BrianBurnes wrote:
Thu Oct 15, 2020 10:02 pm
On the other hand, lens II performs differently than expected. It may just be that imaging the filament exactly at the condenser pupil is not hugely critical, since the condenser is on a moving rack anyway (though 30mm off the focal point seems like a large difference).
Yeah I don't really understand this either. Have you tried to determine how close the filament is to being conjugate with the condenser diaphragm in the 410? I have been wondering, but of course the frosted lens makes it difficult to tell. I was considering trying to defeat the frosting by sticking glass (maybe some cut pieces of cover glass?) to it with immersion oil. If the they are not conjugate, possibly that is intentional to get some further smoothing (in addition to the frosting) of illumination in the rear focal plane of the objective?
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Re: Understanding Microscope Patents

#8 Post by apochronaut » Fri Oct 16, 2020 11:58 am

Having the filament focus at the conjugate plane ( field diaphragm, object, visual) is critical illumination.
The illumination beam needs to be defocused at the conjugate plane just enough that the illumination beam or filament image just equals the diameter of the field, not be focused at the conjugate plane.
The frosted glass assists in the dispersion of the refracted image of the filament, providing a whiter, cleaner field.

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Re: Understanding Microscope Patents

#9 Post by hans » Fri Oct 16, 2020 8:27 pm

I had in mind, and I think Brian was referring to, the other set of conjugate planes -- filament, condenser aperture diaphragm, objective rear focal plane, exit pupil? The filament is clearly fairly close to being conjugate with the others in both the patent design and the actual 410, but... Is the model correctly representing the design in the patent? If correct is the slightly offset focal point of the filament relative to the condenser diaphragm intentional? If intentional, why? What is the actual arrangement in the 410? (Hard to tell because of the frosted lens.)

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Re: Understanding Microscope Patents

#10 Post by Bemoc » Fri Oct 16, 2020 10:29 pm

Have any of you ever wished you could be a fly on the wall, watching some amazing or interesting event taking place that you knew you could never be a part of? That's how I feel watching this thread right now. It's like van Leewenhouk (sic) on the wall in a contemporary lab, as far as I am concerned. Thanks for pulling back the corners a bit for me.

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Re: Understanding Microscope Patents

#11 Post by wporter » Sat Oct 17, 2020 12:09 am

Apo is correct. If you have a frosted glass, you are using 'critical illumination', which is what the 410 uses: the frosted glass, making an evenly-lit field, is right before the field iris which is to be conjugate with the specimen. Look upon the frosted glass as 'the filament' in this kind of system, slightly defocused from the specimen plane so you don't see the granularity of the actual frosted surface. If your light is bright enough and heat is not an issue, this is actually superior to Kohler; no messy uneven filaments to compensate for.

Some microscopes have a pivoting frosted glass, which enables you to move it out of the way to get 'true' Kohler. But moving it back into place does still even out the light field quite a bit, at the cost of some brightness.

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Re: Understanding Microscope Patents

#12 Post by hans » Sat Oct 17, 2020 1:36 am

wporter wrote:
Sat Oct 17, 2020 12:09 am
...the frosted glass, making an evenly-lit field, is right before the field iris which is to be conjugate with the specimen. Look upon the frosted glass as 'the filament' in this kind of system, slightly defocused from the specimen plane so you don't see the granularity of the actual frosted surface.
Agree that the field diaphragm can be viewed in some sense as a "virtual" round, uniform light source providing critical illumination via the collimating lens and condenser. But doesn't that interpretation/equivalence work just as well regardless of where a diffusing element is placed, or even in "true" Koehler with no diffusing element at all?

In the 410 the frosted glass is not really close to the field diaphragm at all, it is the surface of the collector lens facing the bulb.

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Re: Understanding Microscope Patents

#13 Post by wporter » Sat Oct 17, 2020 2:43 am

Right, it doesn't make any difference in critical illumination where the field iris is placed, if the illumination after the frosting is collimated. It could be 10 feet away. The frosting is placed as close to the lamp as possible to make it as bright as possible. The iris is after the frosting to control the diameter of the light source, and to prevent excess light & glare.The collimation is to prevent wasted light, but old microscopes functioned fine without it when the mirror was aimed at a cloud ferinstance.

So in Kohler the field iris would do the same thing, but since there is no diffuser, the filament has to focused inside the condenser to achieve the same even field at the specimen as critical already has.

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Re: Understanding Microscope Patents

#14 Post by hans » Sat Oct 17, 2020 3:13 am

I guess I am not really following the broader argument...
apochronaut wrote:
Fri Oct 16, 2020 11:58 am
Having the filament focus at the conjugate plane ( field diaphragm, object, visual) is critical illumination.
Then my following comment was suggesting that maybe we were talking about different things, since I (and I think Brian) were discussing whether or not the filament is expected to be exactly focused in the plane of the condenser diaphragm (not object) and I didn't understand the relevance of apo's comment.

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Re: Understanding Microscope Patents

#15 Post by wporter » Sat Oct 17, 2020 3:55 am

Apo (if I can put words in his mouth) was talking about the wide light sources of old-time microscopes that used critical illumination: the sun, a cloud, an oil-lamp flame, or indeed, one of the older filaments seen in some light bulbs from the 50's-60's that were actually strips of tungsten that might have been 2mm wide & 10mm long. These old filaments were wide enough to function as an extended source of light when projected by the condenser onto the specimen.

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Re: Understanding Microscope Patents

#16 Post by hans » Sat Oct 17, 2020 4:14 am

wporter wrote:
Sat Oct 17, 2020 3:55 am
These old filaments were wide enough to function as an extended source of light when projected by the condenser onto the specimen.
Yes, and as we were just discussing, a pure Koehler system with no diffuser can still be though as critical illumination system behaving as if the opening in field diaphragm were such a source, right? I still don't really see how this relates to the discussion preceding apo's comment...

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Re: Understanding Microscope Patents

#17 Post by hans » Sat Oct 17, 2020 5:23 am

Adhering a piece of cover glass to the frosted collector lens with Cargille type B worked well and the filament is clearly visible through a phase telescope, so I guess I now have a 410 with a "less-modified" Koehler system. The filament appears pretty close to conjugate with the condenser diaphragm and the stop in the objective as best I can tell through a phase telescope. I also checked roughly that the field diaphragm is collimated coming out of the collimator lens below the condenser using a mirror to redirect the illumination to a DSLR manually focused at infinity.
BrianBurnes wrote:
Thu Oct 15, 2020 7:32 pm
...but the focal point of the second lens falls short of the suggested condenser aperture F2 (marked by the white line on the right in the image).
Not sure how accurately I can place the image in terms of axial position looking through the phase telescope. I kind of doubt I could detect a relatively small shift like your model shows, would need to experiment a bit moving things around to tell, I think.
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Re: Understanding Microscope Patents

#18 Post by hans » Sat Oct 17, 2020 6:00 am

I popped the second collector lens out of my assembly that was already missing the first one (came out very easily which probably explains why the first one was missing) and got a photo of a reflection of a ruler in the aspheric surface which shows the shape pretty well. The curvature definitely does change sign about half way our radially, kind of like the patent drawing.
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Re: Understanding Microscope Patents

#19 Post by hans » Sat Oct 17, 2020 7:09 am

BrianBurnes wrote:
Thu Oct 15, 2020 10:02 pm
I have a broken Microstar IV that I have been stripping for parts, and from what I recall that lens did look aspheric. According to the patent it is intended to be, but a lot less dramatically so than the drawing makes it look - according to the text and the lens surface equation they give it's simply a parabola, though the drawing shows negative curvature at the rim.

This may just be a standard way of indicating an aspheric lens, but I vaguely recall the lens from the Microstar to also have that curvature. The simulation I did models the aspheric lens using the aspheric equation they give, but of course this just results in a parabola. I should dig out that lens and try to do some measurements.
I played with the aspheric element alone a bit and there appear to be two relatively distinct focal lengths, 50 mm for the inner region out to 10 mm radially and 70 mm for the annulus going from 10 to 20 mm radially. Perhaps it could be reasonably approximated by a surface with piecewise-constant curvature radially, if your software can model such a surface?

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Re: Understanding Microscope Patents

#20 Post by MichaelG. » Sat Oct 17, 2020 11:22 am

BrianBurnes wrote:
Thu Oct 15, 2020 10:02 pm

This may just be a standard way of indicating an aspheric lens, but I vaguely recall the lens from the Microstar to also have that curvature. The simulation I did models the aspheric lens using the aspheric equation they give, but of course this just results in a parabola. I should dig out that lens and try to do some measurements.
Section 1.9 of this might help a little :
http://www.raymak.com/wp/wp-content/upl ... pdf#page13

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Re: Understanding Microscope Patents

#21 Post by BrianBurnes » Sat Oct 17, 2020 6:25 pm

wporter wrote:
Sat Oct 17, 2020 12:09 am
Apo is correct. If you have a frosted glass, you are using 'critical illumination', which is what the 410 uses: the frosted glass, making an evenly-lit field, is right before the field iris which is to be conjugate with the specimen.
I would have to disagree with this - the presence of a field lens that projects the field diaphragm at infinity and focuses the filament at (or close to) the condenser pupil makes this Kohler. The only mystery is the offset of the filament focal plane to the condenser pupil. There may be a real reason for this, but it may also just be commonplace to fudge the numbers in the patent a bit. Either way something interesting could be learned here.
hans wrote:
Sat Oct 17, 2020 5:23 am
Adhering a piece of cover glass to the frosted collector lens with Cargille type B worked well and the filament is clearly visible through a phase telescope, so I guess I now have a 410 with a "less-modified" Koehler system.
Phenomenal work as always Hans! Those are very interesting findings. With the filament being visible now, it may be possible to find its focal plane by moving a viewing screen (e.g. frosted class or tissue paper) up and down underneath the condenser and see where it lands.

The curvature of the aspheric lens is fascinating. Both this patent and the patent of the fluorescence system use the standard formula for aspheric surfaces, but set most parameters to zero to obtain a parabolic surface. I suspect that in the implementations of both of these, the real lens is more complex. Most likely the polynomial coefficients are non-zero in the real system, but kept secret.

I wrote the simulation software, so the lens surface could be modified arbitrarily. I will have a play with it, but I am also not sure what I am looking for - being only casually versed in optics design, I'm not sure of the purpose of the additional curvature and so it will be difficult to tell when I have it right.

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Re: Understanding Microscope Patents

#22 Post by hans » Sat Oct 17, 2020 7:40 pm

BrianBurnes wrote:
Sat Oct 17, 2020 6:25 pm
With the filament being visible now, it may be possible to find its focal plane by moving a viewing screen (e.g. frosted class or tissue paper) up and down underneath the condenser and see where it lands.
I did try this briefly last night but the results were confusing due to the aspheric surface and its interaction with the field diaphragm, which I had not really understood at that point. Now after messing with the aspheric element, what I plan to do is make two stops: 20 mm disc to block the light through the central portion, and 40 mm disc with 20 mm hole to block the outer annulus. I also need to remove the stage for better access. Then I think I will be able to more accurately determine the two focal points of the filament corresponding the two distinct focal lengths I saw with the lens alone.
BrianBurnes wrote:
Sat Oct 17, 2020 6:25 pm
The curvature of the aspheric lens is fascinating. Both this patent and the patent of the fluorescence system use the standard formula for aspheric surfaces, but set most parameters to zero to obtain a parabolic surface. I suspect that in the implementations of both of these, the real lens is more complex. Most likely the polynomial coefficients are non-zero in the real system, but kept secret.
I wonder how well that standard formula could approximate two relatively distinct regions of curvature? Would obviously require using the radial power series terms, I think, but if curvature as a function of r looks somewhat like a step function, then a power series is not a very efficient way to approximate it.
BrianBurnes wrote:
Sat Oct 17, 2020 6:25 pm
I wrote the simulation software, so the lens surface could be modified arbitrarily. I will have a play with it...
Very impressive, I had been wondering if this was the case after stalking around the site your photos are hosted on a bit, was the simulation done with Tantalum Renderer?
BrianBurnes wrote:
Sat Oct 17, 2020 6:25 pm
...I'm not sure of the purpose of the additional curvature and so it will be difficult to tell when I have it right.
I don't know if any configuration of the 410 had an optional swing-in auxiliary lens on the bottom of the condenser like some of the previous generations (I have never seen one) but perhaps the varying focal length aspheric surface placed relatively close to the field diaphragm is serving a similar purpose optimizing across varying magnification objectives while not requiring manual intervention?

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Re: Understanding Microscope Patents

#23 Post by hans » Sat Oct 17, 2020 11:56 pm

I'm calling the two regions of the aspheric surface "inner" (0-10 mm radially) and "outer" (10-20 mm radially). The inner region actually images the filament just before the collimating lens, 5 mm below the face of the casting where the collimating lens rests. The outer region and collimating lens together image the filament 10 mm above the uppermost lip of the plastic mounting ring holding the collimating lens. So total axial distance 25-30 mm between the images with the collimating lens in between. The image from the inner region is quite sharp while the image from the outer region is hazier with the focus point not quite as obvious. Before I took the stage off I measured 56 mm from the lip of the collimating lens mount to the condenser diaphragm with the nosepiece near the bottom of its travel. So definitely the filament is imaged somewhat in front of the condenser aperture, perhaps even more than in the simulation of the patent design. The focus points are obviously sensitive to bulb position, which does not seem to be controlled very precisely in the 410 and probably doesn't really matter with the diffuser. I estimate play in the bulb mounting could correspond to several mm, maybe as much as 10 mm, variation in the image positions.
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410-filament-outer-image.jpg
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410-filament-outer-stop.jpg
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Re: Understanding Microscope Patents

#24 Post by hans » Sun Oct 18, 2020 12:41 am

Just occurred to me -- possibly the reason the outer image is hazier with less distinct focus is because my crudely-fractured piece of cover glass is not covering the periphery of the first lens well.

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Re: Understanding Microscope Patents

#25 Post by apochronaut » Sun Oct 18, 2020 3:18 pm

hans wrote:
Sat Oct 17, 2020 3:13 am
I guess I am not really following the broader argument...
apochronaut wrote:
Fri Oct 16, 2020 11:58 am
Having the filament focus at the conjugate plane ( field diaphragm, object, visual) is critical illumination.
Then my following comment was suggesting that maybe we were talking about different things, since I (and I think Brian) were discussing whether or not the filament is expected to be exactly focused in the plane of the condenser diaphragm (not object) and I didn't understand the relevance of apo's comment.
The original thread began as a question. The relevance of my comment was to answer the question. The Microstar IV does not have Critical Illumination, it has a modified Koehler Illumination system. Modified by the dispersion filter. The diagram posted at the beginning of the thread shows a Koehler illumination system, with the beam focusing ahead of the object plane and providing a defocused sphere of even light at the object plane conjugate with the field diaphragm and image plane.

If the simulated diagram focused the illumination beam at the object plane it would be critical illumination.

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Re: Understanding Microscope Patents

#26 Post by hans » Sun Oct 18, 2020 5:24 pm

apochronaut wrote:
Sun Oct 18, 2020 3:18 pm
The Microstar IV does not have Critical Illumination, it has a modified Koehler Illumination system. Modified by the dispersion filter. The diagram posted at the beginning of the thread shows a Koehler illumination system, with the beam focusing ahead of the object plane and providing a defocused sphere of even light at the object plane conjugate with the field diaphragm and image plane.
I guess the reason I am confused is because I don't think anyone was suggesting that the illumination was critical, emphasis added:
BrianBurnes wrote:
Thu Oct 15, 2020 7:32 pm
The beam emerges roughly collimated out of the first lens group as it should, but the focal point of the second lens falls short of the suggested condenser aperture F2 (marked by the white line on the right in the image).

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Re: Understanding Microscope Patents

#27 Post by BrianBurnes » Sun Oct 18, 2020 9:06 pm

hans wrote:
Sat Oct 17, 2020 7:40 pm
I wonder how well that standard formula could approximate two relatively distinct regions of curvature? Would obviously require using the radial power series terms, I think, but if curvature as a function of r looks somewhat like a step function, then a power series is not a very efficient way to approximate it.
I played around a bit with the formula in graphing software and it seems like it can produce that kind of surface:

Image

The formula is not parametrized in terms of anything intuitive like curvature, so it's not immediately obvious how these parameters relate to focal length. However, it's pretty clear that the parameters in the patent are bogus at least as far as the Microstar IV system is concerned: Looking closer at the diameters of the first (planoconvex) and second (aspheric) element of the collimator in the real microscope, I measure their diameters as 32mm and 42mm. However, the suggested spherical radii in the patent (9.173 and 12.494) do not result in a valid surface at those lens diameters. The intended diameters are not given in the patent, but I would roughly estimate them to be 16.2mm for the first (Lens "A") and 24mm for the second (Lens "B") element in the collimator, quite different from the real system.

From the filing date, it's likely this patent describes a different system (as apo suggests). I would also guess that the numbers were fudged quite a bit in the application so as not to give away the real system.
This is a bit unfortunate, as I was hoping to recycle the collimator optics from the Microstar into something else, but that becomes challenging without knowing much about the lens itself.
hans wrote:
Sat Oct 17, 2020 7:40 pm
Very impressive, I had been wondering if this was the case after stalking around the site your photos are hosted on a bit, was the simulation done with Tantalum Renderer?
This was using a more accurate (C++ based) version of the software. It's roughly based on the same algorithms, but can more accurately model different types of glasses and allows to render time-resolved ("femto-second") animations of light pulses passing through lens assemblies. It mostly sees use for collaborations with research groups that build their own microscopes (two-photon systems and the like) that I understand little about, but more recently it has come in handy for helping this microscopy hobbyist :)

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Re: Understanding Microscope Patents

#28 Post by apochronaut » Sun Oct 18, 2020 9:26 pm

Is there not a place for the last collimator in the system? The one between the mirror and the condenser? It seems that without it, the filament image would appear at a shorter focal length. No longer Koehler.

I don't see it's affect on the system included. Not diagramatically, anyway.

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Re: Understanding Microscope Patents

#29 Post by hans » Sun Oct 18, 2020 9:42 pm

BrianBurnes wrote:
Sun Oct 18, 2020 9:06 pm
I played around a bit with the formula in graphing software and it seems like it can produce that kind of surface:
Looks like a Mathematica plot? I do have access to Mathematica and was also playing with the parameters a bit yesterday, have you tried plotting the second derivative? My suspicion is that the curvature varies too gradually to produce the two relatively distinct focal lengths I observed, which I think would require a fairly abrupt transition from one curvature value to another.
BrianBurnes wrote:
Sun Oct 18, 2020 9:06 pm
This is a bit unfortunate, as I was hoping to recycle the collimator optics from the Microstar into something else, but that becomes challenging without knowing much about the lens itself.
After putting the stage and objectives back on and playing around some more with the less-modified Koehler system, I am strongly suspecting that the outer region of the aspheric surface has effect mainly with illuminated field diameters greater than about 2 mm. I am going to try projecting light backward through the system from the object plane to see how sharply-defined the shadow of the field diaphragm is on the aspheric surface.

hans
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Re: Understanding Microscope Patents

#30 Post by hans » Sun Oct 18, 2020 9:59 pm

apochronaut wrote:
Sun Oct 18, 2020 9:26 pm
Is there not a place for the last collimator in the system? The one between the mirror and the condenser?
Perhaps the confusion is because the collimator (lens II in the patent drawing) comes before the mirror in the design in the patent, but is placed horizontally after the mirror in the 410? In any case I assume Brian omitted the mirror from his simulation for simplicity, since the mirror does not change anything fundamentally.
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