Condenser corrections aplanatic, achromatic, etc. -- which planes are they referring to?

Everything relating to microscopy hardware: Objectives, eyepieces, lamps and more.
Message
Author
User avatar
patta
Posts: 402
Joined: Sun May 10, 2020 6:01 am
Location: Stavanger Norway
Contact:

Re: Condenser corrections aplanatic, achromatic, etc. -- which planes are they referring to?

#31 Post by patta » Sun Aug 01, 2021 7:34 am

hans wrote:
Fri Jul 30, 2021 5:42 pm
patta wrote:
Fri Jul 30, 2021 7:46 am
In the aperture planes, the "aperture" is the field. For an infinite microscope with tube length 200mm and field 20mm, the NA of aperture is constant for all objectives, about (20/2)/200 ~ NA 0.05. Compare it with NA 0.90 or 1.40 used in the object plane...
On the image side, but on the illumination side the condenser images the aperture iris at higher NA when the illuminated field is large, I believe? For example MicroStar IV system goes up to 5 mm with ~10 mm EFL condenser at the normal height, so NA 0.25? (2.5 mm / 10 mm)
.
Yes/no/I don't know? For Brightfield, I'd say that the field stop at the eyepiece/camera adapter is the one ruling them all, so the NA is restricted. For scattered light (darkfield etc) I fear that you're right, the field gets larger, so the NA, and spherical aberration nastier.
-
hans wrote:
Fri Jul 30, 2021 5:42 pm
Regarding telecentricity, this is equivalent to saying that the limiting aperture stops are located at the condenser FFP and objective BFP as usual? Not sure it makes sense to say eyepieces themselves are inherently telecentric, rather projection of the intermediate image near infinity by the eyepiece is telecentric only because the objective BFP is the limiting aperture stop in the system? Actually I have read that newer camera lenses designed for digital (particularly mirrorless systems) are often telecentric on image side so maybe could work as condenser with modest NA?
That's getting above my paygrade... guesses:
Yes the condenser FFP - objective BFP should match, but that must be implemented explicitly in the design, doesn't happen naturally. If both are telecentric (same "zero aperture convergence" ) then they match; but can made to match also if they're complementary convergent-divergent; some manufacturer may have chosen the latter road, making mix & match of condenser-objective a gamble, like with compensating eyepieces.
There is no "natural" place for the aperture plane, exactly halfway from the field; you can put the aperture where you want, between field planes.
You can tweak LWD objectives and eyepieces to be pericentric (hypercentric) by imposing an aperture at the "wrong" place with a relay lens:
https://wordpress.com/post/patta1072853 ... ss.com/620
Or tweak high NA objectives to become fisheyes (with defocused Bertrand lens).
https://wordpress.com/post/patta1072853 ... ss.com/445

But, images are not so good with those tweakings.
Because the designers, choose a place for the aperture, then optimize the optics around this position. Then,if we move the aperture away from this position, the lens doesn't work well, extra aberrations chime in. So, eyepieces are optimized for (approximately) telecentric; yes with the objective BFP being the working aperture. But if I place the aperture nearer, image from the eyepiece gets worse.

Camera lenses, are never exactly telecentric image-side; but, true, they need to be less divergent than old film lenses, because digital sensor have narrow "acceptance angle", they won't record light that is coming from a grazing angle, better if it comes almost perpendicularly.
DSLR lenses needed a "back focal length" or "flange distance", because of the mirror; the lens need to be away from the sensor. That forced to use Retrofocus for wide angle lenses, which has the added benefit of projecting light on the sensor from not-so-grazing angles (but still far from telecentric).

With mirrorless, the need for Retrofocus disappeared; so people started experimenting with old wide angle lenses designed for film rangefinder (aka film mirrolress), that do not have retrofocus.
But, then, horrible images; because the sensor is not sensitive to the narrow-angle rays those lenses were projecting. So, the need for telecentricity came back. This time with "telecentric" name (while before, it was called "back focal length").
Manufacturers today are scrambling to make sensors with wider acceptance angle; and mirrorless are likely to accept less-telecentric lenses than old DSLR.
Many confused words, but a couple of images may explain the above very easily

User avatar
patta
Posts: 402
Joined: Sun May 10, 2020 6:01 am
Location: Stavanger Norway
Contact:

Re: Condenser corrections aplanatic, achromatic, etc. -- which planes are they referring to?

#32 Post by patta » Sun Aug 01, 2021 4:59 pm

Here
image 1
objective and condenser should match; easiest if they're both telecentric. Look at the blue cone of light.
In case 1 and 2, there is match condenser FFP - objective BFP.
if they don't match (third case):
in brightfield, there is loss in NA away from field center
in phase, the annulus doesn't match up away from the field center (as Leitz 10x image)

image 2
photographic lenses
the lens #2 is what mirrorless photographers would like to use (cheaper, sharper) but they can't because the CMOS sensors don't like inclined light.
The lens #4 is true telecentric, but they're too expensive
The lens #1 is the standard 50mm f/2; would-be candidate for DIY achromat-aplanat-plan condenser. Bot does not work well, as for previous illustration
.
Most probably, those images are available, better, from websites denigrated in previous post. anyway. Let's clog the net with repetitions.
.
hope is understandable.
hope is understandable.
telecentricity condenser.jpg (92.35 KiB) Viewed 11588 times
.
Raytracing images borrowed without formalities from Kats Ikeda  [url]https://www.pencilofrays.com/lens-design-forms/[/url]<br />And opto-e, https://www.opto-e.com/
Raytracing images borrowed without formalities from Kats Ikeda [url]https://www.pencilofrays.com/lens-design-forms/[/url]
And opto-e, https://www.opto-e.com/
telecentric lenses.jpg (108.28 KiB) Viewed 11588 times

hans
Posts: 977
Joined: Thu May 28, 2020 11:10 pm
Location: Southern California

Re: Condenser corrections aplanatic, achromatic, etc. -- which planes are they referring to?

#33 Post by hans » Sun Aug 01, 2021 8:13 pm

I was under the impression that at least in microscope context FFP/BFP (and similar variations on those terms) refer specifically to the planes shown in your first case with infinity focus on the other side of the lens. So then when typical microscope systems are shown with stops at FFP/BFP then object space telecentricity is already implicit/assumed?

I have wondered about your second case. With my MicroStar IV phase setup which I am pretty sure is all correct original parts there is no significant variation in magnification of annulus relative to diffraction plate when raising/lowering the condenser. That is what is expected in the telecentric case, I think.

However the B&L Dynoptic with phase here does show noticeable variation in magnification of the annulus although the phase effect seems decent and uniform across the field. I think maybe that is what would be expected in you second case. The condenser top lens I am using is from a basic B&L 1.25 Abbe which threads in to the turret but I'm not sure is the correct one to use for phase since the top lens was missing when I bought the phase stand. Have been meaning to post some photos showing the magnification variation asking about correct top lens but not gotten around to it yet...
patta wrote:
Sun Aug 01, 2021 4:59 pm
...anyway. Let's clog the net with repetitions.
A vicious cycle -- internet clogged with basic stuff over-simplified or written by people without deep understanding leads to further cloggage with confused speculation by those trying to understand.

apochronaut
Posts: 6233
Joined: Fri May 15, 2015 12:15 am

Re: Condenser corrections aplanatic, achromatic, etc. -- which planes are they referring to?

#34 Post by apochronaut » Sun Aug 01, 2021 11:48 pm

The other thing of course is the difference between theoretical information and empirical information. Theoretical information is pretty much limited to nerdville if it doesn't end up having a practical and proveable application. Nerdville is possibly the largest metropolis in existence. Tokyo is but a bedroom community of Nerdville but likely the biggest one.
Sometimes a theory will result in a practical application and sometimes design experiments based on theory usually result in unforseen variables that force the theorist to modify the design beyond the simplistic principals envisioned. More often than not it is empirical evidence that both supports theories and opens it's arms to practical refinements outside those envisioned.
One could argue that the pure sciences are more precise and that in them, theory is more closely hitched to application but in the case of optics as a branch of physics, as the example in question, math provides the recipe but it is the designer as chef that tweaks the inadequacies of the raw ingredients to get all of the nuances of the design into the correct relationship.

User avatar
patta
Posts: 402
Joined: Sun May 10, 2020 6:01 am
Location: Stavanger Norway
Contact:

Re: Condenser corrections aplanatic, achromatic, etc. -- which planes are they referring to?

#35 Post by patta » Mon Aug 02, 2021 7:54 am

Ok, ok, let's check if this Telecentric story has some relevance in practice or instead should be relegated to the realm of silly mental masturbations...

hans
Posts: 977
Joined: Thu May 28, 2020 11:10 pm
Location: Southern California

Re: Condenser corrections aplanatic, achromatic, etc. -- which planes are they referring to?

#36 Post by hans » Mon Aug 02, 2021 7:33 pm

There is some relevant discussion at the beginning of chapter 3 of Bennett's book:
The condenser diaphragm and the diffraction plate perform definite functions in the phase microscope. The performance of these functions is modified by both the specimen and the optical design of various components of the microscope. The spherical aberration of the objective and curvature of field in the image of the condenser diaphragm, for example, may introduce limitations. The minimization of the adverse effects produced by these modifications leads to some of the most difficult problems of designing and making a phase microscope.
The essential requirement governing the relative location of the condenser diaphragm and of the diffraction plate is that the condenser diaphragm shall be focused upon the diffraction plate by the lenses which lie between the condenser diaphragm and the diffraction plate. The choice of the first focal plane of the substage condenser as the location of the condenser diaphragm makes the most practicable use of the diffraction phenomena. However, it is not essential that the condenser diaphragm he placed at the first focal plane of the condenser. If the condenser diaphragm is put at the first focal plane of a well-corrected substage condenser and if an image of the light source is formed on the condenser diaphragm, then the object specimen is illuminated by substantially parallel light. With an Abbe-type substage condenser, the spherical aberration necessarily present in this type of condenser destroys to some degree the parallelism of the rays which are incident on the object specimen. However, an Abbe-type condenser is a satisfactory substage condenser for the phase microscope, provided that the condenser has the numerical aperture required by the design of the diffraction plate. It can be shown theoretically that the departure from parallelism of the illuminating rays plays only a secondary part in modifying the contrast produced by the phase microscope. Experiment also shows that very little effect is produced on contrast in the image when the rays illuminating the specimen are not parallel. The presence of spherical aberration in the substage condenser can affect the distance between the last surface of the condenser and the specimen slide when the phase microscope is lined up and adjusted for use. This may modify the numerical aperture at which the full aperture of the condenser can fimction if the diaphragm is removed and the position of the condenser is not changed. In the presence of aberrations the magnification ratio between the condenser diaphragm and the conjugate area of the diffraction plate depends on the distance between the last surface of the substage condenser and the first surface of the objective.
The part I put in bold maybe is an explanation for the magnification variation I notice on the Dynoptic with basic Abbe condenser, rather than a lack of telecentricity.
apochronaut wrote:
Sun Aug 01, 2021 11:48 pm
Sometimes a theory will result in a practical application and sometimes design experiments based on theory usually result in unforseen variables that force the theorist to modify the design beyond the simplistic principals envisioned. More often than not it is empirical evidence that both supports theories and opens it's arms to practical refinements outside those envisioned.
One could argue that the pure sciences are more precise and that in them, theory is more closely hitched to application but in the case of optics as a branch of physics, as the example in question, math provides the recipe but it is the designer as chef that tweaks the inadequacies of the raw ingredients to get all of the nuances of the design into the correct relationship.
I think this is agreeing, but I would put it like this: By now this sort of optical design is an optimization/engineering problem, not a scientific one. The accuracy of the theory is not really an issue nor is making predictions. The chefing is about coming up with clever arrangements of the available materials that have unusually good performance relative to the complexity and manufacturing tolerances required.

MichaelG.
Posts: 3970
Joined: Mon Apr 10, 2017 8:24 am
Location: North Wales

Re: Condenser corrections aplanatic, achromatic, etc. -- which planes are they referring to?

#37 Post by MichaelG. » Tue Aug 03, 2021 6:40 am

patta wrote:
Fri Jul 30, 2021 7:46 am
Ok some more reasoning

[…]

- Telecentricity
That may be the main design feature of any condenser and it's never mentioned. The condenser must provide straight-up illumination cones for all the field (not only in the center!); it should not be a diverging beam (cones pointing outwards).
I think it is the issue that pops up when using low magnification objectives, with large field; the borders are darker, because the diverging light from the condenser isn't taken up by the objective.
Permit me, please, to throw a pebble into that pond ^^^ by asking:

Has anyone considered using a ‘fibre optic faceplate’ as a straightener ?

This thought has been at the back of my mind for several years, but I’ve not actually tried it :oops:

MichaelG.
Too many 'projects'

hans
Posts: 977
Joined: Thu May 28, 2020 11:10 pm
Location: Southern California

Re: Condenser corrections aplanatic, achromatic, etc. -- which planes are they referring to?

#38 Post by hans » Tue Aug 03, 2021 7:06 pm

MichaelG. wrote:
Tue Aug 03, 2021 6:40 am
Has anyone considered using a ‘fibre optic faceplate’ as a straightener ?
Between the condenser and sample? Or somehow replacing the condenser?

MichaelG.
Posts: 3970
Joined: Mon Apr 10, 2017 8:24 am
Location: North Wales

Re: Condenser corrections aplanatic, achromatic, etc. -- which planes are they referring to?

#39 Post by MichaelG. » Tue Aug 03, 2021 10:20 pm

hans wrote:
Tue Aug 03, 2021 7:06 pm
MichaelG. wrote:
Tue Aug 03, 2021 6:40 am
Has anyone considered using a ‘fibre optic faceplate’ as a straightener ?
Between the condenser and sample? Or somehow replacing the condenser?
I was thinking of between the condenser and the sample
… context being what patta mentioned.

MichaelG.
Too many 'projects'

User avatar
patta
Posts: 402
Joined: Sun May 10, 2020 6:01 am
Location: Stavanger Norway
Contact:

Re: Condenser corrections aplanatic, achromatic, etc. -- which planes are they referring to?

#40 Post by patta » Wed Aug 04, 2021 7:19 am

The fiber optics faceplate, yes, it seems to work to "straighten" a beam; or, more precisely, it should somehow scramble the orientation while maintaining the NA.
They sell them, so must have some use. But a bit expensive. A frosted glass, does similar thing?
There are for sale are also "taper" fiber optics faceplates, that work just like a condenser by themselves; I think they're used as condensers in fiber optic illumination (like, for an endoscope)


About parallelism and aberrations; here below another trouble/drawing: spherical aberration means also Coma in the field; and this causes the light cones at different NA to have different orientation. Thus, a condenser with SA can't give parallel/telecentric illumination for all NA. In this case, it is parallel for Blue (medium NA) but the cones for larger and smaller NA are tilted.
The correlation condenser position - magnification, still to be understood properly.
Real tests coming soon, maybe.
Parallelism coma NA.jpg
Parallelism coma NA.jpg (41.99 KiB) Viewed 11413 times

MichaelG.
Posts: 3970
Joined: Mon Apr 10, 2017 8:24 am
Location: North Wales

Re: Condenser corrections aplanatic, achromatic, etc. -- which planes are they referring to?

#41 Post by MichaelG. » Wed Aug 04, 2021 8:23 am

patta wrote:
Wed Aug 04, 2021 7:19 am
The fiber optics faceplate, yes, it seems to work to "straighten" a beam; or, more precisely, it should somehow scramble the orientation while maintaining the NA.
They sell them, so must have some use. But a bit expensive. A frosted glass, does similar thing?
Many uses
Fibres are usually coherent [i.e. the plate can convey an image]
Exit angle of each fibre is ‘known’ [being specific to the fibre material].

MichaelG.
Too many 'projects'

hans
Posts: 977
Joined: Thu May 28, 2020 11:10 pm
Location: Southern California

Re: Condenser corrections aplanatic, achromatic, etc. -- which planes are they referring to?

#42 Post by hans » Wed Aug 04, 2021 5:17 pm

MichaelG. wrote:
Wed Aug 04, 2021 8:23 am
Fibres are usually coherent [i.e. the plate can convey an image]
Note confusing terminology, for example from https://www.rp-photonics.com/fiber_bundles.html:
Fiber bundles may be ordered or unordered. In the former case, there is a one-to-one correspondence concerning the arrangement of input and output fibers; this is required for imaging applications, for example. Ordered fiber bundles are also called coherent, although that has nothing to do with the usual meaning of coherence in optics.
So if the specimen is placed directly on the plate I guess you can get an image in some sense of the field iris, but not through a slide, and there would be no image of the aperture iris in any case? Like patta said, not obvious to me how the effect would differ from a diffuser in this case.

MichaelG.
Posts: 3970
Joined: Mon Apr 10, 2017 8:24 am
Location: North Wales

Re: Condenser corrections aplanatic, achromatic, etc. -- which planes are they referring to?

#43 Post by MichaelG. » Wed Aug 04, 2021 5:31 pm

hans wrote:
Wed Aug 04, 2021 5:17 pm
MichaelG. wrote:
Wed Aug 04, 2021 8:23 am
Fibres are usually coherent [i.e. the plate can convey an image]
Note confusing terminology, for example from https://www.rp-photonics.com/fiber_bundles.html:
Fiber bundles may be ordered or unordered. In the former case, there is a one-to-one correspondence concerning the arrangement of input and output fibers; this is required for imaging applications, for example. Ordered fiber bundles are also called coherent, although that has nothing to do with the usual meaning of coherence in optics.
Snivelling apologies if you feel I have mis-used the term ‘coherent’ … call it ‘ordered’ if you prefer
[ that is the sense in which I used it ]

Incidentally, this page is perhaps more directly relevant: https://www.rp-photonics.com/fiber_optic_plates.html

MichaelG.
Too many 'projects'

hans
Posts: 977
Joined: Thu May 28, 2020 11:10 pm
Location: Southern California

Re: Condenser corrections aplanatic, achromatic, etc. -- which planes are they referring to?

#44 Post by hans » Wed Aug 04, 2021 6:52 pm

MichaelG. wrote:
Wed Aug 04, 2021 5:31 pm
Snivelling apologies if you feel I have mis-used the term ‘coherent’ … call it ‘ordered’ if you prefer
[ that is the sense in which I used it ]
Sorry, just pointing out a possible confusion since it seems like these fiber plates are already assumed to be ordered by default (so I wasn't sure which meaning of coherent you had in mind), but they do not preserve coherence in the usual sense that a condenser does. With a fiber plate between the condenser and object plane do you agree it is not possible to "image" the field iris in the object plane unless the object plane is the surface of the plate? And that imaging of the aperture iris is not possible at all?

MichaelG.
Posts: 3970
Joined: Mon Apr 10, 2017 8:24 am
Location: North Wales

Re: Condenser corrections aplanatic, achromatic, etc. -- which planes are they referring to?

#45 Post by MichaelG. » Wed Aug 04, 2021 9:02 pm

hans wrote:
Wed Aug 04, 2021 6:52 pm
Sorry, just pointing out a possible confusion since it seems like these fiber plates are already assumed to be ordered by default (so I wasn't sure which meaning of coherent you had in mind), but they do not preserve coherence in the usual sense that a condenser does.
With hindsight, it was clearly a mistake for me to include the word ‘usually’
Fibres are usually coherent [i.e. the plate can convey an image]
I should have left it out, and risked some unknown expert being aware of a disordered plate.

Sometime I will do some experiments, and if I find anything useful I will share it.

The gist of my idea is that because the individual fibres [hopefully] all have the same known exit angle … which is much smaller than that of a common diffuser … adding the plate might provide good illumination, for the low powers, with less fall-off.

Please don’t let my musings disturb your analysis of the high NA system.

MichaelG.
Too many 'projects'

MichaelG.
Posts: 3970
Joined: Mon Apr 10, 2017 8:24 am
Location: North Wales

Re: Condenser corrections aplanatic, achromatic, etc. -- which planes are they referring to?

#46 Post by MichaelG. » Wed Aug 04, 2021 9:15 pm

To be clear … This is specifically what prompted me to throw my ‘pebble in the pond’
patta wrote:
Fri Jul 30, 2021 7:46 am

[…]

The condenser must provide straight-up illumination cones for all the field (not only in the center!); it should not be a diverging beam (cones pointing outwards).
I think it is the issue that pops up when using low magnification objectives, with large field; the borders are darker, because the diverging light from the condenser isn't taken up by the objective.
MichaelG.
Too many 'projects'

hans
Posts: 977
Joined: Thu May 28, 2020 11:10 pm
Location: Southern California

Re: Condenser corrections aplanatic, achromatic, etc. -- which planes are they referring to?

#47 Post by hans » Wed Aug 04, 2021 11:30 pm

Yeah it is an interesting thought. I came across a patent or paper a while ago that I think was talking about using a fiber bundle (not necessarily ordered) cut at an angle to get smooth (vs. NA, like Dodt gradient) and uniform (across the field) oblique illumination without a normal condenser, probably saved it, will see if I can find it.
MichaelG. wrote:
Wed Aug 04, 2021 9:02 pm
I should have left it out, and risked some unknown expert being aware of a disordered plate.
Issue of whether unordered plates exist aside, another reason I wanted to clarify "coherent", doesn't a thin diffuser also "convey an image" in the same sense that a fiber plate/bundle does when using the "ordered" meaning of the term coherent:
MichaelG. wrote:
Wed Aug 04, 2021 8:23 am
patta wrote:
Wed Aug 04, 2021 7:19 am
... A frosted glass, does similar thing?
... Fibres are usually coherent [i.e. the plate can convey an image] ...
(Of course a thin diffuser does not displace the image significantly, so not saying they are equivalent in general. And I would say neither really "conveys an image" when talking about coherence in the usual sense.)


MichaelG.
Posts: 3970
Joined: Mon Apr 10, 2017 8:24 am
Location: North Wales

Re: Condenser corrections aplanatic, achromatic, etc. -- which planes are they referring to?

#49 Post by MichaelG. » Thu Aug 05, 2021 8:29 am

hans wrote:
Wed Aug 04, 2021 11:30 pm
And I would say neither really "conveys an image" when talking about coherence in the usual sense.)
There is no point in us dancing with semantics, Hans … we are never likely to disambiguate the word ‘coherent’
[ is there perhaps a strange poetry about that observation ? ]

This, however is what I mean when I refer to coherent fibres being able to convey an image:
https://www.schott.com/en-us/products/f ... t-variants
… There are several tabs on that page

MichaelG.
Too many 'projects'

MichaelG.
Posts: 3970
Joined: Mon Apr 10, 2017 8:24 am
Location: North Wales

Re: Condenser corrections aplanatic, achromatic, etc. -- which planes are they referring to?

#50 Post by MichaelG. » Thu Aug 05, 2021 9:52 am

hans wrote:
Thu Aug 05, 2021 12:06 am
Patent I was thinking of, haven't read it carefully:
Then I would commend it to your attention, as the underlying invention is the effective use of an incoherent bundle of fibres to particular advantage.
Furthermore, it is to be observed that the end of the glass fiber bundle which is at the side of the lamp is not smoothly cut-off, rather completely irregularly broken off and frayed or spliced. Owing to the unequal lengths and diverging fiber ends there can be realized a particularly high incoherence of the light which is guided through the fibers of the light conductor.
This is a very interesting find, thank you Hans …
and worthy of investigation [in a separate thread, I would suggest].

MichaelG.
Too many 'projects'

User avatar
patta
Posts: 402
Joined: Sun May 10, 2020 6:01 am
Location: Stavanger Norway
Contact:

Re: Condenser corrections aplanatic, achromatic, etc. -- which planes are they referring to?

#51 Post by patta » Thu Aug 05, 2021 11:08 am

Let's keep clogging the forum
Here a fanciful raytracing of what frosted glass and fiber faceplates may do.

- Frosted glass scatters light around, final NA depending of surface roughness
- Microlens array do the same, just the NA can be more tightly controlled
- Straight fiber faceplate transmits the NA, and straighten the beam but scrambles the direction, so if the input is tilted, the output gets homogenized and spread to a higher NA (alpha-beta angles in the image; beta = alpha + tilt)
- a flexible fiber bundle can be used to transport illumination in difficult location (endoscopes, patent at post #48)
- Fiber optic tapers do some things, what exactly, is fishy
- Similar to fiber optic tapers, the eyes of moths and shrimps, focus a straight beam to a point

"acceptance angle" of fiber optics, another complication to take into account...
.
Frosted and Fiber.jpg
Frosted and Fiber.jpg (99.71 KiB) Viewed 11302 times

MichaelG.
Posts: 3970
Joined: Mon Apr 10, 2017 8:24 am
Location: North Wales

Re: Condenser corrections aplanatic, achromatic, etc. -- which planes are they referring to?

#52 Post by MichaelG. » Thu Aug 05, 2021 1:33 pm

patta wrote:
Thu Aug 05, 2021 11:08 am
Let's keep clogging the forum
Here a fanciful raytracing of what frosted glass and fiber faceplates may do.
[…]
Interesting speculative analysis ^^^
But I’m almost sure that you will find that large beta never actually exists on a fibre optic
… The acceptance angle and the output angle are both prescribed
… they depend upon the fibre material [and the medium with which it interfaces].

MichaelG.
Too many 'projects'

User avatar
patta
Posts: 402
Joined: Sun May 10, 2020 6:01 am
Location: Stavanger Norway
Contact:

Re: Condenser corrections aplanatic, achromatic, etc. -- which planes are they referring to?

#53 Post by patta » Thu Aug 05, 2021 3:47 pm

big dreams of testing all aberrations of all world's condensers, got resized
Here below, a simple test for parallelism/telecentricity
A camera with lens focused at infinity looks at the slide; the slide has a row of small pinholes, spaced ~1.2mm to each other.
The condenser illuminates the slide from below, with iris closed to minimum. if the illumination is not parallel/telecentric, we'll see many "bokeh balls", for each pinhole. If the illumination is perfectly parallel with no aberrations whatsoever, the bokeh balls should merge into one.
The 45 deg mirror is just for convenience.
It is the same method as the one described previously, "shot at the ceiling"; but here is easier to take a photo.

Tested two condensers, one probably Abbe (Swift Polarizing) and another one Achromatic (Leitz 402a); both dry, NA ~0.90
For each one, tested with and without the top lens
And, condenser aperture in two vertical positions,
for Swift, the built-in iris and a pinhole in the filter tray (about 8mm distance)
for Leitz, the built-in iris and the built-in phase annulus. (about 5mm distance) The latter was actually too big to be imaged properly.

Results: illumination is never exactly telecentric; however is off by few degrees only.
This non-parallelism may get relevant when put against objectives with large field and small NA ( NA 0.1 -> 6 degrees half-angle).
Removing the top lens seems to reduce the overall NA and the tilt runoff too, so it is good for low-power objectives.
High NA objectives, with narrow field, probably won't be affected at all by the lack of parallelism.
There is some change if the condenser is moved up and down, but not much. Maybe another time.

Bizarre to see the phase annulus that is explicitly projected not telecentric. Likely the objective phase plate is designed to match it.
.
Condenser parallelism setup.jpg
Condenser parallelism setup.jpg (89.96 KiB) Viewed 11274 times
.
Condenser parallelism photos.jpg
Condenser parallelism photos.jpg (160.86 KiB) Viewed 11274 times
Last edited by patta on Thu Aug 05, 2021 5:47 pm, edited 10 times in total.

User avatar
patta
Posts: 402
Joined: Sun May 10, 2020 6:01 am
Location: Stavanger Norway
Contact:

Re: Condenser corrections aplanatic, achromatic, etc. -- which planes are they referring to?

#54 Post by patta » Thu Aug 05, 2021 4:01 pm

MichaelG. wrote:
Thu Aug 05, 2021 1:33 pm
Interesting speculative analysis ^^^
But I’m almost sure that you will find that large beta never actually exists on a fibre optic
… The acceptance angle and the output angle are both prescribed
… they depend upon the fibre material [and the medium with which it interfaces].
Aha, is then so important this a maximum angle that the fiber can accept/ transport/ output ?
I'd thought that this angle was very large, much less than the "alpha" that we are feeding in. But, if the "alpha" is already the acceptance angle, so yes, the faceplate should output uniform, straight up lightning with the same angle. Or similar fantasies.

Edit
I see now, this acceptance angle is pretty small, like 10 degrees, or NA 0.18. I was expecting 45°, NA 0.70 or more.. :oops:

MichaelG.
Posts: 3970
Joined: Mon Apr 10, 2017 8:24 am
Location: North Wales

Re: Condenser corrections aplanatic, achromatic, etc. -- which planes are they referring to?

#55 Post by MichaelG. » Thu Aug 05, 2021 5:33 pm

This is a useful overview of fibre-optic acceptance [and, by symmetry, emission] angle:
https://www.fiberopticstech.com/technic ... -aperture/

and here are a couple of images from my own demonstration of
the emission from a 1mm bundle, illuminated by a green laser pointer:
.
Spot at 10mm distance
Spot at 10mm distance
F9392E55-AB95-4E52-AFA9-5260EE7D33CB.jpeg (154.26 KiB) Viewed 11251 times
.
Emission angle
Emission angle
A8608A98-5CB0-49AA-98D0-417A6C616E00.jpeg (137.8 KiB) Viewed 11251 times
.

MichaelG.

.
Important Edit: … having noted yours, patta

There does seem to be a wide range of values quoted !!
Compare this with my previous link
https://www.rp-photonics.com/acceptance ... ptics.html
Too many 'projects'

MichaelG.
Posts: 3970
Joined: Mon Apr 10, 2017 8:24 am
Location: North Wales

Re: Condenser corrections aplanatic, achromatic, etc. -- which planes are they referring to?

#56 Post by MichaelG. » Thu Aug 05, 2021 8:01 pm

.

I’ve just tried to estimate the output angle from my photo

My best guess is 26° for the half angle [sorry about the -334° dimensioning]
.
Estimated output angle of 1mm bundle
Estimated output angle of 1mm bundle
F6F4FD63-FF5F-4F28-B7F4-08C15DFCC7F0.jpeg (130.32 KiB) Viewed 11237 times
.
MichaelG.
Too many 'projects'

hans
Posts: 977
Joined: Thu May 28, 2020 11:10 pm
Location: Southern California

Re: Condenser corrections aplanatic, achromatic, etc. -- which planes are they referring to?

#57 Post by hans » Thu Aug 05, 2021 9:01 pm

patta wrote:
Thu Aug 05, 2021 3:47 pm
A camera with lens focused at infinity looks at the slide; the slide has a row of small pinholes, spaced ~1.2mm to each other.
The condenser illuminates the slide from below, with iris closed to minimum. if the illumination is not parallel/telecentric, we'll see many "bokeh balls", for each pinhole. If the illumination is perfectly parallel with no aberrations whatsoever, the bokeh balls should merge into one.
Nice experiment, for the bolded part to be true the camera lens cannot be limiting aperture in the overall imaging from condenser FFP to sensor, I think? Did you check whether the results depend on distance to or aperture setting of the camera lens?
patta wrote:
Thu Aug 05, 2021 3:47 pm
It is the same method as the one described previously, "shot at the ceiling"; but here is easier to take a photo.
I did the "shot at ceiling" check with my Dynoptic's phase condenser while messing with that water immersion objective last night, didn't take any photos but the phase annuli are imaged quite close to infinity, while the iris which is ~10 mm lower is not. Still confused about whether that condenser is a correct combination of parts though, should try with the MicroStar IV one...
MichaelG. wrote:
Thu Aug 05, 2021 9:52 am
hans wrote:
Thu Aug 05, 2021 12:06 am
Patent I was thinking of, haven't read it carefully:
Then I would commend it to your attention, as the underlying invention is the effective use of an incoherent bundle of fibres to particular advantage.
Basic similarity I saw with your suggestion is the idea of using exit angle behavior of the fibers to get illumination that varies with angle but not spatially, which I think is the main point of that patent, similar to the telecentric case using a condenser with aperture (or oblique mask) at FFP. (Separate, more fundamental behavior of the bundle than ordered vs. unordered.)
MichaelG. wrote:
Thu Aug 05, 2021 8:29 am
There is no point in us dancing with semantics, Hans … we are never likely to disambiguate the word ‘coherent’
The only ambiguity I was trying to clarify was which of two precise meanings of the word (unordered vs. this) we were talking about. I understand now, you never had in mind the coherence (physics) meaning, as Wikipedia calls it, only the "ordered fiber bundle" meaning.
MichaelG. wrote:
Thu Aug 05, 2021 9:52 am
...worthy of investigation [in a separate thread, I would suggest].
Started a separate topic:
Use of fiber acceptance/exit angles in microscope illumination

hans
Posts: 977
Joined: Thu May 28, 2020 11:10 pm
Location: Southern California

Re: Condenser corrections aplanatic, achromatic, etc. -- which planes are they referring to?

#58 Post by hans » Fri Aug 06, 2021 4:36 am

Shined a flashlight through some more condensers. Various AO/Reichert "Abbe aspheric" and achromatic/aplanatic condensers from several generations in brightfield mounts all projected the iris sharply near infinity. The 1205 turret with 1201 achromatic/aplanatic condenser was interesting, lots of variation among the annuli. The 10X annulus is mounted at a different height within the threaded insert that goes into the turret than the 40X and 100X. The 40X annulus projects very sharply at infinity but the 10X and 100X do not, the 10X being surprisingly blurry. Reaching in through the 100X annulus with a bent needle to judge where the FFP is, the annulus is several mm below it despite being mounted at the same mechanical height as the 40X -- lots of field curvature.

Since the projected image of the 10X annulus was so blurry I tried the same thing with 10X phase objectives 1742 (for Reichert MicroStar IV) and 1750 (for Leica ATC 2000): 1742 gives a similarly-blurry image of the diffraction plate while the diffraction plate in the 1750 projects sharply near infinity. Seems like this is almost certainly the cause of the poor phase contrast effect I got with the 1750 in the MicroStar IV here although I'm not sure how those symptoms (brown tint, phase effect fading out to oblique toward the periphery) can be explained optically. The defocus of the annulus relative to the diffraction plate was not obvious when looking with a phase telescope, I guess due to the small aperture stop (really more like a field stop in the context of the whole microscope) that phase telescopes have.

User avatar
patta
Posts: 402
Joined: Sun May 10, 2020 6:01 am
Location: Stavanger Norway
Contact:

Re: Condenser corrections aplanatic, achromatic, etc. -- which planes are they referring to?

#59 Post by patta » Fri Aug 06, 2021 10:44 am

hans wrote:
Fri Aug 06, 2021 4:36 am
The 10X annulus is mounted at a different height...

The defocus of the annulus relative to the diffraction plate was not obvious when looking with a phase telescope, I guess due to the small aperture stop (really more like a field stop in the context of the whole microscope) that phase telescopes have.
Nice, we are learning that is not only aberrations, but also WHERE the phase annulus and corresponding phase plate are, plays a big role.

1) About the method to check for parallelism, yes, it is independent on cmera lens distance; more distance, it only vignettes. The setup at previous post, was to get a lens with large aperture as near as possible to the slide.
Actually I've realized today that the same thing can be done with the damn phone camera, just put it over the pinhole slide on the stage. It is much easier and works better.

2) About the difficulty of seeing aberration with the phase telescope, here below, I've mounted a macro lens over the tube; it works as a focusable Bertrand/Amici lens, or as a phase centering telescope; just with much larger aperture (field). You can then focus easily in different positions inside the objective. I've done only for the Swift microscope.

3) setup to visualize Spherical Aberration in the object plane. Illumination is from a pinhole at infinity (actually 50 cm away) and I've made a row of pinholes in a filter that goes in the filter tray; each of those makes a ray for a specific NA.
The condenser project the light on a slide; I've used a diffuser/frosted slide, made with Sour Cream squashed under the coverslip. Sour Cream is the new thing, forget about obsolete fiber optics.
The image of the illumination on the slide can be visualized with 4x objective or with the macro lens (I've used the macro because is 1x magnification, larger field)
If the condenser has no SA, all rays converge in one point.


Resulting images may come soon, hopefully before I forget which is which.
.
Setup for Phone Telecentricity check and Macro Bertrand
Setup for Phone Telecentricity check and Macro Bertrand
phone and macro condenser.jpg (103.26 KiB) Viewed 11196 times
.
Assessment of condenser spherical aberration with sour cream
Assessment of condenser spherical aberration with sour cream
sph abn condenser.jpg (96.46 KiB) Viewed 11196 times

User avatar
patta
Posts: 402
Joined: Sun May 10, 2020 6:01 am
Location: Stavanger Norway
Contact:

Re: Condenser corrections aplanatic, achromatic, etc. -- which planes are they referring to?

#60 Post by patta » Fri Aug 06, 2021 11:25 am

Here, the images obtained with the "phone telecentricity check"; phone lens focused at infinity.
Seems compatible with measurements a post #53
I haven't cropped the images, so to keep calibration; the crop is actually much nicer

Racking the condenser up and down, scales a bit the whole image, but the bokeh balls keep more or less the same relative separation.
.
Condenser paerture visualized through 2 pinholes by phone camera
Condenser paerture visualized through 2 pinholes by phone camera
Condenser parallelism photos phone.jpg (87.27 KiB) Viewed 11190 times
Edit, swapped two images... :?
Rest, next week

Post Reply