Condenser correction types - how to test a condenser?

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MicroBob
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Condenser correction types - how to test a condenser?

#1 Post by MicroBob » Wed Jul 03, 2019 7:49 pm

Hi together,
in a recent thread the topic of condenser correction types came up.
I think this is a topic that isn't treated a lot and it would be useful to collect some information on this topic.
I myself have difficulties to understand the effect, the planarity and color correction has on the image.
It is also difficult to identify the correction level of many condensers.
On objectives the correction level is quite well marked. Some of my condenses have "Apl." or "Apl. Achr." on them but some don't have a single inscription. My microscope equipment is mostly 30-60 years old and things could also be mixed up since new.

Is there a practical way to test a condenser for it's quality?

@Apochronaut: Detailed and precise informations are as always very welcome!


Bob

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Re: Condenser correction types - how to test a condenser?

#2 Post by Hobbyst46 » Wed Jul 03, 2019 8:04 pm

Hi Bob,
An important subject - thanks for posting.
A basic level "appetizer": I own an Abbe Zeiss condenser, NA 1.3 with flip-out top lens; and an achromat-aplanat turret phase contrast condenser.
With the former, the margins of the FOV are clearly bluish (or purple - can't remember), at least with the low magnification objectives. With the latter, only a thin yellowish margin around the FOV.
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Re: Condenser correction types - how to test a condenser?

#3 Post by 75RR » Wed Jul 03, 2019 8:07 pm

Always an interesting topic. Here is an extract from Fundamentals of light microscopy and electronic imaging by Douglas B. Murphy to get the ball rolling:
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Re: Condenser correction types - how to test a condenser?

#4 Post by MicroBob » Wed Jul 03, 2019 8:14 pm

Hi Doron,
is there really written "Abbe" on your condenser?

I have this different image on the field diaphragm too. What I don't know is whether it is safe to conclude that this leads to a better image quality of the object on the stage.

Bob

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Re: Condenser correction types - how to test a condenser?

#5 Post by ImperatorRex » Wed Jul 03, 2019 8:19 pm

75RR wrote:I have this different image on the field diaphragm too. What I don't know is whether it is safe to conclude that this leads to a better image quality of the object on the stage.
I do not think it has negative impact on image quality, you simply need to open the field diaphragm a bit more, so the colors will not pass to the objective.

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Re: Condenser correction types - how to test a condenser?

#6 Post by 75RR » Wed Jul 03, 2019 8:22 pm

With the latter, only a thin yellowish margin around the FOV.
I believe the thin yellow line on the outside edge of the FOV indicates the use of a correcting eyepiece (Kpl) with the higher NA objectives.
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Re: Condenser correction types - how to test a condenser?

#7 Post by Hobbyst46 » Wed Jul 03, 2019 10:04 pm

MicroBob wrote:Hi Doron,
is there really written "Abbe" on your condenser?

I have this different image on the field diaphragm too. What I don't know is whether it is safe to conclude that this leads to a better image quality of the object on the stage.

Bob
No, Abbe is not printed, only a number is printed, yet the catalogue says that it is the simple condenser. I strongly believe that it is an Abbe.. :) .
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Re: Condenser correction types - how to test a condenser?

#8 Post by Hobbyst46 » Wed Jul 03, 2019 10:06 pm

75RR wrote:
With the latter, only a thin yellowish margin around the FOV.
I believe the thin yellow line on the outside edge of the FOV indicates the use of a correcting eyepiece (Kpl) with the higher NA objectives.
Yes, agreed. Hopefully later on I can take some sample photos of the FOV.
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Re: Condenser correction types - how to test a condenser?

#9 Post by Hobbyst46 » Thu Jul 04, 2019 5:24 pm

Here is some more details of the "appetizer" (in the meanwhile, soups and main dishes are lagging behind...)
Nothing new, just a small demo which is probably familiar to most microscopists.

The simple Zeiss condenser, NA=1.3 with swinging out top lens, I guess ~0.3-0.35 without top lens but I did not measure it. I guess it is an Abbe condenser.
And the turret phase condenser achromat-aplanat, NA=1.4. Model 465277, BF position.

Tested with a 10X0.30 Neofluar objective.
Specimen - a strew slide of diatoms in Pleurax. Focusing on the specimen, the field aperture is fairly sharp (as much as I could).
The photos below show the FOV when the field aperture is closed (minimum aperture), and when it is slightly open.

Photos are cropped to show a similarly sized bright circle in each position, and are resized.
It appears that the simple condenser is not precisely horizontal - possibly the swinging out lens carrier is twisted somewhat. It is very old and underwent hard usage.
All comments are welcome.
Attachments
simple BF condenser.jpg
simple BF condenser.jpg (147.33 KiB) Viewed 1869 times
(1) Simple condenser, closed field_aperture, partially closed iris, 10X0.30 Neofluar.jpg
(1) Simple condenser, closed field_aperture, partially closed iris, 10X0.30 Neofluar.jpg (114.15 KiB) Viewed 1869 times
(2) Simple condenser, partially open field_aperture, partially closed iris, 10X0.30 Neofluar.jpg
(2) Simple condenser, partially open field_aperture, partially closed iris, 10X0.30 Neofluar.jpg (146.54 KiB) Viewed 1869 times
(3) Turret condenser, closed field_aperture, partially closed iris, 10X0.30 Neofluar.jpg
(3) Turret condenser, closed field_aperture, partially closed iris, 10X0.30 Neofluar.jpg (134.89 KiB) Viewed 1869 times
(4) Turret condenser, partially open field_aperture, partially closed iris, 10X0.30 Neofluar.jpg
(4) Turret condenser, partially open field_aperture, partially closed iris, 10X0.30 Neofluar.jpg (155.63 KiB) Viewed 1869 times
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Re: Condenser correction types - how to test a condenser?

#10 Post by farnsy » Fri Jul 05, 2019 4:42 am

Condenser-related aside: as a practical matter, is it really necessary to put oil on the condenser and bring it up to touch the bottom of the slide when using a 100X oil objective?

I actually have never used my oil objective except with water (*blush*) but I plan to soon. Putting a drop of oil on the cover slip isn't really that much of a hassle, but putting on my dang condenser and then cleaning it off later seems like something I'm not eager to do.

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Re: Condenser correction types - how to test a condenser?

#11 Post by 75RR » Fri Jul 05, 2019 5:13 am

Condenser-related aside: as a practical matter, is it really necessary to put oil on the condenser and bring it up to touch the bottom of the slide when using a 100X oil objective?
Only if you want to realize its maximum NA. See quote and link to article below.

In practice it means you obtain the magnification but not the resolution the objective is capable of.
Best to try both methods, that way you can see if you can 'live' with the difference.


"3) One particular fact which is I think misunderstood by those starting microscopy, is that when a condenser is used 'dry' (no oil contact to the undersurface of the slide) its maximum theoretical effective NA can be no more than 1.0, and in reality slightly less."

http://www.microscopy-uk.org.uk/mag/ind ... dense.html
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Re: Condenser correction types - how to test a condenser?

#12 Post by Wes » Fri Jul 05, 2019 7:24 am

This could be a fun topic to explore experimentally. You'll need a phase telescope and a diatom test slide. Put some oil only on the 100x objective and after focusing on your favorite diatom look at the diffraction pattern at the back focal plane of the objective using the phase telescope (maybe even take a photo). Then repeat the same after oiling the condenser and see if there is a difference in both the level of detail in the image plane and the maximum order of diffracted light at the back focal plane.

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Re: Condenser correction types - how to test a condenser?

#13 Post by mrsonchus » Fri Jul 05, 2019 2:09 pm

Wes wrote:This could be a fun topic to explore experimentally. You'll need a phase telescope and a diatom test slide. Put some oil only on the 100x objective and after focusing on your favorite diatom look at the diffraction pattern at the back focal plane of the objective using the phase telescope (maybe even take a photo). Then repeat the same after oiling the condenser and see if there is a difference in both the level of detail in the image plane and the maximum order of diffracted light at the back focal plane.
Diffraction pattern? What would this look-like, with the diatom in focus and the phase-telescope focused on the objective's back focal plane? Interesting to try.

I did this a couple of days ago with the Olympus BX PlanC N UIS2 100x with the phase-contrast condenser used in the brightfield position of course. The condenser is n.a. 1.25 nominally. I focused on chromosomes at 100x with the objective-slide oiled and the condenser-slide oiled, then compared to the same image with just the objective-slide oiled, the condenser left dry.
In all honesty I couldn't see a difference. However the inherent lack of a clear edge to most stained chromosomes and even plant structures stained at the 100x level makes this far less informative than perhaps with a diatom slide... The slide I unfortunately chose to use is not the best, the EH is also pretty poor on this sldie.....

I begin to suspect that it may be OK in a lot of circumstances to only oil the slide-objective for less than critical examination pf plant slides.
I suppose closing-down the condenser may reduce the n.a. of the 100x below 1.0 also, as is done routinely with other objectives to give useful contrast at the loss of n.a. ? I'll have a few more tries of this comparison with other, sharper-focused material than chromosomes, which are also not flat when dividing, more in a spherical arrangement....

The images, for what they're worth - the chromosomes are about 1-1.2µ thick...
With slide oiled only,
Image

With objective AND condenser oiled,
Image

Sorry there's not much value in the above somewhat blurry images, I'll try to get a better comparison made....

John.
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Re: Condenser correction types - how to test a condenser?

#14 Post by Hobbyst46 » Fri Jul 05, 2019 4:02 pm

mrsonchus wrote:Sorry there's not much value in the above somewhat blurry images, I'll try to get a better comparison made....
Why, this IMO is a real-life example, that provides a definite answer per case. The actual benefit of oiling the condenser to the slide in brightfield has been in dispute. I have seen in several research articles, in the Methods section, that oiling the condenser to the slide was specifically mentioned. Namely, it is not a self-evident or "standard" microscopy procedure.
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Re: Condenser correction types - how to test a condenser?

#15 Post by Wes » Fri Jul 05, 2019 6:33 pm

mrsonchus wrote:Diffraction pattern? What would this look-like, with the diatom in focus and the phase-telescope focused on the objective's back focal plane? Interesting to try.
I got the idea from this excellent video (highly recommended if you've not seen it yet)


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Re: Condenser correction types - how to test a condenser?

#16 Post by Roldorf » Fri Jul 05, 2019 8:18 pm

Really excellent video.
I tried to search for Peter Evernett on the internet but didn't come up with any results. By his delivery he must have been on the lecture circuit for many years as he had all the mannerisms of the perfect speaker. He could be a research professor as it would seem from his presentation that he developed the equipment himself.
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Re: Condenser correction types - how to test a condenser?

#17 Post by 75RR » Fri Jul 05, 2019 9:07 pm

Comparison dry and oiled condenser.

(Semiplan) F100x/1.25, objective oiled to slide - first image with a dry condenser, second with oiled condenser. Kemp 8 Form Test: Nitzschia sigma

Illumination = COL using # 3 Phase annulus of rotary condenser.
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Re: Condenser correction types - how to test a condenser?

#18 Post by MichaelG. » Fri Jul 05, 2019 9:52 pm

Roldorf wrote:Really excellent video.
I tried to search for Peter Evernett on the internet but didn't come up with any results.
Try searching for Peter Evennett

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Re: Condenser correction types - how to test a condenser?

#19 Post by Roldorf » Fri Jul 05, 2019 10:06 pm

MichaelG.
Thanks I found him (got to get my fingers working properly, or take a course in smelling, errr spelling I mean). :shock:
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Re: Condenser correction types - how to test a condenser?

#20 Post by MichaelG. » Fri Jul 05, 2019 10:09 pm

:D

You're welcome

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Re: Condenser correction types - how to test a condenser?

#21 Post by ImperatorRex » Sat Jul 06, 2019 6:20 am

75RR wrote:Comparison dry and oiled condenser.

(Semiplan) F100x/1.25, objective oiled to slide - first image with a dry condenser, second with oiled condenser. Kemp 8 Form Test: Nitzschia sigma

Illumination = COL using # 3 Phase annulus of rotary condenser.
Hi 75RR,
I wonder why the images look so different - image two has this big black border at the the frustule.
Such difference should not be the result of the oiled condensor?
Bye the way: I often immergate the condensor with water, just because it is easier to remove and n.A. of 1,2 is sufficient for my purpose.

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Re: Condenser correction types - how to test a condenser?

#22 Post by MichaelG. » Sat Jul 06, 2019 6:51 am

ImperatorRex wrote:
75RR wrote:Comparison dry and oiled condenser. [...]
Illumination = COL using # 3 Phase annulus of rotary condenser.
Hi 75RR,
I wonder why the images look so different - image two has this big black border at the the frustule.
With the greatest respect to 75RR : I suggest that we are seeing the artificial bas relief effect that I mentioned recently ... caused by some offset in the illuminating cone.
Note the shadowed 'crater' effect
Note the shadowed 'crater' effect
IMG_3170.JPG (45.17 KiB) Viewed 1690 times
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.
Interesting notes by Ted Clarke http://www.microscopy-uk.org.uk/mag/ind ... c-col.html
Last edited by MichaelG. on Sat Jul 06, 2019 7:04 am, edited 1 time in total.
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Re: Condenser correction types - how to test a condenser?

#23 Post by 75RR » Sat Jul 06, 2019 6:57 am

ImperatorRex wrote:
75RR wrote:Comparison dry and oiled condenser.

(Semiplan) F100x/1.25, objective oiled to slide - first image with a dry condenser, second with oiled condenser. Kemp 8 Form Test: Nitzschia sigma

Illumination = COL using # 3 Phase annulus of rotary condenser.
Hi 75RR,
I wonder why the images look so different - image two has this big black border at the the frustule.
Such difference should not be the result of the oiled condensor?
I think oiling the condenser required a new setup which I did not do. Perhaps something to do with COL? It can be finicky.

I will try again today attempting to get the best out of each - i.e. individual setups
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Re: Condenser correction types - how to test a condenser?

#24 Post by 75RR » Sat Jul 06, 2019 7:01 am

Thanks for the link
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Re: Condenser correction types - how to test a condenser?

#25 Post by MichaelG. » Sat Jul 06, 2019 8:30 am

75RR wrote:
Thanks for the link
As you will see Fig 11 in that article is by Osamu Oku, and is probably the definitive 'light microscope' image of your subject.

I have just found this page: https://micro.sakura.ne.jp/bod/typeslide.htm
Which covers all the types on the Klaus Kemp slide :!:

MichaelG.

.
Edit: Google seems to make a reasonable job of translation
https://translate.google.com
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Re: Condenser correction types - how to test a condenser?

#26 Post by MichaelG. » Sat Jul 06, 2019 8:51 am

For convenient reference, here is Google's translation:
Diatoms have long been used as test specimens for microscope objectives. It seems that people in the United Kingdom called Solit have been in it since 1841 (by Shiro Tojo “Lens”). There is an imprint of a periodic structure so fine that humans can not make it, and it may have been used for a long time because it is relatively easy to obtain. The size of the mark of diatoms is almost constant depending on the species, and it can be said to be a natural micro ruler. In the middle of the 19th century, when microscopes became popular as a hobby, microscope optics were under development, and products were also created based on the experience and intuition of the craftsman. It is thought that it was important.

The top image is a test slide glass using diatoms that is still commercially available, and will be produced by Mr. Klaus D. Kemp in the UK. As you can see in the image, eight representative test diatoms are arranged using advanced technology. A beautiful interference color can be confirmed when observing with dark field illumination using a low numerical aperture objective lens. The color of diatom species differs depending on the period of the pattern engraved on the shell. In the above image, roughly, the interference color of the fine periodic structure is blue to amber, and it becomes yellow to orange when the periodic structure becomes relatively large. By observing the structure of these diatoms, the quality of the objective lens is determined based on whether it is visible or not.

The quality of modern research microscopes is well-controlled, so it is unlikely that you will see lenses that would otherwise fail with diatomite test slides. Here, let’s taste the beauty of the delicate structure of diatoms that have played a role in quality control of the objective lens.

A test slide (test preparation) using Amphipleura pellucida, which is famous for the inspection of oil immersion objective lenses, is supplied from MWS as [RL-TEST].
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Re: Condenser correction types - how to test a condenser?

#27 Post by MicroBob » Sat Jul 06, 2019 9:14 am

Hi together,
COL gives a nice combination of resolution and contrast, but it also tends to produce artifacts and is not consistently repeatable. So this result doesn't surprise me very much. For a direct comparison bright field would be easier to interpret.

According the condenser types: Apochronaut wrote in the other thread that the Abbe condenser was designed when achromatic condensers were already availabe. I think at this time microscopes were mainly used with mirror and white clouds as light source, so the image of a field diaphragm was not important.
In Dorons diatom pictures the two condensers of different correction grade don't show much difference in image quality.

Bob

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Re: Condenser correction types - how to test a condenser?

#28 Post by 75RR » Sat Jul 06, 2019 11:49 am

MichaelG. wrote: As you will see Fig 11 in that article is by Osamu Oku, and is probably the definitive 'light microscope' image of your subject.
Agree, always nice to have something to aim for.
MichaelG. wrote: I have just found this page: https://micro.sakura.ne.jp/bod/typeslide.htm
Which covers all the types on the Klaus Kemp slide :!:
Nice to have them all on display. Have been thinking of getting another.

Must say that there are also some very good individual images there. Pity there are no details on how this was achieved.
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Re: Condenser correction types - how to test a condenser?

#29 Post by apochronaut » Mon Jul 08, 2019 2:07 pm

All lenses or lens systems are quite accurate when the light is passed through them on axis or close to the axis. For this reason an abbe condenser and an achromat condenser can perform quite similarly when the image is viewed within a section of the center of the field. With non plan objectives, and those with poorer off axis corrections, the inability of a two lens condenser to correct for off axis aberrations isn't all that apparent because the aberrations of the objective itself are more evident. When microscopes were fitted with standard achromats , an abbe condenser was fairly acceptable. It was only when the same microscope was fitted apochromats, that more stringent recommendations for more highly corrected condensers were voiced, because the off axis aberrations of the condenser could cause the off axis performance of the objective to suffer. There might also be a need for a higher N.A. of condenser too but that is a separate issue. Any condenser design can be built to whatever N.A. is required, it is just that over time certain norms have evolved.
With the evolution of plan and wider field optics, better off axis performance of condensers became required, even when used with moderate N.A. achromats . A conventional 2 lens abbe will initiate rather severe aberrations off axis and especially at the perimeter, as the field increases. Defocusing the illumination beam helps somewhat but ultimately better corrections at the exterior of the illumination beam are necessary for the condenser to support well corrected plan optics accurately.

A solution was to add a third and sometimes a fourth lens, which preferentially corrects the beam off axis; usually referred to as an aplanat. Aplanats were used from the first w.w. on , usually in connection with achromatic condensers but sometimes as an amendment to a simple abbe condenser too.

More recently, some companies used an aspheric bottom lens in in place of the standard spherical lens. Known usually as abbe aspherics, the bell curve shaped bottom lens goes a long way towards fixing those distortions that plague an abbe's off axis performance. In overall performance, an abbe aspheric can rival an achromat aplanat of the same N.A.

A further idea, which goes back some time was to simply make the lenses of greater diameter. In this way, the "cleaner" part of the illumination beam ; the portion passing more central in the lens is wider and therefore more coherent. PZO for one, did this with a simple 2 lens condenser, which passes a wider aberration free beam to the objective.
Much later AO made an abbe aspheric with very wide lenses, which when oiled provides surprising peripheral performance.

Achromatic aplanats continue to be the standard and are usually offered in N.As. of a higher number than smpler condensers, in order to support better corrected objectives. I have never seen an achromat aspheric but such could exist.

The performance difference of various condensers is critically matched to the objective being used. An uncoated, unoiled, 2 lens abbe is going to reduce the performance of a 1.4 N.A. planapo a lot more, than it would a 1.25 achromat. An oiled 1.4 N.A. achromat aplanat isn't going to take the 1.25 achromat above itself but it will maximize it's potential, something an oiled 1.25 abbe won't likely do.

Are the differences startling? In some cases, with samples that have lots of difficult to resolve details; yes. In other cases, not so much but one of the overall effects of using a poorly corrected condenser isn't so much the loss of resolution, it is the blurring of margins and distortion in the depth of field. Diffraction can become prominent. Many people look towards the center of the field and crop photos to show the performance of a condenser but there is coherent condensation of the light mostly at the center . It's increasingly off axis and more towards the periphery, where a condenser's defects more easily show up. Well corrected plan optics demand more of a condenser.


And then there is the ongoing debate about whether a dry condenser completely reduces the N.A. of the objective to the level of the condenser , like a limiter switch. You can find numerous , seemingly qualified comments to support this theory. Another was copied over in this thread. The Rayleigh criterion for resolution says, this is not so. The objective N.A. will be reduced by a factor but not limited to the N.A. of the condenser because the objective N.A. is entered in as a separate value, that value being variable based on the choice of the objective not based on the choice of the condenser.

However, here is a little test one can use to prove this to themselves, if you have a high N.A. objective( 1.25 or over would be good), that has an iris diaphragm. Using the Rayleigh criterion for resolution : R = 1.22lambda/N.A.objective+N.A.condenser the objective N.A. can be changed to whatever one chooses. So, if the objective has an iris diaphragm and a max. 1.4 N.A., and the condenser is .90 N.A., using 500 nm light, the limit of resolution will be
265.2 nm, if the iris diaphragm is wide open.

If you close down the iris to .90 , the limit of resolution will be 338.9 nm. Most people can probably see this difference when viewing fine structures. If the objective N.A. were to be limited by the condenser N.A. there would be no difference , when the iris was closed.

Take your microscope , put on a fairly hard to resolve diatom sample or whatever you choose that is difficult, and using your dry condenser, and an oiled objective, proceed to close the objective's iris while viewing. If it has the N.A. marked, you should be able to read it at the point where you notice a resolution drop and when the iris is closed to .90. What you will find is that it takes a while for the resolution to fall off. If the objective were already limited to .90 or .95, whatever your condenser is, the resolution would begin to decline almost immediately.

Another way to do this, if you do not have an objective with an iris, is to take your chosen slide and compare an oiled objective with a high ( 1.25 or over) N.A. used with a .90 condenser to a .90 objective from the same series used with a .90 condenser. You will find that the resolution with the oiled objective to be superior to that of the .90 objective. Obviously this is dependent on having this sort of objective pair but in some cases people have them.

It is pretty apparent from many angles, that a condenser of a lower N.A. than that of the objective reduces the effective N.A. of the objective but doesn't limit it to that of the condenser. N.A.

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Re: Condenser correction types - how to test a condenser?

#30 Post by Sauerkraut » Mon Jul 08, 2019 3:53 pm

This thread has inspired great curiosity about condensers. Perhaps this question is off-base, but how does a standard flip top condenser compare to something like this with a swing-out bottom lens? Do the 2 types effectively work the same way with different mechanical designs or are they fundamentally different from an optics standpoint?

https://www.ebay.com/itm/aus-Jena-Labov ... SwFZZcDaas

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