A condenser quest.

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apochronaut
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A condenser quest.

#1 Post by apochronaut » Mon Jun 29, 2015 1:43 am

Abbe condensers are like bald tires. They can do a basic job and get you where you want to go but if there are any changes in the conditions , you need to make a change to take advantage of them. Almost all of the AO/Reichert Microstar 400 series microscopes were fitted with a very good 1.25 N.A. abbe aspheric oil condenser, cat. # 1970. It is pretty much the same as any other abbe aspheric condenser, except that the glass elements are a little wider than most others. It therefore seems to fill the field a little better than some I have used for 4X objectives, with wider field eyepieces. It still needs an aux. lens for the 2.5X. AO had 1.30 planfluorite objectives available for this scope and they offered an N.A. 1.4 achromat condenser cat.# 1973 as an option for those objectives. It seems though, that given their ownership of Reichert and the possibility of using 1.32 N.A. planapo objectives made for the Reichert research microscopes, that the N.A. 1.4 spec. used for that condenser left the door open for that possibility. However, try to find an AO/Reichert 1.4 N.A. achromat condenser.

The #1970 1.25 abbe aspheric condenser is a coherent unit but the #1973 1.4 achromat is an assembled lens pack in a threaded nose that fits into the older series 100 condenser body, that can take the # 1201 .90 achromat or a # 1087 1.25 abbe aspheric. However, a # 1973A 1.4 N.A. achromat also exists and I have been unable to find out anything about it.Superficially, it looks identical to the #1973 1.4 N.A. achromat.

One of those 1973A came my way but it was the housing and top lens only. It was a new unit that was missing the middle cell and lower cell of elements and retaining rings. I threaded it into a body and tried it out on a 420 Diastar. It worked well with the 2.5X, 4X 10X and 20 X achromats or about up to N.A. .50 but started to show deficiencies with the 25X N.A. .65 planapo. I knew roughly what the conformations and characteristics of the middle and lower cell were because I had an older Spencer 1.4 achromat to disassemble and copy, however I could not find the right lenses, with which to make a copy, let alone the spacers and retainers.
So, I set out to make an estimation of the way I wanted this condenser to work and assembled a prototype from lenses I had on hand. Here's the first try.

It is a far cry from what was originally engineered into that housing but it seems to work even better than the older 1.4 achromat I have to compare it to, when used as a dry condenser.. Oddly, it consists of 4 individual elements( no cemented doublets) but shows excellent achromatism and a very high N.A.. which seems to be higher than the other 1.4 condenser is capable of.

In use the D.I.Y. condenser is brighter than the 1.4 achromat and fills the field of lower power objectives with a more even light. It seems to easily meet the N.A. requirements of the higher power objectives and even works well without oil when used with an N.A. 1.0 oil immersion 40x planapo. With the 1.30 and 1.32 objectives, I've always felt I needed to oil the condenser to get maximum illumination and resolution.

I had a few plano convex aux. lenses and found one with a very flat curvature, that could be used to fill a 20mm field for a 2.5X objective, as an aux. swing in lens . The condenser must be racked down to it's limit to do this but that has been the case with every other condenser I have tried anyway. Oddly the aux. lens can be left in place, even with a 25x .65 planapo with no loss of quality. With the previous condenser , I had to take it away for anything above 10x .25.

I don't know what the formulations of the lenses I used are. They are convex/concave,double convex(f.l. 20mm) and convex/concave. A couple have an odd lavender coating. Given the fact that this is an air spaced condenser and appears to show excellent achromatic charactersistics, it is possible that I accidentally hit on one or more fluorite or flint glass lenses.
Some day I will find a #1973 achromat in complete condition and have a chance to compare them.
Attachments
The D.I.Y. condenser based on a # 1973A 1.4 N.A. achromat top lens and housing , left and a Spencer-AO 1.4 N.A. achromat condenser right.
The D.I.Y. condenser based on a # 1973A 1.4 N.A. achromat top lens and housing , left and a Spencer-AO 1.4 N.A. achromat condenser right.
DSC00485 (1280x719) (575x1024).jpg (105.31 KiB) Viewed 12832 times
The D.I.Y. on the left and the 1.4 achromat on the right. The D.I.Y. appears to be capturing a wider angle than the 1.4 achromat. At the perimeter of the achromat condenser a small amount of chroma can be seen. The D.I.Y. is chroma free. The structure imaged that looks like a drip on the lenses is actually a line on the backboard. The D.I.Y. condenser is imaging that closer to the centre and also other things at a greater angle, which the N.A. 1.4 appears to not be seeing.
The D.I.Y. on the left and the 1.4 achromat on the right. The D.I.Y. appears to be capturing a wider angle than the 1.4 achromat. At the perimeter of the achromat condenser a small amount of chroma can be seen. The D.I.Y. is chroma free. The structure imaged that looks like a drip on the lenses is actually a line on the backboard. The D.I.Y. condenser is imaging that closer to the centre and also other things at a greater angle, which the N.A. 1.4 appears to not be seeing.
DSC00488 (1280x719) (1024x575).jpg (119.7 KiB) Viewed 12832 times
The D.I.Y. on the left and 1.4 achromat on the right. The image of marks on the background board indicates that the D.I.Y. is capturing a wider angle than the 1.4 achromat.
The D.I.Y. on the left and 1.4 achromat on the right. The image of marks on the background board indicates that the D.I.Y. is capturing a wider angle than the 1.4 achromat.
DSC00489 (1280x719) (1024x575).jpg (106.85 KiB) Viewed 12832 times
Last edited by apochronaut on Thu May 10, 2018 11:07 am, edited 4 times in total.

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Re: A condenser quest.

#2 Post by apochronaut » Mon Jun 29, 2015 2:11 am

Here are some further pictures with illumination added in.
Attachments
D.I.Y. collector lens being illuminated with an led flashlight from above and being viewed from an oblique angle. The lower edge of the top lens in the pack is still visible and the illumination beam clearly visible. There is a much greater angle that this condenser will be able to see than the 1.4 achromat. Image is deliberately upside down.
D.I.Y. collector lens being illuminated with an led flashlight from above and being viewed from an oblique angle. The lower edge of the top lens in the pack is still visible and the illumination beam clearly visible. There is a much greater angle that this condenser will be able to see than the 1.4 achromat. Image is deliberately upside down.
DSC00491 (1280x719) (1024x575).jpg (99.78 KiB) Viewed 12828 times
1.4 achromat collector lens being illuminated with an led flashlight from above and being viewed from an oblique angle. The illumination beam is just visible indicating that the maximum angle of acceptance is being reached. Image is deliberately upside down.
1.4 achromat collector lens being illuminated with an led flashlight from above and being viewed from an oblique angle. The illumination beam is just visible indicating that the maximum angle of acceptance is being reached. Image is deliberately upside down.
DSC00490 (1280x719) (1024x575).jpg (86.59 KiB) Viewed 12830 times
D.I.Y. condenser viewed from the side, while being illuminated from about 7cm. below with an led flashlight.
D.I.Y. condenser viewed from the side, while being illuminated from about 7cm. below with an led flashlight.
DSC00492 (1280x719) (1024x575).jpg (79.63 KiB) Viewed 12830 times
1.4 achromat condenser viewed from the side , while being illuminated from about 7cm. below with an led flashlight.
1.4 achromat condenser viewed from the side , while being illuminated from about 7cm. below with an led flashlight.
DSC00493 (1280x719) (1024x575).jpg (79.01 KiB) Viewed 12830 times
D.I.Y. condenser illuminated from about 7cm. below with an led flashlight.
D.I.Y. condenser illuminated from about 7cm. below with an led flashlight.
DSC00495 (1280x719) (1024x575).jpg (81.22 KiB) Viewed 12830 times
Last edited by apochronaut on Mon Jun 29, 2015 2:49 am, edited 1 time in total.

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Re: A condenser quest.

#3 Post by apochronaut » Mon Jun 29, 2015 2:19 am

Last picture of the 1.4 achromat being viewed from below with the led flashlight about 7cm. below the collector lens.
Attachments
DSC00496 (1280x719) (1024x575).jpg
DSC00496 (1280x719) (1024x575).jpg (78.33 KiB) Viewed 12828 times

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Re: A condenser quest.

#4 Post by 75RR » Mon Jun 29, 2015 1:52 pm

So, I set out to make an estimation of the way I wanted this condenser to work and assembled a prototype from lenses I had on hand. Here's the first try.
Can you give us an idea of what you mean by this? What was the theory behind this?
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Re: A condenser quest.

#5 Post by apochronaut » Mon Jun 29, 2015 7:17 pm

The theory was whether it was possible to build a wide angle, high N.A. achromatic condenser from the materials I had at hand.
I certainly didn't approach it mathematically. My parameters were. 1) achromatism 2) as wide an aperture as possible 3) as broad a field coverage as possible.
What I had to work with was an existing circa 1955 Spencer-AO N.A. 1.4 achromat condenser, that I had been using in preference to the N.A. 1.25 Abbe that came on the microscope, a schematic of the CAT. # 1973 N.A. 1.4 achromat and a bunch of various lenses. I did not have much in the way of lens groups that could match what the schematic showed. In fact none of my various usable lenses were doublets or triplets,usually a requirement for chromatic correction , so initially I felt that achromatism was not possible with the material at hand but recognizing that air spaced achromats do exist, I did a few tests with air spacing a few sets and got favourable results. I ruled out a bunch of lenses due to them being either too large or too small and made some rough sketches of the light pathways with various arrangements of what I had left and settled on a design. Bench comparisons with my other 1.4 achromats( Nikon, B&L, Spencer, Tiyoda) , indicated that I could get a lens pack that could perform as well as or better than them.

This lens pack, that I settled on( 4 air spaced elements) seemed the most promising and when I assembled and tested it it seemed to work well. I used rubber O-rings from plumbing or engine applications as spacers and as retention collars. The final lens pack is held in place by a fairly tightly pressed in O-ring. Further testing on the microscope with N.A. 1.0, 1.25, 1.30 and 1.32 oil immersion objectives have proven promising. It is exceptionally bright, provides a very even background and seems to be at least an achromat. Usually, when you turn a condenser sideways, and look through it at an oblique angle,either through the bottom or top lens, you get varying degrees of chromatic aberration towards the edge of the field. With abbe condensers, this begins sometimes before you get to a 45 degree angle. With achromats it takes until about 70 degrees or so. This varies depending on who made the condenser but it is there. With this one, I am getting the tiniest amount at the most extreme angle , just before the light disappears at 85 degrees or so. It seems to have a broader field coupled with an extreme aperture too.

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Re: A condenser quest.

#6 Post by billbillt » Wed Aug 05, 2015 6:29 pm

Hi apochronaut,
I just discovered this thread you started... I found it very interesting... Do you have any pictures you have obtained using your DIY condenser?..
BillT

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Re: A condenser quest.

#7 Post by apochronaut » Sun Aug 09, 2015 7:29 pm

I have done a little. The original direction I was going was to try to make as close a condenser to a high N.A. achromat as possible to use with the 1.30 and 1.32 N.A. planfluorite and planapo objectives, so it needs best to be compared for performance as an oil immersion condenser with those objectives. I haven't had the time to do a careful immersed assessment yet but I did do some as a dry condenser, along with a .90 achromat, a 1.25 oil abbe aspheric, and a 1.40 oil achromat. All were however used, dry , set up using kohler principles and stopped down to same f stop for the photograph. Aside from slight resolution differences, some depth of field differences and a small amount of chromatic aberration difference, the 4 condensers are pretty close. I didn't bother setting up a 1.25 oil abbe type for this test because based on other tests I have done it would have been a clear also ran, or not so clear also ran, as the case may be.
Here are my guesses based on the physical observation of the various condensers, as to their potential working N.A. as a dry condenser. .90 achromat ; .90 : 1.25 abbe asheric ; .75 : 1.40 achromat ; .85 : D.I.Y. ; .95. One of the noticeable things about the performance of the D.I.Y., is how much brighter it is than the other 3.
I tested them with a 40x .70 planfluorite, and a 60X .80 planachro. The 60X has a tighter working distance than the 40, so in order to maintain kohler , all of the condensers had to focus a little closer with that objective.

I will do oil at a later date.
Attachments
.90 achromat dry<br />  60X .80 planachro dry
.90 achromat dry
60X .80 planachro dry
DSC00918 (1024x575).jpg (186.62 KiB) Viewed 12734 times
1.25 abbe aspheric dry<br />  60X .80 planachro dry
1.25 abbe aspheric dry
60X .80 planachro dry
DSC00917 (1024x575).jpg (189.51 KiB) Viewed 12734 times
D.I.Y. dry <br /> 60X .80 planachro dry
D.I.Y. dry
60X .80 planachro dry
DSC00916 (1024x575).jpg (195.5 KiB) Viewed 12734 times
1.4 N.A. achromat dry<br /> 60X .80 planachro dry
1.4 N.A. achromat dry
60X .80 planachro dry
DSC00915 (1024x575).jpg (176.07 KiB) Viewed 12734 times

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Re: A condenser quest.

#8 Post by apochronaut » Sun Aug 09, 2015 7:36 pm

Results with 40X objective.

I took these a week or so ago( 60X images too), and hadn't really looked at them as closely as I have now. The results for the condensers with known specifications are pretty well what one would expect. The .90 achromat is overall the best because it is working within it's stated parameters. The abbe aspheric does have the advantage of having aspheric lenses, so it works very well , as long as the N.A. required is within it's capabilities but once it is getting pushed , as is the case with the .80 objective, it can't keep up.
High performance oil achromats, when used dry, don't seem to do well as dry condensers, so the 1.4 is only marginally better than the other two, maybe not even better than the .90 achro.
The D.I.Y. is the clear winner, most noticeably , when the N.A. demands are higher as is the case with the 60X. A big part of this is due to the much higher light level it is passing. However, it works so well as a dry condenser, I am suspicious regarding it's potential as an oil condenser, which is unfortunately what I was aiming for. Maybe water?....which could get it up as high as 1.33 , theoretically.
Attachments
.90 achromat dry<br />  40X .70 planfluorite dry
.90 achromat dry
40X .70 planfluorite dry
DSC00911 (1024x575).jpg (169.47 KiB) Viewed 12732 times
1.25 abbe aspheric dry<br /> 40X .70 planfluorite dry
1.25 abbe aspheric dry
40X .70 planfluorite dry
DSC00912 (1024x575).jpg (172.06 KiB) Viewed 12732 times
D.I.Y. dry<br />  40X .70 planfluorite dry
D.I.Y. dry
40X .70 planfluorite dry
DSC00913 (1024x575).jpg (168.05 KiB) Viewed 12732 times
1.4 achromat dry<br />  40X .70 planfluorite  dry
1.4 achromat dry
40X .70 planfluorite dry
DSC00914 (1024x575).jpg (179.8 KiB) Viewed 12732 times
Last edited by apochronaut on Mon Aug 10, 2015 2:11 pm, edited 3 times in total.

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Re: A condenser quest.

#9 Post by billbillt » Sun Aug 09, 2015 7:55 pm

Thanks for the reply and photos... I am glad that the new condenser worked out for you.. Maybe you could possibly present this as an article for the Microbehunter magazine.. I feel it would certainly cause a stir of interest...

The Best,
BillT

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Re: A condenser quest.

#10 Post by apochronaut » Sun Aug 09, 2015 8:15 pm

I may do. It really hasn't worked out, yet. I need something to carry the ball with the higher N.A. oil immersion objectives and the standard factory 1.25 oil abbe aspheric isn't quite good enough. The 1.4 achromat, I used here for the test, although it fits and works, is from another instrument, so it is only available temporarily.

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Re: A condenser quest.

#11 Post by billbillt » Sun Aug 09, 2015 8:19 pm

Hi,
I just thought an article on you experiments here may stimulate others to give it a try... It still looks viable to me..
BillT

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Re: A condenser quest.

#12 Post by apochronaut » Sun Aug 09, 2015 9:41 pm

Thanks . May yet do.

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Re: A condenser quest.

#13 Post by gekko » Sun Aug 09, 2015 10:40 pm

Interesting quest. I have refrained from commenting so far because my eyesight is so bad that, even with reading glasses clipped onto my prescription glasses I can only discern a barely visible (to me) difference in contrast, otherwise I cannot tell them apart. (My eye doctor appointment is in a few weeks :) )

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Re: A condenser quest.

#14 Post by billbillt » Sun Aug 09, 2015 10:48 pm

Hi gekko,
I must have bad eyesight also... I can tell very little, if any difference in the photos...
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Re: A condenser quest.

#15 Post by apochronaut » Sun Aug 09, 2015 11:43 pm

Have a closer look.
When I initially did them, I took a fairly cursory look and had a similar opinion. Mostly, I was looking at the 40X images because that is an objective I use more because it's image is quite free of optical artifacts. I don't use post processing much, certainly not for chromatic aberration, so the lenses I use need to be as clean as possible. In actual fact the 60X images had more lateral chromatic aberration than the camera captured but the 40X images are pretty close to what the eye sees.
With respect to the 40X images, there isn't a lot of difference. Down near the foot the granular material in the tapered part towards the foot is sharper and more defined in the last two images( D.I.Y. and 1.4), with a slight improvement in the overall definition also for the last two images.
I've taken some time to look more carefully , now, at the 60X pictures.
There is a much greater difference with the 60X images, where the overall definition and contrast of granular material and fine lines is poorest for the abbe aspheric, slightly better maybe for the 1.4 achromat, or for the .90 achromat, depending on what parameters one is using. The 1.4 is a little more 3 dimensional. There seems to be a big jump for the D.I.Y. condenser. The grain structure is sharper, the fine lines , finer and if you look towards the foot, the whole structural shape of the foot and it's surround has a slight 3d look, with better definition and depth . The bacteria in the surrounding water, especially around the anterior end are much more evident and oddly, a bit irridescent, along the lines of what one gets with bright phase or dark field. Many of the very small details evident, are not even seen with the other condensers. This same effect is evident with the 40X planfluorite but in a reduced way.

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Re: A condenser quest.

#16 Post by gekko » Mon Aug 10, 2015 12:18 am

Thank you, apochronaut. I think following your analysis, I can see (or I think I can see) what you describe. Probably looking at the original size images you can distinguish the differences even better.

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Re: A condenser quest.

#17 Post by charlie g » Mon Aug 10, 2015 2:54 am

I like the images of the spread of the light cone being compared both top and lower lens elements from your LED torch.

Wouldn,t a fixed prepared slide offer more control for compareing performances of these two condenser top elements?

I am facinated by your speculation on the air-spaced lens pack performance in instances indicating flourite glass in some of the lens elements! Your trained eye on these matters is terrific and practicle...thank you!

In my shed my current 12 horse-1 cylinder 1967 Cub Cadet 124 clucks like a hen on roost....whereas the 1984 Simplicity 17 horse-2 cylinder purred like a kitten...you can hear the difference (the Simplicity gave it up in 6/15).

This is great practicle microscopy for us to learn from, to have our eyes opened to! When I low cost purchased an Ebay Nikon-Ske..it had no field lens...it's condenser functioned well for my wetmount slides...I went through DIY quest for a field lens for it...I think I have the setup now!? Your thread here is a guide for me, apochronaut.

For my 'poor mans DIC/ transmitted light with the Olympus 40X objective with it's Waloston (?sp?) prism attachment...well I needed a substage condenser to use with a polarizer filter+ a substage Olympus Wolaston prism filter...I had to cobble a frees tading substage condenser holder with rack and pinon track...I think I have the setup now!?

Thank you for your through the lens and lens behavior shared thoughts. charlie guevara

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Re: A condenser quest.

#18 Post by zzffnn » Mon Aug 10, 2015 3:07 am

apochronaut,
Nice work there.

Are you sure those differences (at 60x) were not caused by different depth of focus? I would suggest to use a flatter mounted diatom as yardstick (your sample may be a little too thick for a 60x NA 0.8 objective).

Also, have you tried oblique contrast? "Bald tire" uncorrected Abbé would probably perform much better with oblique.
Last edited by zzffnn on Sat Dec 23, 2017 3:08 pm, edited 1 time in total.

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Re: A condenser quest.

#19 Post by apochronaut » Mon Aug 10, 2015 1:57 pm

That's a good observation , Fan. I presume you mean, that the objective wasn't focused at the same depth for each image, not that the depth of focus increased with certain condensers? That would be a whole other circumstance. I should re-do with a thinner subject, diatoms perhaps and in fact will, when I get around to testing this out with oil immersion. For now, it certainly seems to work well as a high N.A. dry condenser.

Regarding the consistency of focus; I did check that carefully and although the objective was not moved relative to the slide between exposures, the focus was trimmed slightly, using about 5 small details scattered around the field. These were selected during the initial exposure. One of them specifically, that I used for the 60X, was the internal structural details of the toes. Rotifers have a sort of exoskeleton called the lorica and in the toes of this subject the lorica can be distinguished , surrounding the cellular material encased inside it. If you imagine the toe as an elongated tulip shaped glass, they kind of resemble a very thick walled glass filled with finely crushed ice. The finely crushed ice part was difficult to image and only came into focus briefly with all of the condensers but you can see it in all the images.
I used different focus points for the 40X.

I understand that using the condenser as an oblique lighting source, would improve the detail and contrast. Presumably though, each condenser would be improved to a degree, commensurate with it's original performance as a centered condenser, so in this way an abbe condenser, although it might provide unusually good imaging for it's type , would still be the also ran in comparison to the 4 tested here if they also were adjusted to provide oblique illumination.
With oblique illumination, there comes a point where an angle of extinction is reached, where the bottom lens of the condenser , can no longer see the light source. This would be determined by it's angle of aperture. A higher angle of aperture, should provide higher N.A. illumination, improving resolution.
If you go back to my initial pictures, the ones I supplied, showing the D.I.Y. and 1.4 achromat in various comparison shots. Scroll down to pictures 4 and 5 or the first 2 in the second group ; the ones where I am shining an led flashlight through the top lens and it is being dispersed through the bottom lens for each of the two condensers. The bottom of the top lens is visible in each picture, even though the picture has been taken from about 70 or so degrees off axis. For the 1.4 N.A. objective it is seen as a diffuse roundish glow , just above the lower lip of the condenser housing. Much more of a viewing angle and it would disappear. That would be the limit of the angular aperture and since this is a 1.4 N.A. condenser, it is pretty extreme.
For the D.I.Y. condenser, the picture looks surprisingly different. First of all, the intensity of the illumination coming through the condenser is visibly much greater. Presumably, the achromat is losing it through internal reflection and scattering. The other thing is a much greater surface of the bottom lens is being illuminated and the bottom of the condenser's top lens, is much more visible. It is seen much more evidently in actual than photographically but it spans about 1/4 of the diameter of the condenser, seen as a dome of light almost touching the lower surface of the bottom lens. There is a little tulip shaped projected beam sitting just atop it. It would take relatively more rotation of the condenser in order to lose visible contact with that top lens , than it would for the 1.4 achromat, which indicates that the N.A. of the D.I.Y. condenser is probably greater than 1.4.
I know it is easy to get lost in this muddle of words but basically; if the bottom of the top condenser lens can be seen from below, then it follows that a ray of light emanating from that point of view below, can be seen by the top lens and therefore be focused through the condenser. It looks , from these demonstration pictures, that the D.I.Y. condenser can "see" at a broader angle ,than the 1.4 N.A. achromat and as well, absorb more light from a greater angle, producing a brighter image.
It follows then, that in oblique illumination ,it would provide a higher N.A. and outperform an abbe condenser.

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Re: A condenser quest.

#20 Post by zzffnn » Tue Aug 11, 2015 2:01 am

Thank you for your comments, Phil.

Yes, I meant different focus plane. Sorry for my unclear wording. It sounds like it should not be the case, since you focused on rotifer's toes as reference.

Sure, better corrected higher NA condenser will still outperform plain 1.25 Abbé in oblique. I was just saying plain Abbé is quite decent with oblique. Many people may want to upgrade/improve their objectives, contrast technique and sample preparation first.
Last edited by zzffnn on Sat Dec 23, 2017 3:09 pm, edited 3 times in total.

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Re: A condenser quest.

#21 Post by einman » Sat Dec 23, 2017 2:55 am

Phil,
As discussed perhaps trying to incorporate a LOMO aplanatic 1.4na condenser may work. I modified one to fit an old B&L scope I had for use with water immersion objectives.

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Re: A condenser quest.

#22 Post by MichaelG. » Sat Dec 23, 2017 2:32 pm

zzffnn wrote: I was just saying plain Abbé is quite decent with oblique.
If I may just add a note to this ^^^

It is my undertanding that Abbé actually designed that eponymous condenser for oblique illumination.

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Re: A condenser quest.

#23 Post by zzffnn » Sat Dec 23, 2017 3:15 pm

MichaelG. wrote:
zzffnn wrote: I was just saying plain Abbé is quite decent with oblique.
If I may just add a note to this ^^^

It is my undertanding that Abbé actually designed that eponymous condenser for oblique illumination.

MichaelG.
If you likes to use strong offset oblique at its best though, apl achromat condenser is indeed better. But only upgrade condenser after upgrading to apo objectives (achromat objective -> apo objective upgrade is more visibly significant).

manu de hanoi
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Re: A condenser quest.

#24 Post by manu de hanoi » Fri May 04, 2018 4:30 pm

why would a condenser need to be achromatic/apochromatic ? As I understand this is not necessary/helpfull. If some colors have a bit more or less NA than others it's ok as long as they are all above the NA of the objective

billbillt
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Joined: Mon Nov 10, 2014 10:01 pm

Re: A condenser quest.

#25 Post by billbillt » Fri May 04, 2018 4:45 pm

manu de hanoi wrote:why would a condenser need to be achromatic/apochromatic ? As I understand this is not necessary/helpfull. If some colors have a bit more or less NA than others it's ok as long as they are all above the NA of the objective
This is the way I understood it also...

BillT

Hobbyst46
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Joined: Mon Aug 21, 2017 9:02 pm

Re: A condenser quest.

#26 Post by Hobbyst46 » Fri May 04, 2018 5:41 pm

billbillt wrote:
manu de hanoi wrote:why would a condenser need to be achromatic/apochromatic ? As I understand this is not necessary/helpfull. If some colors have a bit more or less NA than others it's ok as long as they are all above the NA of the objective
This is the way I understood it also...

BillT
In general, an incompletely corrected optical component will introduce chromatic aberrations that deteriorate image quality. What I found interesting, reading the Wikipedia entry "condenser", is that Zeiss was quite late in producing achromatic condensers for their microscopes, and did that only in about 1870... apparently because aberrations are especially problematic for high NA objectives (conforms with Murphy's Law :lol: )...
Zeiss Standard GFL+Canon EOS-M10, Olympus VMZ stereo

apochronaut
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Re: A condenser quest.

#27 Post by apochronaut » Mon May 07, 2018 2:55 am

manu de hanoi wrote:why would a condenser need to be achromatic/apochromatic ? As I understand this is not necessary/helpfull. If some colors have a bit more or less NA than others it's ok as long as they are all above the NA of the objective
Chromatic aberration, whether it be created in the illumination beam or introduced by inadequately corrected elements within the image beam makes it difficult to realize the theoretical resolution of the entire system. Light that is separated into elements with chromatic differences in magnification cannot be utilized to resolve fine detail.

It doesn't matter whether the N.A. is low or high, chroma distorts the image nonetheless, however, imaging through a lower N.A. system can often visually sustain chromatic distortion more , because the details being sought are gross, whereas those being sought with higher N.A. are fine and easily obscured by chroma.

manu de hanoi
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Joined: Wed May 02, 2018 2:04 pm

Re: A condenser quest.

#28 Post by manu de hanoi » Mon May 07, 2018 6:24 am

Hobbyst46 wrote:
billbillt wrote:
manu de hanoi wrote:why would a condenser need to be achromatic/apochromatic ? As I understand this is not necessary/helpfull. If some colors have a bit more or less NA than others it's ok as long as they are all above the NA of the objective
This is the way I understood it also...

BillT
In general, an incompletely corrected optical component will introduce chromatic aberrations that deteriorate image quality. What I found interesting, reading the Wikipedia entry "condenser", is that Zeiss was quite late in producing achromatic condensers for their microscopes, and did that only in about 1870... apparently because aberrations are especially problematic for high NA objectives (conforms with Murphy's Law :lol: )...
I dont get it on the theoretical standpoint, the objective will chop off all light that has NA too large. As long as within the NA of the apochromatic objective you have all 3 colors you'll be fine. The color intensity distibution may vary a bit but you shouldnt get color fringes regardless of the condenser being plain or corrected as long as condenser NA for all colors is > objective NA

billbillt
Posts: 2895
Joined: Mon Nov 10, 2014 10:01 pm

Re: A condenser quest.

#29 Post by billbillt » Mon May 07, 2018 6:40 am

manu de hanoi wrote:
Hobbyst46 wrote:
billbillt wrote:
This is the way I understood it also...

BillT
In general, an incompletely corrected optical component will introduce chromatic aberrations that deteriorate image quality. What I found interesting, reading the Wikipedia entry "condenser", is that Zeiss was quite late in producing achromatic condensers for their microscopes, and did that only in about 1870... apparently because aberrations are especially problematic for high NA objectives (conforms with Murphy's Law :lol: )...
I dont get it on the theoretical standpoint, the objective will chop off all light that has NA too large. As long as within the NA of the apochromatic objective you have all 3 colors you'll be fine. The color intensity distibution may vary a bit but you shouldnt get color fringes regardless of the condenser being plain or corrected as long as condenser NA for all colors is > objective NA
I guess I have been wrong about this.. I thought this was a method to match objectives to condensers..

Hobbyst46
Posts: 3123
Joined: Mon Aug 21, 2017 9:02 pm

Re: A condenser quest.

#30 Post by Hobbyst46 » Mon May 07, 2018 7:43 am

manu de hanoi wrote: I dont get it on the theoretical standpoint, the objective will chop off all light that has NA too large. As long as within the NA of the apochromatic objective you have all 3 colors you'll be fine. The color intensity distibution may vary a bit but you shouldnt get color fringes regardless of the condenser being plain or corrected as long as condenser NA for all colors is > objective NA
To add just a few words, the condenser is not just a mechanical variable diaphragm that blocks some of the light rays. It consists of glass lenses and must be focused properly (for Köhler illumination) in order to achieve the best quality image. An uncorrected glass lens condenser has different focal lengths for the different colors (from 390-700nm, an infinite no. of colors that you bin into red green blue). This is true for all rays that pass through the condenser, whether entering the objective or not.
Zeiss Standard GFL+Canon EOS-M10, Olympus VMZ stereo

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