Fixed Köhler

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deBult
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Re: Fixed Köhler

#31 Post by deBult » Thu Jul 09, 2020 4:45 pm

The flare issue is way less of an issue with modern coated objectives though.

I have the Kohler option set of my Olympus CH-2 with DPlan achromatic objectives and hardly ever mount or use it.
To my eyes the Kohler difference is only noticeable when taking pictures. YMMV though.
Last edited by deBult on Thu Jul 09, 2020 4:53 pm, edited 1 time in total.

david_b
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Re: Fixed Köhler

#32 Post by david_b » Thu Jul 09, 2020 4:46 pm

75RR wrote:
Thu Jul 09, 2020 3:52 pm
A field diaphragm is one of the essential parts of what they are now calling Full Köhler, I think Fixed Köhler is perilously close to being a kissing cousin to 2000x magnification.
That's what I'm thinking, but if so, I'm surprised to see Olympus adopting it.

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75RR
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Re: Fixed Köhler

#33 Post by 75RR » Thu Jul 09, 2020 4:50 pm

david_b wrote:
Thu Jul 09, 2020 4:46 pm
75RR wrote:
Thu Jul 09, 2020 3:52 pm
A field diaphragm is one of the essential parts of what they are now calling Full Köhler, I think Fixed Köhler is perilously close to being a kissing cousin to 2000x magnification.
That's what I'm thinking, but if so, I'm surprised to see Olympus adopting it.
They are providing both, the Fixed Köhler only on the Student/University microscopes. Saving money or was Köhler too complicated?

Somewhat like Boy Scouts and knots perhaps.
Zeiss Standard WL (somewhat fashion challenged) & Wild M8
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david_b
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Re: Fixed Köhler

#34 Post by david_b » Thu Jul 09, 2020 6:10 pm

I meant adopting the term 'fixed Kohler', not referring to the technology.

Zuul
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Re: Fixed Köhler

#35 Post by Zuul » Thu Jul 09, 2020 7:28 pm

Perhaps “NeoKöhler” would be better? :D

david_b
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Re: Fixed Köhler

#36 Post by david_b » Thu Jul 09, 2020 7:40 pm

Zuul wrote:
Thu Jul 09, 2020 7:28 pm
Perhaps “NeoKöhler” would be better? :D
NoKohler ?

Scarodactyl
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Re: Fixed Köhler

#37 Post by Scarodactyl » Thu Jul 09, 2020 8:03 pm

Zuul wrote:
Thu Jul 09, 2020 7:28 pm
Perhaps “NeoKöhler” would be better? :D
In olympus lingo this would mean epi brightfield/darkfield kohler, wouldn't it? I'd like to see that.

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Re: Fixed Köhler

#38 Post by Zuul » Fri Jul 10, 2020 12:24 am

Scarodactyl wrote:
Thu Jul 09, 2020 8:03 pm
In olympus lingo this would mean epi brightfield/darkfield kohler, wouldn't it? I'd like to see that.
I don’t speak Olympus, I guess. In Reichert-speak “Neo” means nearly or almost. The NeoPlan objectives are close to plan, but slot in under the Plan Achros.

MichaelG.
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Re: Fixed Köhler

#39 Post by MichaelG. » Fri Jul 10, 2020 9:27 am

Strictly speaking [which is increasingly uncommon] :

Neo means New ... in the sense of ‘fresh/young/recent’

... Very conveniently covers a multitude of sins

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Element 56
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Re: Fixed Köhler

#40 Post by Element 56 » Fri Jul 10, 2020 5:30 pm

I have a good friend who is a Zeiss representative and after seeing this thread I was curious what he had to say about it.

" Basically “Fixed Kohler” is a way to lock the centration and height of the condenser so that users/students can’t mess it up. The reason for Fixed Kohler is to offer a microscope that will “always” give a good image for the non-microscope user/expert. We offer this on our Primostar model which has been out since the early 2000’s. You would be amazed on how many users love this and do not care/want to align a microscope."

Full Kohler vs Fixed Kohler:
(Red Arrow) Condenser alignment screws are set screws on the Fixed Kohler stand. Thus, users cannot center the condenser unless they use a tool
(Yellow highlighter) The Fixed Kohler version does not have a field diaphragm. Thus, users do not complain that the image is dark or “there is dark ring around their image”.
Last, not shown. There is a bolt on the condenser focus so that it is locked into focus. Thus, users cannot de-focus light/misaligned the (Z) alignment of the condenser.
Fixed Kohler.png
Fixed Kohler.png (156.82 KiB) Viewed 1925 times
Kirby

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Re: Fixed Köhler

#41 Post by BramHuntingNematodes » Fri Jul 10, 2020 6:02 pm

So basically they take a look at the factory then bolt everything in place.

Maybe works OK if you're not trying to cobble together a working system from second-hand parts.
1942 Bausch and Lomb Series T Dynoptic, Custom Illumination

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75RR
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Re: Fixed Köhler

#42 Post by 75RR » Fri Jul 10, 2020 7:26 pm

Element 56 wrote:
Fri Jul 10, 2020 5:30 pm
I have a good friend who is a Zeiss representative and after seeing this thread I was curious what he had to say about it.

" Basically “Fixed Kohler” is a way to lock the centration and height of the condenser so that users/students can’t mess it up. The reason for Fixed Kohler is to offer a microscope that will “always” give a good image for the non-microscope user/expert. We offer this on our Primostar model which has been out since the early 2000’s. You would be amazed on how many users love this and do not care/want to align a microscope."

Full Kohler vs Fixed Kohler:
(Red Arrow) Condenser alignment screws are set screws on the Fixed Kohler stand. Thus, users cannot center the condenser unless they use a tool
(Yellow highlighter) The Fixed Kohler version does not have a field diaphragm. Thus, users do not complain that the image is dark or “there is dark ring around their image”.
Last, not shown. There is a bolt on the condenser focus so that it is locked into focus. Thus, users cannot de-focus light/misaligned the (Z) alignment of the condenser
So it is true, we are devolving as a species!
Zeiss Standard WL (somewhat fashion challenged) & Wild M8
Olympus E-P2 (Micro Four Thirds Camera)

Element 56
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Re: Fixed Köhler

#43 Post by Element 56 » Fri Jul 10, 2020 8:12 pm

Don't you kind of think this was inevitable in today's society of click and have?

Kind of like cars that drive themselves and refrigerators that order your groceries. Why the heck would we want to go through the steps of setting up Kohler when you can just buy a microscope with it built in! Probably no need to understand its principles either!

Kirby

david_b
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Re: Fixed Köhler

#44 Post by david_b » Fri Jul 10, 2020 8:45 pm

Kirby, thank you for posting this.
If it were the case that setting Kohler illumination is fully automated then that would indeed be a convenience.
But...would you/your friend agree that without a field diaphragm, the flare and contrast cannot be optimised for each objective, according to the Kohler principle, and therefore it must be a compromised system?
Again, I understand that the illumination is pre-centred, but this is only half of the Kohler story... no?

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Re: Fixed Köhler

#45 Post by Zuul » Fri Jul 10, 2020 10:23 pm

Every design has compromises; cost, size, etc. If you taught a few biology classes every day, this compromise means you don't have to check every single microscope after every single class to see who fiddled with what. Then it might seem like a very good compromise. Not every setting requires that last 5% of possible performance.

Element 56
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Re: Fixed Köhler

#46 Post by Element 56 » Fri Jul 10, 2020 11:22 pm

david_b wrote:
Fri Jul 10, 2020 8:45 pm
Kirby, thank you for posting this.
If it were the case that setting Kohler illumination is fully automated then that would indeed be a convenience.
But...would you/your friend agree that without a field diaphragm, the flare and contrast cannot be optimised for each objective, according to the Kohler principle, and therefore it must be a compromised system?
Again, I understand that the illumination is pre-centred, but this is only half of the Kohler story... no?
Hi David,

You're welcome.

My friend said, "The reason for fixed Kohler is to offer a microscope that will "always" give a good image for the non-microscope user/expert." Pretty much what Zuul just pointed out, in a classroom setting this would be logical.

I agree with you that it cannot be perfect but I don't think it's intended as an instrument for someone who demands the very best out of their optics and it sounds like Zeiss thankfully isn't marketing it as such.

I'm curious and want to try one for myself to see what it's like! Wonder if I can get a DEMO!! :mrgreen:

Kirby

MichaelG.
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Re: Fixed Köhler

#47 Post by MichaelG. » Mon Jul 27, 2020 7:48 am

Reviving this discussion because I think I may have identified the origin of the ‘fixed Köhler’ concept:

See p10 of the Leitz DIALUX 20 brochure:
http://earth2geologists.net/Microscopes ... ochure.pdf

Edit: a better quality scan of that page is included in this extract:
http://www.science-info.net/docs/leitz/ ... y-20-B.pdf

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75RR
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Re: Fixed Köhler

#48 Post by 75RR » Mon Jul 27, 2020 8:15 am

No mention of how it works though. Perhaps someone who has a Standard SK condenser or the Universal UK condenser can show us photos of the mechanical workings.

This is the relevant extract:
.
Attachments
Köhler zero vertical adjustment.png
Köhler zero vertical adjustment.png (216.64 KiB) Viewed 1852 times
Zeiss Standard WL (somewhat fashion challenged) & Wild M8
Olympus E-P2 (Micro Four Thirds Camera)

david_b
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Re: Fixed Köhler

#49 Post by david_b » Mon Jul 27, 2020 2:33 pm

The full text mentions that both condensers are used in conjunction with a field diaphragm that can be adjusted 'in all directions'.
The Olympus models mentioned in the OP do not appear to have an adjustable field diaphragm.

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Re: Fixed Köhler

#50 Post by MichaelG. » Mon Jul 27, 2020 5:14 pm

david_b wrote:
Mon Jul 27, 2020 2:33 pm
The full text mentions that both condensers are used in conjunction with a field diaphragm that can be adjusted 'in all directions'.
The Olympus models mentioned in the OP do not appear to have an adjustable field diaphragm.
That’s why I emphasised the word concept

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Geode
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Re: Fixed Köhler

#51 Post by Geode » Sun Aug 16, 2020 1:16 am

From my understanding, and I asked a few dealers about this feature, some scopes come with a condenser focus knob, so you can move it up and down and focus the condenser to the slide (by holding a paper/tissue to the light source and focusing the condenser till the edge of the tissue is crisp.
The only reason I know this is because an instructor of mine showed this to us in a microscopy course. They may be wrong but it made the resolution better.

I was told by an experienced dealer that this is an old technique and that the feature is obsolete in new scopes that come "pre-fixed".
So, Full-Kholer being you can focus the condenser (the presence of an adjustable condenser focus knob), and fixed-Kohler being the lack of the knob.

Just my two cents :)

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Re: Fixed Köhler

#52 Post by BramHuntingNematodes » Sun Aug 16, 2020 2:19 am

well it's obsolete technique for those scopes that have condenser adjustment knob bolted in place because you don't have the option to do anything if the paper shows bad focus
1942 Bausch and Lomb Series T Dynoptic, Custom Illumination

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