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Re: Fixed Köhler

Posted: Thu Jul 09, 2020 4:45 pm
by deBult
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.

Re: Fixed Köhler

Posted: Thu Jul 09, 2020 4:46 pm
by david_b
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.

Re: Fixed Köhler

Posted: Thu Jul 09, 2020 4:50 pm
by 75RR
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.

Re: Fixed Köhler

Posted: Thu Jul 09, 2020 6:10 pm
by david_b
I meant adopting the term 'fixed Kohler', not referring to the technology.

Re: Fixed Köhler

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

Re: Fixed Köhler

Posted: Thu Jul 09, 2020 7:40 pm
by david_b
Zuul wrote:
Thu Jul 09, 2020 7:28 pm
Perhaps “NeoKöhler” would be better? :D
NoKohler ?

Re: Fixed Köhler

Posted: Thu Jul 09, 2020 8:03 pm
by Scarodactyl
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.

Re: Fixed Köhler

Posted: Fri Jul 10, 2020 12:24 am
by Zuul
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.

Re: Fixed Köhler

Posted: Fri Jul 10, 2020 9:27 am
by MichaelG.
Strictly speaking [which is increasingly uncommon] :

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

... Very conveniently covers a multitude of sins

MichaelG.

Re: Fixed Köhler

Posted: Fri Jul 10, 2020 5:30 pm
by Element 56
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 1916 times
Kirby

Re: Fixed Köhler

Posted: Fri Jul 10, 2020 6:02 pm
by BramHuntingNematodes
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.

Re: Fixed Köhler

Posted: Fri Jul 10, 2020 7:26 pm
by 75RR
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!

Re: Fixed Köhler

Posted: Fri Jul 10, 2020 8:12 pm
by Element 56
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

Re: Fixed Köhler

Posted: Fri Jul 10, 2020 8:45 pm
by david_b
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?

Re: Fixed Köhler

Posted: Fri Jul 10, 2020 10:23 pm
by Zuul
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.

Re: Fixed Köhler

Posted: Fri Jul 10, 2020 11:22 pm
by Element 56
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

Re: Fixed Köhler

Posted: Mon Jul 27, 2020 7:48 am
by MichaelG.
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

MichaelG.

Re: Fixed Köhler

Posted: Mon Jul 27, 2020 8:15 am
by 75RR
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:
.

Re: Fixed Köhler

Posted: Mon Jul 27, 2020 2:33 pm
by david_b
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.

Re: Fixed Köhler

Posted: Mon Jul 27, 2020 5:14 pm
by MichaelG.
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

MichaelG.

Re: Fixed Köhler

Posted: Sun Aug 16, 2020 1:16 am
by Geode
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 :)

Re: Fixed Köhler

Posted: Sun Aug 16, 2020 2:19 am
by BramHuntingNematodes
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