Köhler illumination Parts

[Marc]

Hi,

I'm reading articles like this about Köhler illumination although they don't talk about special condensers to use:

https://www.zeiss.com/microscopy/int/so ... ation.html



Having a similar condenser with two centering screws, It would be enough adding one ligth with iris diafragm to get Köhler illumination?

Köhler Illumination need of an special condenser or additional parts?

[Dubious]

Which microscope do you have? Does it have a condenser under the specimen stage? if so, it has an aperture diaphragm in the condenser. The field diaphragm used in Kohler illumination is an additional diaphragm in the lens at the base of the microscope that directs light up toward the condenser/specimen stage.

Kohler illumination is a technique that (1) provides even lighting, particularly with tungsten/halogen lamp filaments and (2) improves contrast a bit by closing the field diaphram to restrict light to the field where it is actually needed, decreasing splatter and reflections. Many microscopes do not have Kohler illumination, relying instead on factory-adjusted light sources and emitting lenses, often with a diffuser of some sort, to accomplish even lighting. With LED lighting, Kohler is less beneficial than it was with filament lamps. Usually, if the microscope is not designed for Kohler illumination, it is not practical to add it, but it would depend on the microscope.

[Marc]

Hi Dubious,

yes, the condenser is under the specimen stage. It is an Abbe 1.25 with diaphragm and 2 centering screws. I have one hallogen bulb. Good to know it is best for filament light.

My doubt about Kohler is precisely to know if there is any additional part besides that diaphragm embedded into the light source. The articles I'm reading are not very clear on this or perhaps I don't understand-

If I understand your words, you mean the field Kohler diaphragm is embedded into the light part and no more parts are needed. Is this right?.


Thanks!

[BramHuntingNematodes]

You will want the condenser itself to be moveable up and down and also there should be a field lens to focus or rather collimate the light prior to it getting to the condenser. The field lens was Kohler's trick to not having to look at a filament coil. The iris is optional. Kohler used cardboard cutouts of various sizes.

[MichaelG.]

Marc

May I suggest that to watch the first section [21 minutes] of Peter Evennett’s video demonstration:
https://youtu.be/60_jgZtyR6U

He shows, with unusual clarity, how Köhler illumination works
… far better than trying to follow static descriptions and ray diagrams.

MichaelG.

[Marc]

May I suggest that to watch the first section [21 minutes] of Peter Evennett’s video demonstration:
https://youtu.be/60_jgZtyR6U

He shows, with unusual clarity, how Köhler illumination works
… far better than trying to follow static descriptions and ray diagrams.

thank you. Very good video. I agree this is the best I have seen to learn how it works

You will want the condenser itself to be moveable up and down and also there should be a field lens to focus or rather collimate the light prior to it getting to the condenser. The field lens was Kohler's trick to not having to look at a filament coil. The iris is optional. Kohler used cardboard cutouts of various sizes.

condenser is moveable to any direction and it can be centered with screws. Although I don't see a lens previous to the condenser diaphragm.




question is because I have no option to update, and I'm exploring possibilities to print a 3D piece to replace the light part to include one iris diaphragm into.

up view part


down view part


still one point to clarify is what you says, about the key part for the Köhler system would be one lens previous to the condenser diaphragm.

Is this what you are saying or I'm not understand you well?

In the previous video (18:00), this man is moving the diaphragm in the light part, together with the condenser diaphragm. Although it seems there is no any lens between both:

[youtube]https://www.youtube.com/watch?v=60_jgZtyR6U&t=1080s[/youtube]

my English is not very good at hearing, and I'm not sure if Peter Evennett explain something about a previous lens to concentrate the focus.
I believe he don't mention some intermediate lens although I would be happy to clarify this point.

Thanks for the help

[MichaelG.]

my English is not very good at hearing, and I'm not sure if Peter Evennett explain something about a previous lens to concentrate the focus.
I believe he don't mention some intermediate lens although I would be happy to clarify this point.

.
Watch this bit again, Marc … You are doing well
.

18CD5222-79E7-43B5-947C-E78A30D79FBF.jpeg (72.72 KiB) Viewed 5134 times

.
MichaelG.

[Marc]

Do you mean modern microscopes like this also are using a similar lens system?.



Or maybe they are integrating an special lens in the light part to focus the light?

Or they are putting that lens in the condenser therefore Köhler system are using a different condenser?

[75RR]

.

... still one point to clarify is what you says, about the key part for the Köhler system would be one lens previous to the condenser diaphragm.
Is this what you are saying or I'm not understand you well?

A lens is needed between the lamp and the condenser in order to be able to focus the lamp filament on the front focal plane of the condenser
(i.e. the underside of the condenser diaphragm) see diagram conjugate aperture planes (right side)

[75RR]

.
Don't want to seem unhelpful but you might want to leave Köhler illumination for your next microscope upgrade.

Critical illumination, the default if you do not have Köhler, will do you well enough for that microscope.

[MichaelG.]

Do you mean modern microscopes like this also are using a similar lens system?.

[…]

Or maybe they are integrating an special lens in the light part to focus the light?

Or they are putting that lens in the condenser therefore Köhler system are using a different condenser?

.
Whether [or not] the additional lens is needed will depend upon the light source and the design of the Collector Lens [see Fig.1 in your link] … You need whatever gives the appropriate output beam at the Field Stop Diaphragm.

MichaelG.

[Marc]

Whether [or not] the additional lens is needed will depend upon the light source and the design of the Collector Lens [see Fig.1 in your link] … You need whatever gives the appropriate output beam at the Field Stop Diaphragm.

thanks. I think I understand now. The confussion was the different design. The video shows a system similar to this:



it has a mirror reflecting the light beam previously collected, and later this is modulated with the diaphragm covering the mirror. This interactive tutorial is quite good to understand and complement the explanations of that video:

https://www.olympus-lifescience.com/es/ ... ansmitted/

It seems many microscopes with Köhler illumination mounts some aespherical lens over the light with a diaphragm? And that's all. So the only difference seem to be here:



in eXAmple, this model exist with or without Köhler and the only difference seems to be in that diaphragm covering the light:


so I believe I could try to add a diaphragm in that part.

Don't want to seem unhelpful but you might want to leave Köhler illumination for your next microscope upgrade.
Critical illumination, the default if you do not have Köhler, will do you well enough for that microscope.

I made a recent update with a new microscope. I hope no hard problems to support this type of upgrade.
Just I have the interest to check difference using Kohler and also with the camera.
Few money to lose in any case. If no cheap parts available, the diaphragms and 3D print are cheap.

[75RR]

If no cheap parts available, the diaphragms and 3D print are cheap.

.
It seems that Euromex do have a Köhler upgrade for the bScope. You might want to ask what that entails.

Also, they say that their illumination is adjustable - perhaps they can clarify that.

"I L L U M I N A T I O N
The microscopes of the bScope are equipped with a 3 W NeoLED adjustable illumination system
for increased light output and a 100-240 Vac integrated power supply.
On request, rechargeable batteries are also available"
.

[Marc]

If no cheap parts available, the diaphragms and 3D print are cheap.

.
It seems that Euromex do have a Köhler upgrade for the bScope. You might want to ask what that entails.
Also, they say that their illumination is adjustable - perhaps they can clarify that.

I don't have have that microscope. I include that microscope only like one example of Kôhler illumination different from using a reflecting mirror
That microscope model has the Köhler option, and the only change seem to be the diaphragm covering the light.
I believe "adjustable" refers to open and close the diaphragm.

[75RR]

I don't have have that microscope. I include that microscope only like one example of Kôhler illumination different from using a reflecting mirror

Always best when you show an actual image of your own microscope, as the advice given may then vary.

However in this case (as in a completely different microscope) it would seem that the difference is the inclusion of a field diaphragm

[Marc]

I don't have have that microscope. I include that microscope only like one example of Kôhler illumination different from using a reflecting mirror

Always best when you show an actual image of your own microscope, as the advice given may then vary.
However in this case (as in a completely different microscope) it would seem that the difference is the inclusion of a field diaphragm

yes, this is what I said, it seems this is the only difference.

my microscope is this



is quite upgradeable. I have seen this same chassis with led, filament, different heads and objectives.
I.e: https://www.homesciencetools.com/produc ... an-optics/

I have upgraded recently with one universal trino head (42mm) and no problem