Kohler Illumination

Here you can discuss different microscopic techniques and illumination methods, such as Brightfield, Darkfield, Phase Contrast, DIC, Oblique illumination, etc.
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LouiseScot
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Kohler Illumination

#1 Post by LouiseScot » Sun May 08, 2022 11:45 am

I don't currently own a microscope with proper Kohler but expect to quite soon :) I have set up and used Kohler at Uni in the past though :) However, I decided it would be useful to remind myself of the correct steps in the procedure. I came across this video from down under which I found useful, so thought I'd share. It shows how to achieve Kohler on some different microscopes, and even something approaching Kohler but without a field iris.

https://www.youtube.com/watch?v=aaU3mkPI53k

Louise
A Nikon CF plan 20x; A Swift 380T; A DIY infinity corrected focus rail system with a 40x/0.65 Olympus Plan, a 10x/0.30 Amscope Plan Fluor, and a 20x/0.75 Nikon Plan Apo

Greg Howald
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Re: Kohler Illumination

#2 Post by Greg Howald » Sun May 08, 2022 12:43 pm

Thanks for that review. I saw a step or two there I had been neglecting.

LouiseScot
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Re: Kohler Illumination

#3 Post by LouiseScot » Sun May 08, 2022 1:46 pm

Greg Howald wrote:
Sun May 08, 2022 12:43 pm
Thanks for that review. I saw a step or two there I had been neglecting.
Hi Greg

It's something that one could make into a document, print out, and leave next to scope :) I should be getting the Amscope T680A in the next couple of weeks so will be trying out the scope's Kohler set up. If it works ok I hope it will improve my imaging, if only a bit...

Louise
A Nikon CF plan 20x; A Swift 380T; A DIY infinity corrected focus rail system with a 40x/0.65 Olympus Plan, a 10x/0.30 Amscope Plan Fluor, and a 20x/0.75 Nikon Plan Apo

Greg Howald
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Re: Kohler Illumination

#4 Post by Greg Howald » Mon May 09, 2022 12:03 am

The 680 is a fine scope. I have some macular degeneratiin in the right eye, so the 23mm eyepieces aren't best for ne, but I found some 23mm eyepieces on Amazon with larger eyepiece lenses that help a great deal with the problem, and also found a pair of adaptors to go from 23 to 30mm.
You should enjoy the scope very much.

LouiseScot
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Re: Kohler Illumination

#5 Post by LouiseScot » Mon May 09, 2022 12:35 am

Greg Howald wrote:
Mon May 09, 2022 12:03 am
The 680 is a fine scope. I have some macular degeneratiin in the right eye, so the 23mm eyepieces aren't best for ne, but I found some 23mm eyepieces on Amazon with larger eyepiece lenses that help a great deal with the problem, and also found a pair of adaptors to go from 23 to 30mm.
You should enjoy the scope very much.
Hi again

I think I'd have to class it as a 'budget' scope but a step up from my low budget Swift 380T :) I'm looking at the T720Q also, and as an infinity optics instruments though haven't finally decided yet. I think it does have 30mm EPs but still probably only 10x/18. It has LED illumination but the don't specify wattage. I may ask but the sales staff probably won't know. It might be possible to diy a LED upgrade anyway. It's a bit more expensive than the T680 but still a budget scope. There is the T800 which is quite a bit more expensive but I can't see what more you get with the T800 for the extra money. Sorry about your Macular Degeneration - hope it can be treated?

Louise
A Nikon CF plan 20x; A Swift 380T; A DIY infinity corrected focus rail system with a 40x/0.65 Olympus Plan, a 10x/0.30 Amscope Plan Fluor, and a 20x/0.75 Nikon Plan Apo

Greg Howald
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Re: Kohler Illumination

#6 Post by Greg Howald » Mon May 09, 2022 12:54 am

Two things. I own the 720q. It is a very good scope. Led lighting is bright enough. I think it is 3 watt. It came with tight fitting 30 mm eyepieces. One pair is 10/22 and the second pair is 25/19. The is no focus or diopter on the eyepiece barrel, but both eyepieces are focusable and they work great. I was amazed at the size of the image at 10x. Rather larger than expected. I enjoy the scope very much.
I do not have a 680 but am considering it.
I have an Amscope t420. It is an infinity scope with 30mm eyepieces. I bought it on clearance and it is no longer available. I changed the lighting from 1 watt to 3 watt led and that helped greatly. It doesn't have k lighting, but I had a spare iris diaphragm that fit perfectly on top of the illuminator, and the condenser is centerable, so I use it like k lighting, and I wonder if it is the same thing because I have good results.

LouiseScot
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Re: Kohler Illumination

#7 Post by LouiseScot » Mon May 09, 2022 8:03 am

Greg Howald wrote:
Mon May 09, 2022 12:54 am
Two things. I own the 720q. It is a very good scope. Led lighting is bright enough. I think it is 3 watt. It came with tight fitting 30 mm eyepieces. One pair is 10/22 and the second pair is 25/19. The is no focus or diopter on the eyepiece barrel, but both eyepieces are focusable and they work great. I was amazed at the size of the image at 10x. Rather larger than expected. I enjoy the scope very much.
I do not have a 680 but am considering it.
I have an Amscope t420. It is an infinity scope with 30mm eyepieces. I bought it on clearance and it is no longer available. I changed the lighting from 1 watt to 3 watt led and that helped greatly. It doesn't have k lighting, but I had a spare iris diaphragm that fit perfectly on top of the illuminator, and the condenser is centerable, so I use it like k lighting, and I wonder if it is the same thing because I have good results.
Oh ok, thanks for the info. They charge a lot for the extra EPs which aren't really of much use since resolution comes from the objective.
Cheers
Louise
ps good to know they are 10x/22 and 25x/19 might have some use :)
A Nikon CF plan 20x; A Swift 380T; A DIY infinity corrected focus rail system with a 40x/0.65 Olympus Plan, a 10x/0.30 Amscope Plan Fluor, and a 20x/0.75 Nikon Plan Apo

Phill Brown
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Re: Kohler Illumination

#8 Post by Phill Brown » Mon May 09, 2022 5:37 pm

Thanks for the link.
I'm glad I didn't spend that much on a Nikon with a sticky substage and tacky plastic bits.
Wonder where it was assembled.
Can clearly see where the margins are up.
Stick a bright blue LED inside and a darker blue LED on the outside somewhere and move the decimal point on the tag to the right.
The olympus wasn't very co-operative or aspirational either.
The joy had been absorbed by the specimen.
Got to love the contrast though.

LouiseScot
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Re: Kohler Illumination

#9 Post by LouiseScot » Mon May 09, 2022 7:09 pm

Phill Brown wrote:
Mon May 09, 2022 5:37 pm
Thanks for the link.
I'm glad I didn't spend that much on a Nikon with a sticky substage and tacky plastic bits.
Wonder where it was assembled.
Can clearly see where the margins are up.
Stick a bright blue LED inside and a darker blue LED on the outside somewhere and move the decimal point on the tag to the right.
The olympus wasn't very co-operative or aspirational either.
The joy had been absorbed by the specimen.
Got to love the contrast though.
I'm sorry, I don't understand your post...

Louise
A Nikon CF plan 20x; A Swift 380T; A DIY infinity corrected focus rail system with a 40x/0.65 Olympus Plan, a 10x/0.30 Amscope Plan Fluor, and a 20x/0.75 Nikon Plan Apo

MichaelG.
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Re: Kohler Illumination

#10 Post by MichaelG. » Mon May 09, 2022 9:43 pm

If you have an iOS device … this free interactive tutor is worth a look
https://apps.apple.com/gb/app/koehler-t ... 1281328178

MichaelG.

.
Edited to correct the typo in my ‘signature’ :oops:
… I was rushing to contribute something useful
Last edited by MichaelG. on Mon May 09, 2022 10:02 pm, edited 2 times in total.
Too many 'projects'

LouiseScot
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Re: Kohler Illumination

#11 Post by LouiseScot » Mon May 09, 2022 9:50 pm

MichaelG. wrote:
Mon May 09, 2022 9:43 pm
If you have an iOS device … this free interactive tutor is worth a look
https://apps.apple.com/gb/app/koehler-t ... 1281328178

MichaelH.
I don't own any Apple devices but I don't need help to understand or set up Kohler.

Thanks

Louise
A Nikon CF plan 20x; A Swift 380T; A DIY infinity corrected focus rail system with a 40x/0.65 Olympus Plan, a 10x/0.30 Amscope Plan Fluor, and a 20x/0.75 Nikon Plan Apo

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Re: Kohler Illumination

#12 Post by MichaelG. » Mon May 09, 2022 9:57 pm

LouiseScot wrote:
Mon May 09, 2022 9:50 pm
I don't own any Apple devices but I don't need help to understand or set up Kohler.
.

Pardon me for polluting your topic by trying to contribute to the general level of awareness.

MichaelG.
Too many 'projects'

LouiseScot
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Re: Kohler Illumination

#13 Post by LouiseScot » Mon May 09, 2022 10:02 pm

MichaelG. wrote:
Mon May 09, 2022 9:57 pm
LouiseScot wrote:
Mon May 09, 2022 9:50 pm
I don't own any Apple devices but I don't need help to understand or set up Kohler.
.

Pardon me for polluting your topic by trying to contribute to the general level of awareness.

MichaelG.
I'm sorry, I didn't mean to sound rude! But it's a fact I don't own any Apple devices and there are plenty of Kohler videos on YouTube in addition to the link I posted. Anyone who watches the YouTube videos can jot down the steps for a crib sheet.

Louise
A Nikon CF plan 20x; A Swift 380T; A DIY infinity corrected focus rail system with a 40x/0.65 Olympus Plan, a 10x/0.30 Amscope Plan Fluor, and a 20x/0.75 Nikon Plan Apo

GerryR
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Re: Kohler Illumination

#14 Post by GerryR » Thu Jun 30, 2022 12:15 pm

An older thread, but rather than start one on the same subject, I thought I would ask my questions here. On the posted video, and from other sources, they say to realign the optics every time you change powers (objectives). Being somewhat illiterate in this area (Wil Rogers once said, "Everyone is illiterate, just on different subjects."), this doesn't make much sense to me, if you start your alignment on the lowest power. Once centered and focused on the lowest power, and then opening the condenser diaphragm, the field is then coherent as you go up in power because of the smaller field of view of the higher power objectives. So why realign? Also notice that when you close down the field aperture, you are assuming that the light source is perfectly centered /aligned with the rest of the optical system. (There are very few scopes that I have seen that have centering screws for the light source; AO made some.) You then proceed to center the beam of light with the condenser, and then you open the field diaphragm and adjust the condenser diaphragm for full field view. To top that, you then go to the oil type objectives, which requires the condenser be very close to the slide (assuming you are using oil on the condenser), which may not be the focused position of the field diaphragm, so what has been accomplished? How much does the image suffer if you don't align each time you change objectives; that would seem to be the bottom line. Like I said, I'm relatively ignorant in this area and would like some clarification. Thanks for any input.

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Re: Kohler Illumination

#15 Post by Hobbyst46 » Thu Jun 30, 2022 12:40 pm

GerryR wrote:
Thu Jun 30, 2022 12:15 pm
...the field is then coherent as you go up in power because of the smaller field of view of the higher power objectives. So why realign?
That statement is true if the objectives are exactly parcentered. That might be true for modern high-class research microscopes. Not necessarily on others - at least not on very old microscopes and where the objectives on the nosepiece are an "assortment" rather than an originally planned set of objectives. Not to mention "foreigners" from other microscopes or even manufacturers.
Also notice that when you close down the field aperture, you are assuming that the light source is perfectly centered /aligned with the rest of the optical system. (There are very few scopes that I have seen that have centering screws for the light source; AO made some.) You then proceed to center the beam of light with the condenser, and then you open the field diaphragm and adjust the condenser diaphragm for full field view.
Indeed, if the lamp is fixed in position, Kohler setup becomes simpler. Remember, though, that the distance between the lamp and the collector optics (or whichever optical part resides downstream of the lamp) can sometimes be modified as well, and the distance affects the illumination. On some modern microscopes, with epi-illumination and fluorescence, the lamp housing has adjustment knobs that allow axial as well as parallel allignments of the beam.
...which requires the condenser be very close to the slide (assuming you are using oil on the condenser), which may not be the focused position of the field diaphragm, so what has been accomplished? How much does the image suffer if you don't align each time you change objectives; that would seem to be the bottom line....
In my experience, after setting up Kohler, oiling the condenser to the slide bottom (messy and apalling, so seldom done) had little effect on either the illuminated field or the image - at least for my limited purpose.

LouiseScot
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Re: Kohler Illumination

#16 Post by LouiseScot » Thu Jun 30, 2022 12:46 pm

GerryR wrote:
Thu Jun 30, 2022 12:15 pm
An older thread, but rather than start one on the same subject, I thought I would ask my questions here. On the posted video, and from other sources, they say to realign the optics every time you change powers (objectives). Being somewhat illiterate in this area (Wil Rogers once said, "Everyone is illiterate, just on different subjects."), this doesn't make much sense to me, if you start your alignment on the lowest power. Once centered and focused on the lowest power, and then opening the condenser diaphragm, the field is then coherent as you go up in power because of the smaller field of view of the higher power objectives. So why realign? Also notice that when you close down the field aperture, you are assuming that the light source is perfectly centered /aligned with the rest of the optical system. (There are very few scopes that I have seen that have centering screws for the light source; AO made some.) You then proceed to center the beam of light with the condenser, and then you open the field diaphragm and adjust the condenser diaphragm for full field view. To top that, you then go to the oil type objectives, which requires the condenser be very close to the slide (assuming you are using oil on the condenser), which may not be the focused position of the field diaphragm, so what has been accomplished? How much does the image suffer if you don't align each time you change objectives; that would seem to be the bottom line. Like I said, I'm relatively ignorant in this area and would like some clarification. Thanks for any input.
Hi Gerry

The condenser won't necessarily be correctly centred on other objectives - it depends on the quality and tolerance of the manufacturer and assembler. Certainly, with my AmScopes there is a definite need to re-centre as well as refocus of condenser between objectives. The subsequent adjustment of the field diaphragm to be just beyond the field is to optimise the lighting. The condenser diaphragm is only used to match numerical aperture and also to get the contrast you desire (at the expense of resolution). Ideally the NA of the objective and condenser are matched (up to ~1 in air). Kohler systems have the ability to centre the condenser. Adjustment of the condenser focus allows you to focus on the field iris diaphragm - not the actual light source which can be diffused.

Here is a step by step guide which is quite good:

https://www.photometrics.com/learn/micr ... mination-2

Scroll down to 'Stepwise Instruction'

Louise
A Nikon CF plan 20x; A Swift 380T; A DIY infinity corrected focus rail system with a 40x/0.65 Olympus Plan, a 10x/0.30 Amscope Plan Fluor, and a 20x/0.75 Nikon Plan Apo

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Re: Kohler Illumination

#17 Post by blekenbleu » Thu Jun 30, 2022 7:10 pm

I have issues with both https://www.youtube.com/watch?v=aaU3mkPI53k
and https://www.photometrics.com/learn/micr ... mination-2.
Disclaimers:
  • I use mostly lower power objectives; field uniformity is an issue.
  • My microscopes still use halogen lamps.
Issues:
  • Neither shows examples of what one wants to see, looking down an eye tube with ocular removed.
  • Both resources seemingly assume diffuse illumination, despite the second concluding with:
    "Köhler illumination is critical to removing illumination source structure from the image of the sample."
  • The video supposes that illumination port is nearly parfocal with field diaphragm (and image plane),
    while many other sources for Köhler alignment suppose that port is parfocal with objective focal plane (and illumination filament plane).
In my admittedly limited experience, that illumination port has been parfocal with neither. Further,
  • getting condenser iris correct at objective focal plane is hard, at least for me..
  • getting illumination filament in focus at objective focal plane is even harder;
    I have tried using a Bertrand lens to help, but no joy...
  • field aperture focus varies appreciably among parfocal objectives of different powers
  • filament focus varies even more among objective powers, so far as I have been able to determine,
    and can be seemingly impossible for some microscopes with objectives < 10x, where it becomes increasingly critical.
My source for illumination alignment is https://micro.magnet.fsu.edu/primer/jav ... amentalign.
Sadly, that demo requires Java, which is now considered a security liability.
Metaphot, Optiphot 1, 66; AO 10, 120, EPIStar, Cycloptic

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Re: Kohler Illumination

#18 Post by LouiseScot » Thu Jun 30, 2022 7:38 pm

blekenbleu wrote:
Thu Jun 30, 2022 7:10 pm
I have issues with both https://www.youtube.com/watch?v=aaU3mkPI53k
and https://www.photometrics.com/learn/micr ... mination-2.
Disclaimers:
  • I use mostly lower power objectives; field uniformity is an issue.
  • My microscopes still use halogen lamps.
Issues:
  • Neither shows examples of what one wants to see, looking down an eye tube with ocular removed.
  • Both resources seemingly assume diffuse illumination, despite the second concluding with:
    "Köhler illumination is critical to removing illumination source structure from the image of the sample."
  • The video supposes that illumination port is nearly parfocal with field diaphragm (and image plane),
    while many other sources for Köhler alignment suppose that port is parfocal with objective focal plane (and illumination filament plane).
In my admittedly limited experience, that illumination port has been parfocal with neither. Further,
  • getting condenser iris correct at objective focal plane is hard, at least for me..
  • getting illumination filament in focus at objective focal plane is even harder;
    I have tried using a Bertrand lens to help, but no joy...
  • field aperture focus varies appreciably among parfocal objectives of different powers
  • filament focus varies even more among objective powers, so far as I have been able to determine,
    and can be seemingly impossible for some microscopes with objectives < 10x, where it becomes increasingly critical.
My source for illumination alignment is https://micro.magnet.fsu.edu/primer/jav ... amentalign.
Sadly, that demo requires Java, which is now considered a security liability.
Have you actually got a Kohler setup? The objective is focused on the sample. The the Field iris should be centred and moved into focus according to the condenser adjustment. The Condenser iris is only used to control NA and contrast. You have to be careful not to confuse the field iris and the condenser (aperture) iris. Originally, by focusing on the field iris the bulb filament was expected to be out of focus. Sometimes instructions suggest focusing an a an item above the illumination source which is used as a faux diaphragm. A proper Kohler setup with a field diaphragm is better, I think. You might be able to get away with placing an add-on field iris above the illumination source. You can get Kohler Illumination attachments as an add-on for some scopes e.g. Omax

Louise
A Nikon CF plan 20x; A Swift 380T; A DIY infinity corrected focus rail system with a 40x/0.65 Olympus Plan, a 10x/0.30 Amscope Plan Fluor, and a 20x/0.75 Nikon Plan Apo

LouiseScot
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Re: Kohler Illumination

#19 Post by LouiseScot » Thu Jun 30, 2022 8:14 pm

Here is Omax upgrade version:
https://omaxmicroscope.com/microscope-a ... tment.html

Seems expensive for what it is. I'm sure there must be others around.
There is one available for the Euromex iScope:

https://www.astroshop.eu/condensers/eur ... r_0_select

Louise
A Nikon CF plan 20x; A Swift 380T; A DIY infinity corrected focus rail system with a 40x/0.65 Olympus Plan, a 10x/0.30 Amscope Plan Fluor, and a 20x/0.75 Nikon Plan Apo

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Re: Kohler Illumination

#20 Post by blekenbleu » Thu Jun 30, 2022 8:31 pm

LouiseScot wrote:
Thu Jun 30, 2022 7:38 pm
Have you actually got a Kohler setup?
Yes, both AO 120 and Nikon Optiphot have field and condenser apertures,
as well as lamp and condenser focus and centering provisions.
The lamp wants centering when replaced
but refocus with each objective change, which is done looking at objective back
(or reprojected image of objective back for infinity objectives)
with ocular removed, while adjusting condenser aperture.
Metaphot, Optiphot 1, 66; AO 10, 120, EPIStar, Cycloptic

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Re: Kohler Illumination

#21 Post by LouiseScot » Thu Jun 30, 2022 8:46 pm

blekenbleu wrote:
Thu Jun 30, 2022 8:31 pm
LouiseScot wrote:
Thu Jun 30, 2022 7:38 pm
Have you actually got a Kohler setup?
Yes, both AO 120 and Nikon Optiphot have field and condenser apertures,
as well as lamp and condenser focus and centering provisions.
The lamp wants centering when replaced
but refocus with each objective change, which is done looking at objective back
(or reprojected image of objective back for infinity objectives)
with ocular removed, while adjusting condenser aperture.
Although some instructions say to remove the ep it's not absolutely necessary to do so. After first focusing objective on the slide, next - reduce field diaphragm so that only a smallish circle of light is visible. Next - centre that circle using condenser adjusters. Then adjust condenser height to focus (as best as possible) on the visible edge of the field diaphragm. Lastly, open diaphragm to be just bigger than the field you can see through the ep. It's just a judgement which isn't difficult to do without taking the ep out. Repeat each of the steps if you change objective.

ps you probably want the condenser aperture diaphragm wide open from the start. As mentioned, it doesn't come into the actual Kohler adjustment!

Louise
A Nikon CF plan 20x; A Swift 380T; A DIY infinity corrected focus rail system with a 40x/0.65 Olympus Plan, a 10x/0.30 Amscope Plan Fluor, and a 20x/0.75 Nikon Plan Apo

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Re: Kohler Illumination

#22 Post by GerryR » Fri Jul 01, 2022 1:05 am

My old AO Sixty doesn't have a field diaphragm so I made a fixed hole diaphragm that slips over the light source and is dead-center to the source (I have a lathe, milling machine, etc. so not a big deal.) The hole in the "diaphragm" is 1.5mm. When looking at it with the 10X objective, the hole edge is sharp once the the condenser is focused, and covers about 1/2 the field of view. I changed to the 20X objective and can see the slightest shadow in the lower right field of view, indicating the objective is slightly off center from the 10X objective. There are no centering screws for the condenser, but using a pointed object over the source, the condenser is focused in the same location as the 10X objective. The 1.5 mm hole is the smallest diameter most iris diaphragms go, which is why I chose that size for my fixed field "diaphragm." How can you then focus on the field diaphragm with the higher powered objectives if the field of view is narrower than what the 1.5mm hole is projecting. I know I must be missing something, but I don't know what. I'd like to see a video that goes through the Kohler process with something higher than the 10X objective that everyone seems to use, perhaps a 40X or 100X.

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Re: Kohler Illumination

#23 Post by LouiseScot » Fri Jul 01, 2022 1:39 am

GerryR wrote:
Fri Jul 01, 2022 1:05 am
My old AO Sixty doesn't have a field diaphragm so I made a fixed hole diaphragm that slips over the light source and is dead-center to the source (I have a lathe, milling machine, etc. so not a big deal.) The hole in the "diaphragm" is 1.5mm. When looking at it with the 10X objective, the hole edge is sharp once the the condenser is focused, and covers about 1/2 the field of view. I changed to the 20X objective and can see the slightest shadow in the lower right field of view, indicating the objective is slightly off center from the 10X objective. There are no centering screws for the condenser, but using a pointed object over the source, the condenser is focused in the same location as the 10X objective. The 1.5 mm hole is the smallest diameter most iris diaphragms go, which is why I chose that size for my fixed field "diaphragm." How can you then focus on the field diaphragm with the higher powered objectives if the field of view is narrower than what the 1.5mm hole is projecting. I know I must be missing something, but I don't know what. I'd like to see a video that goes through the Kohler process with something higher than the 10X objective that everyone seems to use, perhaps a 40X or 100X.
It's well past my bedtime but I just checked on my T720 and the diaphragm goes down to about 1.5 - 2mm (hard to measure exactly). You may need to turn the brightness down. I can certainly see it as a fairly small opening with a 40x objective. You need to be able to centre the condenser so that the diaphragm aperture is close to the centre of the object field seen via the objective otherwise you can't really then open it up to just fill the field with the illumination. You might be able to approximate it, I'm not sure. I mean, if you can't do it properly then maybe there's little to be gained? Kohler isn't essential to view things but it should give more even illumination for imaging. Oh, another thing may be the distance of your field 'diaphragm' from the condenser aperture diaphragm. Again, difficult to measure on my 720 but it's about 70mm. The field diaphragm assembly on my T720 looks very similar to the Euromex iScope part I linked to above. I don't know how easy (or not!) it might be to fit to your scope. Failing that, you can buy iris diaphragms quite cheaply and one could make a suitable diy housing for it. Maybe you could also upgrade your condenser too? It really is necessary to be able to centre the field diaphragm via the condenser.

Louise
A Nikon CF plan 20x; A Swift 380T; A DIY infinity corrected focus rail system with a 40x/0.65 Olympus Plan, a 10x/0.30 Amscope Plan Fluor, and a 20x/0.75 Nikon Plan Apo

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Re: Kohler Illumination

#24 Post by LouiseScot » Fri Jul 01, 2022 11:21 am

I made a quick video showing Kohler adjustment using a 40x objective. It's not brill as my eyesight is not great these days... So when I say focus on the slide you should do it better than I did...

Anyway, hope this is useful:

https://www.youtube.com/watch?v=QFjEwiw2yEY

I've noted the basic steps again with the YouTube info. There is a little vignetting with the Canon 1100d but obviously that's not present when viewing via the EPs 8-)

Louise
A Nikon CF plan 20x; A Swift 380T; A DIY infinity corrected focus rail system with a 40x/0.65 Olympus Plan, a 10x/0.30 Amscope Plan Fluor, and a 20x/0.75 Nikon Plan Apo

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Re: Kohler Illumination

#25 Post by GerryR » Fri Jul 01, 2022 1:04 pm

Well Louise, thank you for all your efforts! I didn't mean for anyone to lose sleep over this. :) There is no way for me to get results like you have shown on anything higher than the 10x objective. I have adjusted the height through its entire range, about 5mm, and the condenser diaphragm is only about 18mm above the field diaphragm, so not much room. As this was a student microscope, I expect that it must have been "optimized" for no adjustment. In fact, when looking through the manual again, it actually states that the condenser height should not be adjusted as it has been factory adjusted. Their propaganda goes like this: "Modern AO microscopes with built-in illuminators eliminate the necessity for refocusing the substage condenser for all routine Bright-Field illumination through the complete range of magnification. Provision is made, however, for adjustment of condenser height for any unusual requirements." (You know, when all else fails, read the directions!) So I doubt there is enough room to incorporate true Kohler adjustments.
Again, thank you Louise for your efforts (get some sleep!) and others for your inputs. I guess I will have to just live with this "optimized" scope for now.

LouiseScot
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Re: Kohler Illumination

#26 Post by LouiseScot » Fri Jul 01, 2022 1:24 pm

GerryR wrote:
Fri Jul 01, 2022 1:04 pm
Well Louise, thank you for all your efforts! I didn't mean for anyone to lose sleep over this. :) There is no way for me to get results like you have shown on anything higher than the 10x objective. I have adjusted the height through its entire range, about 5mm, and the condenser diaphragm is only about 18mm above the field diaphragm, so not much room. As this was a student microscope, I expect that it must have been "optimized" for no adjustment. In fact, when looking through the manual again, it actually states that the condenser height should not be adjusted as it has been factory adjusted. Their propaganda goes like this: "Modern AO microscopes with built-in illuminators eliminate the necessity for refocusing the substage condenser for all routine Bright-Field illumination through the complete range of magnification. Provision is made, however, for adjustment of condenser height for any unusual requirements." (You know, when all else fails, read the directions!) So I doubt there is enough room to incorporate true Kohler adjustments.
Again, thank you Louise for your efforts (get some sleep!) and others for your inputs. I guess I will have to just live with this "optimized" scope for now.
Oh well. Obviously adjustments have to be possible - as is the case on many scopes. But it sounds like there would be no real benefit on your one anyway. At the end of the day Kohler is just the icing on the cake if you need to have fine illumination control. For most usage you don't really. The Amscopes I bought recently are the first ones I've owned personally that have a built in Kohler capability. 12-13 yrs ago I was doing research using an Olympus BX with water immersion objectives and Infra Red DIC, as well as laser scanning confocal imaging, so fine adjustments were quite important in those cases!
If you get another microscope you might consider one with Kohler :)

Louise
A Nikon CF plan 20x; A Swift 380T; A DIY infinity corrected focus rail system with a 40x/0.65 Olympus Plan, a 10x/0.30 Amscope Plan Fluor, and a 20x/0.75 Nikon Plan Apo

Greg Howald
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Re: Kohler Illumination

#27 Post by Greg Howald » Fri Jul 01, 2022 6:20 pm

Hi Louise,so... between the 680 and the 720, which comes out on top? Greg

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Re: Kohler Illumination

#28 Post by LouiseScot » Fri Jul 01, 2022 6:44 pm

Greg Howald wrote:
Fri Jul 01, 2022 6:20 pm
Hi Louise,so... between the 680 and the 720, which comes out on top? Greg
Well I've hardly used either yet... I bought the 720Q because it's an infinity scope, has Kohler illumination and a quintuple nosepiece. The 680 is a finite scope also with Kohler. Both scopes are trinocular. The 720Q has LED illumination. The 680 is 20W halogen but I upgraded it to be able to use both halogen and LED via an external psu. Amscope US had sent me a version which expected US mains input... The 720Q I got quicker with a lucky discount and without import duty from Amazon UK (in the Netherlands...) so it was overall better value for money. Build quality of both is about what you'd expect from Amscope... Both scopes use standard 45mm parfocal RMS thread objectives. Plan achromats x5 on the 720Q, Ordinary achromats x4 on the 680 (which I upgraded to two from the Swift 380T and Nikon Plan Fluors - 40x and 100x. Not much else to say that I can think of.

Louise
A Nikon CF plan 20x; A Swift 380T; A DIY infinity corrected focus rail system with a 40x/0.65 Olympus Plan, a 10x/0.30 Amscope Plan Fluor, and a 20x/0.75 Nikon Plan Apo

Dubious
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Re: Kohler Illumination

#29 Post by Dubious » Sat Jul 02, 2022 5:31 am

LouiseScot wrote:
Thu Jun 30, 2022 8:14 pm
Here is Omax upgrade version:
https://omaxmicroscope.com/microscope-a ... tment.html

Seems expensive for what it is. I'm sure there must be others around.
There is one available for the Euromex iScope:

https://www.astroshop.eu/condensers/eur ... r_0_select

Louise
It's interesting that Omax and Euromex sell add-on field diaphragms--apparently someone thinks Kohler illumination is worthwhile even on lower end scopes. A pity, though, they didn't just incorporate a field diaphragm into the original design. Probably would have added all of $5 to the manufacturing cost...

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blekenbleu
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Re: Kohler Illumination

#30 Post by blekenbleu » Sat Jul 02, 2022 12:04 pm

Dubious wrote:
Sat Jul 02, 2022 5:31 am
It's interesting that Omax and Euromex sell add-on field diaphragms--apparently someone thinks Kohler illumination is worthwhile even on lower end scopes. A pity, though, they didn't just incorporate a field diaphragm into the original design. Probably would have added all of $5 to the manufacturing cost...
A field diaphragm improves image contrast by blocking stray light,
which may be more problematic in lower end scopes.
If, as it seems, these diaphragms are added between field lens and condenser,
then they cannot be at an illumination focal plane unless extra lenses are also involved.
Metaphot, Optiphot 1, 66; AO 10, 120, EPIStar, Cycloptic

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