A Choanoflagellate and Lacrymaria

[Pau]

David, thanks for the follow-up.

In base on your observations I tend to think that the fly eye lens is acting as the light source for Köhler in place of the lamp filament or LED, as this would explain its tolerance to the lamp position and could explain its function of providing even illumination not explained at the Nikon papers I've seen.

Any other ideas out there?

[viktor j nilsson]

David,

Really nice setup, many thanks for sharing. Interesting to see how Nikon has implemented the fly's eye lens - quite different from what I'm used to. Clearly works well! And I can see that it actually makes this type of dual illumination setup easier: as long as most of the light hits the fly's eye lens, you're golden.

I agree that the fly's eye lens acts as the light source. But I'm curious: how large area of the the fly's eye lens can you see at the back focal plane? And how much of it is illuminated? The fly's eye lens looks pretty big - if you're seeing a large part of it at the BFP, the optics of the light train must be quite different from that of classical Kohler systems like my Vanox AH, that projects a 3x3mm filament at the back focal plane.

[dy5]

I found a little bit more information from Nikon on the fly-eye illumination system. Still not much detail on the optics.

It looks like just the central region of the array, not all the lenses. With the condenser adjusted, the lens array fills the BFP and the many images of the filament are in focus. The flash has a 'model light' for constant illumination, and the LED source is also in focus at the BFP.

[Pau]

Thanks again for the further info, I still can't find the last figures document online but it has pointed me to the patent documents where it seems better explained
https://patents.google.com/patent/US6507434B2/en with one fly-eye lens and one diffuser
and
https://patents.google.com/patent/US20030223108 with two fly-eye lenses like in your 80i and 90i pictures allowing to change the distance between both lenses to change the focal length of the system.

It seems that basically I was right, well, few millimeters close

[tjlmicro]

One thing I have wondered about in relation to the last 2 comments. If you set up Kohler illumination carefully with the lamp filament in focus but then put a diffuser in the light path to produce a more uniform field of illumination, what difference does it make to be sure that the lamp filament is in focus? I have an LED lamp on my Zeiss Photomicoscope III and I don't know that I can actually focus on a "lamp filament". It doesn't seem to matter and I have excellent. even illumination. Is there something I am missing?

Tim

[dy5]

Pau -

Great find with the patent documents. Very interesting.

The source of the last figures was a Nikon internal sales manual, probably from the early 2000s. I can't remember where I got it, but would be happy to send a pdf to anyone interested. Just PM me your email address.

Cheers, David

[Pau]

One thing I have wondered about in relation to the last 2 comments. If you set up Kohler illumination carefully with the lamp filament in focus but then put a diffuser in the light path to produce a more uniform field of illumination, what difference does it make to be sure that the lamp filament is in focus? I have an LED lamp on my Zeiss Photomicoscope III and I don't know that I can actually focus on a "lamp filament". It doesn't seem to matter and I have excellent. even illumination. Is there something I am missing?

Tim

I mostly use Zeiss Standard 16,18 and WL scopes, so the situation could be close to the big stands of the same era.
I find that getting "true" Köhler illumination without diffusers is pretty tricky. They put opal glass diffusers in different places of the light train, in some cases removable. For high magnification I prefer to use a configuration without diffusers despite being more difficult to set-up while for low magnification the diffusers help a lot, and the use of the sub condenser lens also helps (and for very low magnification the use of a piece of paper over the light base or a low power "lupen condenser" for Luminars are the best option to have even illumination)


I think that a strong diffuser acts as the actual light source while a weak opal glass placed close to the lamp like in 60 and 100 lamp houses produces some kind of intermediate situation