Re: Köhler illumination question...

Hi Gregor,

Both "etched.jpg" and "other.jpg" were recorded with a Nikon Coolpix
5000 mounted on a Leica M420 with a 2X suplemental objective. I used
oblique incident illumination from a single fiber optic cable. The
nominal magnification at the camera is about 60X. but that is not
valid once it is displayed on a computer screen.

The point is that both of these "filters" appear similar to the eye;
what we describe as "frosted filters". I agree that the surface of
the "fliter" ought to have bearing on the character of the lighting.

Etched.jpg is the image of the element just in front of the halogen
lamp in the Zeiss 100W lamphouse. This is the element that is swung
into place after the procedure for Kohler illumination is performed.

Other.jpg is an image of a 32mm filter that might be placed in the
well over the field diaphragm or in a filter tray below the condenser
on a Zeiss Standard series microscope.

I have since located some ground surface filters and a sandblasted
glass slide. These are different still. I will try to collect some
more examples. I have much more sophisticated equipment to examing
the surfaces. If this becomes a matter of greater curiosity I may
image these and post them.

Aaron

On Mon, 02 May 2005 01:23:54 GMT, "GTO" <gregor_o@xxxxxxxxxxxxxxx>
wrote:

>Hello, Aaron:
>
>Thanks a lot for these images. This is really interesting stuff!
>
>Your image from an uncolored glass filter reminds me of investigations of
>amorphous materials with AFM (such as amorphous metals). The features on
>this glass filter might be so small that their impact is negligible for
>light microscopy applications.
>
>However these structures of approx 0.01-0.05 mm in diameter on the element
>in your 100W Zeiss lamp most certainly impact the light that passes through
>them. What is the technique you used to obtain this very informative image?
>
>Great work! I think that we just started to find an interesting aspect,
>which is very important for the implementation of a well working
>illumination.
>
>We most certainly should more clearly define "frosted" vs. "edged" vs. other
>surface treatments that might appear like "frosted".
>
>What would be interesting to see, is an image of a frosted glass.
>
>Thanks,
>
>Gregor
>
>
>"Aaron" <nghy@xxxxxxxxxxx> wrote in message
>news:qlna71p6ema6tb9cg2poa5c0345q7hp0qc@xxxxxxxxxx
>> Hi Gregor,
>>
>> It sure looks like it. I just posted a response to Klaus which I will
>> tag on here so you don't have to hunt for it.
>>
>> Hello Klaus and friends,
>>
>> The minute I read your post, I could not wait to see the "frosted
>> element" under magnification.. Indeed I found things as you said.
>> I started to look at other Zeiss filters. They are not what might be
>> expected either. We need to review and define the terms "diffuser"
>> and "frosted element".
>>
>> The "element" in the Zeiss 100W lamp house has the little lenses
>> etched into the surface. These are approx 0.01-0.05 mm in diameter
>>
>> http://home.comcast.net/~nghy/mywebpages/test/etched.jpg
>>
>> In comparison I imaged an "uncolored glass" filter. The pattern has
>> recular undulations, minute bubbles and wrinkles. Toatally
>> unexpected.
>>
>> http://home.comcast.net/~nghy//mywebpages/test/other.jpg
>>
>> I expected to see something similar to the sand blasted edge found on
>> slides that have a random faceted appearance.
>>
>> Aaron
>>
>>
>>
>>
>> On Sun, 01 May 2005 05:28:57 GMT, "GTO" <gregor_o@xxxxxxxxxxxxxxx>
>> wrote:
>>
>>>Einen schönen guten Morgen!
>>>
>>>
>>>
>>>Excellent point! This could explain some new designs that are recently
>>>sold.
>>>One example is the fly-eye optics design by Nikon (see Eclipse 80i), which
>>>are used to ensure even illumination.
>>>
>>>
>>>
>>>I just looked at the Leitz Ortholux lens in the illuminator, and although
>>>it
>>>looks like a "frosted" lens at first sight, it is possible that also Leitz
>>>created the mat surface using a similar process (?). How big are these
>>>bowl-like concave hollows in the lens-surface?
>>>
>>>
>>>
>>>Nette Grüsse aus Kalifornien,
>>>
>>>
>>>
>>>Gregor
>>>
>>>
>>>
>>>...
>>>> reading your qestions to Andy Resnick and earlier contributions in
>>>> this thread, it seems to me, the term "frosted" does not take into
>>>> account properly, that the first lens-surface of some Zeiss
>>>> lamp-collectors ist not ground. Its mat surface is achieved by
>>>> hydrofluoric acid, which leaves thousands of little bowl-like concave
>>>> hollows in the lens-surface. They are of different diameters, but all
>>>> of the same focus-width - tiny concave lenses on the surface of a
>>>> concave lens.
>>>>
>>>> The result is, that light-rays are not being scattered in all
>>>> directions, as would be the result of a simple ground glass, but the
>>>> light beams entering the first collector lens, are just "widened" and
>>>> defocussed, changing the image of the lamp filament into a homogeneous
>>>> image, mixed together out of thousands of little lenses. This design
>>>> does not fully destroy the definition of the field diaphragm.
>>>>
>>>> Frosted in that special way the lighting force is reduced about
>>>> 20-40%; that is not much, compared with reduction of 60-80% through a
>>>> normal ground glass.
>>>>
>>>...
>>>
>>
>

.

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