The improper use of a condenser with swing out lens. An observation.

[The QCC]

The linked presentation shows the relationship between the condenser, resolution and contrast when the condenser is improperly used.
The microscope is a Labomed polarizing unit with swing out condenser and field diaphragm.
The condenser with the swing out lens in place has a N.A. of 1.15 and a N.A. of 0.9 when swung out.

The subject, a rock thin section, was photographed using a 10x and 40x obj.
The camera / microscope / objectives were set up with Kohler illumination, the top condenser lens in place and the condenser aperture stopped down approximately 50% to achieve good, but not excessive contrast. The standard setup for higher power obj.

If no settings are changed except the top condenser lens is swung out, the contrast increases sharply and resolution falls like a stone.
The result is similar to stopping down the condenser aperture too much with a condenser without a swing out lens.

Click the image to see the photo presentation.

Ruble_13_5MLX_40x_04_NoTopCon.jpg (85.86 KiB) Viewed 4894 times

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Edit: The titled was edited by the author.

[Crater Eddie]

Very interesting presentation. The difference in the image is obvious when presented in this way.
CE

[billbillt]

Yes, I am glad someone did this... Makes a person think about it while in use...

[jwsmith]

I have an American Optical scope with swing-out condenser lens and no field diaphram.
The light source has a swing-out lens.

The scope condenser does have a diaphram.

I am (have always been) uncertain why my scope is so-configured.
Experimentation (combined/single use of these features) has not led me to any clear conclusions as to use/advantage.

Comment?

Judd

[The QCC]

Judd:
I am not familiar with AO microscopes with light source swing out lens, but I can tell you what the condenser and its aperture do in a not very technical way.

When you are using a low power objective, one less than 10x, the condenser lens should be OUT. when using a higher power obj, 10x and above, the condenser lens should be IN.
The condenser creates a light cone that illuminates the specimen and the obj. field of view. The swing out lens adjusts the light cone to match the higher power objects narrower field of view.
The photos in my presentation show what happens when the swing out lens is in the correct and wrong position.

Without a field diaphragm in the light source, the condenser aperture is also used to adjust the light illuminating the specimen and obj. The aperture also has the effect of increasing contrast and resolution. The latter can be overdone resulting in loss of resolution.

Edit: Added sample images
4x obj. Top condenser out, aperture set to N.A. .5

Top condenser lens OUT

SilconTaconite_5MLX_4x_01_NA.5TCO.jpg (219.4 KiB) Viewed 4856 times

4x obj. Top condenser lens IN N.A. .1

Top condenser lens IN

SilconTaconite_5MLX_4x_02_NA.1TCI.jpg (258.98 KiB) Viewed 4856 times

10x obj. Top condenser lens IN, aperture set to N.A. .3

Top condenser lens IN

SilconTaconite_5MLX_10x_04_NA.3TCI.jpg (174.66 KiB) Viewed 4856 times

10x ob., Top condenser lens OUT. aperture set to N.A. .9

Top condenser OUT

SilconTaconite_5MLX_10x_05_NA.9TCO.jpg (251.97 KiB) Viewed 4856 times