DIY High N.A. Oblique Illumination Filter

[Suphot]

After I made Gradient Universal Filter (GUF) and use it for a while for Oblique Illumination, it is not work very well with High N.A. Objective (40X and Higher). So I try to improve it to use with High N.A. 40X and 60X dry Objective that I have.

Pic 1. GUF Filter size that I made by stacking 4 layers of Transparency and use PVC electric tape on left hand side. For more details How to make GUF Filter, please follow this link;
viewtopic.php?f=28&t=5449

[Suphot]

I found that, if I remove the Gradient area from the GUF filter, by cut the Black Poster paper in to “L” shape like this. It seem to work well for Oblique Illumination with 40X and 60X Objective.

Pic 2. Oblique Filter size, cut from Black Poster paper. The edge of cut paper is white, So I reduce scattering light at the edge by painted it all sides with black pen.

[Suphot]

Using this Oblique Illumination Filter is the same way as GUF Filter. It is a trial and error approach, first step you have to fully open the condenser diaphragm and slide the filter in to the condenser filter tray. Then slide back and forth, Left and Right until you get the optimum result. You may close microscope condenser diaphragm to improve the contrast.

When you change Objective lens, you have to adjust the position of Filter again, little by little. For the microscope that I used (it is OEM AmScope from China), this filter work very well with my 20X, 40X and 60X Dry Objective.

This is example of small water droplet under cover slip that I use to show effect of this filter from 20X, 40X and 60X Objective.

[Suphot]

Pic 3. Show 20X Objective Bright Field image (Total Magnification is 200X with 10X Eyepieces).

[Suphot]

Pic 4. Show 20X Objective with Oblique Illumination Filter (Total Magnification is 200X with 10X Eyepieces).

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Pic 5. Show 40X Objective Bright Field image (Total Magnification is 400X with 10X Eyepieces).

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Pic 6. Show 40X Objective with Oblique Illumination Filter (Total Magnification is 400X with 10X Eyepieces).

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Pic 7. Show 60X Objective Bright Field image (Total Magnification is 600X with 10X Eyepieces).

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Pic 8. Show 60X Objective with Oblique Illumination Filter (Total Magnification is 600X with 10X Eyepieces).

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Note: This small water droplet is very difficult to see under Bright Field Illumination. It is colorless and small under cover slip in my wet mount sample. It is easier to see when using the Oblique Illumination Filter and make the droplet look 3D Image.

All photo samples above made by Afocal Photography, using my smart phone take photo at the eyepiece with home made adapter. Sorry for some photo that did not snap in to perfect focus.

I hope you enjoy trying this filter, it is cheap, very easy to make and work well for high N.A. up to 60X Dry Objective. By the way I am not try this filter with 100X Oil Objective. Because I remove it from microscope and replace by 60X Dry.



Suphot

[Rossf]

Great post Suphot ! Will try this-for some reason I’m getting a collection of 60x-70x objectives the last few months…
Regards ross

[MichaelG.]

Pic 4. Show 20X Objective with Oblique Illumination Filter (Total Magnification is 200X with 10X Eyepieces).

That shot, in particular, shows the benefit of oblique illumination quite beautifully !

One unfortunate ‘side-effect’ [please forgive the pun] is that the technique introduces chromatic aberrations.
… this is almost certainly inevitable

MichaelG.

[Suphot]

Thank You very much for your comment Ross, I hope it work well for your Objective. Please share your result if it is available.


Thank you very much for your comment MichaelG. My microscope has simple Abbe condenser, it clearly show Chromatic aberration that you saw in the picture. I just don't know if the condenser is Apochromatic, can it reduce Chromatic aberration in Oblique Illumination or not. Someone who have it may try to see.


Cheers,


Suphot.

[Sansub2]

Suphot, you are awesome. I have seen the GUF filter but never got to try it given I didn't have a way to create that gradient. Tried many different Oblique patches. Your idea is the simplest one and remove many different patches I have. It is simple to create and use. It only took 5 minutes to create band here is the sample. I tried it in 4, 10, 20 and 40 and all came beautifully. Bonus is, the same sheet can create dark field as we at lower power.

Max resolution view is best..


I am waiting for my WI 40x. Hope it will work even more beautifully.

[Sansub2]

Here is output by combining this Oblique with DIY CPL. 40x acromat on AMScope microscope. Given the budget level microscope and with simple DIYs, the output seems very nice.

See it in high res for best result...

[Suphot]

Thank you very much for your comment and video, Sansub2.

Your video is beautiful sample, I can see detail inside Paramecium clearly.
I'm glade to hear that this Oblique filter work well with your microscope.

Hopefully it work well with your WI 40X.


Cheers,

Suphot.

[Sansub2]

Thanks Suphot. I have posted more videos in this link below.

viewtopic.php?t=15221

[Suphot]

Very beautiful video Sansub2, the 2nd video which has blue background is very nice.


cheers,


Suphot.

[Rudi Venter]

That shot, in particular, shows the benefit of oblique illumination quite beautifully !

One unfortunate ‘side-effect’ [please forgive the pun] is that the technique introduces chromatic aberrations.
… this is almost certainly inevitable

MichaelG.

I agree the chromatic aberration is an unfortunate biproduct but it can be removed during post processing in images. I always take images in RAW format and process in Adobe Lightroom where the chromatic aberration can be removed with a click.