Oblique filter suggestions

Here you can discuss different microscopic techniques and illumination methods, such as Brightfield, Darkfield, Phase Contrast, DIC, Oblique illumination, etc.
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Plasmid
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Oblique filter suggestions

#1 Post by Plasmid » Sat Nov 07, 2020 7:32 am

I started to experiment with substage filters, so far my success rate has been disappointing. I've order some filters from ebay but they just fall right out of the filter holder, my 1970 abbe condenser is supposed to be 32mm in diameter If I recall correctly, so instead I started to make my own filters. Im looking to get a sort of 3d effect sort off like a poor mans phase contrast and so any recommendations would be appreciated as far as the material , but mostly in ways to shape/cut the filters.
This video was taken with one of the filters I was able to get an effect from.
https://youtu.be/9YCZ5k-ksBI

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janvangastel
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Re: Oblique filter suggestions

#2 Post by janvangastel » Sat Nov 07, 2020 7:38 am

This is clearly oblique illumination. It works best, in my experience, with medium magnifications. I use my 25 and 40 m objective most of the time with this kind of illumination. With my orthoplan, the 10 mm objective does not work for oblique illumination and my 63 mm does work, but is somewhat more difficult. In all cases, less then a millimeter more or less light can make a relevant difference.

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Re: Oblique filter suggestions

#3 Post by Plasmid » Sat Nov 07, 2020 1:44 pm

With oblique Illumination, is there a light source aside from the substage light? , I've seen pics on some of the threads where a secondary light source is used.

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Re: Oblique filter suggestions

#4 Post by rnabholz » Sat Nov 07, 2020 2:44 pm

Here is the approach that I used.

Very pleased with the results

viewtopic.php?t=4653

Rod

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Re: Oblique filter suggestions

#5 Post by Plasmid » Sat Nov 07, 2020 3:47 pm

So far these are the one I've made, the material used was plastic from kitchen Tupperware, The only one that has given me a decent effect is the yellow one with the half moon cut, and so I wonder if there is a certain pattern or design that is more prominent in giving the oblique look. Also I question the material Im using, is there supposed to be any light going through or does it have to be completely obscured on the rest of the filter?

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Re: Oblique filter suggestions

#6 Post by Greg Howald » Mon Nov 09, 2020 1:05 pm

Oblique filters are usually made with opaque materials.
What you have done looks good. So far as design or shape of the filter is concerned I found that the shape which worked depends upon the scope. I made a set for one scope which worked well but would not work on a different scope. I think it has to do with the intensity of light and the design of the optics as in the type of illumination and design of the condenser lens. You did a good job with what you have done.
Mike Swartz has published a book on the making of Rheinberg and oblique filters and I used that to design what I have. It is available on kindle. Some things work well in my Amscope B340 with led lighting, but have little or no effect with my Amscope B660 with its halogen lighting and I haven't solved that yet.
Many of the people in the forum are experts. I'm not.
I have to do things by trial and error but have been rather successful with it so far.
I like the design of your yellow filter. I'll have to try that.
Good luck with it.
Greg

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Re: Oblique filter suggestions

#7 Post by Greg Howald » Mon Nov 09, 2020 1:25 pm

Check out the post "Oblique Masks" under the topic in "home made adaptations". I think you will find this very helpful. Greg

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Re: Oblique filter suggestions

#8 Post by Crusty » Sat Dec 05, 2020 7:21 pm

I can sometimes achieve obliqued-ness by setting the phase contrast condenser between stops. This is photo is 40x and the condenser set between 0 and 10 (Olympus BH2 BHTU setting). The same setting using the 20x objective gets me to dark field.

https://www.smugmug.com/app/organize/Mi ... /i-f6JJdhD

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Re: Oblique filter suggestions

#9 Post by MicroBob » Sat Dec 05, 2020 8:55 pm

Hi,
oblique lighting is a bit fiddly to set up and difficult to repeat. This and the fact that it tends to introduce arifacts probably lead to the low use in professional science work today.
I use what is at hand, often the filter holder or one of my fingers. I heard that decentering an auxillary lens gives an especially good effect.
More difficult it is with circular oblique lighting, where only the outer rays are used but all around. For this I made an acrilic glass disc with a small brass centering pin and aluminium discs of different sizes that can be fitted on it.

Bob

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75RR
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Re: Oblique filter suggestions

#10 Post by 75RR » Sun Dec 06, 2020 6:14 am

MicroBob wrote:
Sat Dec 05, 2020 8:55 pm
Hi,
oblique lighting is a bit fiddly to set up and difficult to repeat. This and the fact that it tends to introduce arifacts probably lead to the low use in professional science work today.
I use what is at hand, often the filter holder or one of my fingers. I heard that decentering an auxillary lens gives an especially good effect.
More difficult it is with circular oblique lighting, where only the outer rays are used but all around. For this I made an acrilic glass disc with a small brass centering pin and aluminium discs of different sizes that can be fitted on it.

Bob
I have found that COL (circular oblique lighting), once one has found the matching rings for each objective to be used, is much more consistent than most other forms of oblique. I find it quite effective on diatoms.
For this I made an acrilic glass disc with a small brass centering pin and aluminium discs of different sizes that can be fitted on it.
Do you have a link to your COL rings and where you place it? I must have missed it.
Zeiss Standard WL (somewhat fashion challenged) & Wild M8
Olympus E-P2 (Micro Four Thirds Camera)

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Re: Oblique filter suggestions

#11 Post by MicroBob » Sun Dec 06, 2020 11:32 am

Hi Glen,
I dug this out for you. The aluminium discs are from 0,4mm foil, punched out with an expensive french double punch set on a piece of wood end grain.
Oblique and COL are probably let down by their improvised use. If one would dedicate a turret condenser with stops for specific objectives just for this task, repeatability would be vasty increased.

Bob
Attachments
COL (Circular oblique lighting) Set.jpg
COL (Circular oblique lighting) Set.jpg (154.37 KiB) Viewed 1145 times

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75RR
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Re: Oblique filter suggestions

#12 Post by 75RR » Sun Dec 06, 2020 6:06 pm

.
Thanks for posting that. Like the idea. I take it you are using the diaphragm to provide the outer opaque ring. Do you place it in a filter holder?

Dedicated rotary COL condenser sounds pretty good too.
Zeiss Standard WL (somewhat fashion challenged) & Wild M8
Olympus E-P2 (Micro Four Thirds Camera)

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Re: Oblique filter suggestions

#13 Post by MicroBob » Sun Dec 06, 2020 7:11 pm

Yes, I placed it in the filter holder unter the condenser. When I place one of the aluminium discs on the acrylic glass disc I get a hollow cone of light from the gap between outside aluminium disc and inside filter holder. These filter holders are placed not alike. The position doesn't matter much for a green or pol filter but it does matter for these stops. So some microscopes are better for use with COL this way than others. Using a phase condenser should eliminate many questions.

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