Looking at opaque objects with compound microscope

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jm1234567890
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Looking at opaque objects with compound microscope

#1 Post by jm1234567890 » Wed Jul 20, 2022 6:04 am

I tried searching online but didn’t find the answer to this question.

Why can’t you look at opaque objects with a compound microscope at high magnification? Is it because the focal plane is very narrow? It is hard to light the object when it is so close to lens? Or some other reason?

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woyjwjl
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Re: Looking at opaque objects with compound microscope

#2 Post by woyjwjl » Wed Jul 20, 2022 6:43 am

The question is unexpected. :?

Can opaque objects glow?
Micrographers from China, thanks to the forum for providing a platform for exchange

Adam Long
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Re: Looking at opaque objects with compound microscope

#3 Post by Adam Long » Wed Jul 20, 2022 8:25 am

You can, but you need epi-illumination which means the light comes from the top through the same objective used for viewing.

Yes, the focal plane and working distances become very limited, but in my experience it can be more user friendly at higher mags than working with water-on-slide mounts and trans-illumination. This is for two reasons - if it is truly opaque you are just looking at the top surface rather than seeing an optical section, and the issue of spherical aberration is less obvious as there is typically no cover glass or mounting fluid between the subject and objective. Epi objectives are corrected for use like this, but for the highest NA (>0.9) you still need oil.

Generally the flatter the object, the easier it will be to get a good view. Due to the lighting method reflective surfaces can be problematic so crossed polarisers are often used.

Scarodactyl
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Re: Looking at opaque objects with compound microscope

#4 Post by Scarodactyl » Wed Jul 20, 2022 4:26 pm

Through-lens epi works great at high magnifications--the limitations apply more to oblique illumination which is very dependent on working distsnce to be able to get light in. It is much harder but actually possible to get high quality images at fairly high magnifications up to around 50x. As an example Olympus has a 50x/0.80 fluor objective for metallurgical use with 1mm working distance which produces a great image and has just enough space to squeeze in some outside light depending on the shape of the subject. Or there's always the mitutoyo 50x/0.75 with like 5mm working distance if you have bottomless pockets. But once you're at 100x your options are very limited, since a dry 100x will already be resolution deficient and making it a longer working distance makes that a lot worse. But at that scale and resolution epi illumination works great and seems to sometimes give less flat results, perhaps because the high NAs are sampling a wider range of light angles.

jm1234567890
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Re: Looking at opaque objects with compound microscope

#5 Post by jm1234567890 » Wed Jul 20, 2022 8:13 pm

Thanks for the info!

J_WISC
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Re: Looking at opaque objects with compound microscope

#6 Post by J_WISC » Tue Aug 09, 2022 2:44 am

Hello.

Here's the back of a Stinging Nettle leaf photographed through a compound microscope.
life_on_nettle_10x_1916.jpg
life_on_nettle_10x_1916.jpg (73.28 KiB) Viewed 1683 times
This is the first time I tried it. I used an eyepiece camera (in place of ocular), a 1916 Spencer Buffalo compound microscope, and a 16mm 10x objective. I used a gooseneck LED desk lamp for light (just acquired and tried on a whim after asking questions about substage lighting). I believe the field is about 0.6 mm across.

Here's the same leaf through a stereo microscope, 3x magnification.
life_on_nettle_A.jpg
life_on_nettle_A.jpg (92.51 KiB) Viewed 1683 times
I'm definitely going to try more side illumination using the compound microscope. The challenge might be the objective blocking the preferred angle of lighting. But the Spencer I have has a rotating stage and the original 10x objective has good working distance. 10x might be the limit for me.

Chas
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Re: Looking at opaque objects with compound microscope

#7 Post by Chas » Tue Aug 09, 2022 9:54 am

1916...How nice to see :-)
Those little creatures look like they could be quite photogenic too.
(Have you tried pulling out the drawtube to get a bit more magnification ?)
If the creatures are a bit glass-like then dangling a bit of white bin-liner between the LED light and the stage can help get rid of some sparkling.

It is a big jump between 16mm and 4mm ... and the issue with 4mm is not so much sufficent light but having a leaf or whatever that is flat enough (without stingers!) so as not to be pushed by the objective as you focus down.
Old english 8mm objectives are not that uncommon ... Others will know about old Spencer objectives.

EDIT I have just had a go on a nettle leaf with an 8mm and it only just allowed me to see the leaf-surface texture without pushing down on the hairs of the midrib and sadly the depth of focus is very minimal, so maybe sticking with your max 10x is wise !

Here is an 8mm focussed on the leaf's surface:
Attachments
8mm objective focussed on leaf surface 800.jpg
8mm objective focussed on leaf surface 800.jpg (66.27 KiB) Viewed 1562 times

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