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Invisiblefastfred
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Darkfield microscopy!
    #6456833 - 01/13/07 10:01 PM (17 years, 4 months ago)

Ok, so I was looking to get a darkfield stop for my Olympus CH30. I found a few but the price was too high, so I decided to try making my own from the pictures.

I edited images of the stop and then printed them out. Then I cut them out with a razorblade and inserted one just above the filter.

It is SO awesome! I can't believe that I never did this before! It was my first experience with darkfield microscopy and I am highly impressed.

I was bummed out at first because it didn't seem to work. But then I reseated the filter holder since it was off-kilter, then I opened up the condenser and walla!

All of a sudden the specimin just lit up in amazing color! It is so much cooler than brightfield!

I suggest everyone with a microscope try this. It really is amazing.


-FF

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OfflineRogerRabbitM
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Re: Darkfield microscopy! [Re: fastfred]
    #6456840 - 01/13/07 10:04 PM (17 years, 4 months ago)

Take some pictures please.
RR


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Invisiblefastfred
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Re: Darkfield microscopy! [Re: RogerRabbit]
    #6456849 - 01/13/07 10:08 PM (17 years, 4 months ago)

Here are some tips from a post I made awhile back...

From: http://www.olympusmicro.com/primer/techniques/darkfield.html

"There are several pieces of equipment that are utilized to produce darkfield illumination. The simplest is a "spider stop" placed just under the bottom lens (in the front focal plane) of the substage condenser (Figures 3(b) and 4(a)). Both the aperture and field diaphragms are opened wide to pass oblique rays. The central opaque stop (you can make one by mounting a coin on a clear glass disk) blocks out the central rays. This device works fairly well, even with the Abbe condenser (Figure 3), with the 10x objective up to 40x or higher objectives having a numerical aperture no higher than 0.65. The diameter of the opaque stop should be approximately 16-18 millimeters for a 10x objective of numerical aperture 0.25 to approximately 20-24 millimeters for 20x and 40x objectives of numerical apertures approaching 0.65."

"Almost any brightfield laboratory microscope can be easily converted for use with darkfield illumination. As discussed above, central opaque stops can be fashioned from a small coin, cardboard, plastic, or black paper that can be placed in a filter carrier beneath the condenser (or taped to the condenser bottom with adhesive tape) to block light from entering the front lens of the objective. The diameter of the opaque stop will vary from objective to objective and should be carefully measured by placing a transparent ruler in the substage filter carrier and holding it steady against the bottom of the condenser. Next, determine the opening size by removing an eyepiece and observing the image of the ruler at the back focal plane of the objective using a phase telescope (or by inserting a Bertrand lens). Make certain that both the substage condenser aperture and field diaphragms are opened to their widest position before performing this maneuver. The number of ruler divisions visible in the back focal plane will be equal to the size of the stop necessary to block zeroth order light from entering the objective. Change to the next largest size objective and take another measurement, repeating until stop sizes for all objectives are known."


The promlem with this method is that it only works up to a NA of 0.65, which means that it will work only up to about 400X. That's still pretty decent though.


-FF

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Invisiblefastfred
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Re: Darkfield microscopy! [Re: fastfred]
    #6456856 - 01/13/07 10:11 PM (17 years, 4 months ago)

> Take some pictures please.

Sure thing RR. It will probably take me awhile since I have no good specimins at the moment and I only have the most ghetto webcam/microscope interface, but pictures will be comming.

The lightstop that I made is pretty ghetto, but now that I know it works and how cool it is I'm going to try making some better ones.

I just printed out a picture of a lightstop on regular paper and then cut it out. It's just paper so I got more of a "greyfield" than darkfield effect, but it's still really cool.


-FF

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Invisiblefastfred
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Re: Darkfield microscopy! [Re: fastfred]
    #6456948 - 01/13/07 10:52 PM (17 years, 4 months ago)

I'm noticing that going darkfield changes the focus and makes it a fair bit softer.

One cool thing is that darker objects like the center of a mass of myc becomes lit up pretty nice though.

It seems a bit limited at higher powers since less light gets through and the softer focus becomes much more of a problem.

That's all to be expected though. It might turn out to not be all that usefull, but it sure was cool when it first kicked in.


-FF

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