Dark field using Amscope 720

[Sinar]

Hi, I was wondering if anyone can advise, I recently got an Amscope 720 microscope and I want to try using it dark field but I can’t seem to locate a filter holder to put the dark field patches, Is it possible to use dark field with this microscope? Thanks for reading

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[apochronaut]

It isn't something that too many modern designs incorporate because they sell both dry and oil DF condensers. In the old school days there weren't too many dry DF condensers, so the filter location was closer to the iris diaphragm and spider DF stops were commonly available from most mfg. to perfectly fit the location.

Your microscope does have a filter tray, it is just over the illuminator port but it just isn't a great location for a DF stop. If you can rig something up just under the condenser, that is about as good as you will be able to get but it won't be easily centerable to the condenser axis, a common problem with add on DF stops unless there is a precision stop and tray built in.

If I was doing it, I would look out for an old AO DF cardioid or spherical condenser and adapt it to your system. They are often really cheap and there were tens of thousands of them sold for use in doctor's offices, so they continue to come out of the woodwork. They have built in centering screws. You will get 40X DF and up. They are quite short but have about a cm. of vertical adjustment. On a scope such as yours, mounting the entire condenser on top of the dovetail yoke in some secure fashion will get slide contact and maintain the centering mechanism.

[Sinar]

Thankyou for your detailed reply, that’s given me a lot to think about

[Chas]

I dont know if the optical part of your condenser unscrews from the top of it's mounting tube, but if it does (and I am guessing that it should do) then a small pea-sized blob that strange aimed-at-children silicone putty can be squashed onto the back lens of the condenser:

Black silicone putty blob as a DF stop 800.jpg (105.8 KiB) Viewed 1891 times

.. It is a rather nice material in that rather than being oily, it seems to lift off oil. I have some black coloured putty but maybe no need to use black; black coloured putty (not the magnetic version with metal in it) now seem quite hard to find.
But I notice that there is a shop in the US called 'Crazy Aaron's ' that does a 'Ditch black' version :
https://crazyaarons.com/search?q=Ditch+black

[apochronaut]

What a capital idea. However, I suggest using a pontefract cake instead, then when he has to disassemble his condenser everytime he wants to go back to BF, at least he has the satisfaction of being able to eat his DF stop, while he cleans the bottom lens.