Help with 'Darkfield' please

Mo Vaughan · Post by **Mo Vaughan** » Wed Aug 29, 2007 11:43 am

the microscope is a Model XSP - 10 Series, it has magnification of 25.2X - 1600X, and has an Abbe condenser, Dry Darkground Condenser & Immersion Darkground condenser.
Illumination is built in Kochler.

My question is what do I need to carry out darkfield photography?
I have read articles by Wim van Egmond and this has been of help, but what material should I get to construct these filters?
What size holes are recommended?
And any other information would be of great help.
Many, many thanks to those who reply.
Mo,

Charles Krebs · Post by **Charles Krebs** » Thu Aug 30, 2007 10:16 am

Mo...

and has an Abbe condenser, Dry Darkground Condenser & Immersion Darkground condenser.

If you really have a a "Dry Darkground" and "Immersion Darkground" condenser (darkfield=darkground... just a different phrase) then you are in great shape and do not need to fool around with different home-made "stops".

To give exact advice I would need to know a few more specs about your equipment, but generally a "dry darkground" condenser should be OK for objectives up to, and including, a 40X. An "Immersionl darkground" condenser would generally be useful with a 100X (although you could use it with a lower power... it just get a little more messy with the oil)

Charlie

Wim van Egmond · Post by **Wim van Egmond** » Sat Sep 01, 2007 12:51 am

Hello Mo, Hi Charlie,

Yes, you don't need scissors and paper when you have this set up!

Some quick suggestions: Make sure the condensor is as high as possible and when there are apertures in the condensor and field diaphragm, set them wide open. Make sure everything is centered well!!!

Start with the dry method and start with the lowest magnification. It is easier to get darkfield with low magnifications. With higher magnifications the 'light cone' from the condensor should be wider and the dark field 'stop' should be wider too so the light will only illuminate the subject and not enter the objective. The higher the magnification of the objective the wider this stop has to be because higher magnification objectives have a higher numeric aperture. (Try to read into this a bit by searching the web) Anyway, with your condensors it should be possible to get darkfield at all magnifications! So you can do more than I can!

There is a bit more to it to get the illumination as good as possible. But this should work. You could read more about setting up the illumination of a microscope on many microscopy webpages

If you search for 'kohler illumination dark field' search terms like that you will find many good articles. Just a quick search: http://www.microscopy-uk.org.uk/mag/art ... field.html My articles are always a bit simple. That's me!

Good luck and perhaps we will see some nice darkfield images in the forum soon!

best regards,

Wim

Mo Vaughan · Post by **Mo Vaughan** » Sun Sep 02, 2007 3:55 am

Hi Gentlemen,
Many thanks for your help and enthusiastic comments. Just by you replying has given me an incentive to try out this type of Amateur microscopy.
Charlie, you wanted to know more details re my microscope, here goes.
Specifications: Tube length 160mm, Conjugate distance 195mm, Magnification 25.2x - 1600x, Nosepiece four holes, Mechanical stage 140mmx140mm, Longitudinal movement 50mm Transversal 70mm, Condenser Abbe condenser, dry darkground condenser, immersion darkground condenser, Observation tube Trinocular, Illumination system built in Kochler - type Illumination, Objectives Achromatic 4x 10x 40x 100x Plan Achromatic 4x 10x 25x(s) 40x (s) 100x(s)what is ment by (s)? Plan Field eyepieces 10x 16x, Focusing system Coarse 30mm Fine 0.002mm.
Thats it. The photograph of the microscope is at the begining of this message. I hope this is of help Charlie.
Its a shame that I cant pop over and have a chat and for you to explain and demonstrate 'how its done'.
I will be publishing some of my attempts in the future and look froward to constructive comments.
All the very best to you all,
thebeeman

Charles Krebs · Post by **Charles Krebs** » Mon Sep 03, 2007 12:32 am

Mo... typically a darkfield condenser will be marked with two numbers that indicate the NA (numerical aperture) of the ring of light it creates. Your various objectives will be marked with their numerical aperture. This way you can see what objectives will work with the condensers.

If this is all new to you don't worry about the numbers. As I mentioned earlier, the "dry" darkfield condenser should be fine for your objectives up to the 40X. For a 100x you will need an "oiled" darkfield condenser, and even then it may be a close call depending on the NA of the condenser and objective. (100X objectives that are intended for darkfield often have a built-in aperture).