Dark-field of a sort - spooky Sonchus..

[mrsonchus]

Hi all, I've had a little dabble with darkfield-ish images. Actually I just pushed the filter-carrier off-center to give a terribly amateurish dark-field effect to a stained slide (TBO stained) I was 'surfing' this evening..

I rather like the spooky effect and the vivid colours of the image - it looks almost as though the featured florets with their developing achenes below (LS) are floating deep below the surface of an icy ocean....

Anyway, I like the effect and the colours!

ws_dfield_sonchus_HDR.jpg (189.57 KiB) Viewed 3859 times

Amazing what a nudge of the filter-carrier can do!

[zzffnn]

Interesting, JB!

I remember JimT successfully imaged a TBO stained section in darkfield as well.

Other stains, such as Fast Green, Safranin and Harris Hematoxylin, at least the ones that I have, do not seem to look so nice in darkfield. They look somewhat brownish.

The right side of your image seems brighter than the left side. Usually, darkfield filter would be placed exactly dead center at objective back plane, blocking the entire aperture, but not going over too much to block too much light. Table 1 of the following article gives a good starting point for darkfield stop sizes:

http://www.olympusmicro.com/primer/tech ... field.html

[mrsonchus]

Haha! It's really just a little nudge of the filter-tray - a bit of oblique and DF - not really sure what on Earth to call it! I like the effect for the colours but it's value as a source of information....hmmmm...maybe not....

Thanks for the encouragement and the link old chap.

[billbillt]

Hi John,
That IS an interesting effect... Hmmm... That would look to need further study... I think you are on to something here!..

BillT

[gekko]

Very nice image. Out of curiosity, what was the color in brightfield?
It looks to me that what you have is oblique darkfield, which is what you suspected you had. If the darkfield stop is somewhat oversized so you could move it to one side and still block all direct light, most or all of the light will be from one direction, giving an oblique, 3D effect while still maintaining darkfield. At least that is what I think. Once Rod (rnambolz) showed a similar 3D-looking darkfield, and that prompted me to experiment with the idea, and it does work (at least to my eyes). At the prompting of JimT, I was trying to write a short article for the Microbe Hunter magazine about this idea, but so far it is still in an early draft form. Here is a diagram I had prepared for the manuscript that I hope shows what I believe is happening:

[mrsonchus]

That diagram says it all gekko - thanks. Your article would be very interesting when you get a chance to get to it.
The stain is Toluidine Blue - a metachromatic stain of shades of blue, purple and red - no reds in the brightfield as far as I remember though.
I'm going to have a little try at oblique first and perhaps darkfield further on, one technique at a time for me!

Thanks for your interest gekko old chap.

[Johann]

No need to blush, it looks very aesthetically (thanks spell checker) pleasing

I do the same thing for oblique, get better results than any oblique filter I've tried. But I'm probably doing something wrong

[gekko]

John, to get oblique, you do the same thing, except start with the filter tray (with an opaque stop in it) all the way out of the way (brightfield) then slowly nudge it inward until you get the oblique result you like. Looking at my diagram above, you will be moving the patch stop (green) further to the right (or to the right) so only about half of the objective's aperture is "uncovered" (if that makes any sense). And for darkfield, you simply center the darkfield stop (as zzffnn suggested above).

[mrsonchus]

Thanks gekko, I'll give it a 'proper try' - it's an interesting technique to add to the arsenal I think.

[Johann]

I've been using a filter of which one half is transparent and one half is opaque, and moved the filter ring in and out as you suggest. Will try with a complete opaque stop - thanks Gekko.

[gekko]

I've been using a filter of which one half is transparent and one half is opaque, and moved the filter ring in and out as you suggest. Will try with a complete opaque stop - thanks Gekko.

Tha half-transparent, half-opaque filter is just a slightly different path to the same end point. If you wish you could try different shapes to get slightly different oblique image results, see for example:
http://www.microbehunter.com/oblique-illumination/