MicrobeHunter.com Microscopy Forum

I love to experiment and when I saw this article on Micscape UK site I had to try it:

http://www.microscopy-uk.org.uk/mag/ind ... field.html

It's really simple but I can't get it to work.

He uses a 4 watt LED on a gooseneck to get close to the specimen with no other lighting. I have a 40 watt LED in a gooseneck desktop lamp aimed right at the specimen. I see nothing, all is black. It seems to me that would be enough light for me to at least see an image. My specimen is the same as his - epithelial cells. I even tried my cell phone camera light used as a flash with no result.

p3aul wrote:I have a 40 watt LED

Did you mean 40 W tungsten or tungsten-halogen? If so, I would be concerned about heating your objective too much. Did you try first with lower power objectives? The 40x would be so close to the object that it leaves little room for direct light from the lamp; lower powers are easier and would be what I would use, at least to diagnose the problem.

I agree with gekko.

I suspect that author used very long exposure at camera. In other words, what you observed is probably normal, if you did mostly what he did (monocular head, avoiding reflection, ect).

I did exactly what he said and only got good VISUAL images up to 20x NA 0.40. Too dim for 40/0.65, without super long exposure.

His 60/0.85 darkfield diatom resolution is not very good. With a real oil darkfield condenser, you will get better resolution at that magnification and NA.

Your 40w LED, though - is it a LED replacement bulb for an incandescent bulb (say, for desk lamp)? Does it say "40w LED" or "40w equivalent/replacement" (to incandescent)? There are both types on the market and their wattage differs by around 8 folds (40w vs around 5w). Also light spread angle matters. A 30w with 180 degree spead is only as bright as a 10w with 60 degree spread, onto a tight spot.

Maybe use a small prism to project the light down on the slide?..

Did you mean 40 W tungsten or tungsten-halogen? If so, I would be concerned about heating your objective too much. Did you try first with lower power objectives? The 40x would be so close to the object that it leaves little room for direct light from the lamp; lower powers are easier and would be what I would use, at least to diagnose the problem.

40 watt equivalent bulb. The kind they make to replace the incandescents and CFI's with. It says 450 Lumens on the side. I thought the same thing about the 40X gekko, I went down to the 4X and could still get no light. Fan I think you hit it on the head. Spread. especially in a lamp housing. I found the exact light the OP used at the IKEA web site and Amazon. It' cheap enough at $10 US. The OP gives no indication of having to use a long exposure, and I think he would have, if he were a good amateur scientist.

Paul,

Edit: Sorry, I think regular bulb type may have a even wider spread, more like 360 degree spread.

I think 40w incandescent bulb equivalent means around 5w LED with 180 degree spread. That means around 1.7w at 60 degree spread. That 4w IKEA light is likely a solid 4w with 60 degree spread, which would be more than twice brighter than yours.

This LED headlight should he brighter than the IKEA, as all its output can be focused onto the size of a big coin:
http://www.amazon.com/Water-resistant-H ... detailpage

I have one, but still don't consider that bright enough for viewing at a regular (non-LWD) 40x NA 0.65.

I have also tried a 23w (actual) 1600 lumens LED bulb (180 degree spread). It works fine for 10x NA 0.25, but not higher.

Thanks, Fan. rather than throw money at what might not work anyway, I think I'll forget it and go back to oblique illumination along with Rheinberg Illumination.

Paul

Achieving Darkfield by using "stops" on low power objectives, say up to 16x is relatively easy. You should try it.

Link to a "stop" making article:
http://www.microscopy-uk.org.uk/mag/ind ... -tips.html

I'm ahead of you there 75! I'v made some stops out of expired gift cards and have used them up to 40X with a great deal of success. I have one in my Infinity Plan MS right now. Compared what I got with an online image from MicroscopyU's image of a Phase Contrast image of epithelial cells and my image of DIY/DIC cells looked the same. So there you have it. I sent back my Phase Contrast kit. DIY/DIC works just fine for me. Unfortunately(and I noticed this with MicroscopyU's Image also) You loose resolution in the nucleus with that approach.

Here's one shot with only top light.
4x objective.
Led point source on a gooseneck for lighting.

I've only had success with the 4x and 10x objectives, because the higher power ones are too close to get the top light on the specimen.