A DIY LED ring for darkfield

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MichaelG.
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Re: A DIY LED ring for darkfield

#61 Post by MichaelG. » Sun Jul 22, 2018 4:17 pm

Just to revive this fascinating topic: I happened across a striking example of edge-lighting [total internal reflection] operating in reverse ... the slide is on my stereo microscope and the colour comes from the vintage mountant, which is presumably Canada Balsam. The edges of the slide are lightly ground, which obviously enhances the effect.

MichaelG.
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P1240217_xs.jpg
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Hobbyst46
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Re: A DIY LED ring for darkfield

#62 Post by Hobbyst46 » Sun Jul 22, 2018 5:40 pm

I have done some more on the DIY-WSI (Whole Slide Imaging is the term used in the research article about it) in the past month. Attached a long cylindrical lens in front of the tiny diode strip. Compared to the more common DF (i.e. by means of the condenser). To my slight dismay, DIY-WSI is not always successful - depending on the specimen and perhaps on the mounting medium as well. I was planning to report on the results soon. But, just received an intriguing raw sample of lake mud, with diatoms(?)...must work it on before it starts to give off the smell...
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iconoclastica
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Re: A DIY LED ring for darkfield

#63 Post by iconoclastica » Mon Jan 21, 2019 6:55 pm

I was thinking along the same lines before I reached the end of this thread. I even ordered some acrylic rods this afternoon to cut in half: the semi-cylinders just might work as acceptable condensers. An oblique fs-mirror allows a 90 degree angle in the design (leds vertical) and perhaps fine adjustment of the light rays' inclination.

How much led-power do you need, I wonder? If as much as I think, the strip leds you're using wouldn't be my first choice. They have been made for easy installation, but the diodes are widely spaced and in the wrong orientation, with their long axes vertical. Even then, there are strips at least as narrow as 3mm - did you select one of these extra narrow strips?

If much light is required, I am inclined towards smd leds, a series of the x014 leds or even the 1206 (for those not familiar with these numbers: the four figures denote the dimensions of the led module in 0.1mm, so 7014 is 7.0x1.4mm). Soldering these tiny devils may be hard, but in series it shouldn't be too difficult.

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Re: A DIY LED ring for darkfield

#64 Post by Hobbyst46 » Mon Jan 21, 2019 8:09 pm

iconoclastica wrote:I was thinking along the same lines before I reached the end of this thread. I even ordered some acrylic rods this afternoon to cut in half: the semi-cylinders just might work as acceptable condensers. An oblique fs-mirror allows a 90 degree angle in the design (leds vertical) and perhaps fine adjustment of the light rays' inclination.

How much led-power do you need, I wonder? If as much as I think, the strip leds you're using wouldn't be my first choice. They have been made for easy installation, but the diodes are widely spaced and in the wrong orientation, with their long axes vertical. Even then, there are strips at least as narrow as 3mm - did you select one of these extra narrow strips?

If much light is required, I am inclined towards smd leds, a series of the x014 leds or even the 1206 (for those not familiar with these numbers: the four figures denote the dimensions of the led module in 0.1mm, so 7014 is 7.0x1.4mm). Soldering these tiny devils may be hard, but in series it shouldn't be too difficult.
Nice to find the thread revived. There was a discussion about the design, the possibility of directly using tiny narrow and well-oriented LEDs was suggested (by MichaelG). For me, handling and soldering such "glowing microbes" was beyond my capability, so I went the easy road and used the densest LED strip I could find. It is 204 LEDs per meter, and the LEDs are 3014, so they are 3.0mm in height. Certainly, this LED strip is far from ideal, but is easy to work with.

I managed to attach it more or less horizontally on a metal plate carrier, that eliminates all heat problems, and equipped with leveling screws. I masked most of light beam of each LED, except for the center, by means of a black cardboard strip that runs end-to end in front of the LEDs. Shown below as a black strip. So, I could send a relatively narrow beam into the edge of the slide.

Later, I devised a "convex lens": cut a 30mm section of a 0.6mm-diameter quarz optical fiber; exposed it totally, and epoxied it in front of the slit. The right and left ends of the fiber are epoxied (a crude job really). This cylindrical lens is located exactly in front of the unmasked centers of the LEDs.
The reason I chose a quarz fiber rather than acrylic fiber is exactly to minimize light loss.

Nowadays I have a stereoscope so better equipped for such jobs, but I am still hoping for someone else to come with a better gadget of this sort, maybe!

Please note, that it was all made using just plain hand tools and no machines.
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iconoclastica
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Re: A DIY LED ring for darkfield

#65 Post by iconoclastica » Mon Jan 21, 2019 9:48 pm

Hm, I think I just would like to try that, although metoo has too many projects at hand right now. It's not as if my other solution to get DF works that well. First I'll see if I can scavange a whole array of them from a light bulb, for ordering from China takes ages these days.

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Re: A DIY LED ring for darkfield

#66 Post by MichaelG. » Mon Jan 21, 2019 10:28 pm

Hobbyst46 wrote: .... There was a discussion about the design, the possibility of directly using tiny narrow and well-oriented LEDs was suggested (by MichaelG).
I have the LEDs, but have not yet had the courage to try soldering them :oops:

I could present a list of excuses, but that's the basic truth of it.

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Hobbyst46
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Re: A DIY LED ring for darkfield

#67 Post by Hobbyst46 » Sat Jan 26, 2019 11:10 pm

Later, I devised a "convex lens": cut a 30mm section of a 0.6mm-diameter quarz optical fiber; exposed it totally, and epoxied it in front of the slit. The right and left ends of the fiber are epoxied (a crude job really). This cylindrical lens is located exactly in front of the unmasked centers of the LEDs.
The reason I chose a quarz fiber rather than acrylic fiber is exactly to minimize light loss.
The intensity of illumination can be enhanced by oiling the optical fiber to the slide edge, by placing a small drop of immersion oil on the edge before the "lamp" is placed against the slide such that the optical fiber nearly touches the slide edge. Not my own original idea but I adopted it.
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iconoclastica
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Re: A DIY LED ring for darkfield

#68 Post by iconoclastica » Sun Jan 27, 2019 2:44 pm

Instead of LEDs, it might also be feasable to use the CCFL tubes that are used in lcd-displays. These are very thin fluorescent tubes.

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Re: A DIY LED ring for darkfield

#69 Post by iconoclastica » Mon Feb 04, 2019 7:57 pm

iconoclastica wrote:Instead of LEDs, it might also be feasable to use the CCFL tubes that are used in lcd-displays. These are very thin fluorescent tubes.
Just tried that. I inherited a pair of 8x10cm displays, the lcd already removed. In the frame is a U-shaped light tube and its high-voltage converter is on board. It's a bit large for the intended purpose, but for a test, it will do. And the slide quite nicely fits in the bend of the U. The tube diameter is about 2.5mm, so the slide had to rise about a mm. The pile of magnets prevents the frame from tipping off the stage.

It works in a way, but the light is not bright enough for viewing. The photo took 5 seconds at ISO 800.

I am going to find a handful of miniature LEDs.
Attachments
slide fluff, DF, light from a CCFL-tube around the slide, top covered by tape
slide fluff, DF, light from a CCFL-tube around the slide, top covered by tape
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the setup
the setup
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Hobbyst46
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Re: A DIY LED ring for darkfield

#70 Post by Hobbyst46 » Mon Feb 04, 2019 10:01 pm

iconoclastica wrote:It works in a way, but the light is not bright enough for viewing. The photo took 5 seconds at ISO 800.
I am afraid that the disadvantage is that the light tube shines not only into the slide edge but also to some extent on the top (slightly - since it is covered) and bottom surfaces, this in principle might add some direct illumination that masks the DF.
I am going to find a handful of miniature LEDs.
Cross my fingers to the success of the mission. Soldering these teeny-tiny LEDs, crowded along a straight line... will you fabricate the printed circuit as well ? wow.
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iconoclastica
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Re: A DIY LED ring for darkfield

#71 Post by iconoclastica » Mon Feb 04, 2019 11:37 pm

I had not expected wonders from the tubes, but it was just too easy to try.

I am not sure at all I can do the leds, but I won't know until I try. We'll see.
But no pcb: for one thing I can't make them, and neither do I think it's a useful approach here, for the leds will sit on a narrow (1-3mm) edge. Any way, leds in series is just adding a drop of solder in between each of them and hope it catches...

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mrsonchus
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Re: A DIY LED ring for darkfield

#72 Post by mrsonchus » Mon Feb 04, 2019 11:46 pm

Would a fiber-optic 'slit-light' be useful here, up against an edge of the slide it will perhaps give the effect you seem to be trying to achieve.

Here's the light-pipe for a fiber-optic light source...
Fostec-Schott-Fiber-Optic-Slit-Light-attachment-nice.jpg
Fostec-Schott-Fiber-Optic-Slit-Light-attachment-nice.jpg (84.32 KiB) Viewed 5810 times
Just thought it may help....

John B. :)
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MichaelG.
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Re: A DIY LED ring for darkfield

#73 Post by MichaelG. » Tue Feb 05, 2019 12:12 am

It probably would, John

But last time I looked they were a bit pricey !!

MichaelG.
.

Edit: That one on ebay looks very reasonable at 60 USD
... until you add shipping, VAT and the Post Office charge for collecting that VAT
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Hobbyst46
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Re: A DIY LED ring for darkfield

#74 Post by Hobbyst46 » Tue Feb 05, 2019 2:02 pm

Thanks, John B. These light guides are great in general but the beam they produce, I am afraid, is too wide for the specific slide edge job. It is very important to direct the beam into the edge and not above and below it. In the past I used a quarz fiber optic, essentially similar but of a diameter of 0.6mm, and it worked, but it was mechanically cumbersome - to align the fiber tip along the stage and right up to the slide edge. Quarz fibers are not that flexible. Acrylic fibers are more flexible but light loss is worse. Not to mention that several fibers in parallel are required...
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MichaelG.
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Re: A DIY LED ring for darkfield

#75 Post by MichaelG. » Tue Feb 05, 2019 2:14 pm

Hobbyst46 wrote:Thanks, John B. These light guides are great in general but the beam they produce, I am afraid, is too wide for the specific slide edge job.
That said ... there are some interesting variations on the theme:
https://www.us.schott.com/lightingimagi ... ine+lenses

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Hobbyst46
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Re: A DIY LED ring for darkfield

#76 Post by Hobbyst46 » Tue Feb 05, 2019 4:20 pm

John B wrote:...
MichaelG wrote:...
My sincere appologies, folks! my mind was elsewhere, totally missed the link to the Schott site and detailed description!
I now see that these devices are MADE for DF in microscopy. It appears that the height of the beam is actually 0.76mm. That should be fine. If the beam can be made flush with the stage. Or alternatively the slide can be raised by a few mm above the stage, since the understage optics are irrelevant.
How much could it cost?
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Re: A DIY LED ring for darkfield

#77 Post by MichaelG. » Tue Feb 05, 2019 7:08 pm

Hobbyst46 wrote:How much could it cost?
I have assumed that John B found this ebay item:
https://www.ebay.co.uk/itm/Fostec-Schot ... 2940010160
The offer price looks very reasonable to me.
... Methinks you would struggle to find one significantly cheaper.

Assuming that the Seller makes an honest customs declaration ... to the UK the total would probably be
(Declared Value + Shipping Cost) + 20% for VAT + Royal Mail Handling Fee

Details here: https://www.gov.uk/government/publicati ... post-users

Note: They use an exchange rate prevailing at the time of import, not necessarily what you actually paid at the time of purchase [yes, I have been caught by this one].

MichaelG.
.
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Edit: Whilst not an exact equivalent ... this might provide a useful 'sanity check'
https://www.lambdaphoto.co.uk/schott-li ... 0-100.html
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Re: A DIY LED ring for darkfield

#78 Post by DonSchaeffer » Thu Jul 16, 2020 8:24 pm

This works great! When is it going on sale?

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75RR
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Re: A DIY LED ring for darkfield

#79 Post by 75RR » Thu Jul 16, 2020 8:45 pm

MichaelG. wrote:
Tue Feb 05, 2019 7:08 pm
Assuming that the Seller makes an honest customs declaration ... to the UK the total would probably be
(Declared Value + Shipping Cost) + 20% for VAT + Royal Mail Handling Fee
"Assuming that the Seller makes an honest customs declaration ..."The word honest in this context is nothing short of surreal!

But to my mind the worst bit is the "Royal Mail Handling Fee" assuming it is the same procedure as in Spain.

You pay for postage door to door, customs intercept your package, holds it for days and days (read ransom) and then have the gall to charge you for shipping it to you, when you have already paid for that.

To add insult to injury they do not even give you the option to choose economical shipping, no, they pretend they are doing you a favor by sending it express!

Talk about wanting to discourage imports by individuals!
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