Fiber optic illuminators?

[Jesse]

Sorry, I don’t know the term of art for this. I see stereo and epi microscopes with snake arm Illuminators. I think maybe they are referred to as coaxial Illuminators?

Anyway, I was thinking these looked good for lighting a subject from the side rather than transmissive lighting. Are there makes and models that are particularly good? Anything I should be aware of or look for?

I was also wondering if I could use a plastic fresnel lens to condense light from my flat led video lighting panels into a fiber optic cable... thoughts, suggestions?

Thanks

[johan]

Small thing, but one thing to watch out for is how noisy they are, this can get irritating.

I have a cheap and cheerful Chinese one and it's perfectly good, but makes a ton of noise.

I replaced the internal fan with a $50 one and this did the trick

[enricosavazzi]

Sorry, I don’t know the term of art for this. I see stereo and epi microscopes with snake arm Illuminators. I think maybe they are referred to as coaxial Illuminators?

Anyway, I was thinking these looked good for lighting a subject from the side rather than transmissive lighting. Are there makes and models that are particularly good? Anything I should be aware of or look for?

There are a few different types of flexible light guides.

The (probably) most common is a bundle of optical fibers wrapped within a gooseneck metal spiral. This one is the simplest to use, but relatively stiff. Especially near the limit of its bending radius it is difficult to position with precision, and usually springs back a few mm to one cm after bending and releasing it.

Then there is a bundle of optical fibers wrapped in a "floppy" plastic pipe. It does not remain bent as you manipulate it, and the illumination end must be supported with an articulated mini-arm. However, it can be positioned with absolute precision (as long as the mini-arm is precise).

With time and bending, some of the optical fibers break (especially the ones made of glass), and portions of the bundle end become "dark". I have gotten some second-hand gooseneck guides where some 40% of the fibers were broken, others in prime condition. Most sellers don't know and cannot tell the difference.

Some light guides for special uses (e.g. spectroscopy, data transmission and alarm systems) contain a single thick plastic fiber. They have their uses, but in general not for illumination of macrophotography subjects.

Then there are liquid light guides, which externally look like fiberoptic ones but contain a liquid instead of fibers. They are far more expensive, and unless the sheath is damaged or kinked they are more durable than fiber ones. Some of them are made to transmit from NIR to UVB (some possibly UVC) in addition to VIS.

I might also mention that there are rigid light guides, usually made from perspex or solid glass. Some are straight, others (usually the ones used by dentists) have a 30 degree bend in the middle. They can have their uses when attached right at the front of a small LED illuminator (with a single powerful LED, not a LED panel), and in this case you mount the whole illuminator on a mini arm.

I was also wondering if I could use a plastic fresnel lens to condense light from my flat led video lighting panels into a fiber optic cable... thoughts, suggestions?

I would not recommend building a fiberoptic illuminator from scratch. Besides, to efficiently collimate light into the end of a light guide you need a point-sized light source (or at least just a few mm across), not a flat panel. To project a small image of a large light-emitting surface you need a long focal-length lens, which means a slow effective aperture that will waste most of the light.

[Chris S.]

Jesse, perhaps what you're thinking of is a fiber optic illuminator, such as the ones in this Schott Fostec catalog. I use Ace I units shown on page 12 and like them quite a bit. They are easily obtained on the second-hand market. They may be labeled either Schott, Fostec, or Schott Fostec.

I'm currently in the process of converting an Ace I illuminator from halogen to LED. Assuming that my mod works (likely), I'll document it for the forum.

I was also wondering if I could use a plastic fresnel lens to condense light from my flat led video lighting panels into a fiber optic cable... thoughts, suggestions?

Probably not the best approach. I've tried converging overlarge light sources into fiber optic light guides, and recall that others have tried it as well. No doubt it could be done, but not easily, so far as I can see. I find it difficult to avoid light loss and obtain an evenly bright output beam (a round beam with a dark center is, for example, not something I like).

On the other hand, what is working for me so far is a round LED COB similar in diameter to the input side of the light guide. Properly heat-sinked, the LED COB, puts out so little heat on the front side that I see no reason not to mount it almost touching the light guide. (In my testing, I have a thermocouple mounted to the COB to measure temperature.) In this configuration, the light from the COB is very nicely transmitted down the light guide into a bright, even output. (I've tried other, more complicated approaches, none of which produce nearly such nice results.)

The LEDs I'm using are 5600K Yuji VTC Series High CRI COB LEDs. These are daylight balanced and have a very high CRI, with a spectral output that nearly mimics a black-body light source. Once my project is complete, I'll share details including a parts list.

BTW, there is nothing particularly wrong with the halogen bulbs that are native to illuminators such as the Ace I--I've been happily shooting with them for years. I'm trying this conversion for several reasons: One is to be able to electronically gate exposure by cycling the LEDs on and off, which would quickly kill halogen bulbs; another is to obtain dimming without changing color temperature; another is to be shooting with a daylight-balanced light source, which I think may reduce blue-channel noise for some subjects; and lastly, LEDs produce so much less heat that I'll either be able to use passive cooling alone, or if active cooling is needed, be able to do it with a smaller, slower-moving fan than required by halogen illuminators. The fans in my halogen illuminators produce enough vibration to require isolation from the macro rig (I have them on a shelf suspended from the ceiling, which works very well). Also, these fans produce a bit of air movement capable of stirring very lightweight specimens (spider silk comes to mind).

--Chris S.

[Pau]

Jesse, take a look at
http://www.photomacrography.net/forum/v ... 014#197014
It's a long thread with lots of links and ideas, the most interesting parts at pages 2 and 3

Other old long related threads:
http://www.photomacrography.net/forum/v ... 2873#92873

http://photomacrography.net/forum/viewt ... 2872#42872

If you plan to use it with your new microscope it would be only useful with your 4X objective, very likely the others have too short working distance for this kind of external illumination

[Scarodactyl]

No point in making your own, as they can be found relatively inexpensively on eBay and the like. They are great for lots of things, and you don't need all that much working distance to pump light in with them. I suspect you'd need to keep them vibrationally isolated for anything really fiddly though.

[Pau]

No point in making your own, as they can be found relatively inexpensively on eBay and the like.
... and you don't need all that much working distance to pump light in with them. I suspect you'd need to keep them vibrationally isolated for anything really fiddly though.

Scarodactyl, have you read the former posts and linked related threads?

Chris S. has clearly stated the advantages of modern LEDs as light sources, being one of them the lack of vibration, but not the only one.

Saul, in a linked thread, has made a most useful compact device and his images speak for themselves

On the other hand my comment about working distance is referring to the objectives just bought by Jesse with his microscope. WD in the order of 4mm to 0.14mm are not easy to illuminate with external sources http://www.photomacrography.net/forum/v ... 346#236346

Of course, I agree with you about the easiest way being to buy a complete used illuminator, it's what I did several years ago

[Jesse]

Jesse, take a look at
http://www.photomacrography.net/forum/v ... 014#197014
It's a long thread with lots of links and ideas, the most interesting parts at pages 2 and 3

Oh man, that's a really cool thread. Thanks for the link.

Youtuber DIY Perks built a similar 1000w LED light source years ago: https://youtu.be/c--5c3Egv4E

The fans in my halogen illuminators produce enough vibration to require isolation from the macro rig (I have them on a shelf suspended from the ceiling, which works very well). Also, these fans produce a bit of air movement capable of stirring very lightweight specimens (spider silk comes to mind).

It's good to know about the vibration issues. I hadn't considered that.

The LEDs I'm using are 5600K Yuji VTC Series High CRI COB LEDs. These are daylight balanced and have a very high CRI, with a spectral output that nearly mimics a black-body light source.

Thanks for the links to the high CRI LEDs. I'm painfully aware of CRI issues as I have crappy Philips low CRI LED lights in my basement and I have regularly filmed how-to videos with them in the past, before I bought my high CRI LED light panels. Even white balanced, those old Philips LEDs make everything look terrible.

If you plan to use it with your new microscope it would be only useful with your 4X objective, very likely the others have too short working distance for this kind of external illumination

Regarding working distance, I noticed that the APO objectives have lower working distances before I bought them, so that definitely isn't a surprise.

I am curious about the math behind this issue, however. Are we physics constrained here in the amount of light we can deliver in a 4mm gap? Or is it an engineering issue?

What determines the intensity of light a single fiber optic cable can transmit?
What happens if we attempt to exceed that threshold? Does the light bounce out like a cup that is full of water running over, or does it destroy the fiber optic cable?

Sorry, I know I'm all questions. Thanks.

[Jesse]

I was also wondering if I could use a plastic fresnel lens to condense light from my flat led video lighting panels into a fiber optic cable... thoughts, suggestions?

Probably not the best approach. I've tried converging overlarge light sources into fiber optic light guides, and recall that others have tried it as well. No doubt it could be done, but not easily, so far as I can see. I find it difficult to avoid light loss and obtain an evenly bright output beam (a round beam with a dark center is, for example, not something I like).

This company appears to use fresnel lenses to condense (is that the right word?) sunlight into fiber optic cables for "daylighting" purposes: https://www.buildinggreen.com/blog/fibe ... aylighting

I'm not sure how much different a point source like the sun is from an LED panel for this purpose, however.

I have three of these http://www.dracast.com/led1000-pro-specs.html and it looks like 300mm square fresnels are just $60 for a two pack on amazon. Might give it a try just for kicks.

[Pau]

Youtuber DIY Perks built a similar 1000w LED light source years ago: https://youtu.be/c--5c3Egv4E

Not really similar beasts

If you plan to use it with your new microscope it would be only useful with your 4X objective, very likely the others have too short working distance for this kind of external illumination

Regarding working distance, I noticed that the APO objectives have lower working distances before I bought them, so that definitely isn't a surprise.

I am curious about the math behind this issue, however. Are we physics constrained here in the amount of light we can deliver in a 4mm gap? Or is it an engineering issue?

NA is a function of the entrance angle of the light into the objective. Because Plan Apos usually have high NA, to have a wide angle they need to be close to the subject or to have a very big front lens. Because the front lens usually needs to have big curvature to provide high magnification there are both physics and engineering limitations. The first issue is well illustrated at https://www.microscopyu.com/microscopy- ... l-aperture interactive tutorial. Nikon CFI 60 still have good WD compared with other makers biological objectives.

Long WD Plan Apos like the Mitutoyo have big frontal lenses and modest NA for these reasons

[Saul]

My 2 cents ... What I would do differently after my experience with Scienscope/Cree XHP 70/HomeDepot combo ? I would use not Y type but two separate single same type pipes with Cree XHP 70 (or similar type/size) LED on each FO pipe and attached similar way to the 8020 type stacking frame.
Benefit - more light output per pipe, I could adjust light output with separate dimmers and ability to use single pipe (not every time I'm using both of them)

[Jesse]

Probably not the best approach. I've tried converging overlarge light sources into fiber optic light guides, and recall that others have tried it as well. No doubt it could be done, but not easily, so far as I can see. I find it difficult to avoid light loss and obtain an evenly bright output beam (a round beam with a dark center is, for example, not something I like).

I've been trying to figure out what you mean by a dark center. Are you referring to Fresnel diffraction?

[Chris S.]

Probably not the best approach. I've tried converging overlarge light sources into fiber optic light guides, and recall that others have tried it as well. No doubt it could be done, but not easily, so far as I can see. I find it difficult to avoid light loss and obtain an evenly bright output beam (a round beam with a dark center is, for example, not something I like).

I've been trying to figure out what you mean by a dark center. Are you referring to Fresnel diffraction?

Jesse,

As you will expect, a fiber optic light guide with a round cross section (i.e., every light guide of which I'm aware) and no beam-changing attachment on the distal end (such as a ring light or flat panel) projects a round circle of light. Unfortunately, in many arrangements I've tried, the central portion of this circle is darker than the periphery. While it's certainly possible to work around this, an output beam having uniform intensity everywhere is much easier to work with than an output beam with a dark center.

Having played with varied ways of concentrating light into a FO light guide, I can say that non-uniformly bright output beams seem more the rule than the exception. The dreaded dark center seems almost a default.

The simple approach of placing a round LED COB to almost touch the FO light guide is the simplest approach I've tried. Happily, it also works the best of anything I've tried, producing a bright--and importantly, evenly-bright--output beam.

For completeness, let me add two more things: FO light guides can be placed in two groups: randomized and non-randomized. In non-randomized light guides, the light-conducting fibers run parallel to one another, and there is tight spacial correspondence between the position of each fiber's input and output relative to the other fibers in the light guide. The result of this is that the light guide acts a bit like a lens, in that any unevenness in light input results in similar unevenness in light output. OTOH, randomized light guides purposefully mix up the position of optical fibers between input and output, in hope of homogenizing the output beam. I have quite a few FO light guides, but none of them are randomized. If purchasing on the second hand market, it will be difficult to get vendors to identify one from the other.

Also, it's possible to interpose things like opal glass into an FO system to randomize light and produce a more even output. However, any such addition will cause light loss and increase complexity and cost.

Does any of this answer your question?

--Chris S.

[Scarodactyl]

I imagine a light guide with a flattened tip might be really nice for pumping light under objectives with limited working distance. I wonder if those are available.

[enricosavazzi]

I imagine a light guide with a flattened tip might be really nice for pumping light under objectives with limited working distance. I wonder if those are available.

They are, although they are generally not designed for this specific purpose and the line-shaped end of the light guide in usually encased in a thick parallelepiped of epoxy and metal.

Total internal reflection microscope illuminators also often use light guides (or sometimes light sources) with a line-shaped exit.