Picture of Lines in Fiberscope images

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The above are actual images of the lines in the fiberscope images I took up with a camera. I merely added the white arrow to point to the alternating lines which appear in all images. In the picture, it is sky above the city.

So how do you think the lines were caused by? bent, broken fiber bundles or tube inside the lens? Any ideas or theories? Thanks.

Mu

Reply to
Mu
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No one has any theories what could have caused it? If bending damage can't cause it, could heat or even radiation produce the lines like interference patterns? Also is the lens in front a convex and the back simple eyepiece? Is there no twisting in between the fibers to produce correct left-right image? What problems in the lens could cause the lines in the image? Is there no optics major here or is this rocket science?

Mu

Reply to
Mu

It's my opinion that the dark arc you see has to be a problem at either the objective or eyepiece end, not anything which could take place in the fiber bundle itself. I'd suggest you carefully inspect the lenses and ends of the fiber bundle. My best guess would be some contamination on one end of the bundle since it's fairly well in focus. It might be a manufacturing artifact that you didn't notice until recently. I don't believe it's anything caused by over-bending or crushing the fiber bundle. How could that cause a smooth arc in the image? That makes no sense.

Reply to
Louis Boyd

Thanks. You made sense.

There is something that I've been researching for the past few hours and I didn't seem to quite understand it. It concerns how the fiberscope can maintain the correct image left to right and up to bottom. In a refractor telescope, if you don't use a diagonal, what you'd see is a reverse image upside down and reverse left to right. Now in a fiberscope, it uses the same refractor objective lens and eyepiece as far as light path is concerned, but how come the image in the fiberscope is correct (not reversed upside down and left to right). Imagine putting constant fiber bundles inside a refractor telescope tube, what happen would be the the light rays would be similarly imaged at the eyepiece end resulting in upside down and reversed left to right. So how does the fiberscope design do it. Unless a fiber bundle has twisting in the middle to maintain the correct image such as "G" seen at both ends? But how can the twisting be arranged such that the letter "G" is similar at both ends? Does it mean for every say

18", 1 meter, 2 meter, etc. length fiberscope, they have to design the fiber bundle for that particular length to coincide both ends to produce the correct image "G"? After reading all available sites in the net for hours. I can't find the answer. Maybe you or others know. Thanks.

Mu

Reply to
Mu

The bundle is rotated 180 degrees in it's "normal condition". You can get the image you expect by rotating either end 180 degrees in either direction. Most image intensifiers (gen II and Gen III) used in monoculars or riflescopes have a rigid fiber bundle which rotates the entire image 180 degrees and it's only about 2 centimeters long. The intensifier's green phosphor screen is coated on one end of the bundle, you view the other end with the eyepiece.

You seem to be under the mis-assumption that each fiber carrys an image. It does not. Each fiber only carries light and while it has some dependency at the output on the angle that light entered at the input, anything resembling an image is lost. The bundle only shows an image because each fiber is effectively one pixel like the picture elements (pixels) in a CCD camera or an LCD display. One pixel only provides intensity and color information. The array of those pixels makes an array of dots which the eye and brain interpret as an image. In fact the cones and rod of the eye are also in array form, though with better resolution. In the case of your viewer with it's 7200 fibers you end up with an image with a resolution of roughly 100 pixels across If you aim your scope at a white paper with a very small "G" printed on it such that the image of the G only lands on one fiber you will not see a tiny little "G" in the corresponding fiber at the other end. You'll only see the end of one fiber a little darker than the surrounding fibers. No, there are no "images" formed at intervals along the fiber bundle.

There are borescopes which use relay lenses which DO form virtual images at intervals along the borescope using GRadient Index Lenses (GRINs) but they are not fiber bundles. Those are rigid borescopes, not flexible.

Reply to
Louis Boyd

I knew before each fiber only held one pixel of the image. My only concern is how come the image is not upside down and reversed left to right just like in refractor. You can't remedy the refractor image by rotating the eyepiece because you'd still have the view reversed left to right. I am guessing that in the eyepiece end in borescope. It is not positioned like in refractor where a say 10mm eyepiece is positioned 10mm behind the focal point. I guess that in borescope or fiberscope, the eyepiece is nearer than the focal point creating some sort of virtual image like in magnifying glass. I'm just not sure what happen to the light ray that enter the fiber bundles. For example. As the objective lens converge the light rays (from a certain angle) to a point and it enters a single fiber, would it come out diverging in the other side reaching the eyepiece which make parallel rays output to the eyes. If its the latter, the eyes should detect it as upside down and reversed left to right which can't be remedied by rotating the other end 180 degrees just like in telescope refractor. Know where I got it wrong in my analysis? Thanks.

Mu

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Reply to
Mu

If I understand correctly what you're saying, your analysis is correct.

One way to think of the fiber bundle would be to first reduce its length to a thin wafer of very short fibers. Clearly, the objective lens images the object upside down and backwards on its side of the fiber plate, and that image transfers directly through to an inverted image on the eye side. What then does the eyepiece do for the image the user sees?

A simple convex lens would give the user an enlarged view of the inverted image, and yes, it would still be rotated 180 degrees.

The advantage the long fiber bundle has over the thin plate is that the entire "rope" of parallel fibers can be twisted 180 degrees along its length. Then the output face would present an erect image to the eye lens.

Dave

Reply to
Dave Bell

But this isn't exactly so. Because if you try to untwist it to 0 degrees (or straighten the fiberscope). You don't see inverted image in it.

Before continuing. Hope we agree what is meant by inverted image. It's not just seeing something upside down.. but the entire images are reversed so instead of seeing "G", you won't see upside down "G" but "G" reversed where no keyboard has character for. You have to see thru a refractor to get what I mean.

If you already get what I mean. Then how would twisting the fiber tube 180 degrees makes a correct image out of the inverted image ("G" mirror reversed). Does this mean that if you can physically rotate the light path in the middle of a refractor, the eyepiece would end up with a correct image provided no diagonal or any image erector is used?

Mu

Reply to
Mu

Mu wrote:-

"G" is a poor choice as it has no rotated or mirrored counterpart character. You can use the ASCII character P and d represent a 180 degree rotated but not an odd number of reflection mirrored image. The characters 6 and 9 work to show rotation or even number mirroring too. Some characters like [ and ] are ambiguous as they could be achieved by rotation or mirroring or both. The characters b and d can be used to show odd number of reflection mirroring which cannot be archived by rotation alone.

You're being somewhat sloppy with the terms inverted and reversed. If you do BOTH the results are the same as 180 degree rotation. You can invert AND reverse simultaneously by simply twisting a fiber bundle. Hold one end still and rotate the other end 180 degrees. What goes on in the middle of the bundle doesn't matter. You could tie it in a a loose knot and the results wouldn't change.

A fiber bundle could be manufactured to invert or reverse but not both, but the fibers would have to be laid out in a different pattern at one end to accomplish that. I've never seen a fiber bundle made that way, but there's no reason it wouldn't work. Anyone seen an example? Some fiber bundles are purposely designed to scramble images. That can be used to produce uniform illumination from a focused lamp, or if and image is recorded though a scrambled fiber bundle then viewed at the same image scale in the reverse direction it gets descrambled. I've seen early non-electronic security badges which used that method, though they aren't very secure by modern standards.

What's the difference between 180 degree image rotation and mirroring in two orthoginal axes? None!

if you have a matrix with positions:

1 2 3 4 5 6 7 8 9 then any way you end up with: 9 8 7 6 5 4 3 2 1 constitutes 180 degree rotation whether you do it by moving the numbers around the edge by scooting them all around the 5 in either direction by four steps (as by twisting a fiber bundle)

or by swapping all items on opposite sides of the 5 all at once (as with an erecting lens

or by first flipping the top and bottom positions and then the left and right positions in a separate step (as with a porro prism)

or by storing the positions serially and reading them back in reverse sequence (as with some DSP CCD cameras with horizontal and vertical mirroring functions.)

Or by computer image manipulation (many image viewers have "rotate" functions, usually in 90 degree steps. some allow apparently continuous rotation).

or by using a dove prism which also provides continuous smooth image rotation optically. It's a combined refractive and reflective device. If the prism is rotated 90 degrees the image rotates 180 degrees in the same direction.

The results are essentially the same with all of the above methods though the three methods differ in image quality, angle of acceptance, complexity, etc etc. In some cases you can just rotate your eye position or physically rotate the object being viewed.

The English language has no really good term for an image which has been orthogonally mirrored twice or "erected" by a lens. Words like reversed, inverted, flipped, and erected have various degrees of ambiguity. The word rotated is faulty as you have to state how much rotation. Pi/2 radians or 180 degrees or a half revolution are needed and the term seems to expect a direction of rotation which usually doesn't matter but sometimes does.

A lot of the problem of this and other discussions about mirrors and optics comes from our language. Left and right are horrid as they're almost always ambiguous. Up and down would be as bad if it weren't for the fact humans aren't very close to being vertically vertically. What does left and right mean if you're laying down?

Reply to
Louis Boyd

Well. I actually viewed the above numbers with a refractor a while ago without diagonal. You are right, the image is like 180 degrees rotations. I always used a mirror diagonal so I thought the image without diagonal had the same effect where the "b" when rotated becomes a "d" but not so at all. So it's the mirror diagonal odd effect that changes a "b" into "d". Now the mystery is resolved. Anyway. In designing fiberscope objective lens. You think the almost parallel rays outside after passing thru the lens converges into a point that is exactly the surface of a fiber (a pixel) of the bundle? And say you have a 2 meter long fiber bundle, does the light travel inside as a point or does it diverges while inside the fiber bundle? Or does it only diverge after coming out of the other fiber end?

Another. When I use a fiberscope, the images seen from afar is very small. I understood telescopes optics where the angle Beta subtended in the eyepiece is greater than the angle alpha in the original object and the Beta divided by Alpha is the magnification. But I can't seem quite understand how the opposite works where the image viewed would become smaller (like when the fiberscope is aim at far away object).

Anyway. What size of objective lens must be used to make the image the same size as viewed direct from the eyes, supposed you want a fiberscope to ack like a periscope? Normally fiberscope lens is about 2mm in size, must I make it 7mm to make the object seen thru the eyepiece as large as normal?? or can extra lens be used to make the 2mm size objective lens work at larger image scale?

Well. I spent 2 days researching in the net about all this but there is not much references. They are mostly about telescopes and microscopes.. not much stuff about endoscope or fiberscope light paths and principles. Many thanks for your valuable assistance.

Mu

Reply to
Mu

Maybe it's resolved. You need to realize that there are two common but different types of "diagonal" eyepiece adapters. The older type has a single reflection and inverts the image in one axis. I can be made with a simple first surface mirror or a 90,45,45 prism. The other type uses prism or pair of mirrors which give two refections. Google on "roof prism", "penta prism", and Amici prism" to see what some look like. Any light passing though two orthogonal reflections undergoes mirroring in both axis, which as stated before is equivalent to a 180 degree rotation. If you look at the matrix through the diagonal mirror (without looking though the refracting telescope and rotating the original bring it back to normal then your diagonal is one of the two mirror types. Amici or roof prisms are the most common.

Anyway.

That's correct, assuming the lens is correctly focused.

And say you have a 2

It does not travel as a point. the light cone repeatedly undergoes total internal reflection as the light bounces off the inside of the fiber. It's very efficient process. when the light reaches the end of the fiber and the light emerges as a cone. The light is no longer a point after two meters of cable, rather the entire surface of the end of the fiber is carrying energy. You can see this by looking at your own photo of the watch. All of fiber, out the the cladding, are filled nearly uniformly with light. That's true even if the image entering the fiber was smaller than the diameter of the fiber.

Or does it only diverge after coming out of

Picture firing a shotgun down a pipe. The pellets bounce off the walls. The main difference is the reflections are much less lossy than pellets bouncing off the inside of a pipe. Total internal reflection takes place when light comes to an interface from a higher refractive index to a lower refractive index at a shallow angle. The specific angle depends on the relative refractive indices of the core and cladding of the fiber. At steeper angles the light leaks out the side of the fiber and is lost. For most fibers included angles of around 60 degrees are typical.

The apparent "magnification" is simply the ratio of the focal length of the objective lens and the eyepiece lens. If they were equal, he view would appear to be unity magnification. Most fiber scopes use a shorter focal length objective lens to give a wider field of view. Some borescopes have interchangeable lenses.

Various focal lenght lenses or even compound micorscopes can be used as the objective. You could put fiber bundle on a meter class telescopes and see apparent magnifications of a few hundred times looking at distant objects. You always need to take into account the angle of the light cone which will pass though the bundle as discussed before.

Google for "multimode fiber total internal refection " It will describe how light propagates though fibers which are large compared to the wavelength of the light they carry. You won't find much about borescopes and endoscopes. The majority of fiber optic devices are used for communications and theres plenty of information about that subject.

Reply to
Louis Boyd

Most amateur astronomers use mirror diagonal with single reflection. So what you are saying is that if one uses 2 mirror diagonals and stick them together, the output would be a correct image. Well. My refractor tube is not short so if I use 2 mirror diagonals, the light won't reach focus in the eyepiece because I can't rack the focuser inwards to the center of the tube. I have to saw the tube to test this. BTW.. using two mirrors would produce better quality than using prism because the internal reflections would produce attenuation and the surface inaccuracies can degrade the wavefront as well as cause scatterings.

What? Suposed a fiber bundle has 7400 fibers. Each light from the objective lens passes thru each of them, so naturally, a point would come out from one of the 7400 fibers in the other end. So I can't understand what you mean that the entire surface of the end of the fiber is carrying energy. I guess each of the

7400 fibers have point of light that diverges at the end and the combination is of course carrying photonic energy. Is this what you mean?

I wonder what's your thought about negative magnification.. that is.. the image seen in the eyepiece is smaller than the original. This is what you will see in a fiberscope when it is aimed at infinity or far away object. Therefore the magnification being ratio of focal length of objective lens and eyepiece lens needs changing. Perhaps it looks like this. In a typical telescope.

focal length = 800mm, eyepiece 20mm. Magnification is 800/20 = 40X.

In a fiberscope, maybe the following occurs:

focal length = 10mm, eyepiece 20mm, Magnification is 0.5X or 1/2 smaller. If this is possible I still can't imagine what would happen to alpha and beta angles that makes the object smaller than the original.

Do you agree that to turn the fiberscope into a periscope where the object you'd see is the same size as directly viewing it, the objective lens must be at least 5mm in diameter, or do you think it's not related?

I don't get what you mean putting a fiber bundle on a meter class telscopes. What's "meter class"? And what's the sizes of the objective lens of compound microscopes?

Yes, I already understood about single mode vs multimode fibers. Btw.. I wonder if high quality endoscope uses single mode fiber or all of them uses multimode, any ideas?

Reply to
Mu

using two

Maybe you should tell Leica and Zeiss to quit using prisms in their top end binoculars.

I'm only saying that the objective lens on your borescope can focus a parallel beam of light much smaller than the diameter of one fiber. The fiber is a huge pipe compared to the wavelength of visible light, and the light rattles down thorough the pipe bouncing off the lower refractive index walls. When the light gets to the other end it's traveling in random directions up to the limiting reflectance angle inside the pipe and the energy spews out in a cone. You put one end of a single multimode fiber in a box thats white inside with a bright light and aim the other end of that fiber at a screen, you'll see that the light coming out of that one fiber is a cone with an angular extent of about 30 degrees from the direction the fiber is pointed. The exact angle depends mostly on the refractive index of the materials the fiber is made of. If you look at the end of that fiber where the light is coming out the core of the fiber will be fully illuminated, not just a point in the center of the fiber. Look at you photo of the watch. Each fiber is a uniform disk of light. The image information withing the area of one fiber is lost.

A smaller apparent image is magnification between 0 and 1, not negative. A magnification of -1 would be an normal size 180 degree rotated image.

Thats true for a telescope or a fiber bundle scope

Thats just a telescope with a magnification of 0.5x

Sure it's possible. Have your ever looked though low power monocular backwards? That works for the same for a fiber bundle scope too.

A single mode fiber at visible wavelengths would have a core diameter of about 3 microns and there are thickness requirements for the cladding to work. Square packed fibers have 1-(pi/4) or about 21% dead space between the fibers while hexagonal (honeycomb) packing has

1-(PI*3^0.5)/6 or about 9% dead space between them. Even large core multimode bundles have over 10% light loss just from injection losses. It would be more like 80 to 90% if single mode fibers with minimum practical cladding was was used. All imaging fiber bundle devices I'm aware of use multimode transmission, which along with cost limits the practical length of fiber bundle image transmission. Also, no fiber materials have nearly as low of attenuation at visible wavelengths as are available in the 1 to 2 micron infrared. You can send superb quality video images many kilometers over a singlemode fiber as serial data using a ccd camera and a video monitor.

Today most endoscopes are being built using CCDs instead of fiber bundles. They're smaller and for high quality images they're cheaper. Commercial CCD endoscopes are available as small as 1.8 mm diameter with

120,000 pixels. Try to do that with a fiber bundle!
Reply to
Louis Boyd

Thanks for all enlightening thoughts. Last inquiry :)

The fiberscope I returned to the manufacturer is 5.8mm in diameter. The 5.8mm includes the light fibers surrounding the image fibers. The image fibers themselves are about 2mm total with 7400 fibers and 2mm lens at the end . If you view thru one with the target across the room, the effect is like looking at a binocular backwards, the image scale is very small. Now to create large scale image. I wonder if the objective lens focal length has to be merely increased to make the magnification more than unity. Do you think increasing the focal length is enough to make the fiberscope view at normal scale or does the lens have to be increased in sizes too as well as the fiber bundles? This is the last mystery to be solved.

I got a fiberscope to use as periscope because I saw this movie Executive Decision where Kurt Russel inserted a fiberscope into the plane bottom to see the surrounding area. When I got my fiberscope, first thing I noticed was that the image from across the room was so small that I can't see details that I'd otherwise see with my normal eyes.

After browsing thru all fiberscope/borescope sites. I can't see one where you can see a large or normal scale. Is it because it is impossible to create this with a 2mm fiber bundle and lens? Meaning the only way to do it is to create 7mm fiber bundles and 7mm lens?? What do you think?

Mu

Reply to
Mu

Hopefully ;-)

Is that 2mm it's diameter or focal length?

Have you never compared a microscope to telescope? In their simplest forms, you increase the magnification of a telescope by increasing the focal length of the objective lens to make the image viewed by the eyepiece larger. With a microscope you make the focal length of the objective lens shorter , but you move the object to be observed closer to the lens to increase magnification. In both cases the magnification comes from the ratio of the distances from the objective to the focal plane viewed with the eyepiece becoming greater relative to the distance from the objective to the object being viewed. It's no different at all with a fiberscope. If you put the object near the objective and move the lens away from the fiber bundle it magnifies. Your borescope isn't made for looking at distant objects any more than a microscope is intended for looking at the moon.

Simply put, you didn't do your homework before you purchased. If you want unity magnification of distant objects (distant meaning the distance from the lens to the object is many times the distance of the lens to the fiber bundle) you need to have the focal length of the eyepiece equal to the focal length of the units objective lens. The focal length of the eyepiece is determined by the apparent field of view you want and the diameter of the bundle you want to look at. They're built for the average human eye, so you don't want to change the eyepiece lens, you need to change the objective lens instead.

No, it's not impossible. But consider what borescopes and endoscopes are normally used for. What you want to do is not what the market caters to. If the objective lens on your unit is removable you can remove it and put on a longer focus lens. There are other way to look inside a room. You can knock and be let in or pick the lock. There are other was too, but they tend to be messy.

When stating a lens is "2mm" most people would assume you mean the focal length, but it helps to clearly state both the diameter and focal length or focal length and f/ratio of a lens. It helps in understanding what it does.

What you want for viewing at unity magnification is to have the same focal length objective lens as the focal length of the eyepiece lens. both lenses should be around f/3, that is the focal length of the lens should be about 3 times it's diameter. A smaller diameter lens will give a dim image though it will still work, larger and the "extra light" will simply be wasted. The f ratio of a human eye in dim illumination is around f/3 too. The lens should be an achromat for good results. Lenses made to be objective lenses with flat fields will give the best images, but they tend to come in unnecessarily large packages for your intended use. Whether such a lens will operate correctly with the bundle's illuminator I can say but it probably won't. You haven't said if you're trying to look into a dark room. Doing that will probably take more light intensity than your unit provides. You'd probably be better off with two fiber bundles side by side with one only providing illumination under a door with the illuminator coupled to a xenon arc lamp or similar. With todays technology a CCD camera with a white LED illuminator beside it would probably give the best performance for the price. The biggest part would be the heatsink for the LED.

One last thing. Do you think the unit used in the movie was really a unit built for looking under doors or just an endoscope being used as a Hollywood prop? No doubt such units exist, but very often Hollywood uses something else which the prop department thinks the audience will buy into. Why would a device for looking under doors be made round? I'd expect it to be flat and wide, at least for the illuminator portion. No device which will do the job you want is going to be cheap simply because the development effort to package an otherwise cheap camera or design a proper lens assembly for a fiber bundle is fairly difficult and the market is very small. If tens of millions were being sold you could buy them at Walmart for $100. Look at what cell phones with their tiny cameras and LCD video displays cost. The difference is just packaging.

Reply to
Louis Boyd

Say the fiber bundle (composing of 7200 fibers) is 2mm in diameter. How do you calculate the apparent field of view to be used and the focal length of the eyepiece given human eyes will view it.

No. The 2mm I mentioned is the diameter of the objective lens as well as the fiber bundles (I assume the lens and bundle is same diameter size). It couldn't be the focal length because how could I know it is 2mm when it is not stated in any endoscope or fiberscope manual.

The fiberscope would be used at fairly bright environment so the maximum pupil size of a person would be roughly 2.5mm. Therefore the lens and the bundle must be roughly 2-2.5mm in diameter. Since the eyepiece is f/3 and one can't change the eyepiece diameter, then the objective lens must be 2-2.5mm in diameter and about

6-7.5mm focal length. But even at this size, the eyepiece diameter is still bigger. So I wonder what would be the exotic effect. In telescopes where I have thorough experience, the eyepiece lens is always smaller in size than the objective lens. Perhaps the effect would be that the bigger diameter eyepiece (compared to objective lens) would see wider angle??

Do you know where I can order or purchase a 2.5mm diameter objective lens with focal length of 7.5mm? Or something close to this so I can replace the objective lens of the fiberscope with this unity lens? Also since magnfication has to do with the relationship of the focal lengths of the objective lens and eyepiece, this means by changing a short focal length eyepiece, I can make it work without changing the objective lens with the downside that I'd get a smaller apparent field of view. I wonder if I can just remove the build-in eyepiece of the unit and replace it with telescope eyepieces with 3mm focal length or so. (?) I no longer have the fiberscope now since I returned it to the manufacturer for factory defect so I can't experiment.

Thanks dude. You may be a master optician now or someday. :)

Mu

Reply to
Mu

Sorry for piggybacking...

"Mu", could you please remove the space in your groups line when you post? It is causing my news provider to drop your posts as it does not meet protocol.

You should write,

sci.optics.fiber,sci.optics

instead of,

sci.optics.fiber, sci.optics

Spaces are not allowed in the groups line. Apparently Google's interface is too stupid to strip them and my NSP is too anal.

Brian

Reply to
Skywise

Lets say the effective focal length of the eyepiece is 4mm so a 2mm diameter bundle would appear to be 2/4 radians or about 29 degrees. using radians is a rough approximation but useful for small angles.

Maybe the lens can be unscrewed and you measured it or you could have measured the adjustment distance required for best focus between two distances and calculated it with he formula 1/f = 1/a + 1/b where f is the focal length of the lens and a and b are the distance of the image planes on either side of the lens. Again, it's an approximation but it works for reasonable values of a and b.

If the bundle is really 2mm diameter that would give a field of 2/7.5mm radians or 15 degrees. Is your field really that small?

exotic effect ?????

I suppose you've never seen a 2.5x20 riflescope with an eyepiece lens close to twice the diameter of the objective. Eye relief and angular field size play a part in sizing an eyepiece lens.

Guessing about eyepiece design doesn't work very well. I'm not at all certain your eyepiece description so far indicates it's is close to

7.5mm focal length. It's probably not a single element lens.

The only common lenses that small I'm aware of are low power microscope objectives. You'd use them turned around. While small CCD camera lenses are available in that focal length range their f ratios are usually faster than you need.

There is a simple formula for microscope objective focal length. That is f lens = f reference / power (power like the 20 in 20x which gets multiplied by the eyepiece power to give total magnification) Unfortunately not all Manufacturers use the same reference length. For example the Nikon reference distance is 200mm, so a 50x lens would have a 4 mm focal length. The reference length is the effective distance from the objective lens to the focal plane at the eyepiece. For Zeiss the reference is 160 mm so a 50x Zeiss objective would have a 3.2mm focal length. For cheap Asian microscope lenses you'll just have to measure it or guess.

Thanks dude. You may be a master optician now or someday. :)

I'm not now and not likely to become an optician. I design and construct automated astronomical research telescopes as my profession Thats mostly electronic and mechanical work with just a bit of optical design. It's hard to teach an old dog tricks. I leave the details of lens and mirror design to my optics suppliers.

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Reply to
Louis Boyd

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The above is the fiberscope in question. It is 5.8mm total diameter. This includes the larger size illuminating fibers that surround the image fibers. All of which are surrounded by nylon. Based on the lens size, it is only 2mm so I assume that the image bundles composing of 7400 fibers are also 2mm in size.

Are you sure that fiberscope design has to be f/3 at the eyepiece? I saw the following specs of a high quality fiberscope with the field of view listed thus:

2.4mm Models 60 degrees field of view 1mm Models 55 degrees field of view

Based on your formula that actual field is diameter divided by focal length. The 1mm model would be about 1mm diameter/1mm focal length = 1 radian or 57 degrees. The scope uses 1mm focal length. It doesn't follow your f/3 rule. Can you explain why? Based on it, The 1mm model has lens of 1mm too and since focal length is 1mm, then it's f/1.

Got any idea what would happen if you view an f/1 fiber lens using an f/3 eye? Would the image be dimmer of what? Why the f/3 rule?

Going back to the above fiberscope (see url). If after receiving it again and I just chop off the lens head and the pull off the eyepiece main body as well as removing the nylon and the illuminating fibers. I'd be left with the pure 2mm image bundle composing of 7400 fibers. If you are to design an objective lens and eyepiece for it from scratch. What would be the specs. Based on what you described before. I guess the lens size is also 2mm and it is f/3 giving focal length of 6mm, But actual field would be very tiny 2/6 = 1/3 radian or ~19 degrees. So to increase actual field of view, I guess the lens must be made f/1 so that diameter/focal length=

1/1=1 radian= 57 degrees. This means the eyepiece is also f/1. Provided the target image is distant object like across the room. The object would be very dim from the f/1?? Let's say the target image is 1" from the lens typical of fiberscope/borescope, does it have to follow the f/3 rule and what would be the consequences if it is f/1 and not f/3?

This calculation and theoretical exploration is design to gauge whether a 2mm diameter unity periscope fiber bundles is sufficient or efficient or whether it is not appropriate for the task.

BTW... do you think they are selling pure imaging fibers without any lens or eyepiece so one can just design them from scratch. Have you seen this stuff being sold elsewhere? Thank you.

Mu

Reply to
Mu

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After researching for hours in the net. I think fiber optics imaging concept is more complex than either telescope or microscopy so it is like rocket science. For instance see:

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numerical aperture is a thing of microscopy and not telescopy, yet it is included in fiber optics imaging principle.

I hope someone can point me out to microscopy discussion groups where this can be inquired. Or if fiber optic imaging is beyond them, perhaps a specialized group that discusses this. Telescope-making experts such as Louis may not be able to tackle such unrelated stuff as microscope optics or the more advanced fiber optic imaging technique which is combination of telescopy and microscopy and even quantum mechanics so this belongs more to particle physicists.

I'd like to build a fiberscope from scratch by grinding my own lenses (I have some grinders in my basements and some broken clear glasses from cokes which I can use as lenses). I can't find books about constructing fiberscopes although there are many books on telescopes and microscopes. For interested parties, pls. contact me in private as this can even give us a headstart to manufacture fiberscope/borescopes which has quite good profit margin. Note there are so many made in china telescopes yet no made in china fiberscopes for the reasons that the latter requires sophisticated understanding which china people may lack but which we can acquire by international cooperation. Fiberscope constructions may be as complex as manufacturing nuclear materials but with the former, at least the FBI won't be hot on our trail.

Mu

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Mu

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