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Daryl
06-17-2005, 05:40 PM
See this at http://www.pinhole.com/archive/371

Anyone try this?
I've been trying to figure out how to fabricate the hole/hemisphere module.

I'm irritated an not being able to shoot IR in my 32mm 6x6 without
the idea of measuring winding knob rotations.

Would this be cheating? Is this refractive element permissable?
OR is that a L3||$ !?!! * * ;)

moot
06-17-2005, 07:55 PM
The hemisphere part is easy. Edmund Industrial Optics (www.edmundoptics.com) has half-ball lenses from 2 mm to 10 mm diameter for about US$25-30. They are BK7 glass with a refractive index of 1.51 so it is like his example. Not sure how to mount it but I'd suggest being careful about centering.

Daryl
06-17-2005, 09:46 PM
The hemisphere part is easy. Edmund Industrial Optics (www.edmundoptics.com) has half-ball lenses from 2 mm to 10 mm diameter for about US$25-30. They are BK7 glass with a refractive index of 1.51 so it is like his example. Not sure how to mount it but I'd suggest being careful about centering.

Thanks moot! :D
Just what I was looking for! :D

You saved me from continuing to search for data on CD-ROM player lenses, glass marbles and beads of questionable amorphous uniformity! :)
(Another option was trying to find a transparent cubic crystalline material).

moot
06-17-2005, 10:13 PM
My pleasure.

Incidentally, that arrangement of the stopped-down, very-short-focus lens looks an awful lot like a single-lens microscope of the type used by Anthony van Leeuwenhoek. His lenses were mostly double convex (a few were actually aspheric) and were captured between two pieces of thin brass or silver.

Leeuwenhoek was able to get magnifications of over 400x with single lenses. The field was not flat but the center of the image was surprisingly good. I tried a plastic aspheric CD-ROM player lens and was able to see the nuclei of onion skin cells.

On the other hand, I'm talking about those inferrnal glass things so I'll stop. Good luck with the experiment.

Daryl
06-17-2005, 10:50 PM
It has been a long time since I was over at the edmundoptics site.
What a heretic's delight! Singlets, doublets, triplets! Woohoo!
Near IR and UV! Primitive L3||$3$ can be lots of fun! *:D

Well, I went and ordered a L3||$ HALF-BALL BK7 6MM.
Hopefully the pinhole police will be remain unaware of my seditious activities
as I try to figure out how to play visual music with this "L3||$".

I think Mr. Anthony van Leeuwenhoek was looking at a 'virtual' image (close-up).
I'm looking to record a 'real' image on film.

moot
06-18-2005, 01:15 AM
I think Mr. Anthony van Leeuwenhoek was looking at a 'virtual' image (close-up).
I'm looking to record a 'real' image on film.


Indeed he was looking at a virtual image. However, a Leeuwenhoek microscope also produces a real image, just like any simple lens. For example:

http://www.olympusbioscapes.com/gallery/2004/honorable24.html

was shot through one of AVL's instruments.

The photographer, an Englishman named Brian Ford, has made a detailed study of Leeuwenhoek and his microscopes, and published photographs taken with an original Leeuwenhoek microscope, a modern Leitz microscope, and a scanning electron microscope, all using some of Leeuwenhoek's original specimens that were preserved at the Royal Society in London. The Leeuwenhoek instrument holds its own surprisingly well.

Here is an image I took with a little trashy digital camera (I removed the lens) with the aforementioned CD-ROM drive lens as the microscope objective. It's nothing to write home about, but the little dots are individual red blood cells, which are about 20 microns across. Not bad for a quick & dirty lashup with plastic magnifying glass *;)

Sorry, I know that's all 'way off topic, except that it is an example of what can be done with almost no optics. Attached files http://f295.f295.org/uploads/red_cells_1994.jpg (http://f295.f295.org/uploads/red_cells_1994.jpg)

moot
06-18-2005, 05:03 PM
If anyone has the desire to try such a thing, it is extremely important that the lens be stopped down. Arrange some sort of mask in front of (and prefereable behind as well) with an aperture of about 1 mm or even less. Otherwise the field is flooded with scattered light and you won't see anything. I held my lens between two little metal plates. Distance to the image sensor was about 3 cm.

Now, enough of my heretical ramblings. My apologies to anyone who was annoyed by this, I didn't really intend to go off on this tangent. It's not quite as pure as pinhole, but it is still very primitive.

ImageMaker
06-18-2005, 08:26 PM
I note in the article that it was calculated that the optimum refractive index to avoid distortion beyond 70 degrees off axis was 1.3, which is at or about that of water. There are plastics that have essentially the same index as water (and become effectively invisible in water) and are water clear; they aren't used much in optics because they require a thicker lens to do the same job (high-index plastics have a higher index even than crown glass; those are used a lot now for eyeglass lenses), so you'd probably have to make the lens yourself, but such a lens could produce a near-perfect.

The lower index would widen the internal light cone slightly -- IIRC from reading about the effect of looking upward from water (i.e. "What a fish sees"), the new figure would be about 47 degrees instead of the 42 for index=1.5, but I don't recall enough of my high school physics optics section to verify that by calculating the critical angle -- is it arc-sin 1/index?

I am intrigued, however, by the brief mention in the Pinhole Visions article of cascaded pinholes, which seemingly sharpen focus -- it appears the spacing relative to diameter is critical; does anyone know how to translate the Greek into something a guy with lots of brass shim stock and a needle might be able to build? Or point to a copy of the original Journal of Optical Society of American article?

moot
06-19-2005, 12:37 AM
It appears that the JOSA archives are not open.

However, the author of the paper appears to still be teaching at the University of Ontario Institute of Technology. A link to his information is:

http://www.science.uoit.ca/Faculty_Staff/j_lit_main.html

Most scientists are willing to mail a reprint, especially if the application sounds interesting. Worth a try, and his email address is on the page linked above.

ImageMaker
06-19-2005, 09:09 PM
I've just e-mailed him -- we'll see if a) I get a response, and b) I can make any sense at all out of the original papers (I'm concerned that nothing beyond the first paragraph or two will include words I recognize other than prepositions and conjunctions). I've taken physics, but both my physics and my calculus are incredibly rusty (the latter essentially unused since the early 1980s); hopefully, behind all the calculations that prove the situation, there'll be something I can comprehend well enough to determine if it's at all applicable. Or alternately, perhaps he'll directly answer my implied question concerning whether the work is at all applicable to imaging in visible light.

Please cross your fingers!

moot
06-19-2005, 11:11 PM
With regard to the physics and calculus, same dog bites me :P

All fingers crossed. Let's hope he is flattered that a 1972 paper is still seen as relevant. *Good luck.

ImageMaker
06-20-2005, 07:05 AM
Actually, the ones that interest me are 1970 and prior; the original was a conference paper from 1966. :)

Daryl
06-21-2005, 09:48 PM
I received this pretty little thing today.

Attached files http://f295.f295.org/uploads/prettylittlething_3706.jpg (http://f295.f295.org/uploads/prettylittlething_3706.jpg)

Daryl
06-21-2005, 09:57 PM
I very carefully centered it on a pinhole and built a moat around it with rubber cement.

Put in on the SLR and the images on the glass STUNK!
Repeated the process and they still STANK!
Not worth wasting the film to show all of you.
Using the sun it did look promising to cover - 120 degrees????? :o

Must be doing something wrong. Attached files http://f295.f295.org/uploads/fgluearoundhemisphere_8792.jpg (http://f295.f295.org/uploads/fgluearoundhemisphere_8792.jpg)

moot
06-22-2005, 03:17 AM
I found another reference to the Franke camera in an article ostensibly by Jerle Walker: http://www.wesjones.com/pinhole.htm

The relevant section is:

"Another solution to the problem was invented by John M. Franke of the National Aeronautics and Space Administration's Langely Research Center. Franke positions a glass hemisphere just behind the pinhole of a camera in which the film is held in a normal flat plate. As the light passes through the pinhole and into the glass it is refracted. The full field of view, which occupies an angle of 180 degrees, is reduced to a cone of light occupying an angle of 84 degrees. When the light emerges from the glass, it is perpendicular to the surface of the glass. Hence the angle of the cone of light is unaltered. The reduction in the angle from 180 to 84 degrees enables Franke to position the film at an appropriate distance from the pinhole and still make a wide-angle photograph with a field of view of approximately 180 degrees.

Franke's glass hemisphere is made from BK-7 glass and is 25.4 millimeters in diameter. Its index of refraction is about 1.5. The diameter is not critical, but different results are obtained with glass that has a different index of refraction. You might like to experiment with other glasses or even with plastic of good quality. If you want a field of view of 180 degrees, you will encounter some distortion of the image toward the edges of the photograph."

The lens from Edmund is BK7 and has the correct index of refraction. Franke's hemisphere was apparently one inch in diameter, a fact not mentioned by Young, though Walker states that diameter is not critical, which makes sense. I wonder if Walker misinterpreted Franke and was just paraphrased by Young?

What did the images look like? Geometric distortion, poor focus, or ?

Daryl
06-22-2005, 05:39 PM
Thanks for the link, moot.
I suspected it would fisheye.

The sun thru the pinhole is a nice round small bright spot.
Thru the widefield set up it was several times bigger and an irregular splotch.

ImageMaker
06-23-2005, 07:19 AM
The more recent link posted above has an example of an image made with a Franke camera -- it does have considerable distortion, mostly in the outer edges of the field.

I got a reply back from Dr. Lit today concerning cascaded apertures -- as I suspected (but wasn't sure of -- zone plates and seives are magic, based on the way I think of optical physics), the cascaded aperture approach works very well on axis but degrades very rapidly off axis, with the result it isn't any good for photographing real objects with larger than point dimensions.

earlj
06-23-2005, 08:45 AM
Would cascaded apertures help in creating a pinhole camera to image the face of the sun? Daryl has discussed the building of a long pinhole camera for photographing sunspots or planetary transits. If cascaded apertures help in focusing, could they help to make a larger image sharper in a camera with a shorter than 'optimal' focal distance for a given hole size?

ImageMaker
06-23-2005, 12:48 PM
As I understand it, they'll make the focus of the central point sharper than the optimum simple pinhole for the same focal length, but according to Dr. Lit, the precision required to fabricate them is beyond our methods -- he suggested we'd need a precision laser setup. Also, the spacing is critical; though it's not clear from the second hand references, I think it's required that the holes be at the near-field diffraction limit from each other, which is equivalent to our "optimum distance", but in that case it's very unclear to me how you'd image an object even a half degree across -- it'd be like looking through a pipe 1/64" in diameter and a couple feet long.

The original application was keeping a precollimated microwave beam tight without the losses associated with a continous metal waveguide, and that application was long ago superceded by optical fiber and all the gradient density and internal reflection enhancements that go with those. There was no conception of an imaging application.

However -- one is moved to wonder if zone plates or seives can be combined the way lenses are...

Daryl
06-25-2005, 04:55 PM
>:(

After blackening a pinhole, I proceeded to attached the hemisphere like last time.

No joy. The image of the sun looked the same.

Shot film thru it anyway this time thinking the light coming in from the finder onto the glass was brighter than that of the pinhole - and maybe strange relections were causing the flare.

You can see that bend in the garage door in the middle pic.

I suspect it has to be about 33mm from the film on 6x6.
I wanted that coverage out at 78mm.
Attached files http://f295.f295.org/uploads/balltest_9935.jpg (http://f295.f295.org/uploads/balltest_9935.jpg)

Daryl
06-25-2005, 06:34 PM
Tried it on the 4x5 at about 63mm.

>:(

It is so wide that you can see the camera bed even though it has been dropped for wide angle.

I'm throwing in the towel on this one.
Besides - I'm now convinced it isn't pinholin'.
Pinholin' with the film flat and square is rectilinear. Attached files http://f295.f295.org/uploads/setupfor63mm_3341.jpg (http://f295.f295.org/uploads/setupfor63mm_3341.jpg)

earlj
06-25-2005, 07:01 PM
You're a good man, Daryl. Thanks for going the extra mile. Your dedication to the quest for pinhole knowledge is admirable.

Josh
06-27-2005, 02:59 PM
"I'm throwing in the towel on this one.
Besides - I'm now convinced it isn't pinholin'.
Pinholin' with the film flat and square is rectilinear." - Daryl

Nothing ventured, nothing gained. Thanks for your work.

"make mistakes, get messy" - Miss Frizz, the Magic School Bus


On a side note. I was thinking about those sieves in containers for sprinkling i.e parmesan cheese that have diffrent sized apertures. If you had a fixed disc and a rotating disc you could alter the number of holes in a pinsieve. Ignore my ramblings.

Daryl
06-27-2005, 05:58 PM
. . . .

On a side note. I was thinking about those sieves in containers for sprinkling i.e parmesan cheese that have diffrent sized apertures. If you had a fixed disc and a rotating disc you could alter the number of holes in a pinsieve. Ignore my ramblings.

Ramblings? Sounds like creativity to me.
I'd like to see a flat shutter with a 12 blade iris diaphram one could set anywhere
between 0.1 and 1.0mm.

Or how about a 2mm square LCD matrix that could be loaded with any number of
data matrix sets that determine the openings, zones, sieves, slits . . . .???
No more changing objectives.

JoeVanCleave
06-27-2005, 06:07 PM
I recall seeing plastic hemispheres attached to the end of kid's kaleidescopes. These are available in gift shops or toy stores for a lot cheaper than glass hemi's from Edmund's.