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Slit lighting
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ChrisR
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PostPosted: Tue Jan 19, 2010 4:12 pm    Post subject: Slit lighting Reply with quote

I don't know what else to call it. I'm sure it will have been done before and have a better name.

This comes off Paul's thread which threw up some queries about the stack, here .

The problem isone of bright out-of-focus light obliterating the detail in darker subject matter at a different focus-step.

I have experimented with only lighting the plane which is in focus. This was to attack the problem of
"fuzzy light stuff + sharp darker stuff = no useful image".
which Rik refers to in the other thread.

I remember seeing about some work a guy did on that, with a particularly dirty fly, some carefully controlled lighting and I suppose a lot of negatives printed together. Just to see what happened, I used leds at the edge of some thin glass with black tape stuck to each face. It was mounted in the frame of a slide copier



subject slid through the hole by a stiff wire fixed to a micrometer stage.
The next attempt was to use a microscope frame with the edge lighting at stage level, with the subject moved up through the hole, on the condenser holder. Nothing has happened beyond that idea in several months, though. An obvious snag would be that it might work for an egg, but not an eggcup, as no light would get inside. I had ideas for that but got no further.
It worked, on the wasp I started with on this forum, but lack of time and space prevented development. I'm going to be so busy when I retire!

This must have been done before but I haven't found it. ?? What's the proper name for it!!?
Is anyone doing it routinely?


Last edited by ChrisR on Tue Jan 19, 2010 4:41 pm; edited 3 times in total
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lauriek
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PostPosted: Tue Jan 19, 2010 4:18 pm    Post subject: Reply with quote

I have no idea if it's connected to what you're talking about here but if you search eBay now for "slit microscope" you'll find an odd looking microscope I spotted.

I watch this thread with interest!
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ChrisR
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PostPosted: Tue Jan 19, 2010 4:28 pm    Post subject: Reply with quote

Nooo, I remember haviing that done during an eye test!
Paragraph half way down this page explains a bit.
http://www.healthyeyes.org.uk/index.php?id=101
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augusthouse



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PostPosted: Tue Jan 19, 2010 6:24 pm    Post subject: Reply with quote

ChrisR wrote:
Quote:
I remember seeing about some work a guy did on that, with a particularly dirty fly, some carefully controlled lighting


Could you be referring to Ted Clarke's:

"Constructing a Scanning Light Photomacrography System" ?
http://www.modernmicroscopy.com/main.asp?article=60

Craig
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rjlittlefield
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PostPosted: Tue Jan 19, 2010 6:41 pm    Post subject: Reply with quote

The article you saw was probably "Constructing a Scanning Light Photomacrography System" by Ted Clarke.

There used to be a commercial system using this technique, called the "Dynaphot". Google search on Dynaphot turns up some references. The methods section of an article from 2000 contains this summary:
Quote:
We used a Dynaphot Scanning Light Microscope (SLM), manufactured by Irvine Optical of California, to photograph all the species that we discuss. The SLM takes a composite photograph of the specimen as it moves through a lighted focal plane that has a bandwidth of 50-100 micrometers so that the photograph only records the sections that are lighted and in focus.
...
The major limitation of the SLM is that the light bandwidth is sometimes more than the width of some smaller species. Another limitation, related to the light bandwidth, is the magnification obtainable with our system—its maximum is 40x—which is not sufficient for some of the smaller species, but it may explain why even with the smaller species we get good photographs. The images are in focus and can be enlarged photographically, so they are better than ones taken at higher magnifications with other photographic systems. Finally, from a technical point of view, the horizontal, narrow band lighting means that specimens must be mounted in such a way that the light will get into critical regions such as umbilical cavities. Some features are virtually impossible to light; hence, some photographs have dark areas that are unavoidable. Also, some of the angles of specimens are not the "standard" views that micropaleontologists are accustomed to with SEM photographs.

Both of these systems accumulated the composite image on a single piece of film. The idea was for the slab of light to illuminate only those portions of the subject that were in focus.

I don't know whether this technique is still being used. It had some pretty serious limitations and as far as I can tell it has been overrun by focus stacking.

The idea that I think ChrisR is describing is different in that it still relies on focus stacking to do the heavy lifting, and just uses the illumination slit to reduce the problem of contamination by OOF light.

--Rik

Edit: correct spelling of keyword "Dynaphot" in text.


Last edited by rjlittlefield on Sun Jun 03, 2012 6:11 pm; edited 1 time in total
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elf



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PostPosted: Tue Jan 19, 2010 9:12 pm    Post subject: Reply with quote

The foreground object will still occlude the background even when the foreground isn't lighted. Would this technique actually have any benefit?
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rjlittlefield
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PostPosted: Tue Jan 19, 2010 11:13 pm    Post subject: Reply with quote

elf wrote:
The foreground object will still occlude the background even when the foreground isn't lighted. Would this technique actually have any benefit?

Yes. Read the discussion HERE. If the perspective is held constant, then the occlusion is never total. By keeping the foreground dark, you can at least avoid washing out detail in the background. It's analogous to attacking glare by blocking out bright light that would otherwise bleed into dark areas.

--Rik
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ChrisR
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PostPosted: Wed Jan 20, 2010 2:36 am    Post subject: Reply with quote

Yes thanks that was the article, with the wretched fly!
50 - 100 microns is a much thinner slit than I was using, which was glass from old sllide mounts. (I don't have any microscope coverslips - how thin do they go?)
The amount of light I was getting , shone through edgewise from LEDs, was low. A dismantled ring flash could have possibilities.

Regarding the unlit "dip in the middle", digital image processing should be able to come to the rescue. A photoshop mask applied to some or all of the aligned images from a conventionally lit stack, would provide sources for composition.

Masks can be image-derived. I'm going to have to steal Paul's image to demonstrate - I think he's an amenable chap Anxious


This isn't quite the way a mask would be applied to images with unlit parts, but I hope conveys the idea. What it's doing is attempting to recover detail in the "fogged" part of the image.
Before, After, and a couple of the masks:


This is part where the stem is lost behind the petal. The Mask applies a Curves adjustment, to darken and increase contrast, where the mask is White. Some detail is restored, but not all of it.
The masks are produced by clicking in the image, copying, inverting etc, not by laborious painting, so they do apply all over the pic. The hardest part is getting the initial selection right, then the amount of blur, and then the "adjustment" such as the Curves. It's possible that more/different adjustments could be used to better effect.

WHen done though, there are always odd results like colour shifts in small areas which need attention. It's not always quick, though I'm no PS expert. A good PS person is hugely faster than me.
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Charles Krebs



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PostPosted: Wed Jan 20, 2010 1:23 pm    Post subject: Reply with quote

Ahh yes! The Irvine Optical Dynaphot! I remember looking longingly over that broschure in the early '80s (I think it was). Even priced the slit lamps at that time... don't recall the price other than it was far more than I could consider at the time Wink
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dmillard



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PostPosted: Sat Jan 23, 2010 9:16 am    Post subject: Reply with quote

I believe this image was taken with the Dynaphot, and that Darwin Dale and George Lepp demonstrated its use while it was still being manufactured.

The late Nile Root, who had been a professor at RIT, designed and constructed a far less expensive alternative, using a rack and pinion focusing unit from a cheap microscope that raised the object to be photographed on a pedestal, and DC halogen light bulbs projecting a sheet of film between (if I remember correctly) two horizontal sheets of particle board. He published an article about his device in the Journal of the Biological Photographic Association (I have a copy somewhere that I can't currently locate, or else I would post the date).

I had an opportunity to see Nile Root's device in Tucson about 20 years ago. He had bequeathed it to a former student, who graciously took several images of Lycaenid pupae for me.

I started to build my own version, using a lead screw drive, aluminum sheets, and a brass cylinder to block extraneous light, but I never got around to completing it (although I still have all the parts in a box in my garage).

One of the advantages of this device is that you can quickly get great depth of field on a single frame of larger format film with no loss of resolution due to diffraction. A disadvantage (that ChrisR plans to diminish with digital processing) is the occlusion of light from recessed areas - the ideal subject would be hemispherical in shape.

Thanks for bringing this topic up - I'm going to take a fresh look at my project.
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g4lab



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PostPosted: Sat Jan 23, 2010 1:32 pm    Post subject: Reply with quote

I learned about scanning light photography also ages ago and wanted to try it. The amateur version suggested three slide projectors with slits mounted in 35mm slide holders. The motion and adjustments were done by lab jacks.

I was going to comment but really did not have anything to add to what had already been said.

Then one of these fell into my lap. I had never seen one before nor heard of the item.
Would seem perfect for the job. (though its intended use is for a slightly different job)

I had missed this post It was before I joined and I missed it combing through the archive when I did join Smile
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AndrewC



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PostPosted: Sat Jan 23, 2010 1:58 pm    Post subject: Reply with quote

g4lab wrote:
...
Then one of these fell into my lap. I had never seen one before nor heard of the item.
Would seem perfect for the job. (though its intended use is for a slightly different job)
..]


Looks like a fun toy anyway Smile I'm just waiting for a box of the latest Cree leds to arrive which I plan to embed around a disk of acrylic with a sample well in the middle. Would be relatively easy to mask that down into a slit.

Andrew
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ChrisR
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PostPosted: Sat Jan 23, 2010 3:02 pm    Post subject: Reply with quote

Ah joy, I'd missed that post too. BUt similar thoughts had occurred to me, without the well aspect.

Initial thoughts started from:
Years ago I had to photograph about 100 medals. Skim lighting looked good so I did this:
Blue is a transparent cotton-bud container, red is a wrap of black paper and the yellow stuff is light. I could easily control the lighting by sliding the wrap up and down.

I tried the same thing with recently with microscope objective pots, and basically, it's a lot harder. It needs some sort of screwed advance on the wrap.

I've tried drilling a hole through 2mm acrylic (secondary glazing) sheet, and if you polish the inner edge, that works, if you shine leds, flash, anything really, into the edge of the acrylic, with black paper over the top.
You have to extend the black paper further than the edge of the acrylilc, or it scatters light upwards quite a bit. Maybe needs mbetter polishing.

Slightly, I've tried a bevel on the inner (circular) edge of the acrylic sheet, so the light coming in from the side gets refracted downwards on to the subject. With short-but-not-impossible scope objectives, that approach might be ok. I've got a 100x, 2mm ish WD one I hope to have a go with.
BD objectives that strong, are expensive!

---
That's all about plain illumination. For the slit I started waffling on about at the top of the thread, for the purposes of avoiding OOF glare in stacks, thinner "glass" is needed.
The black paper extension sort of collimates the light beam. It should be possible to shape the edge into a convex, positive lens, to help. I don't have a lathe though.

Thoughts came back from schooldays of spark-eroding metal samples for transmission electronmicroscopy. The kit stops sparking when there's a hole, but you get a dish in the surface of the metal. It acts like a solid negative lens, which isn't always what you want, but I digress.
Anyway doing the same thing with a Dremel sanding drum and some acrylic, and a polishing mop, it should be possible to do something similar. You'd stop when you went through, and just make the hole round and polished. (I knew that record-player would come in handy again one day.)
If it worked, you'd end up with a lot of light piped by internal reflection to a narrow ring. (If it hasn't been invented I'll call it a SlightPipe. Smile )
Blue is transparent clear plastic of some sort, and the yellow things could be leds, or other light.


Well?


WELL?
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AndrewC



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PostPosted: Sat Jan 23, 2010 4:11 pm    Post subject: Reply with quote

Something to think about if you are trying to get the light back out of an acrylic pipe is that you don't polish the emitting surface, you make it as rough as possible so that as much light as possible escapes rather than getting internally reflected. Give it a couple of months (Cree XP-G leds are in short supply right now) and I'll post some results.

Polishing down to make a narrow exit, as you show, should work but I think it would be easier to mask off an exit aperture from a light pipe. If i was going to polish it out I'd probably hack a recess out then have at it with grinding paste and a steel ball.

Andrew
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ChrisR
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PostPosted: Sat Jan 23, 2010 4:20 pm    Post subject: Reply with quote

If it's rough it scatters more though, Lambertian-like. If your end is at a steeper angle than the Critical Angle, then the light goes though.
If you want to be able to read the Exit sign from everywhere, roughen the letters, if you want to project light, polish it - like you do with fibre-optics.

Yes, No??
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