Larry Legg's Learner Projects
So it is with Microscopy. The cone of light 'examines' the specimen. 'It' transmits the specimen detail up a long tube to your eye. The cone of light is manipulated from the start of its journey to its finish so as to 'resolve' detail in the specimen and carry it faithfully to our eye. We have constructed a set of devices to manipulate that cone: lenses, discs, grids, color filters, wave-length managers, light sources, apertures (shielded holes) to optimize the cone itself and the way its independent waves of light probe our specimen, and depart from it carrying its quota of detail. This set of devices, correctly aligned, is the microscope - but it is the cone-of-light and 'its' perfection which allows us to see more than just with the naked eye.
If yer would prefer a more formal, and scientifically-eloquent account and description of how a microscope manipulates and 'shapes' this cone of light, I would recommend yer purchase - The Microscope, A Basic Guide by W.G. Hartley from the Onview on-line shop under the books section!
The Lighting Debate
I don't wish to get into such debate. Suffice it to say, and take it from me as gospel - no matter what lighting yer use, nothing you see is a full and complete representation of the true nature of what yer observing. What yer see down a microscope is a deformed, normally dead, falsely colored, clumsily 'propped-up' mess of its former... and living self! Truth is, by the time we've sliced off a wafer, fixed it, pumped all the water, oil, and other liquids out of it and replaced it with something to help support its collapsing structure - we're stuck with a house that's just been through an earthquake.
But... and it is an important 'but', we get enough left to tell bricks from mortar - if yer will excuse me metaphor... and by taking different views on it, and lighting it different ways, we can get a little closer to the truth about how 'it' (our specimen) must have looked and functioned before us microscopists came along and chewed it up this way and that so we could get a chance, the only way we know how, to see it magnified!
We get a better deal when examining living stuff like pond life but even here - we often see less than the truth... but we'll talk about that another day.
The important thing about lighting..? There is only one to really remember: you need it!
That said, I'll take yer through the four most useful forms of lighting. I have never had occasion to use any other form of lighting except these four, so maybe, just maybe, they will do enough for you so yer won't ever need anything more.
The four forms (simplified) are:-
Incident and Transmitted Illumination
Now, yer have to understand these two terms refer to lighting source methods only - from beneath or from above. They don't represent 'forms' of lighting - which will involve a bit more about how light travels from either source, through one or more 'devices' to light up whatever it is yer gonna be looking.
I never call these two light source methods anything else but 'under-lighting' and 'over-lighting'. Much simpler and easier to say to others. Why not call 'em the way I do and help make life simpler for others too.
When using under-lighting, several devices are often used on yer average microscope to get the light onto the specimen in the best way to send a clear image up the tube through the eyepiece lens to yer eyeball and brain. It doesnt matter if yer using a mirror or a built in light to get the light on its way to the underside of the specimen, yer still need to do something to manage the light before it arrives at the specimen.
The idea is to bung some light on the specimen in such a way as to provide maximum resolution - that is: the ability to define detail between two close points of a specimen. Here's some resolution examples for yer. eample 1) " example 2)#
Yer can see two little strokes in example 1 and four strokes in example 2. If the dots on yer screen were bigger, there would come a moment when example 2 say, would just look like this example 3) + (less resolved!)
To obtain some resolution, yer have to get a cone of light going up through the slide. This way, each wave, quantum, point of light, will slowly separate from its neighbour - taking with it a point of image detail from the specimen. The greater the width at the top of the cone, the greater the points of light (and the detail they will be carrying) will separate and this will maximise resolution. The cone is aimed and shaped so that the top of the cone hits the objective at the widest angle. This creates a limitation. If you create a short wide cone too quickly, yer have to get that objective lens very, very, close to the specimen to pick up all the detail and points of light before they whizz past the lens. Wide cone = best resolution! When you create a wide cone (maximising resolution) yer end up with very little space to work between the slide and yer lens and nearly end up trying to plough down thru the specimen to gather up all the cone of light!
A Black Hole
Well if we used our mite above as an example - we would see this:-
I'll show yer how to do this in a moment - it's an easy one to do!
Other ways of manipulating or 'interfering' with the cone-of-light is by 'Phase
Contrast', 'Rheinberg's Differential Color Illumination',
and a few others but not important right now to get going with me projects.
The one below was produced by interferring with the light cone with a device commonly called 'cross-polars' to 'polarise' the light:-
One more thing! I'm using a bad lighting source for my images. It is a desk-top florescent light. It's better to use a round halogen desk-top light if you have either an SP301 or a microscope with a concave mirror. You need an even field of light for best results. You need to line up everything: light, mirror, condenser, iris, filter-holder, so everything is nicely centered and parallel to with every other device in the light cone path. I'm in a hurry to show yer things, so I've cut the frills and messing around with my set-up to show yer results which can be obtained with the most coarse methods.
If I show yer what can be done 'quick and dirty' - yer can soon find out for yerself what can be done with a little patience and fiddling around.
Lets get going then and make a black hole for our cone of light so we can do dark-ground illumination!
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