As far as the fulcrum and vibration is concerned, I agree. But I have some dampeners built into the system and I don't currently believe it is having a major effect on me. The effect can be mitigated by moving the sample further toward the support. Or maybe to be more precise, I think I have far more practice to do, and problems to over come than that particular one at this time.
As far as moving verses stationary light ... You got me ... sort of.
I have proved to myself it doesn't matter.
Lets look at the fist diagram below and not be concerned for a minute about the position of the lights. We first need to agree that moving the object on the platform up toward the main objective lens is no different than moving the microscope(B] down toward the object(A). When we use the large or fine focus knob we are actually moving the entire scope body(B] up or down the base-connecting pole. We are adjusting a worm gear(C) that makes the actual travel happen. Hence only an observer looking from the outside would know if the sample got moved or the scope got moved.
Diagram 1
The only change in the system in the distance between the main capture ocular in the bottom of the scope and the subject matter (object A).
Now lets consider three different lighting scenarios:
Case 1.) light coming straight down from the axis of the viewing lens. (Some scopes actually offer an attachment that provide light through the viewing lens system.) Mine does not have this feature, but if the demo scope in the diagram did, then the lighting would not change whether the scope or the sample moved. The light being connected to the viewing axis and the direction of motion only provides a mechanism for the intensity of the reflection to change. Light falls off by 1/R2 (R squared).
Now this is true for any position of the lights you choose. Even if we keep the distance between the original light and the sample(A) fixed, the other distance (the reflected light) changes by the 1/R2 rule as that distance will change regardless of which moved.
As far as moving the light source with the sample, I did do this initially, not so much to control the various light angles, but because I wanted to use a ring light on the scope and it would typically sit around the main objective housing. So if any of you are currently using this set up then moving then focusing the microscope for multiple image taking will have the same "changing the light" effect as moving the sample.
The idea of using a ring light is to provide even 360 degree illumination and negate this effect. The light is also located as near to the center of focus as possible like the interior lens-light described above, again mitigating the effect. The little gadget I first made is pictured below. I wanted to keep the light as close to the object (sample) as possible to get maximum illumination. I used a plastic cylinder on the moving base and put the sample into the center of it The light was clamped on the outside of the cylinder and the whole unit moved up and down with the slide. Thus the lighting was effectively constant without regard to position. See next photos ...
Moving Light
I discovered that this introduced a new problem which is related to the lighting set-up I will describe below. The light being located near the sample top or an equatorial position on "some" samples produced internal shadow or (more accurately) added diffusion in the sample and provided poor viewing. This was the case in some gemstones where the internal flaw (item of interest) was surrounded by a veil or tiny bubbles.
Case 2.) Assume the light is at nearly a right angle to the object being photographed. If there is only one light source from one side or the other, then a strong shadow is produced on the opposite side. Think of this as the "sun-rise" or "sun-set" scenario. A small change in position of the object, will cast a much wider or shallower shadow with relatively little movement up or down. Thus during morning or night, in the "big" real world shadows are elongated to a high degree and seem to grow or shrink rapidly as the sun sets or rises. I submit in most microscopy photographs we try NOT to use this set up. We supply multiple light sources to open shadow areas. The only time the effect might be warranted is if we need to accentuate a very fine pattern in a sample. For example really fine etch lines is a crystal surface.
If you are trying to light a more or less clear gemstone to highlight an internal feature this lighting can backfire if the feature is within a cloud of other features. If the other features are solid, then they cast little shadows on the object of interest, or if they are translucent they will scatter the light making focus very poor.
Case 3.) light from above but not concentric with the focal axis. In most of my work I use multiple light sources to surround the object being photographed. This is done not just to reduce shadows but also to get sufficient light on the image for reasonable photography. Microscopes "eat light" in their precision and fine optics. Just like the low depth of field problem in a scope, the light passing through multiple layers of even "fine optics" continues to diffuse and remove light.
One thing which helps remove shadows and limit specular highlights is to use diffuse light. This works against the "intensity/strengthening" effect of light, but diffuse light really helps eliminate strong specular reflections where all information is lost. If you look at the second part of the first diagram there is a poor but roughly accurate light path map for a light being reflected from a crystal located below. (Yes it's an over simplified image, there are actually an infinite number of cones rising up from all positions in the sample ... that's just too hard to draw!)
Reflect light never comes from a true point source, and unless the reflected surface is nearly a perfect mirror, it diffuses the reflection itself. The reflected light from a typical light source (even a halogen fiber optic) produces cones of reflection and they spread-out as they travel away from the object. Only those outer most parts of each cone that actually strike the object lens (C1 and C2 in diagram) can be bent back and used to construct the image. Any falling outside the objective lens continue passing on to oblivion as far as the image is concerned. When we change the distance between the objective and the object being photographed we change the "field of view" of the final image. Hence some cones exit in the lower C1 position that will miss entirely in the higher C2 position.
SImple test, put a mm scale under the scope in place of the sample. Set the focus on the scope then adjust the magnification so that the outside edges to two mm markers just appear touching the edge of the field of view. Now move the fine focus knob two full revolutions in either direction. The two markers that were on the edge of the field of view will now be inside or outside the field. This means that items in the original field have either grown or shrunk slightly. Hence light angles hitting portions of them have change in the image.
Or ... look at the first and last photo in a deep stack of images, the outside edge cannot line up as the one taken from one end of focus are not present in the other. The good news for most of us is that much of the software we use will reposition the images in the stack or provide a means for us to do it.
From my (and I admit) limited experience thus far in stacking, if the lighting for the microscope is diffuse and relatively even, this will easily negate the changes in direction from stationary light source and the moving sample. (Basically one of the prime ideas in using a ring light.) Hence after doing about a couple dozen sets of images I have mostly stopped using the moving ring light, I see no major advantage. The only problem I do see is that when I poorly light a subject the specular reflections tend to be slightly larger than they should be. They appear to migrate slightly and broaden.
I personally believe we often spend a way too much time worrying about the "perfect system", there is no such thing. Everything we do to enhance one thing will always negatively effect another. Physics provides us with the saying ... there is no free lunch! Find a system that works for you and turn out results. I think it great to read about what others are doing as it aids us in our own learning and helps us see things in a different way. I enjoy seeing the gadgets and gizmos other use to solve problems.
