MicrobeHunter.com Microscopy Forum

Never having used a darkfield slider, I first discovered that after removing the plastic slider stand-in, that I could not angle in the DF slider without force even though both widths were identical.

A Net search turned up much on DF illumination but almost nothing on hardware implementation. The one exception was a Motic presenter. I then found that the inverted hex head needed to be removed and I could then insert the slider. Why this "stop" exists, I have no idea. A beginner could do more harm forcing in the slider w/o removing the hex head.

I was happy to see that next to the DF stop, I also have a hole for brightfield, which means I can keep my DF slider in the condenser.

Using as an example a permanent diatom slide, under DF, I viewed nothing but black opacity. However, at about 2/3 illumination, hundreds of specimens appeared! The DF seemed to do well on shape outlines and not so great on internal detail/resolution. More practice should teach me when DF is superior to brightfield. I'm thinking it might be useful for transparent organisms.

Is a DF slider the "cheap" option compared to same on a turret or are they the same?

The one puzzle I can't figure out are the long centering screws. I see where they insert and upon turning them, I can see that they change the position of the stop. But it seems impossible to use them when the slider is in my condenser. I will have to check if there is any entry space in the back of my condenser but I doubt it. I have no idea how it would be possible to center without looking through the eyetube.

I have a solution for centering the stop which I found at https://moticeurope.blogspot.com/2016/ ... tion.html

Not having a centering telescope, I place a rectangle of graph paper on the stage. With illumination turned up under DF, I can confirm that the stop is centered. The diagram shows examples both of centered and uncentered stops. If necessary, you then adjust with the screws and re-check. It seems that this only has to be done once.

So, yes, unlike centering the field illumination image on the object plane while you are looking through the eye tube to implement Koehler illumination, this one you do manually and re-check before viewing a specimen.

How to Remove an Artifact

I'm looking at a specimen with proper DF. At a certain brightness, when I turn up the illumination, I see my DF stop in the center of my specimen! Turning down the light causes it to vanish but then I lose some resolution because the image is too dark . . .

Does the artifact of the DF stop go with the territory if the illumination is turned up too high or is there a way to remove it?

Surprising Color Change Observation

When I look at one of my cockatiel's yellow feathers in brightfield the color is black and various shades thereof and I have excellent resolution. When I change same to DF the true color (yellow) appears! How can this be??

I suppose that in BF, the opaque parts of the specimen are black, since no light penetrates, but in DF, light comes in at a sufficient angle to reflect off them, showing color.

@Dubious

Yes, so opacity in BF is an artifact. However, BF gives me superior resolution of internal versus peripheral features. It will be interesting to compare colors of specimens BF vs DF. Some artifacts (a bubble) can be ignored; others, although lacking in one area, provide useful information in another. I could use BF for looking at the morphology of an alga, then switch to BF to see actual color, albeit less detail.