MicrobeHunter.com Microscopy Forum

At my unit we are planning a optical microscopy course. One of the main topics in it would be different contrast techniques, their pros and cons and usage. This is relatively straightforward with stereo microscopes as one can easily use fresh pond/stream/other samples and demonstrate reflected, brightfield, darkfield, polarization and Rottermann Contrast, i.e. what our instruments are capable of. Pretty much the same with inverted scopes at least when the focus is on biology, it's rather trivial to collect fresh zooplankton samples and then demonstrate the options we locally have available in our scopes: brightfield, darkfield, polarization, phase and DIC.

However with upright scopes and slides we would prefer to find a set of good quality prepared slides. Ideally the selection should include subjects that would be helpful in the context of teaching the contrast techniques we have available: brighfield, darkfield, polarization, phase and DIC. Do people here know of prepared slide collections (makers, sets) that might fit the bill?

We are intentionally leaving fluorescence out due to a few reasons. It might be viable as a short course on it's own, though. We are also likely not going to teach slide preparation and microtome use on this course, due to not having the proper gear or enough gear for it, but also due to time constraints. Confocal, SEM and so on would be handled in a different course, run by a unit that is well versed in these (we aren't, at all!).

IMHO, a commercial permanent strew slide (for relatively low cost) or arranged slide (where budget is not limiting) of diatoms sounds to me very practical, in spite of the "vintage" atmosphere that it may broadcast. It will clearly demonstrate all mentioned modalities except for polarization and fluorescence. I believe it will nicely demonstrate DIC although I'm familiar with images of live diatoms rather than fixed frustules. For polarization, a tiny grain of very common quartz sand, glued to the slide with anything, will serve. Home made, but inexpensive and simple to prepare.

Edit: IMHO, slide preparation is a vital part of introduction to microscopy, so I would think it very appropriate that students in the basic class prepare at least some slides.

I need to look up what a strew slide is. I saw some diatom arrangement slides on the web and they might be an option. Depends on how many slides we deem necessary, those things seem to be expensive.

The sand grain tip sounds great!

Recently bought some very nice new diatom strew slides on Ebay, I think they would be ideal for this purpose, I've looked at them in basic darkfield and phase contrast in comparison with brightfield and the difference is evident. I also like to look at filamentous algae or duckweed and the micro-organisms associated with them, a change from brightfield to either phase contrast or darkfield often reveals a lot more detail.

You may want to show how the thickness of specimen preparation affects contrast methods as well. Stains also affect the choices. This will be easier and more beneficial with prepared specimens - so if most everything you're doing is unstained live protists and plankton it is perhaps not as relevant.

Dramatic contrast effects can be obtained with a mix of water and oil (fat, soap, etc.) under a coverslip. The tiny bubbles, pseudo-vesicles, etc., can be dramatic under dic, darkfield, and phase - and it's easy for the user to manipulate things like cover slip pressure.

Hi, rorshack..I'm late to your thread.

Please consider low cost : "Diatom Lab", of Stefano Barone..for wonderful permanent slides which you may use to calibrate, to understand the optical performance of the variety of your optics.

On several occasions I have purchased slides from "Diatom Lab"..diatoms, and radiolarian slides. Please visit his shop..look around.

all the best, charlie guevara/ finger lakes,US

Pete, Charlie & woodytia, thanks for the excellent suggestions! Looks like we have good choices.

A slide of fluorescence beads and a stage ruler will work decently for it all. You can use the beads to demonstrate BF vs phase/DIC, because under BF, they are hardly discernable.
Any petrographic slide for polarised light.
Blood smears for phase, DIC and oblique.

Thanks Macro_Cosmos, good tips!