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Not much has been said about the practical aspects. If you will be imaging slides, then oil immersion condenser is best, although a high NA dry condenser (0.95) may work just fine for your needs and may be more practical. If you will be imaging dishes, chambers, plates, and such, then you can't use an oil immersion condenser, and you may not even be able to properly set Koehler illumination with a dry high NA condenser because their working distance is quite small. We use long working distance (and therefore low NA) condensers on all our inverted scopes, simply because they work with a broader range of samples. Illumination intensity is generally not limiting in bright field, and you often don't need to achieve maximum theoretical resolution either. The only times a low NA long working distance condenser has been a problem for us is when using a 100x/1.4 Phase contrast objective (but we were imaging bacteria in a flow chamber, and a high NA condenser wouldn't work too well either), and also when trying to collect single harmonic signal on a transmitted light detector on a multi photon system, where the collection efficiency of a high NA oil immersion condenser would be much greater. On our upright microscopes that we use primarily for slides, we use high NA (0.95) dry condensers. If you are doing dark field, then NA of the condenser also needs to be greater than NA of objective.

Julio Vazquez, PhD
Fred Hutchinson Cancer Research Center
Seattle, WA 98109
fredhutch.org

On Mar 17, 2016, at 10:50 AM, Kyle Michael Douglass wrote:

> Hello listers,
> 
> 
> I have a couple of questions about condensers for you. I'd like to do some transmitted light imaging in an inverted microscope using high magnification, oil-immersion objectives. For the moment, I don't need to do anything other than brightfield with a high power LED light source. It might be nice to do phase contrast or DIC in the future, but I don't need it now.
> 
> 
> My questions are:
> 
> 
> 1) What are the rules of thumb for matching a brightfield condenser to an objective? I won't be using anything but oil immersion objectives with NA's greater than 1.4.
> 
> 
> 2) If I do want to do phase contrast or DIC in the future, should I put special consideration into the condenser lens selection now? I imagine the condenser NA will determine what phase contrast rings I can use, but does it impact DIC?
> 
> 
> Thanks!
> 
> Kyle