Hi Ron,

I also want to thank you for replying to my darkfield situation. Yes, you are
right, my condenser has that NA range. I think, what I will do is just
experiment further with my available optics and take it from there. As far as
darkfield goes, I am primarily interested in microorganisms.
I have heard of the cassegrain oil darkfield condenser, but I don't think that
Olympus sells them for my microscope type, I am not sure. I will check the info
at molecular expressions also. Once again, thanks.

Ralph

--- In Microscope@yahoogroups.com, "Ron Lisk" <ronaldlisk@...> wrote:
>
> Hi Ralph,
> The condenser you're using has an NA probably between 1.2 - 1.4.
> Therefore, unless the objective is stopped down to around unity you will
> achieve only a muddy grey background rather than black. You can get
> darkground condensers which allow utilisation of the full aperture of an
> oil immersion condenser (eg. cassegrain) but I have no experience of
> these. However, if your interest is in protista then the maximum NA of
> the optical system will, in any event, be constrained to 1.33 by virtue
> of the water content. With such a condenser you may be able to achieve
> darkground with a 100X 1.25NA objective. I must say however that I use
> in the main, two objectives with my OI darkfield condenser:- 40X NA .95
> (dry) & 30X NA .90 (WI): the latter used with the condenser immersed in
> distilled water rather than oil. I don't know that the improvement in
> resolution of c. 80 nms would be worth the incresed technical problems
> associated with centreing the condenser for use with an oil immersion
> objective. Perhaps someone with more experience could comment on that
> aspect.
> In the meantime, I would draw attention to the relevant pages from
> Molecular Expressions.
> http://micro.magnet.fsu.edu/primer/techniques/darkfield.html
> Ron.
> --- In Microscope@yahoogroups.com, "grimra" <ralphg@> wrote:
> >
> > Hi all,
> >
> > I am using darkfield illumination for most of my microscope work. It's
> so beautiful with the jet-black background and microorganisms looking
> like Chinese lamps floating through the night.
> > I have a question though: I want to use higher magnification of say,
> 700-1000x using an oil immersion objective such as an 100x Olympus
> Planachromat with an NA of 1.25 for a BX50 microscope. I am using a
> cardioid oil darkfield condenser with an NA of 1.40. Can I use this
> objective with the condenser as it is, or do I have to use a stop of
> some sort for such an objective?
> > Thank so much.
> >
> > Regards,
> >
> > Ralph
> >
>