Dry vs Oil

Harald · Post by **Harald** » Sun May 22, 2011 7:41 am

Hi there,
I´m new to microscopes, and I have some questions now and then. This is a great forum

What is the differense between Dry and Oil darkfield condenser ??

Pau · Post by **Pau** » Sun May 22, 2011 8:33 am

The oil condenser must be oiled to the slide. Its illumination cone has higher Numerical Aperture (up to 1.4 in some models) and allows to use objectives with higher NA than the dry one.

The objective NA must be smaller than the condenser NA to give darkfield. Usually a dedicated dry darkfiel condenser has an NA up to 0.8 and can be used with objectives up to NA 0.65 or 0.7 while the oil one can be used up to NA 1 or a bit higher.
The dry one is convenient to use with medium power objectives because it has a wider illumination field and is easier to use. With low power objectives a darkfield stop in a brightfield condenser works great.
I can't recommend a dedicated oil dark condenser until you have some experience.

Harald · Post by **Harald** » Sun May 22, 2011 8:39 am

Hi Pau,
Thank you for your quick reply..
I think I will go for the dry one. The oil condenser sounded a bit complicated to me

Charles Krebs · Post by **Charles Krebs** » Sun May 22, 2011 1:52 pm

Harald,

Also, if your condenser has a "filter tray" at the bottom is is extremely easy to do darkfield (at least with a 4X, 10X, and most 20X objectives) without going to a different condenser.