This is caused by the lack of NA in the condenser. If you change to a high NA condenser you may loose the working distance you need. If you are doing photography or video through the microscope you should use an Achromatic-Aplanatic. This is very good for high performance microscopy such as cyto-genetics but it means that the condenser won't provide full field illumination at powers under 10X in most cases. Achromatic-Aplanatic optics are used in most Nomarski condensers.
Nomarski condensers are usually of the pancake type.
The pancake contains a ring that holds the various Wollaston prisms. Since each manufacturer varies in how they make their prisms you need to use a condenser and objectives from the same manufacturer. A Nomarski condenser must also have a polarizer that can be moved in and out of the light path. Usually the polarizer can be adjusted. The easier this is to use the better.