Checking the specifications, the Beseler 23C-iii-XL Variable Contrast Black & White, sports a diffusion lamphouse and its adjustable grade 0 thru grade +5. I think you will find the diffusion lamphouse desirable as opposed to a condenser design. The diffusion design suppresses dust spots greatly reducing spotting time. Plus this design is favored by portrait photographers because the output has less apparent sharpness compared a condenser enlarger. The dust suppression of the diffusion enlarger is due to the fact that light hits the negative omnidirectional. Thus dust mites cast diffused shadows. The drawback is, a diffused enlarger produces prints that are about one paper grade less contrasty.

Conversely, a condenser enlarger features two plano-convex lenses that focus the light so the beams arrive at the negative plane parallel (collumated). These straight on rays cast harsh shadows of the dust motes plus every scratch and fingerprint on the negative is boosted. The condenser design boosts contrast about one paper grade plus the resulting print has increased apparent sharpness. The downside is, get out your spotting brushes because you will see a plethora of dust spots. The increase in contrast has been well studied, look up “Callier Effect”.

I was unable to verify, but I recall that they are dichroic. A dichroic filter is glass with a thin deposit of metal. They pass and hold back based on the thin-film principal. Since they are made using passive (inert) metals, they have longevity in the environment of a hot-bright lamphouse. Dichroic’ filters are a plus.

Also, this model’s lamphouse can be retrofitted to a color head and/or a black & white condenser, if you can find the parts.