Help: has anyone ever used Olympus DCW Darkfield condenser?

[viktor j nilsson]

Your DF condenser should be a mirror/reflectingcondenser of some type. Perhaps Viktor knows which for sure. The degree of ca produced in high N.A. DF condensers is from very low to none. Paraboloids have a small amount, spherical too but cardioids, none.

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I did some checking and the BH2-DCW condenser model # based on it's specs., likely translates as For BH2 model microscope, .dark field condenser, cardioid design, wide field. It's high cost , likely stems from it's wide field design, which can go as low as a 20X objective at an F.N. of 22, which is pretty good. An average oil immersion high N.A. DF condenser would get to an F.N. of about 18 with a 20X. That is one rational for many older microscope systems using 25X objectives, rather than 20X, allowing more conventional DF oil condensers to cover the field at 25X.
The best I have seen are the AO/ Reichert toric DF condensers, which cover an F.N. of 20 at 10X.

Earlier BH era catalogues describes the BH-DCW condenser as being a cardioid type. The detailed specs are very slightly different (7.8mm fl for BH, vs 7.65mm for BH2), but I think it's fair to assume that they are optically very similar.

[apochronaut]

On some DF condensers, there is a slide thickness specification stamped right on the condenser. This would relate to the f.l. of the condenser .
There has been a slow but steady impetus for microscope and related manufacturers to standardize on certain default specifications, one such being the thickness of slides. In todays world, that thickness is 1mm unless otherwise noted. That wasn't always so . Standard slides used to be thicker and those used for DF even thicker, with 1.25mm being a usual maximum for DF.