1- Using different condenser prisms for different magnification objectives. The goal in all cases is to match the interference band of both prisms at the rear focal plane of the objective. This is the original Nomarski design first implemented by Zeiss.viktor j nilsson wrote:Here's a few more question:
1) how is it possible for the first-generation Zeiss inko system to use a single objective prisms for all objectives? The more I think about it the weirder it seems. How would you design such a jack-of-all-trades prism?
2) is it really critical to place the objective prism exactly at the rear focal plane of the objective? It doesn't seem that way to me: some systems place the prisms immediately between the objective and the nose piece, and others (from the same maker) place them well above the objectives inside the nosepiece or inside an intermediate tube. Surely the location of the rear focal plane can't be that different among the objectives for those systems?
Zeiss moved to the individual objective prisms at the nosepiece design in their double arrow system but Olympus still uses the original design although with objective-dedicated changeable condenser prisms
2- In principle it is, although I think that you can place it a bit higher or lower if you still accomplish the condition of matching the interference band of both prisms at the same plane and close to the objective rear focal plane (I suppose that this is what I'm doing when I move a bit the condenser outside the Kölher position to obtain DIC in my hybrid setup)
It depends of the prisms design, the "section or beta angle" referred by abednego1995 is what determines the distance between the interference plane and the objective rear focal plane.
With a Wollaston prism this plane is placed inside the prism but the modified Wollaston prism by Nomarski places it outside the prism. I think that some Leitz DIC systems placed the prisms inside the objective for this reason (and so avoiding to pay Nomarski license fees)