#4
Post
by apochronaut » Thu Aug 20, 2015 4:23 pm
Ii is hard to tell, without seeing the actual optical view but I would say # 1 has the best combination of contrast and resolution. Higher power phase rings also make great low power df stops. On AO the 100X phase ring works great with the 4X objective when using standard 1.0mm slides or thereabouts. Other rings give different and also useful effects.
With darkfield, the thickness of the slide is important. With a df condenser there is always a slide thickness specification following the practice of the U.S. makers or an N.A. specification following the practice of German makers. The two amount to the same thing in practice, with the slide thickness being a predictor of N.A. in the former and the N.A. being determined by slide thickness in the latter. The necessary slide thickness is always thicker than the 1.0mm that is commonly used these days. Usually 1.15-1.35.
With the possibility of varying df stop sizes, as in this test, the slide thickness is as much a determining factor of performance as the stop size. If the slide was thinner, the stop would need to be larger and if the slide thicker, the stop would need to be smaller. The thickness of the cover , also would have some small effect.