In high resolution DF, the objective must be stopped down, either with a funnel stop or an iris. For this reason DF can give surprising depth of field, as well as surprising resolution.
"Surprising resolution" I happily accept ... but surely that resolution can never exceed the resolution provided by the full-aperture configuration of the same objective design.
as far as I know the outer light rays of the light cone contribute more to the resolution than the inner light rays. A DF condenser provides just these outer rays.
A very fair point, Bob ... But ...
[please forgive me if I am being excessively literal
] I am aware of no method by which the resolution
of a good objective can be increased by introducing aperture stops of any shape, size or position. [caveat
: Yes, a bad objective can probably be made to perform less badly].
This thread started with the question of what might be done to improve depth of field; and it has now developed into a discussion of the trade-off between d-o-f and resolution. ... I currently remain convinced that it is impossible [except in the context of focus stacking] to increase d-o-f without decreasing resolution.
I would, of course, be delighted
if someone could demonstrate that I am wrong !