Hi,
coating just the surfaces of porro prisms is not going to improve things so much - after all it's just 4 surfaces (or even two if the prisms are cemented).
Objective is also 4 surfaces in the case of the usual fraunhofer or air spaced doublets (and 2 again for cemented doublet).
The largest gains will in the eyepiece as they usually have 3 or more groups and with 2 surfaces per group huge gains can be had for coating these.
Joachim
Joachim,
You are totally right. But to do a group you still have to disassemble it and also deal with the cemented doublets somehow. If the lenses are coated you need to decoat them, probably. Or maybe not. Someone has pointed out that single coatings are an acceptable first layer for multi-coating.
I was thinking of the Porro prism as a drop-in swap, and of transmittivity as much as of the surfaces, a glass change together with a coating change might make a really perceptible difference to the view. Think absoption spectrum.
In the case of old roof prism binos the dielectric coatings on the prisms makes a huge difference in sharpness with just that change as the paper points out, while in some designs there is an astonishing number of reflections. Maybe one can buy/remake these parts and drop them into old roofs
At some point I guess someone with access to an optics small-run manufacturing or prototyping lab will chime in and tell us what optical parts modern machines can custom make, when it comes to lenses, prisms, and coatings.
Living in France, I have learnt that there is usually some trick to get 80% of the results at 20% of the effort
I suspect that the procedure you suggest is the most rational, for a hobbyist disassembling and cleaning oculars and possibly recoating a couple of lenses there maybe is the most effective time investment, the simplest, and the least risky as it wouldn't interfere with the collimation of the rest of the system.
At least we're having a fun discussion
Edmund
PS. The interesting takeaway from this discussion is that phase-coated prisms define the turning point at which roof-prism designs can truly compete with porros for sharpness.