Hi fellow IIS-ers.

Recent comments about Strehl ratio for one wavelength got me thinking that perhaps I got it wrong. Several much more experienced astronomers used PV value only in estimating Strehl, ignoring the rms wavefront error or even stating that rms wavefront error is meaningless in determining Strehl. This has challenged my understanding, which can be summarised that it is exactly the rms wavefront error that should be used in estimating Strehl, and that PV can be ignored as long as it is within a good standard. I found

this article confirming my line of thinking, but is it a credible source of information?

Here is the relevant part from the article:

*However, it is not the peak-to-valley nominal aberration, which only specifies the peak of deviation, and tells nothing about its extent over the wavefront area. It is the root-mean-square, or RMS wavefront error, which expresses the deviation averaged over the entire wavefront. This average wavefront deviation determines the peak intensity of diffraction pattern and, hence, numerical value of the Strehl ratio (note that the RMS error itself is accurately representing the magnitude of wavefront deviation only when it is affecting relatively large wavefront area, which is generally the case with the conic surface aberrations).*