Dear List, We've been using the older olympus XLUMPFL 20x 0.95 NA objective, and have been getting decent images at large imaging depths. But for two reasons we're looking into purchasing a new objective. First, when we do point spread functions measurements for two-photon fluorescence at 780nm excitation with this lens, we always get measurements that are significantly larger than the size predicted from the diffraction limit (~30% bigger laterally and ~50% bigger axially). We're careful about index matching, overfilling the back aperture, etc., and can get close to diffraction limited PSFs with other lenses, so I believe this is a limitation of the lens, probably at NIR wavelengths. Second, we'd like to get a lens that can be used with a coverslip (preferably one with a correction collar). It seems there are at least two objective lenses I can find that would be good for our upgrade (we also want to have a working distance ~> 1mm): the olympus 25x 1.05 NA W, and the nikon CFI Apo LWD 25x 1.1 NA W. Their specs are very similar, so I'm wondering if anyone has had any experience characterizing them, or can suggest other options that I haven't found. They both say they are "corrected" out to 950-1000nm, but based on our experience with the older olympus, I'm doubtful they perform at the diffraction limit in this range. The Leica HCX 20x 1.0 also seems nice, but doesn't have a correction collar. Has anyone done PSF measurements on any of these objectives? Or compared them in any way? Best Wishes, -Nick