https://www.reddit.com/r/microscopy/comments/v09vdm/is_the_objective_im_looking_for_100x_dry_a_valid/What are you looking for, specifically? Like, if you are just looking to see if your cells light up at all or count nuclei, you don't need a lot of resolution, then low NA is fine. Remember that a decent 40x with like 0.8 NA well have the same resolution as a 100x with 0.8 NA. Same blurring, but the 100x makes it look bigger, while the 40x will let you see many more cells (good if you are counting).
I would usually say an air 100x is not a great option. I go into a LOT of labs and air objectives over 40x are pretty rare in biology (I'm sure there are some fields where it makes more sense). With a40x or 20x air, you'll usually get the same resolution but a much bigger field of view.
I would say get a bit lower mag with better correction. Whether it is plan or achromatic/apo, or both, that will help more then spending the extra on 100x.
But let me know more and I'll take a another look.
