The in-line, digital holographic system that I am designing is similar to this article, https://www.ncbi.nlm.nih.gov/pubmed/21460907, which images a range of particles present in clouds. I understand that for the smallest particle that I want to be able to resolve, I would use the equation, NA = (1.22*lambda)/D, where lambda is the wavelength of light and D is the diameter of the smallest particle is the system. However, once I have found the numerical aperture according to the smallest particle that I want to resolve, what equation would I use to approximate largest particle I can resolve with this numerical aperture?
The resolving power of your system is an issue for the smallest particle that you want to resolve. Provided that you can resolve smaller particles, you would be able to resolve the largest particle as well. A different issue is whether the largest particle can fit into the field of view of your system, but that is usually not a problem.