Resolution power of the Bragg law

A physical system that follows the Bragg law of diffraction, for example an electron scatter, shows interference patterns at some angle that follows the equation $nλ = 2dsin(θ).$ Usually just the first order interference ring is visible. I want to know what wavelength I can use to distinguish between two different crystal lattices, so I use the Rayleigh standard to know if the space between the two rings are enough to solve them.

The Rayleigh standard require to know the position of the destructive interference, or in other words, the thickness of the rings. Are there any formula to solve this?