I am wondering what is the smallest object you can resolve with an optical microscope. I am aware of the equation
that basically gives you the resolution. $\delta$ would then be the minimum distance between two objects which will allow you to say that there are indeed two separate objects. But what if I do not care about how many objects are actually there, but instead of if an object is there in the first place?
Let's assume that I am using an optical microscope with an oil immersion objective. The oil has a refraction index of 1.5, so for a wavelength of let's say 500 nm the $\delta$ is ~166 nm. But what if my particle is smaller than this? 100 nm? 50 nm? Let's assume that this is a perfectly reflective metallic particle embedded in transparent glass. Can I still observe it?
This question is related, however does not address my question directly: Resolving power of a microscope?