What is the difference between these various Angular Resolution formulas? I have recently learned about angular resolution and its dependence on the ratio λ/D. There seem to be three different equations for angular resolution that I have come across. One of these has the number 1.22 (radians), while the other contains the number 206,000 (arcseconds). A third equation states that angular resolution can be found just with the ratio λ/D. I have attached a picture of these three different equations - please pardon the bad merging!
Naturally, this has caused some confusion on what situations each of these equations apply to. Would one of these be more relevant to an interferometer — while another is for a single telescope? I'd like to share that these equations come from the textbooks &quot;Foundations of Astrophysics&quot; (Ryden &amp; Peterson) and &quot;Understanding Our Universe&quot; (Palen, Kay &amp; Blumenthal). If anyone has come across these equations, I'd be grateful for some advice on how to distinguish them (i.e. what situations or conditions they apply to).

$$\theta_\text{min}[\text{rad}] = 1.22 \frac{\lambda}{D}$$
$$\theta = 2.06 \times 10^5 \frac{\lambda}{D}~\text{arcseconds}$$
A telescope's resolution is determined by the ratio $\lambda/D$.
$2.06 \times 10^5$ is the radian arcsecond conversion, equal to $180 \times 60 \times 60 / \pi$ .
The $1.22$ is a geometrical factor applicable to circular apertures, as outlined in Wikipedia.