Calculation. 35 mm equivalent focal lengths are calculated by multiplying the actual focal length of the lens by the crop factor of the sensor. Typical crop factors are 1.26× – 1.29× for Canon (1.35× for Sigma "H") APS-H format, 1.5× for Nikon APS-C ("DX") format (also used by Sony, Pentax, Fuji, Samsung and others), 1.6× for Canon APS-C
Incidentally, this is the point that your linked article is making. If you hold the angle of view, and the aperture diameter fixed (e.g. they used a 50mm f/4 lens on full frame, and a 25mm f/2 lens on 4/3rds), the depth of field will be the same for the same composition (meaning equal focus distances, aspect ratio, and framing).
But put that same 100mm lens on an APS-C body with a 1.6 crop factor and it frames the scene like a 1.6 × 100 mm lens (a 160mm lens) would have done on a full-frame. What’s happening is, the APSC sensor is smaller and only big enough to capture the middle bits of what’s projected by the lens, which quite possibly is the most distant stuff
This extends to the APS-C lenses that people often use with them. For those with smaller hands or who want a lighter option (especially if on the go), this may be preferred. Sony's Full Frame mirrorless cameras are a bit larger and heavier (although still quite lighter and more compact compared to DSLR options).

Adding a teleconverter will also reduce the light by 1 stop for a 1.4x converter and by 2 stops for a 2x. However, adding a teleconverter doesn’t change the lens’ minimum focusing distance. For example, if you add a 2x converter to a 300mm lens that focuses down to five feet, you get a 600mm lens that focuses down to five feet.

Full Frame Sensor vs APS-C Sensor. Full Frame (FE) = Sony A1, A7C, A9 II, A9, A7R IV, A7r III, A7S III, A7sII, A7III, Etc… APS-C (E) – Sony A6600, A6500, A6400, A6300, A6100, Etc… The Sony full frame sensor cameras and APS-C sensor sized cameras BOTH USE the same E-Mount, but the lenses are designed differently for the sensor coverage . 31 188 45 312 300 236 9 256 239

full frame vs aps c lens conversion