I wish the so-called crop factor (magnification factor) never existed. They serve only us gray-hairs that lived and breathed the 35mm film camera. Cameras evolve! My mentors used the 8x10 view camera. My boss used the 5x7 portrait camera. I used the 4x5 and the medium format before switching to 35mm. We never worried about a crop factor as we progressed. Why a crop factor? We gray-hairs discerned the field of view delivered by our arsenal of lenses we used on our 35mm camera. If we converted to a compact digital, we thought a handy prompt would help us identify what lens on our new little camera would delivered a similar angle of view. Hence the crop factor; I think it is of little use to those without a history of 35mm film camera usage.
How the crop factor is computed: We find the diagonal of the larger camera we have grown accustomed to. We use the Pythagorean method to find the diagonal. The 35mm format is 24mm wide by 36mm long the diagonal via square root of (24x24+36x36)= 45 mm. Next we find the diagonal measure of the Sony A6300 a compact digital 16mm wide by 24mm long – diagonal = 30mm. Now we divide to find the crop factor --- 45 ÷ 30 = 1.5.
Another way to look at the 1.5 crop factor! Convert the 1.5 value to a percent. Thus 1/1.5 x 100 = 66%. This tells me that DX (compact digital is smaller. It is 66% of the bigger guy's format.
That’s the crop or magnification factor. What does this tell us? If we know the angle of view delivered by a 70mm mounted on a FX (full frame), we divide by the crop factor -- thus 70 ÷ 1.5 = 45. Therefore a 45mm on a compact digital will deliver about the equivalent angle of view. (Values rounded for convenience).
The Sony RX10III format is 8.8mm wide by 13.2mm long and the diagonal measure is 16mm. The crop factor to compare the venerable 35mm to this format is -- 45 ÷ 16 = 2.8. If a 70mm is mounted on an FX than 70 ÷ 2.8 = 25. This tells me that a 25mm on a Sony RX10III delivers an equivalent angle of view. Another way to look at a crop factor of 2.8 is 1/2.8 x 100 = 35% (the imaging chip is 35% of the size of a FX format.
Nobody said this stuff is easy!