I had intended to use the RF 100-500mm for photoing insects close up because it focusses so much closer than the RF 200-800mm and it has much better magnification. RF 200-800mm mfd is at 800mm is a very long 3.2m, and the highest magnification is 0.25x at 200mm with an mfd of 0.8m. The RF 100-500mm has its mfd at 500mm of a very short 0.9m with magnification 0.33x. Yesterday, to my surprise I got my first butterfly shot of the year and it was with the RF 200-800mm at 673mm and very sharp. So, I tested both lenses close up with photos of a British £20 note. It has lots of areas of different degrees of colour shading and contrast, which are much more informative than monochrome charts. I did images at 3.5m, 2.4m and 2m.