Large Skipper, Ochlodes sylvanus, in flight. My old Canon 6D full-frame digital SLR would never have locked focus quickly enough to get a shot like this. This was taken from about 3 or 4 metres away with a 600mm zoom on a Canon 7D mkii. f/6.3, 1/1600s, ISO 500. I should’ve used a faster shutter speed to freeze the wings as they flap very quickly in this skippy little butterfly.
The 2/3rds cropped sensor of this camera gives the Sigma lens the equivalent “reach” of a 900mm lens, i.e. nominally 50 percent longer focal length. This is an arbitrary fact really, it’s not optical zoom, it’s equivalent to digital zoom on a pocket camera. The photo is also cropped to a much smaller square. Nevertheless, with a similar number of pixels on the smaller sensor and ignoring edge effects, which are negligible except in extremely tightly cropped images, this is far superior to something the 6D would manage.
For those who wonder what the difference is between butterflies and moths, there is none. According to Lepidopterist David Slade asking what is the difference between butterflies and moths is like asking what is the difference between ladybirds and beetles. The butterflies are simply a sub-group of the so-called micro moths (generally considered to be “less evolved” than the macro moths, with a few exceptions), just as any other sub-group within the Lepidoptera (Noctuidae, Pyralidae, Erebidae, Geometridae` is).
The butterflies as a group of moths, however, do differ from all the others, micro and macro in that they lack a mechanical coupling that hooks forewing to hindwing.