Thom doesn't see dSLRs going the way of the dodo. Cameras of all types have their uses, and niches. As mirrorless establishes a larger foothold in the dwindling camera market, the dSLR will become, in Thom's words:
“the new Medium Format. In other words, the ones who are truly serious about extracting all they can from their imaging will still use DSLRs, while the rest will use mirrorless cameras. ”
Many FF 35mm photographers stepping down to smaller sensors notice that lens parity doesn't exist. A m43 sensor attached to a 150mm f/2,8 lens may achieve a similar angle of view as a FF 300mm lens, but its DOF will be closer to a hypothetical and compact 300mm f/5,6 lens.
Size advantages exist only when taking DOF out of the picture. In Thom's words:
“Mirrorless cameras are turning into smaller, lighter, excellent performers that do well in a limited range of focal lengths, typically 16-105mm. It’s when the subject starts moving fast and/or you need lots of reach that those three adjectives (smaller, lighter, excellent) tend to disappear.
I’m not convinced that those three things will be “fixed” in the near term, if ever. Once you get into longer telephoto lenses, the lens size and weight tends to be dictated by focal length and aperture and less by sensor size. A 300mm f/2.8 lens will be at or near 300mm in length and the front element will be over 100mm wide. Sure, m4/3, with it’s crop length, can produce a 150mm f/2.8 lens that’s “equivalent,” but it will still be 150mm in length and feature a 58mm front element or larger, and technically it has a two stop disadvantage to a full frame 300mm f/2.8, so we really should be comparing to a 300mm f/5.6. An APS system will need a 200mm lens, and it’ll have a 72mm front element at f/2.8 and just over a one stop disadvantage. In other words, there’s some scaling, but the size/weight of telephoto options tends to start creeping beyond the small, light category and aren’t delivering the same subject isolation at f/2.8.”
I'm assuming that by 16-105mm, Thom is referring to 35mm FF equivalent focal lengths, as 16mm on 1", on m43, on APS-C frames quite different images. Extrapolating on the above, lenses for smaller sensors returning FF-equivalent framing and DOF to a 300mm f/2,8 would be just as large, if not larger, than the lens they were designed to emulate. Which is why compromises exist.
All systems are limited by two pillars: size and performance. Small-sensor mirrorless cameras have certain advantages. Equating FF DOF and angles of view limit much of their utility and every size advantage they boast. And yet, dSLRs grew up to be beasts. Even Nikon's compact D5000 is a beast next to a typical film-era SLR.
Which is one reason Thom concludes thusly:
“Maybe there isn’t one [be-all, end-all product] any more, and you simply use mirrorless for one set of tasks and DSLRs for another.”
