Canon 5DSR II
- Aug 16, 2012
A 100-400mm with a maximum f/7.1 would be a waste of time and money, being well into the diffraction limited region for resolution for a 32 Mpx sensor and slow shutter speed and poorer AF. The big advantage for APS-C for those of us limited by "reach" is that we get a very high density sensor that we have to crop less than FF with a 1/4 of the number of pixels, which allows for higher frame rates and less demands on storage.But with modern optics and a telescoping lens design, it doesn't need to be as long. And that's got a tangible value to it for a traveling photographer. A consumer-grade 100-400 style lens with a variable aperture to f/7.1 - while slow - would be plenty usable on sunny days for bird watching, etc., and would only require a front opening smaller than 58mm; bump that down to f/6.7 and you're still smaller than a 62mm front opening. A comparison between existing similar models, namely the EF-S 55-250 vs the EF-M 55-200, shows that with a few compromises (the EF-M lens is slower and has 50mm less range), the physical size of the lens can be decreased dramatically.
The question isn't whether or not it's possible. Only whether or not there's enough of a market for it that Canon could recoup the costs of engineering, tooling, and production, and whether or not something else in their lens lineup could take the place of that particular lens. To this point, Canon hasn't seemed to be in a hurry to build anything beyond the 200-250mm range for APS-C sensors anywhere in its line. This makes more sense for EF-S lenses, which have a size and form factor similar to their full-frame counterparts. For the EF-M line, where you'd think size makes a difference, the disparity in size between the EF-M 55-200 and the next steps up in focal length is much more damning.
Frankly, at this point, I am little bit confused as to what the advantages of APS-C are other than to exploit the sensor crop to get a little more "oomph" out of a telephoto lens - most all of which are built for full-frame anyhow. Especially with a smaller M-series body like my M50 - which is a great camera, don't get me wrong, and I am very happy with the results I've gotten. But the size advantage of lens engineering goes mainly into trying to negate the natural weakness of APS-C on the wide angle side of the focal length spectrum. And if I try to position myself with decent quality lenses that I can use on both full frame and APS-C cameras (as with my EF 16-35 f/2.8), I've negated any and all size advantage gained with the M series body.
These are interesting times in the photography world, that's for sure.