Originally posted by ElJamoquio Ah. I guess since I started out on APS-C, I still consider a full-frame F/4 fast enough. I certainly find F/4 on FF to be more capable than F/2.8 on APS-C, as predicted by equivalence.
So far every lens made for the FE mount is faster in my view than an APS-C F/2.8, with the half-exception of the kit zoom which is only F/5.6 (3.7) on the long end.
There 1.15EV difference between the 2 formats. For all practical purposes, one can consider the difference to be 1EV. So APS-C f/2.8 or FF f/4 is the same. The 0.15EV is not significant at all. And at least there is a real offering of fast primes in Pentax echosystem!
That being said, why one choose FF?
- sharper images... Both format now have 24MP and similar sharpness... You need to jump to 36MP FF to really get a difference... And pay much more. So that would be Sony A7r.
- more deph of field control. For practical purposes no sony lens for A7 echosystem achieve this.
- more high isos capability. For practical purposes no sony lens for A7 echosystem enable this. I can just use an f/2.8 zoom on my APSC, use half the iso and get same quality (with same dof). The gain with A7s is really small (0.3EV) and come with a tax of pushing 12MP + low pass filter.
What the A7 familly is also supposed to bring?
- More compactness... Well The APSC lenses are smaller due to the registration distance difference, negating any gain on the A7 familly body.
Really the only thing Sony A7 familly bring toward an APSC DSLR is the EVF. And that's in exchange for loosing an OVF. The other thing A7 echosystem bring is hype... It is the only FF echosystem where one don't get the benefits of FF while still paying a premium for it and having to buy even bulkier lenses.
A used 5D + used tamrons lenses will cost less and while not improving isos, will improve dof control. Get some D610 or equivalent + same tamron lenses, and you beat A7 familly for a fair price.