I often compare M43 to Full Frame, not APS-C, something I am not alone in.
Why?
There are a few of reasons I guess.
First up, it is the only consistent format to compare to. The “ugly” 3:2 compromise format, it has become the base line all are measured against.
The second is that the difference between M43 and APS-C is one of degrees, in other words, there is no upgrade to be had that way. Both have a smaller sensor than Full Frame, Both therefore have advantges and disadvantages when compared to that format, but APS-C is in the middle ground, closer to M43 than the bigger format (especially Canon at 1.6x crop).
Much of what is said about M43 can also be applied to APS-C, and equally the differences to FF are similar. The M43 to FF comparison though is a fair comparison of the two extremes.
The thing should be the priority, not the thing that captures it.
A last factor though is no other maker other than Fuji treats their smaller formats as their “end game”. Fuji and Panasonic/Leica do offer bigger formats, but their smaller format offerings are taken seriously. Their best glass and cameras are available in the smaller formats, their larger format versions are often the same but different, sometimes less refined or more specialised.
Canon, Nikon and Sony are all guilty of under-attending their smaller formats. Canon refuses to make “L” glass for theirs, although of course these can be used with APS-C at different focal lengths and oddly, many of their plastic, non “L” APS-C options are optically identical to their professional siblings, some even better at their launch than their aging full frame predecessors.
One of their best SLR lenses that got very little attention was the 17-55 F2.8. It was big, sharp, fast, but also over priced for a plastic lens and had no red ring of “specialness”. The 10-22 was also a more stable lens than the first 16-35L it was modelled on, possibly being the reason it was upgraded. I owned the 15-85 USM and it ran rings around the 24-105L mk1 (just not red rings).
They were basically saying you need FF to be a pro, and stubbornly feed smaller formats with “scraps”. My biggest bugbear was the lack of decent dedicated primes, something they started to address just after I left the system.
Most rely on the trickle down effect from their larger format options, paying little attention to holes in their range. Ironically, I actually got used to this with Canon. No decent options for years in dedicted primes, wide angles, specialist lenses like tilt/shifts and macros, often forced on me a longer full frame focal length, that it turned out I actually preferred.
I did though have to buy a longer, heavier and dearer lens than I wanted, but that often got around the soft corner issue that plagued early Canon glass (check out any test of the 17-40L wide open at 17mm just for a laugh).
I realised at some point that about 28mm was actually as wide as I personally wanted and 40mm was my perfect standard, so my 24 and 28mm lenses became standards and got a lot more use and the less than perfect 17-40 became a very useful 28-65. Even to this day, I only own wide angles for other peoples needs, not my own.
One of my favourites was the sublime 24 T/S L mk2, that became a perfect 40mm. It allowed three shifts to match a 16mm’s coverage, but it was more natural, better corrected and a much bigger file. Others were the 50mm Macro (80mm), 35 f1.4L ( 55mm), 400mm (640) and 85 f1.8 (135mm).
Olympus has all its eggs in the M43 basket, Panasonic comes close to matching them, before adding FF and that, up till now, has been mostly for video. The two brands combined with a few off brand makers make anything you need.
When comparing M43 to FF you have the natural math of x2, and with M43 being a finished format, it makes sense to compare. It is as much a comparison of formats as brand philosophies.
For me the advantages in depth of field (that’s right, advantages) which increase flash power and light gathering and the size, weight, reach and affordability of premium lens designs all add up in the real world to more than the disadvantages of theoretically more noise and reduced enlarge-ability that the top full frame cameras can provide, because I know what is actually important to my clients.
I have never, ever had a client complain about the subjective quality of my images, quite to opposite usually, with the sometimes embarassingly out dated and under muscled gear I occasionally employ* making me, the weakest link, look good.
*I have shot the Telstra Board, major social events, even the Prime Minister with no more than $4000 worth of gear, often a lot less, which is about the price of a single FF body or Pro lens and even the AFL or NBL gets no more than $6000. I always have what a professional needs, which is options and backups, so no issue.
My sub $1000au event kit at work.
Enough?