As for the original post, "there is no reason whatsoever why Canon or Nikon could not come up with, say, a 4.5cm x 3cm sensor camera and matching lenses". What on earth were you thinking. There's are 2 very big reasons. Cost and Social Norms.
Cost is obviously a big issue.
'Social norms' are quite irrelevant. If you are living in the film world then yes, releasing a new format is a big deal (as I said, and for reasons given, in my original post). In the digital world it's no big deal. If you don't believe me, look at the first diagramme
Here
You can't release a camera sensor and be done with it.
Of course not. It would be an enormous project.
New sensor usually would mean new body housing too (Hassey are BIG)
I know, I have one. But you are making the same mistake as everyone else seems to be making here in assuming you have to jump straight to medium format size.
The example I gave was a 25% (linear) increase but even a 10% linear increase would give a very useful quality improvement.
new Lenses. Note the plural? You can't just release a couple of lenses and convince the world you're serious. You'd need an entire series to make people pay attention. Ok then there's the cost of the larger system, larger sensors are expensive so straight away any camera would need to cost more than their full frame brothers too.
There is no doubt that to do something like this would be a major, multi-million pound project.
But in this day and age it could be a great deal easier than it would have been in the past because every aspect of the design information will be computerised which would save a lot of work.
Now with skyrocketing costs, how do you convince professional photographers (who are the only ones left who can afford your new gear), that your new untried, untested format is the format of choice compared to the medium format used by well established companies. Especially that is when you're targeting the said medium format photographers with your ludicrously high megapixels yet excellent performing 35mm options anyway. You could run a massive marketing campaign creating more cost!
This isn't really an issue because I was never suggesting that (Can/Nik)on start to compete in the MF market.
All the manufacturers brought out 'untried, untested' formats when they introduced crop sensors and they seemed to sell quite well.
With the freedom manufacturers now have to use any format they choose it seems a pity that you need to leap from 35mm FF up to using 6x6 bodies and sensors that do not make use of the costly, bulky and large (but gorgeous) glass that goes with them.
Yes, it would be a costly exercise but Canon and Nikon are prepared to spend what it takes to come up with their flagship products that will sell to only a relatively tiny number of photographers. How many of their longest, fastest lenses do you suppose they sell? Yet they were prepared to design them and tool up to produce them knowing that they would probably only sell in the low hundreds (or even tens) of their most exotic designs.
I see no barrier to Canon entering the medium format market if they actually made a medium format camera compatible with medium format lenses. But create their own entirely new format? The barrier to entry is HUGE because the cost is high and people on the whole simply don't care. (No offence Molex, (Hey, I have connections you know) it's one thing to convince one person that this is a good idea, but it's quite another to convince a 10s of thousands of pros who have been using 35mm since they were old enough to hold them. Which is precisely what they'd need to do to even come close to recovering the R&D cost)
Again, you're almost certainly 100% correct here but it doesn't relate to what I was talking about.
Coming up with a slightly bigger sensor that would only require a slightly bigger camera would be much less of a problem. The main issue I see would be sensor yield. The relationship between sensor size and cost is certainly not linear!
Anyway, this was not an idea that I came up with off the top of my head. It was mentioned in a blog by a professional photographer whom I suspect may have certain information that we are not party to. At least, I hope that's the case.
If anyone remembers the introduction of the film APS system they may recall a great deal of wailing and gnashing of teeth in the photographic press that they did not take the opportunity to increase the negative size a little. At that time there certainly seemed to be plenty of people who would be prepared to buy new glass in order to get the quality boost that a slightly bigger negative would provide.