I was a film SLR user for decades. When I decided to bite the bullet and get back into underwater photography I first considered DSLRs, but soon concluded that technology will replace them.
The first question is do you want to view what the lens sees or what the sensor sees through the lens? It is not necessarily the same thing. The mechanical reflex action of the mirror adds delay time and compromises autofocusing and image stabilization. The physical space that the mechanism takes up also compromises optics optimization.
My conclusion was that the reflex mechanism will eventually be displaced as the eye level displays (tiny monitors really) improve and become less expensive. For my sensibilities, they are good enough now.
Second is the sensor. It will be a long time before larger sensors will no longer outperform smaller sensors. People, mostly pros, still spend $70 grand for digital Hasselblads with their huge sensor, but is still much smaller than their 2¼" film counterparts. Larger sensors will have less noise for the same pixels for a long time. The question becomes what is good enough? That is where the difficult soul searching comes in.
I finally settled on the 4/3 format because it is “good enough” for my needs (desires) and allows housings, lenses, and domes to me much smaller. I also like that lenses are interchangeable between Micro 4/3 manufacturers. I use Panasonic and Olympus lenses. No regrets so far.
