3D? Super fast & accurate focus? Simultatneous dual-image HDR?

To me, one of the big potentials for small-lens interchangeable-lens digital cameras is the possibility of there eventually being a body that will take two lenses side-by-side for true stereo/3D photography, the single image advantages would just be frosting on the cake - but for some, those extra advantages might make such a camera worth buying even if they didn't care about 3D.

Yes, Sony now offers "3D Sweep Panorama," suitable for stationary or slow subjects in good light, for moving subjects - even leaves stirring in a breeze, you want simultaneous exposures, and for dim light you want to be holding the camera very still or have it on a tripod.

I love my Fuji W3, but while it has dual lenses & a glasses-free 3D rear display, it is basically a doubled point & shoot camera, even if the results often have far greater impact - and an impression of "image quality" comparable to better quality lens-and-sensor single image cameras because of the 3D and, I believe, because of some tricks the human eye and brain do when merging visual input that has between-eye variations.

So, I really want a 3D camera with better lenses and sensors, easier use of attachment filters, and interchangeable lenses - especially since over the last year (almost) that I've had the Fuji, I've only done about half my photography in 3D - I still use my "big camera." And a good interchangeable lens 3D camera could do virtually the "big camera" flat-image photography as well, and be better for it, for me, than a single lens camera - think simultaneous HDR - think "one camera" being either fast-wide-prime or zoom (which are different kinds of photography for me) without lens swapping.

I could have both cameras with me. I could go for a hike in the woods and pull the zoom camera out of my pocket or the fast wide prime out of my pocket. One camera. One pocket. One user interface. Little or no manual-swapping of lenses in the field. Lens swapping by pushbutton. Read on.

So here's the deal: the human "interocular distance," or average separation between the lines of sight of an adults eyeballs, is commonly taken as 62mm. The most effective stereo effects in viewing are provided by having the object(s) of interest between 20 and 50 times the lens separation. Obviously we can "sense" distance will beyond the 4 to 10 foot range we get when we put all that together, but we find 3D images of something much more than ten feet away more impressive, more fun, if the image was made with the lenses further apart. But too far apart and closer stuff, especially portraits, can start looking weird. And the cameras start getting ungainly. Too small (like some of the cheap "3D" cameras and "3D" cellphones) and only a tight close-up shows much depth.

So in a fixed body camera, a separation of 80 to 90 mm is probably optimal. Being that that is the distance between the centerlines of the lenses, it also is the distance between an edge of one lens & the same edge of the other lens, which means that it is the absolute maximum diameter of the usable lenses - plus a little so they don't rub and so they can be mounted & dismounted.

Bang. We just eliminated the vast majority of interchangeable lenses sold today from being candidates for a general-use 3D camera.

Hence my interest in small (mirrorless) interchangeable lens cameras, such as those under discussion in these forums. Also I intensely dislike non-silent mirrors and prefer small cameras. I'll accept extra width to get 3D, but I don't want extra height or depth - the more of either, the less likely it is to be in my pocket when I want it.

Then take all the passably decent lenses available today that are too large in diameter and eliminate those that don't have camera-driven power focus or zoom: Manually focusing or zooming on the lens is fine, but it needs to synchronize to the other lens via the camera. In fact, our camera has become a through-the-lens rangefinder, since the pair of lenses is a de facto rangefinder of a significantly wider baseline than my dearly beloved Canonet G-III 17 or any other compact rangefinder I recall. Super-fast auto-focus? Easy manual focus? Here we go!

An alternative to a dual-lens body could be an auxiliary body, something like the lens+sensor modules for the Ricoh GXR, but with a simpler connector and enhanced communications capability - or maybe NO connector and wireless communication?

Put the primary camera lens tight up at one edge and the auxiliary lens could clip to that edge for portraits & closeups, the other edge for intermediate distances, and by cable for distant scenery and other hyper-stereo applications - more good fun!

The Fuji offers options for setting the two lenses differently for non-stereo picture pairs - different zoom levels, etc., and there is no reason that an interchangeable lens stereo camera couldn't offer similar features, including a simultaneous in-camera HDR capability. In fact, the earliest "HDR" I know of is in 19th century stereo views which have one image slightly overexposed & the other slightly underexposed - the eyes adjust & your brain merges them to get better dynamic range! And those folks were presumably timing the exposures by taking the caps off the lenses I'm guessing they did something like left lens off, right lens off, right lens back on, left lens back on - nothing fancy required.

Plus the option of two different lenses - a fast prime and a zoom, with the zoom automatically matching the focal length of the prime when stereo mode is selected (put the zoom on the left side so the prime's better image quality is going to most folk's dominant eye) or switch automatically to the zoom when the zoom control is activated. Even in zoom mode, the prime would help with rangefinder-style auto/manual focusing, and could still be set to make an image - an auto record of the surroundings? a "save the day" bit of extra image around the edges if you found out you over-cropped?

Unfortunately, every time I start trying to compare the various candidate small-interchangeable-lens systems, I don't get very far before I decide I'd rather take one of the cameras I have & go take pictures.

So does anyone want to tackle comparing the various candidate small-interchangeable-lens systems per the dual-lens criteria so we can hypothesize who might actually be heading towards a dual-lens body?

Seems worth discussing, at the very least.