Full-frame, mirrorless and interchangeable lens.

As all photographers know, the world is divided into Nikon and Canon users, so if you're a Canon user - well, let's just leave it there. I've used Canon, Nikon, Leica and Hasselblad at work, but when shelling out my own money on kit, it's been Nikon all the way for me (don't even bother to argue), since I bought my first SLR, a Nikon EM, back in 1979, and for nearly 30 years I've owned an FM2.

Since going digital in 2007, my principal cameras have been Nikon digital single-lens reflexes (DSLRs), although I also have a Nikon Coolpix P900 bridge camera (mainly for its amazing zoom lens) and a Nikon Coolpix A, my travelling-light camera.

Now, the Coolpix A (discontinued in 2015) is a great little camera - solid and sturdy yet light, with an excellent wide-angle lens and amazingly good battery life. But it lacks two things. The fixed lens limits it to landscapes and interiors (too wide for people or wildlife). And the full-frame sensor that would make it equivalent to a 35mm film camera in terms of resolution and coverage.

Nikon has just released its latest full-frame DSLR, the D850. This amazing beast has a 45 megapixel sensor (compared to the 24MP sensor on my D3300 DSLR or the 16MP on my Coolpix A), incredibly fast and accurate autofocus and incredible low-light abilities. BUT with kit zoom lens, it weighs 1,700g (compared to 300g for the Coolpix A and 600g for the D3300 with kit zoom). One point seven kilos is way too much to be lugging around one's neck all day. So pass.

The idea of the mirrorless camera is to remove single-lens reflex's mirror box, reducing the distance between focal plane and the flange where the body meets the lens. The digital mirrorless camera is in effect the old rangefinder camera (of which the Leica M-series was the champion). But Nikon made rangefinders too, ditching them in favour of the SLR shortly after launching the Nikon F.

The Nikon Rumors website is abuzz with stories that having got the D850 launch out of the way, the next big product release will be a mirrorless camera. With a full-frame (FX) sensor rather than the two-thirds size DX-format sensor that my Coolpix A and D3300 both have. Launching an FX- and a DX- model would mean Nikon would have to produce two whole new lines of lens. If it's a toss-up between the two, I'd go for full-frame FX.

To ensure compatibility with Nikon's F-mount 35mm/full-frame lenses, any new mirrorless camera would need to work with an adaptor. But the real beauty of full-frame mirrorless is the ability to launch a whole new range of lenses that are smaller and lighter than those needed for the SLR design. Looking at the leading full-frame mirrorless digital cameras on the market, the Leica M10 and the Sony A9 can give the image quality associated with a DSLR like the D850 in a package two-thirds the weight (just over a kilo for body plus lens).

A DX-format mirrorless digital camera could weigh in at under half a kilo with lens. But it's that full-frame that I hanker after; the depth and richness of detail and colour.

This is what I'd love Nikon to come up with; harking back to the S-series rangefinders of the 1950s, but with a 45MP full-frame sensor with in-body vibration reduction, 25,600 ISO low-light ability (up two stops on the Coolpix A) and a handful of fast standard and wide-angle lenses to begin with. Retro-design but stripped of all unnecessary details.

Below: the lens mount would be based on the Contax bayonet, making it compatible with old Nikon rangefinder lenses. An adaptor for Nikon F-mount lenses would be available too.

Below: Or in black? With current Nikon logo for a more modern look?

Here's a to-scale comparison of the different sensors, the full-frame (FX), the APS-C or DX format, the CX format (Nikon 1) and the 1:2.3 format found in my CoolPix P900. Image sensors on smartphones are more diminutive still (typically 5.8x4.3mm or even smaller).

Commercially, Nikon has to get this one right if it is to stay in the game. The Sony A9 has impressed the reviewers with its abilities - but at the end of the day it's neither a Nikon nor a Canon. The Leica M10 is just too expensive to be of interest to any but the wealthiest and most dedicated amateurs. Introduce a camera that fails to catch on (like the mirrorless Nikon 1, with its CX-format sensor and interchangeable lenses), and financial peril draws near. Get it right, and Nikon will make up lost ground on market leader, Canon, which also lacks a full-frame mirrorless camera in its line-up.

In the meanwhile, I really appreciate the capabilities of the Coolpix A. [I think Nikon did it a disservice by putting it into the Coolpix range - it's as good as any DX-format camera Nikon makes, plus it's made of metal, a really high-quality piece of kit. Here's mine, below. Note the corners where the paint's worn off, showing bare metal beneath. A bit more about the Coolpix A here.

And it performs well too! Below: a pic of my prewar Contax II rangefinder camera taken using available light with the Coolpix A. You can see the genesis of the Nikon rangefinders here.

Earlier posts about my dream Nikon rangefinder (from March 2013 here, and from April 2015 here).

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