Making a flagship product is tough work, and so is improving on it. But Nikon has managed to do that with the D4S, a new flagship camera aimed at professional photographers. It's a souped-up version of 2012's D4, designed to take better photos, faster.

Like the D4 before it, Nikon's not messing with a working formula. You still get a 16.2-megapixel FX-format CMOS sensor measuring 36.0 x 23.9mm, along with a 51-point autofocus system and RGB 3D metering system. And most all of the buttons on the D4S are where they were on the D4, though Nikon says it has changed the grip ergonomics to work with a wider range of hands. There's also still a 3.2-inch display on the back, a 100 percent view optical viewfinder, and compatibility with both FX and DX lenses.

Most changes are under the hood

For the D4S, the majority of the changes are under the hood. That same 16.2 megapixel sensor now has a range of up to 409,600 ISO, an extra stop beyond the D4's 204,800. Nikon's coupled that with a new group autofocus mode it says does a better job at keeping focus on an object that's being tracked, a feature specifically targeted at sports photographers. To pull these tricks off, the D4S has an Expeed 4 image processor which Nikon says results in 30 percent more processing power than the D4. That bumps burst shooting speed up an extra frame from the D4's 10 fps to 11 fps with the D4S. RAW fans can also opt for a newer, smaller RAW SIZE S file, which are half the size of the standard RAW files.

Some of the other major changes come on the video side, where Nikon's made the D4S more versatile than the D4. The D4S can shoot in 1080p60, 1080p30, and 1080p24. There's also a new mode that adds to the D4's capability to record uncompressed video through HDMI with an option to record to a CF or XQD card at the same time. Nikon says that's useful for people who plan to use the camera for live streaming, but who also want a hard copy to archive later. Other tweaks include an adjustable range of audio frequencies, and options to change the captured image area in Live View between FX and DX lenses.

Not the best-kept secret

All this doesn't come cheap. The D4S goes on sale March 6th for $6,499.95. That price is for the body-only, and comes in at $500 more than the D4's $5,999.95 price tag.

The D4S was not NIkon's best-kept secret. Nikon showed off a version still in development at the Consumer Electronics Show in January alongside the D3300 DSLR. It also cropped up at the Olympic Games in Sochi earlier this month, as well as on several online retailers last month. The company says the extra time out in the wild helped "hone" the product ahead of its launch.