Featuring a 24.6 million pixel CMOS sensor and dual Bionz processors 'for detail-packed, low-noise images with high sensitivity up to ISO6400 (with expanded ISO range)', the a850 is due in September at £1800 to £2200 - at least £200 cheaper than Sony's current top-range model, the a900.

Arriving hot on the heels of two new entry-level models, the a850 has a bright optical glass pentaprism viewfinder with 98% coverage, image-stabilising feature delivering a claimed '4.0 steps anti-shake performance with all lenses', plus 'photo quality' (921k dot) three-inch LCD.

'Ruggedly built for unflinching pro-style handling and performance, the a850 shares the same 24.6 megapixel sensor and virtually all features of the flagship a900, introduced last year,' says Sony in a statement, minutes ahead of its planned press conference. 'Like its full-frame sibling, the a850 fully exploits the creative possibilities of the Alpha family of lenses that includes premium full-frame optics from Carl Zeiss, plus five high-performance G Lens models.'

The a900 offers 100% viewfinder coverage and has a faster continuous frame rate of upto 5fps, against the a850's 3fps.

Like the a900, it uses a dual noise control system, and has a nine-point AF system supplemented by 10 focus assist points to aid subject detection, with 'improved out-of-focus detection to reduce focus hunting and a dedicated f/2.8 sensor for enhanced AF accuracy with wide aperture lenses'.

Sonmy adds: 'Like its full-frame sibling, the a850 is ruggedly built for dependable performance in gruelling conditions with a high-tensile aluminium chassis and all-magnesium alloy body shell. Viewfinder, card slots, controls and other sensitive areas are protected from dust and moisture by rubber seals. In addition, an anti-dust system guards the full-frame sensor from the effects of dust entering the body during lens exchange.'

Sony is adding a new 28-75mm f/2.8 SAM zoom lens that will be sold in kit form with the a850 from November.