Changes in the Epson D1s include a new RAW+JPEG shooting mode (which captures both Raw and maximum-quality JPEG images in the same shot), a new AdobeRGB color space option in addition to the existing sRGB (color space of images is indicated in Playback mode). There's also a new long-exposure noise removal function (although it isn't clear at what shutter speed this kicks in), and a Quick View function that displays the just-captured image on the LCD for 3 or 10 seconds, but can be disabled altogether.
The playback zoom function now works for Raw files (not just JPEG images as was the case in the R-D1), and has been extended from the original 9.4x maximum zoom to a new high of 16x. The camera's Film1, Film2 and Film3 user settings groups have also been altered so that they now default to three specific situations - Portrait, Landscape or Night Scene (although they can still be changed by the user, to adjust contrast, saturation, etc. to your preferred settings).
The Epson Photolier software bundled with the camera has been altered to offer a new 13.54 megapixel interpolated resolution when working with Raw files. Adobe Photoshop Elements has been dropped from the camera bundle, and a new leather case (part number RD1SC1) is being offered as an optional accessory.
As with the R-D1, the Epson R-D1s has some very nice design touches, such as a needle gauge on the top which is used to show image quality, white balance, and remaining storage space / battery life, and a small conversion ring on the rear panel showing equivalent focal lengths alongside those that would be marked on your lenses, for example. The APS-C sized image sensor will yield a focal length conversion of 1.53x. Also notable is that the camera has a 1.0x field of view through its viewfinder, giving you the same image you'd see if you were looking at a scene with your naked eye.
The Epson R-D1s, developed in cooperation with Cosina, uses a proprietary rechargeable Lithium Ion battery, which is bundled along with a charger. Also included is Epson's "Photolier" software to convert RAW files, and a RAW conversion plugin for Photoshop.