The K-1 can, of course, still use the Pentax DA lenses designed for the company's APS-C cameras. By default the camera will use a 15MP APS-C-sized crop of the sensor if a DA lens is mounted but can be made to use its full sensor region, if you'd prefer. Ricoh has published a list of those lenses that will produce relatively useable results in full frame mode, if the aperture is stopped down.
DA Prime Lens / Utility on K-1
DA 14mm Crop Mode Only DA 50mm F1.8 Stopped-down
DA 21mm Limited Crop Mode Only DA* 55mm F1.4 Stopped-down
DA 15 F4 Limited Crop Mode Only DA 70mm Limited Stopped-down
DA 35mm F2.4 Stopped-down DA* 200mm F2.8 SDM Fully Functional
DA 35mm F2.8 Macro Stopped-down DA* 300mm F4 SDM Fully Functional
DA 40mm Limited Stopped-down DA 560mm F5.6 Fully Functional
DA 40mm XS Stopped-down RC1.4X Crop Mode Only
The company says that all of the DA zooms will only cover the crop sensor region.
Maar nog even geduld hebben om dit allemaal uit te proberen, K1 op de consumer market in April.