Originally posted by Digitalis the sigma 8-16mm f/4.5-5.6 and Sigma 18-35mm f/1.8 ASPH* both cannot be used on FX format ( with some pretty heavy restrictions) they have no peer in terms of optical quality (especially the sigma 8-16mm) so I will still be using my K5IIs.
If the FF Pentax is 36MP with an Exmor sensor (like the D800, D800e or D810) you would be able to use it in auto-crop mode and your images will look exactly like the output from your K-5, in MP, AOV/DOF, DR, and noise. You wouldn't need to use your K5II with the DX lenses, in other words, unless you wanted a second body.
.
Quote: *though if there is a crop mode on the FX format camera the APS-C specific lenses could still be used, the sigma 18-35mm f/1.8 can be used on APS-H format above 24mm without issue.
Yes. It bears emphasis, because this feature will be a welcome and much-used 'transition' option. Auto-crop or selected crop makes going FF painless, you don't need to dump your aps-c lenses immediately, or at all.
.