Question regarding Lightroom 6.1 handling of Canon 5Ds R 'crop' files in HDR merge to dng. The camera offers three file size options: full frame (5792 x 8688, 50mp); 1.3 'crop' (4456 x 6684, 30mp); & 1.6 crop (3620 x 5430, 19mp). When shooting, for example, in 1.6 'crop' mode, the file imports into Lightroom with full file data (50mp) and lists the full file size (5792 x 8688) as the 'Dimensions' in EXIF, with "Cropped' as 3620 x 5430 (the actual 1.6 crop). The preview shows the crop angle of view, and opening the crop overlay shows the 1.6 crop overlayed on the full frame file. In Develop History, there is only 'Import' but no crop rectangle (although there is a crop rectangle overlay).
So, here's where it gets complicated. Take three 1.6 crop files, 'implement' the crop on each producing the 3620 x 5430 1.6 'crop' file size, and photo merge to HDR. The resultant dng file is indeed a 1.6 crop (3620 x 5430) but with the angle of view of the entire 5792 x 8688 frame. In order to get the actual crop that you composed, you not only have to remember the crop, but one now has to take the full frame angle of view returned at crop size, and further crop it to 2192 x 3157 to get the correct angle of view.
So to work around I tried taking the original file at import (with the crop overlay) and right clicking on 'reset crop' to take the file back to the original 5792 x 8688, 50mp file size, and then blending to HDR. Same result: full frame angle of view, but with cropped dimensions of 3620 x 5430, necessitating the additional crop to achieve the desired 1.6 angle of view.
Workaround # 2: Reset the crop in LIghtroom, select the three images and export to HDR Pro in Photoshop CS6, blend as a 32 bit tif, return to Lightroom and process. In this instance, the full frame file size is blended and returned (no crop). I haven't yet tried implementing the crop overlay in Lightroom and then exporting the cropped files to HDR Pro in Photoshop (I'll bet it does indeed return a 'cropped' tif file to Lightroom) but it's somewhat beside the point. I'd like to use the superior Lightroom HDR blending on 'cropped' files out of the camera.
Workaround #3: compose at 1.6 crop mode in camera, then turn off crop mode and shoot at full frame, import to Lightroom and blend at full frame and then 'remember' the crop you composed for. OUCH!!
Some might ask, why shoot a 19mp file with the latest 50mp camera from Canon? 50mp = awesome for large prints, some clients. 30mp & 19mp = better for most stock and virtually all publication (19mp = 12" x 18").
workaround #4: repeat workaround #3, but shoot a 'reference' crop file that will import into Lightroom with the crop overlay, Then sync this 'crop' (that one composed in the field) to the merged full frames from workaround #3.
confused? sure but workarounds often are a bit of that, eh?