How to open a raw file in Camera Raw full size rather than cropped to in-camera aspect ratio?

You could try the following with exiftool:

• export the RAW image or
• remove the JPEG preview image or
• remove the cropping information

and load the resulting image with Camera Raw. (Make sure you make backups first in a separate directory!!)

ExifTool is avaliable here, but any recent Linux distro has it. There is a GUI available, too.

I can give you explicit steps if you are willing to share one of your incorrectly cropped photos.

This is a function of Adobe Camera RAW. It appears that ACR reads the camera set cropping info and accepts that this is the ratio and limit of the pixels available.

I have done the same with Canon EOS cameras where it is possible to set the aspect ratio via a custom function. Once the images are imported to LR or PS there is no possibility to extend the cropping back to the original full image. However Canon's own software DPP does allow the crop to be ignored.

I know you want to use ACR, but I believe if you use Lightroom you will have access to the whole image. If it doesn't appear by default you can adjust it with the crop tool.

If you have Lightroom set up to always write XMP files, maybe you can then open the file in ACR with your preferred crop.

If you go to "Crop" in the Develop Module, you can choose between "As shot" which will give you the in-camera cropped version, or "Original" which will give you the full frame version of the RAW file.