The camera usually can’t record lens EXIF for that Samyang because the lens is fully manual and has no electronic contacts to tell the camera what lens is attached. So on a Sony NEX-5, there’s no built-in way to force proper lens metadata from that lens.

The missing EXIF is really a lens communication issue, not a camera setting issue. Some camera systems let you manually register non-electronic lenses, but the NEX-5 does not offer that in a way that writes the needed lens EXIF. Sony’s Lens Compensation app also doesn’t solve this by writing lens metadata into the files.

So your practical options are:

• add the lens metadata afterward in bulk during post-processing, or
• keep track of which lens was used and apply metadata later.

In short: you can’t make that lens automatically produce usable EXIF on the NEX-5; you’ll need to add it after capture if your panorama software depends on it.