AFAIK the in-camera focus adjustment only applies to AF, and on the K10D requires modified firmware to be loaded?

Both the K20D and K7 have AF adjustment as part of their standard menu.

Try some AF shots of the same subject with your 300mm at differant apertures and post the results here, together with the same shots taken with MF. Suggest you follow this sequence;

Set ISO to suitable fixed value to ensure reasonably high shutter speed at all apertures.

Put camera on tripod.

Select aperture. Focus on subject using AF.
Use timer/mirror up function to prevent camera shake.
Take shot. Immediately swith to MF. Re-focus.
Use timer/mirror up function to prevent camera shake.
Take shot.

Select new aperture...etc.

If you can complete the above within a few minutes that will hopefully eliminate/reduce any light level variation.

Make sure you don't lose the EXIF data in the process of posting the photos.

Posting shots as suggested will give the experts here a better chance of diagnosing what the issue is.

Welcome to the forum! Suggest you post some examples, making sure you don't strip out the EXIF data.

PM re 50mm

Seems Jaco chose the 43 Ltd (from his sig), but in any event appears to be off elsewhere See here>link

I don't have a K7, but understand you set digital filters on/off in Rec. Mode 2 menu. Further, I understand you must set 'Not use any filters' in the menu to ensure that you don't use any.

It's also possible to set 'Soft' in playback, but presumably it's per image?

'Soft' and other digital filters can't be used in RAW. You could try shooting in RAW and then check exif data again.

And look here> link

Seems OP has one to sell with a K10D (came with a new K7) but is willing to split.

Pot, kettle, black

Although 'made for Canon', perhaps at the price this could be worth playing with?

link

or maybe this?

link

50mm arrived to-day, thanks. very well packed considering it's for spares/repairs, etc. Now to take it apart and play

I'm interested in the 50mm.

PM sent.