I bought a 2nd hand 150/f5.6 Componon-S for 5x4 enlargements a couple of years ago.

I have always focused the lens wide open then stopped down a couple of stops (normally 2 stops to f11)

However, last night I checked the focus again when I stopped down to f11 and found the focus which had been fine at f5.6 was very slightly out.

I then did a couple more checks and found that the focus at f11 was indeed different from the focus at f5.6 – and consistently so.

I can rule out inadvertent movement to the lese stage during stopping down – as it would return to correct focus when the lens was set to its focusing aperture

I don’t know how old the lens is or its history but externally it looks fine and has not scuff marks or dents to show any damage

Has anyone else experience of focus shift on Componons?

Should I just bin it & buy a new lens?