Thanks for all the advice. Been offline past few days. Think I've found the problem & a very obvious one. The 18-55 DA I'd been using had a sticking aperture, simple as that. Feel daft I hadn't checked it but I've never had a problem with my old lenses; assumed it must be the camera.
I always look after my kit so I don't know how this has happened. Not worth getting repaired. Anyone know if it can be fixed at home?

Thanks for all that but I obviously didn't explain in enough depth. I have no problem shooting with any of my pre-digital lenses.

With my 'digitally optimised' lenses, and shooting on manual, I can set the f stop anywhere from 3.5 to 40 and it makes no difference to exposure or depth of field. I guess it is defaultig to a wide exposure because depth of field is always shallow and I seem to be ever having to shoot at a high ISO to compensate.

As suggested, this probably has something to do with why I was having exposure problems in auto - a blessing in disguise because I've found a new lease of life going back to my youth of manual pleasure.

Hi, I've started shooting everything in manual (I found I was having exposure probs in auto) but the camera f stop setting makes no difference to exposure or depth of field. I have to use my old PK lenses if I need any control. Am I missing something? Jon.