Go for it, you might surprise yourself.

Walk in, bold as brass, head in the air, ask the first person you see "How do I join?", and take it from there.

The K10D has a facility too but it's not as complete as that which is implemented in the K20D. The K10D has one adjustment that is applied to all lenses. The K20D has the same adjustment, but it can also deal with 20 lenses individually.

I've no experience of other Pentax DSLR models that might have this feature.

Maybe you could be the first to try whether the 'Apply to all' or 'Apply to one' adjustments are cumulative? That might fix your problem if they are.

Also, I know you've taken pics of cornflake boxes but what about other 'real world' images? What are they like.

Personally, I'd continue testing, adjusting, and retesting with just one lens until I was happy with it.

FWIW, my FA50mm front focusses quite badly wide open and the images look very soft. The softness is expected, the front focus is adjustable and needs -10 to sort it.

Also, if you do have a real problem and you need to refer to Pentax, make sure you have a totally Pentax combination as I doubt very much that they will have any sympathy for results from the Sigma.

I have sevearal DA* lenses and they all focus differently and require individual adjustment. The K10D just can't deal with them all and I've set it to suit my walkabout lens, the DA* 50-135mm.

This issue is not peculiar to Pentax, all the DSLR manufactuers have the same problem but AFAIK only Pentax and Nikon have a facility to deal with it in-camera. I just wonder if we always had it in the days of film.

PS: As Mike-P says, you can't compare the prosumer Sigma 100-300mm EX to your other consumer Sigma lenses. They are like chalk and cheese.

Agreed, but the output of the AF500FTZ is about equivelant to hobbyist mains powered flash heads of around 200/300w, which I think is probably all that's needed for a home setup.

Stands etc will also be needed of course but they are relatively cheap.

You have a PM.

It certainly seems like you need a more sophisticated lighting setup, but it needn't be expensive.

A very versatile Pentax flash for manual operation is the AF500FTZ. It's powerful with a GN of 50 and the output power is adjustable in the range from full to 1/32.

Any flash for studio type portraits is going to need softening a bit. Softboxes and umbrellas are typically used for this but with a bit of imagination you could make your own.

Can we be sure that the reported failures are actually shutter failures?

These crab spiders grab their prey as it passes or lands on the flower. Note the front 2 pairs of legs aren't touching the flower, just hanging in the air primed and ready. He's attached to the flower with his shorter rear 2 pairs of legs. His body length including head and abdomen is about 1 cm.

The plant is known in Spain as Lantana. The flowers change colour from yellow to red, then to a salmon pink before dropping off.

K20D, SMCP-FA 100mm Macro, AF160FC flash (full right, 1/3rd left), 1/125th, f22, ISO800 (dunno why :roll. PP'd in Lightroom 2.3. Image is rotated 180 degrees, he's underneath the flower.

Make sure the TX and RXs are set to the same channel.
There should be a test button on the Tx.
When you press the test button the red light on the Rx should flash, does it?
Does the slave fire if you press the test button?
Which body & lens combo are you using?

You're welcome. I do really like the facial expression you've captured in #2. Having had a longer look at #1, there is a quite harsh shadow, right side of her neck. That's easily fixed in PP but you'll spend less time on your pc if you get it right in-camera.

There are others on here far more qualified than I to critique your work, I just say what I see.