Fair enough. Is there anything the K3ii does that the D500 doesn't?

OK I can think of several. The K3ii has a built in GPS, it has a higher resolution sensor, its got pixel shift resolution, sensor stabilisation, and its cheaper!

What is it that anyone would want extra from a K3iii that either doesn't already exist or couldn't be added with a firmware update to the K3ii ?

Yes

I'd rather reply here so others who are interested can follow the thread.
The adapter screws on like a large filter to the front of the lens.

1. This is a photo using a 50mm lens without the adapter:



2. The 50mm lens with the adapter:



3. A 35mm lens with the adapter:



A 28mm lens would give a complete circle, anything wider would give smaller complete circle!


Edit:
A real fish-eye, the Samyang 12mm:

If you're not sure whether a fish-eye is for you, purchase that adapter I linked to the other day in your other thread which was only £10-20. Served me for years when I couldn't afford a proper fish-eye. It effectively does the same job.
As I've still got it I can take and upload some images from the K-1 with it if you wish. If so let me know which standard lens you use as I'll try and replicate your own set-up.

I'm not aware of any full frame 8mm. The Samyang is APS-C. The FF Samyang fish-eye is 12mm.

The problem is its Corel, and that's how they do things. If you can make it that you have to create a new version or plug-in for something extra that's what they do!

LCE still show a full range of Pentax cameras and lenses for sale on the website so maybe, like Jessops, they don't keep them in branches.

[quote="Mag07"]The short warranty means it's a grey import I would think...not a deal I'd be tempted to go for. [/quote]Six months warranty is pretty typical for second hand. Long enough to identify an issue with the camera.

Didn't know there was such as word as 'can' tspell'.

Well done! As you've found out there's plenty of choice out there.

SDM will work with the HD Pentax-DA AF Rear Converter 1.4x AW and adjust the focal length as reported by the lens.
Alternatively the Kenko (and others) AF/Pz-AF 1.4x will also work with SDM lenses but it doesn't adjust the focal length.
The Pentax 1.7x converter is really an adapter for converting a manual focus lens into an AF lens and does it really well. It's strange mounting an early manual focus K lens and have it respond to a press of the shutter release or AF button. With an A series lens it all works just like having an AF lens attached.