I'm not sure what you mean by 200/100 = 2 stops Algi. The difference between ISO 100 and 200 is 1 stop.

The Pentax K mount is, of course, a full frame mount. It's also slightly wider than the Nikon F mount, which gives the Pentax designers a bit more leeway in lens design.

All the potential is in place, I guess it just needs the will and the resources to do it. That will presumably only happen when the numbers add up.

Excellent images, a revolting subject!

That's impossible Jonathan. The light level remains the same. It will receive twice the light when the light is twice as bright. As for lenses, f/8 is f/8, whatever is behind the lens is irrelevant.

The field of view is different because an APS-C sensor is smaller than a 35mm format FF sensor.

I understand what your thinking is, but the context isn't right in the way it's being expressed.

It's very effective.

I've seen a few photographers move from various makes to FF and to be honest their photography hasn't visibly improved. In some cases it's become worse.

I've also seen some photographers start using smaller formats and in a few cases the photography has improved. I think this is because they no longer lug around huge quantities of kit and they've rediscovered a bit of joy in the process.

In the end we do what suits us, but it's still the photographer that makes the image.

While we're sharing info on this, there's also a list of lenses that the converter should not be used with:

15mm f/4 Limited
21mm f/3.2 Limited
40mm f/2.8 XS

I've briefly tested it on the 55-300mm and that's fine as well.

No sensor affects how much light there is.....what is true that larger photosites can be more sensitive and therefore the signal needs less amplification, but that definitely doesn't affect how much light there is.

Prospective purchasers could also check that the camera body they have is compatible with the AF via the converter. Ten are listed on the leaflet that comes with the lens, but it's dated as of January 2014. I guess that gives us a clue as to how long it takes new items to get through the supply chain!

The cameras listed as OK are: K-3, K-50, K-500, K-30, K-5II, K-5 IIs, K-5, K-01, K-7, K-r. There's a footnote that focus may not be acquired with phase detection AF on the K-7.