Originally posted by Anvh Sony the maker of the sensor makes them by standard from ISO100 to ISO1600, the upper limit i'm not sure off though.
ISO 1600 is indeed the upper limit (higher ISO settings are equivalent to digital pushing in post), but your statement "makes them by standard from ISO100" does not make sense.
Originally posted by Anvh Anyway it's pentax doing that we have ISO80 not sony's and as such it's not a default the sensor comes with.
Have you considered the possibility that the sensor natively supports ISO 80 but that no one other than Pentax chose to exploit it?
I cannot imagine that Pentax has added some magic sauce to create an ISO 80 setting that the sensor does not natively support.
Originally posted by Anvh I've no idea why or how the DR is better with ISO80 then ISO100 since that shouldnt indeed be the case...
No, it should be the case.
Only the lowest ISO setting achieves the optimal dynamic range. Any higher ISO setting reduces dynamic range because the full well capacity will be reached the sooner the higher the (ISO) multiplication factor. If you do not believe me, look at a dynamic range graph at DxOMark and see how DR loses a stop when you add a stop to the ISO setting.
Originally posted by Anvh but the K5 is the only camera that offers ISO80 with this sensor, isnt that strange either?
It is as strange as the fact that ISO 80 is an extended setting on the K-5. You'll have to ask Pentax about the latter and other camera manufacturers why they didn't exploit the ISO 80 capabilities of the Sony sensor. Perhaps they didn't think the marginal increase in DR would be worth the effort of adapting the firmware.
Originally posted by Anvh The best explaination i can come up with is that pentax change the response curve maybe?
The ISO 80 effect exists in RAW data as well, so special JPG tone curves cannot be responsible (they are used for the extended highlights mode).
DxOMark measured true ISO 80 performance. If Pentax had done some trickery, DxOMark would have exposed it.
Originally posted by Anvh With test we see that Pentax DR is often starts lower and also ends lower then other brands so it seems pentax can influence that.
You can extend the highest ISO setting to your heart's content. For the Sony sensor in the K-5, ISO 1600 is the maximum value supported by the chip and Pentax just decided to allow more digital pushing than Nikon did with the D7000.
However, you cannot do the same at the low end. If you use tricks at the low end, they will not increase dynamic range and hence your trickery will be exposed.
To summarize, the Sony sensor must support ISO 80 natively. Why it is an "extended" ISO setting on the K-5 was the question by monk and I know that some explanations are wrong, but can only speculate about the true answer (see my earlier post).