I have been wanting something like this for ages (wide angle converter that's behind the lens)

Wrong. All camera companies use a standard definition of ISO based on exposure (shutter speed + plus F-stop). Here is a quote from Andy Westlake

>"In the simplest fashion, according to SOS if you point the camera at a grey card, meter and shoot it should be rendered as middle-grey (50% luminosity). This makes sense - it's the way most photographers think about exposure.

>DxO's method is based on something different - highlight clipping. This is useful for comparing raw sensor performance but doesn't reflect how cameras will render the image. Expose cameras from various manufacturers based on DxO's measured ISO and they'll all clip whites at the same point, but give images of different brightness.

>"The difference between DxO's measured ISO and the manufacturer's recommended ISO gives an indication of what we call the highlight dynamic range of the camera. Ironically, the greater the difference (i.e. the lower DxO's ISO relative to the indicated), the larger the highlight dynamic range, resulting in smoother rendition and rolloff of highlight detail.

If you want to see the correct "measured" ISO, you should check DPReview who use a calibrated light meter to measure ISO (almost all cameras are similar).

Here is another proof that Dxomark's "measured" ISO doesn't tell you anything about shutter speed and F-stop in real usage (and their definition is not standard anyway to start with).

See Fuji X100

Now if we were to believe dxomark, X100 users won't see a change in shutter speed from ISO 1600 to ISO 6400!

Of course we know that is not true, and the camera behaves normally in real life. Here is X100's F-Stop and Shutter speeds in imaging resources studio

ISO 1600 - F8 - 1/250

ISO 3200- F8 - 1/500

ISO 6400 - F8 - 1 / 1000

Whatever happens under the hood is totally hidden to users. The camera behaves normally as far the user is concerned, and there is nothing wrong with X100's "ISOs".

The point is that if you want to see Nex-7 and 5D Mark III "measured" ISO (they way photographers understand ISO, you should check DPReview (not Dxomark).

Here is Nex-7 on DPReview

"we simply compare the exposure for each shot to the metered light level (using a calibrated Sekonic L-358), middle gray matched. We estimate the accuracy of these results to be +/- 1/6 EV (the margin of error given in the ISO specifications). We found that measured ISO from the Sony NEX-7 is roughly 1/3 stop higher than indicated across the ISO range - so ISO 100 indicated = ISO 125 measured."

Here is 5D Mark III

"In our tests we found that measured ISOs from the Canon EOS 5D Mark III match the marked ISOs within 1/6 stop accuracy, meaning ISO 100 indicated = ISO 100 measured."

If anything, you are going to see faster shutter speeds on Nex-7 at eqv ISO and F-Ssop (compared to 5D Mark III)!

But usually ((if you read DPreview), you should know that most cameras are within range of the calibrated light meter that DPR use. No cheating there by any camera company ...