Another point is to fill the 'simple' dict only with tags that have a value. It will make it easier in the themes to show only the useful tags and not showing them if they don't have a value. Something like:
```
for tag in ('ISOSpeedRatings', 'ExposureTime', ...):
    if tag in data:
        simple[key] = data[key]
```
+ specific tests for the custom tags (exposure, focal).