The difference is in the specs table
If you look at a traditional range you have a focus range table
Focus Range / Vignetting
[TABLE="width: 807"]
[TR]
[TH="bgcolor: #FFFFFF"]Mfr.[/TH]
[TH="bgcolor: #FFFFFF"]Camera
(*5)[/TH]
[TH="width: 75, bgcolor: #FFFFFF"]Housing
(*5)[/TH]
[TH="bgcolor: #FFFFFF, colspan: 6, align: center"]Focus range [at wide end][/TH]
[TH="bgcolor: #FFFFFF, colspan: 3, align: center"]Vignetting
[at wide end](*5)(*7)[/TH]
[/TR]
[TR]
[TH="bgcolor: #FFFFFF, colspan: 2, align: center"]without lens(*4)[/TH]
[TH="bgcolor: #FFFFFF, colspan: 2, align: center"]with UWL-H100 28LD
(*8)[/TH]
[TH="bgcolor: #FFFFFF, colspan: 2, align: center"]with
UWL-H100 28LD
+
Dome Lens Unit
(*8)[/TH]
[TH="bgcolor: #FFFFFF, colspan: 2, align: center"]Underwater[/TH]
[TH="bgcolor: #FFFFFF, align: center"]Air[/TH]
[/TR]
[TR]
[TH="width: 63, bgcolor: #FFFFFF"]Normal
mode[/TH]
[TH="width: 63, bgcolor: #FFFFFF"]Macro
mode[/TH]
[TH="width: 63, bgcolor: #FFFFFF"]Normal
mode[/TH]
[TH="width: 63, bgcolor: #FFFFFF"]Macro
mode[/TH]
[TH="width: 63, bgcolor: #FFFFFF"]Normal
mode[/TH]
[TH="width: 63, bgcolor: #FFFFFF, align: center"]Macro
mode[/TH]
[TH="bgcolor: #FFFFFF"]UWL-
H100
28LD[/TH]
[TH="bgcolor: #FFFFFF"]UWL-
H100
28LD
+
Dome[/TH]
[TH="bgcolor: #FFFFFF"]UWL-
H100
28LD[/TH]
[/TR]
[TR]
[TH="bgcolor: #FFFFFF, align: left"]Canon[/TH]
[TD="bgcolor: #FFFFFF"]PowerShot S110[/TD]
[TD="bgcolor: #FFFFFF"]WP-DC47[/TD]
[TD="bgcolor: #FFFFFF, align: center"] [/TD]
[TD="bgcolor: #FFFFFF, align: center"] [/TD]
[TD="bgcolor: #FFFFFF, align: center"] [/TD]
[TD="bgcolor: #FFFFFF, align: center"] [/TD]
[TD="bgcolor: #FFFFFF, align: center"] [/TD]
[TD="bgcolor: #FFFFFF, align: center"] [/TD]
[TD="bgcolor: #FFFFFF, align: center"]None
(*10)[/TD]
[TD="bgcolor: #FFFFFF, align: center"](*10)
(*12)[/TD]
[TD="bgcolor: #FFFFFF, align: center"](*6)[/TD]
[/TR]
[TR]
[TD="bgcolor: #FFFFFF"]PowerShot D20[/TD]
[TD="bgcolor: #FFFFFF"]WP-DC45[/TD]
[TD="bgcolor: #FFFFFF, align: center"] [/TD]
[TD="bgcolor: #FFFFFF, align: center"] [/TD]
[TD="bgcolor: #FFFFFF, align: center"] [/TD]
[TD="bgcolor: #FFFFFF, align: center"] [/TD]
[TD="bgcolor: #FFFFFF, align: center"] [/TD]
[TD="bgcolor: #FFFFFF, align: center"] [/TD]
[TD="bgcolor: #FFFFFF, align: center"]None[/TD]
[TD="bgcolor: #FFFFFF, align: center"](*6)[/TD]
[TD="bgcolor: #FFFFFF, align: center"](*6)[/TD]
[/TR]
[TR]
[TD="bgcolor: #FFFFFF"]PowerShot S100[/TD]
[TD="bgcolor: #FFFFFF"]WP-DC43[/TD]
[TD="bgcolor: #FFFFFF, align: center"] [/TD]
[TD="bgcolor: #FFFFFF, align: center"] [/TD]
[TD="bgcolor: #FFFFFF, align: center"] [/TD]
[TD="bgcolor: #FFFFFF, align: center"] [/TD]
[TD="bgcolor: #FFFFFF, align: center"] [/TD]
[TD="bgcolor: #FFFFFF, align: center"] [/TD]
[TD="bgcolor: #FFFFFF, align: center"]None
(*10)[/TD]
[TD="bgcolor: #FFFFFF, align: center"](*10)
(*11)[/TD]
[TD="bgcolor: #FFFFFF, align: center"](*9)[/TD]
[/TR]
[TR]
[TD="bgcolor: #FFFFFF"]PowerShot S95[/TD]
[TD="bgcolor: #FFFFFF"]WP-DC38[/TD]
[TD="width: 63, bgcolor: #FFFFFF, align: center"]infinity-
5cm[/TD]
[TD="width: 63, bgcolor: #FFFFFF, align: center"]50cm-
5cm[/TD]
[TD="width: 63, bgcolor: #FFFFFF, align: center"]infinity-
0cm[/TD]
[TD="width: 63, bgcolor: #FFFFFF, align: center"]20.2cm-
0cm[/TD]
[TD="width: 63, bgcolor: #FFFFFF, align: center"]infinity-
0cm[/TD]
[TD="width: 63, bgcolor: #FFFFFF, align: center"]51.6cm-
0cm[/TD]
[TD="bgcolor: #FFFFFF, align: center"]None[/TD]
[TD="bgcolor: #FFFFFF, align: center"](*6)[/TD]
[TD="bgcolor: #FFFFFF, align: center"](*6)[/TD]
[/TR]
[TR]
[TH="bgcolor: #FFFFFF, align: left"]Panasonic[/TH]
[TD="bgcolor: #FFFFFF"]LUMIX FT5[/TD]
[TD="bgcolor: #FFFFFF"]MCFT5[/TD]
[TD="bgcolor: #FFFFFF, align: center"]infinity-
30cm[/TD]
[TD="bgcolor: #FFFFFF, align: center"]infinity-
5cm[/TD]
[TD="bgcolor: #FFFFFF, align: center"]infinity-
10.5cm[/TD]
[TD="bgcolor: #FFFFFF, align: center"]infinity-
0cm[/TD]
[TD="bgcolor: #FFFFFF, align: center"]infinity-
11.2cm[/TD]
[TD="bgcolor: #FFFFFF, align: center"]infinity-
0cm[/TD]
[TD="bgcolor: #FFFFFF, align: center"]None[/TD]
[TD="bgcolor: #FFFFFF, align: center"](*6)[/TD]
[TD="bgcolor: #FFFFFF, align: center"](*6)[/TD]
[/TR]
[TR]
[TD="bgcolor: #FFFFFF"]LUMIX FT4
LUMIX FT3[/TD]
[TD="bgcolor: #FFFFFF"]MCFT3[/TD]
[TD="bgcolor: #FFFFFF, align: center"]infinity-
30cm[/TD]
[TD="bgcolor: #FFFFFF, align: center"]infinity-
5cm[/TD]
[TD="bgcolor: #FFFFFF, align: center"]infinity-
10.5cm[/TD]
[TD="bgcolor: #FFFFFF, align: center"]infinity-
0cm[/TD]
[TD="bgcolor: #FFFFFF, align: center"]infinity-
11.2cm[/TD]
[TD="bgcolor: #FFFFFF, align: center"]infinity-
0cm[/TD]
[TD="bgcolor: #FFFFFF, align: center"]None[/TD]
[TD="bgcolor: #FFFFFF, align: center"](*6)[/TD]
[TD="bgcolor: #FFFFFF, align: center"](*6)[/TD]
[/TR]
[/TABLE]
The lens will have all in focus say between infinity and 0 or 10 cm
Looking at the spec of the zoom lenses
Actual shooting distance (from lens surface) and camera's focus setting
[TH="bgcolor: #FFFFFF"]Shooting distance
[from front edge of the lens] (*5)[/TH]
[TH="bgcolor: #FFFFFF"]Focus position (*4)[/TH]
[TD="bgcolor: #FFFFFF, align: center"]0mm[/TD]
[TD="bgcolor: #FFFFFF, align: center"]280mm[/TD]
[TD="bgcolor: #FFFFFF, align: center"]19.3mm[/TD]
[TD="bgcolor: #FFFFFF, align: center"]500mm[/TD]
[TD="bgcolor: #FFFFFF, align: center"]28.1mm[/TD]
[TD="bgcolor: #FFFFFF, align: center"]600mm[/TD]
[TD="bgcolor: #FFFFFF, align: center"]36.9mm[/TD]
[TD="bgcolor: #FFFFFF, align: center"]700mm[/TD]
[TD="bgcolor: #FFFFFF, align: center"]63.2mm[/TD]
[TD="bgcolor: #FFFFFF, align: center"]1000mm[/TD]
[TD="bgcolor: #FFFFFF, align: center"]107.1mm[/TD]
[TD="bgcolor: #FFFFFF, align: center"]1500mm[/TD]
[TD="bgcolor: #FFFFFF, align: center"]238.7mm[/TD]
[TD="bgcolor: #FFFFFF, align: center"]3000mm[/TD]
So instead of going from 0 to infinity when you are focussed at 30 meters here your focus position is 23 cm. It looks like the zoom wide mechanism does not work the same of a normal lens and you don't have everything in focus
I may be wrong but Chile tried some shots in the distance had they came blurred, I have not yet seen a natural light shot taken with this lens with something in the distance that is in focus