Help me understand focus distance: Sony 24 - 105mm

[Opaul20]

Before I start, I understand that the Sony 24 - 105mm isn't an ideal option for underwater photography. Which has confused me because on paper it should be. With a wide enough 24mm I can shoot the big things and then get some Semi macro of the smaller things at 70-105mm. After using it, and reading on it, that doesn't seem the case.

I bought my housing (Seafrogs A7IV) with the intention of getting a 16-35mm. I unfortunately could not get my hands on one before heading out to Egypt and as my 24-105 fit my housing I thought what the heck I'll take that. While using it out there I felt the focus distance take a massive hit. After doing a fare bit of research I understand that dome ports are great at preventing distortion with wide angles but in return cause an increase in the focus distance, which is definitely not what I wanted. Im struggling to understand how different lens

Some of the solutions I have seen are adding diopter filters, say a +4, to increase that focus distance again. I've seen examples of people using the 24-105mm and getting great upclose/macro shots. Would this be what they would have used?
What are the downsides to using diopters?
Should I just get a flat port for it instead ?

I also wonder if using a 16-35mm I'll have the same problem. Does having a lense with a wider aperture help?

 

[Interceptor121]

Thre 24-105 minimum focus distance is too far to work properly with dome ports therefore the lens is not used
Diopter make the camera focus close but create other issues including addiional aberrations
Something to do in absolute desperate cases

 

[Opaul20]

Ah I see, thank you! Would you then suggest a flat port be better?
The focus distance wasnt bad i thought 0.38m i read ideally anything below 0.5m is good?

 

[Barmaglot]

A flat port will produce pincushion distortion and reduce your field of view. Here are sample shots with a 24mm-equivalent lens (16mm on APS-C) through flat port and a dome:

 

[Opaul20]

A flat port will produce pincushion distortion and reduce your field of view. Here are sample shots with a 24mm-equivalent lens (16mm on APS-C) through flat port and a dome:

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Ah thank you for this, thats not an effect id want on the wider, non macro shots. I know its what everyone wants but, ideally I want to be able to get up close images of large things and some small, like clowns and coral, while also being able to get semi wide shots (16-24mm I mean). I’m really struggling to decide on a lens, what would you recommend, I’m looking at the 16-35mm but with only a 0.10m difference in focus lengths (compared to the 24-105mm) I still worry it isn’t small enough to get thos up close images. Would having the dome port and extensions specifically for the 16-35mm help? Mind you it is only Seafrogs so I doubt it. Feels crazy that my TG6 could do this.