20mm lens in Flat Port

[Compressor]

Wondering how this will work underwater:

If I put a Nikon 10-20 mm lens set @ 20mm in a Ikelite housing and a flat port how will the images be seen underwater? On land, the image is fine. (I have an issue with large dome port for travel on this coming trip; hence reason for asking). Nikon D500 is the camera (AP-C).

I have a feeling that the camera will not be able to focus as in some lens/port combination where a 4x diopter lens filter is needed.
Thank you.

 

[Barmaglot]

Pretty terrible. Focusing shouldn't be a problem, but distortion will be quite significant, and you will lose significant amounts of field of view. Here's a Sony 10-18mm behind flat port @ 10mm:

And the same lens @ 18mm:

For comparison, the same lens @ 10mm and 18mm behind an 8-inch dome:

If you can't bring along a proper dome, at least consider getting a wet dome attachment for the flat port; this will go a long way towards correcting these aberrations.

 

[Compressor]

Thank you @Barmaglot. Very helpful.
Will look into a wet dome attachment. Did not know it existed for Ikelite.

 

[Compressor]

For those interested: Wet Lens for Ikelite.