Underwater focus with flat port

Does anyone know if a flat port effects focus underwater like a dome port does?

What are you trying to ask? There is no negative effects on focus from a flat port.  Dome ports operate a little differently as the camera is seeing the reflection on the inside of f the dome. 

24 minutes ago, ParkerS said:

Does anyone know if a flat port effects focus underwater like a dome port does?

the issue with a dome port is that the virtual image is curved and very close to the dome so you lens needs to focus quite close.  You also need to stop down enough to get all of the virtual image in focus .

A flat port does not have these issues, it does however magnify the image about 1.3x in water.  Technically it does create a virtual image, but that merely appears closer which is the cause of the 1.3x magnification.  For practical p=application though there is no focusing issue associated with a flat port.  This link provides a detailed explanation:  https://oceanity.com.au/articles/view/understanding-flat-port-and-dome-port-theory