Choosing a dome port vs wet lens

I’m on the fence on which route I should go.  A fantasea done port and extension that will support my 16mm sigma or the fantasea wet lens that works with the 16-50 kit lens.    Both end up being $700.   Which is a better option?   It’s for a a4000

14 minutes ago, Emmeriaa said:

I’m on the fence on which route I should go.  A fantasea done port and extension that will support my 16mm sigma or the fantasea wet lens that works with the 16-50 kit lens.    Both end up being $700.   Which is a better option?   It’s for a a4000

What do you like to shoot?  Also a4000 ?  DO you mean a6x00 series camera? 

Also which sigma lens are you talking about - the 16mm f1.4?  and I guess you are talking about the 400F lens which is 0.5x.  Assuming you are talking about an APS-C  sensor, the 16mm lens is equivalent to a 24mm lens which in UW terms is not that wide.  The UWL-400 on the other hand would provide approximately 12-37mm equivalent focal length which would be quite a useful UW range.

11 hours ago, ChrisRoss said:

What do you like to shoot?  Also a4000 ?  DO you mean a6x00 series camera? 

Also which sigma lens are you talking about - the 16mm f1.4?  and I guess you are talking about the 400F lens which is 0.5x.  Assuming you are talking about an APS-C  sensor, the 16mm lens is equivalent to a 24mm lens which in UW terms is not that wide.  The UWL-400 on the other hand would provide approximately 12-37mm equivalent focal length which would be quite a useful UW range.

Im sorry i meant a6400.  The options are my kit lens which is 16-50mm where i could use the flat port and a wet lens(UWL 400f or uwl-09f are the two compatible choices). OR i could get the FML Dome Port A6 for my 16mm 1.4.   Will the A6 dome port give me a wider usable focal length like the wet lenses would.  IF i go the A6 port route, I could also use this for a 10-18mm down the road.   Also is the extra $300 worth it going from the UWL-400 to the UWL 09F?

Thanks for the clarification,  to make things clearer compare the options in full frame equivalent the 16mm lens is 24mm equivalent, while the 16-50 behind the UWL 400 is 12-37mm.  24mm is not very wide for UW photography and of course gives you no flexibility. 

The dome does not increase field of view only restores it what you would get in air and avoids the aberrations introduced by a flat port.  The wet lens, expands the field of view and allows the the camera to focus much closer, generally you can focus on the port.

Fantasea produce a compatibility table here for their lenses:  http://www.fantasea.com/downloads/WetLensesCompatibilityTable.pdf

From this you need to zoom in to 19mm on the 16-50 with the UWL-400 while the UWL-09F you need to zoom into 17mm.  The 400 is 0.5x and the 09F is 0.45x.   This is to remove vignetting. 

Now that we know which camera you are using it changes things a little,  The 400F will be a 14-37mm equivalent and the 09F will be an 11.5 - 34mm equivalent.   The focal lengths in the 11- 16mm are quite useful for wide angle under water photography.    As to which would be the best choice - I don't know what the quality is like on these lenses and it is hard to find samples online and they are mostly quite small on the screen so quality is hard to judge - try googling for reviews of the lenses.

As far as using the 10-18 as well in the 6" dome,  I would think a 6" dome is a little small for a 10mm lens,  the general view for an APS-C sensor is you need an 8" or larger dome for a 15mm equivalent lens, so I expect the corners won't be great zoomed all the way out and you also should expect to need to stop down to f11-13 with to get that performance.  With a 6" dome you would be looking at f13-16 and even then the corners may not be that great.

You didn't mention what subjects you plan to shoot, this can make a difference to the recommended lens.