Very sorry I could not post photos last night. Will post 4 photos tonite taken with the 12-50 to illustrate what is possible.
Storker, you cannot access any macro mode with the firmware update, only 12mm or 50mm by using camera buttons. The lens at 50mm is not semi-macro or anything even close. It is large subjects only like fish head portraits. With that in mind, I think we should look again at the step one option.
You propose the 4" dome as a less expensive step one because you can use the 12-50 in it. But, the cost is 450 for the dome. For that, you get only 12mm fixed, and 50mm fixed with a very, very inconvenient way of having to push camera buttons to access 12mm or 50mm. You have no macro capability at all in your initial system. So, you are in with a system of very limited usefulness and extreme inconvenience of use. You will be cursing many, many missed shots.
Remember, you are dropping 1350 on the housing, 200 on a tray. So, you are "all in" at 2000 for step one with the dome.
Consider the alternative. The 12-50 port/gear is 800 (350 more than the dome). For that you get an excellent general purpose zoom with semi-wide capability for photo and video. You get the full zoom range. You also get "true macro" mode, and instant switching between regular zoom and macro. I found this instant switching to be incredibly convenient in actual use and got many shots I never would have been able to get. In practical use, the 12-50 was on my camera for 70% of the dives I made in Curacao, especially when diving a new site where I did not know what to expect in terms of wide angle or macro.
For this versatility, you are "all in" at 2350. The difference by saving the money is one that you are going to regret every time you hit the water. it will be the difference between cursing your camera and loving it.
Now, consider your additional steps later on. If you already have the 12-50 port/gear, you have macro and general purpose covered. Going into ultra-wide will cost you an additional 600 for the dome port and 9-18 zoom gear. At that point you are done with your system. 2 ports, optimum performance with both lenses, no need for awkward accessories, very fast use.
If you started with the dome port, if you want to add zoom functionality to the 12-50, a zoom gear will cost 150.00. If you want to add macro functionality, you have to add a diopter (200), plus an adapter to mount the diopter on the dome port (200-250). So, you are spending an extra $600 or so just to add macro and zooming on the 12-50. Next, Because of the dome, no diopter on the 12-50 is going to be close enough to the front of the lens to really give you magnification to the true macro level, or good optical quality even with an expensive diopter. Plus, you have no instant switching from general purpose to macro, but instead the inconvenience of screwing the diopter on and off. Thus, you really do not end up with the convenience and functionality as the dedicated 12-50 system. Also, to add the 9-18, you have to spend another 150 for the zoom gear. So, all told, an additional 750. You start off paying less, but end up paying more at the back end, which brings the price savings down to 200 overall. However, your ending system will not be nearly as functional.
So, the issue really boils down to 2350 versus 2000 up front to end up with a much better overall system at the beginning, and a savings of only 200 in the end for a substantially inferior final system.
