Thanks everyone for the insights. The general comments and consciences are that "do it right at the beginning" and " don't go cheap for this system". therefore, dedicated ports for particular lenses are recommended. These messages are well received. On the other hand, I still have concerns about the travelling weight.As quality is important for changeable lenses mirrorless camera, I have reviewed the lens choice after reading Phil's thread in wetpixel about the Oly 12-40mm F2.8 pro lens. The 12-40mm pro lens is a very good lens and it is possible to bring it underwater as a versatile lens from pseudo macro to medium wide shooting. Therefore, I have ruled out the 12-50mm and my lens choice will become:
- Oly 60mm for Macro (in small dome port, Wisnu's photos have proved that the Nauticam 4" semi dome port is suitable for the 60mm Macro)
- Oly 9-18 for Wide for now (In dome port, may wait and see the new Oly 7-14mm F2.8 Pro lens which will be released soon).
- Oly 12-40 Pro lens for general purpose versatile use from pseudo macro to mid wide (in appropriate dome port to get full use of the 12mm wide end)
For the above lenses, I may go for either a single universal dome port for all three lenses or opt for 2 ports solution for travel.
I note that the Zen DP170 n85II dome is suitable for the Oly 12-40mm pro, the Oly 9-18mm wide zoom (and the Pany 7-14 wide zoom as well if I opt for this lens), and 12-50mm zoom. With the extension ring , it may probably be used for the future Oly 7-14mm pro? A really versatile dome ports but a bit large and heavy for us beginners. Not sure if this dome ports can be used for the 60mm Macro? Could any user clarify on this? If it can be used for the 60mm macro, it will be the one dome universal port for me. Understand that dome port of this size may not be very convenient for macro shooting. Therefore, I will probably put this dome port in my list because of its compatibility of the 12-40mm and other mid/wide zoom lenses.
I will definitely get the Nauticam 4" semi dome instead of the 65 macro port for my first port for the EM1 housing. As proved by Wisnu, it works very well with the Oly 60mm macro. The upside is that it can allow the 60mm macro shot a bit wider for some fish portrait. On the other hand, it is designed for the Oly 9-18 meaning that I can use this lens for wide zoom. Thus it covers the 2 key lenses I intend to use. It is also lighter compared with the larger Zen DP170 dome and is smaller providing better convenience for shooting Macro. It will be my essential port for travelling with the 60mm and 9-18mm unless I want to use the 12-40mm pro.
In conclusion, I will buy the Nauticam 4" semi dome port with the EM1 house. Use it for a while to get used to the new set up. Then add to this system the Zen DP170 for the 12-40.
By the way, it seems that it is very difficult to get information about the dimensions, weight and other specifications of various ports. The Nauticam official site not even list a bit these information for their products! All online shops I can search do not has these information. For the Zen ports, it is a bit bette, some online shops lists the weight but not the dimension! Just curious where I can find these information. These are one of the important factors on considering a specific port as travelling weight has become very important now because of the airline limits. The dimensions also have impact in considering easy of handling. Even worse, I can't even tell from the online information if the ports are acrylic or optical glasses??!!