Sony A7R III/A7 III Lens & housing. Advice needed

I'm planning to upgrade from G7X MkII to Sony A7R III or A7 III. Pls advice where to invest. Mainly used for photography. Pls consider that it'll be in the hands of a newbie.

A7R III or A7 III:

The megapixel says it all for sure, pls ignore that part. Surely if budget permits I'll go for the "R". Questions is should I secrifice in everyway possible to go for the "R" & go cheap on the rest. Is the difference really a big jumper?

90mm Macro:

Should be the best for macro right? I've read somewhere that focusing is abit hard at low lights. AF keeps on hunting & slow... Is this the right one or others?

16-35 f4 ZA OSS:

From my research this would be sufficient for starters & would last a very long time till turns pro. Any other to consider to invest?

Housing:

If budget permits I'm surely going for a more reputed one. Currently I'm only looking into SeaFrog. Considerably super cheap. Problem with it is I need to secrifice "joystick" functions, the housing excluded the functions.

Not many might have come across Seafrog Housings. The concern is "Am I going to loose out alot by going cheap & sacrificing joystick functions". Joystick functions really benefits, used constantly or make a big difference?

Reputed housing & ports price TRIPLES the price of Seafrog. That's just too tempting to ignore. If this housing is okay it'll permits me to go for the A7R III body.

Seafrog A7RIII/A7III Housing:

https://seafrogs.com.hk/collections/sony/products/sony-a7r-iii-fe12-24mm-f4g-40m-130ft-uw-camera-housing-kit-with-6-dome-port-including-standard-port-1

Thanking all indavnce for your opinions. It'll help me a lot to decide on which one to prioritize

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You know the Sea frogs A7 housings don't have a zoom control, so you can't zoom under water? The other issue is the domes are one size fits all, for example the 12-24 and 16-35 both "fit" the 6" dome port, if you look at the Nauticam port chart you'll see the 12-24 needs 75mm extension and the 16-35 105mm, so clearly one lens will not be optimised.

In the case of the 16-35mm lens the recommended dome is 230mm, the optical quality is going to suffer particularly in the corners with the smaller 6" and 8" domes. The A7 may have great resolution but you need to use the appropriate domes and extensions to preserve this when using the camera underwater. If budget is a problem I suspect your images will be as good using a lesser camera with a smaller sensor which will work better with smaller domes. Unfortunately you get what what you pay for.

I use a SeaFrogs housing with Sony A6300, 10-18mm wide-angle, 90mm macro, 8" dome and flat macro port. No complaints, all the controls work. Note that with the A7 series housings, they only offer a single fixed 5-pin bulkhead, so you have to use wired triggering with your strobes, and as of yet there is no TTL converter to use sync cords with Sony cameras. UW-Technics is supposed to release one soon, but so far you'll be limited to electric triggering with manual power setting. There is no option to replace the electrical bulkhead with a window for use with LED triggers and fiber optic cables. Also, as Chris Ross pointed out, full-frame cameras with wide-angle lenses need bigger domes than what SeaFrogs offers to achieve optimal performance.

You know the Sea frogs A7 housings don't have a zoom control, so you can't zoom under water?

This applies only to the older model of A7 II housings. The basic A7, the A7 III and the new model of A7 II housing all come with zoom control; the latter two have a vacuum valve port as well, albeit a non-standard one.

You write: "Reputed housing & ports price TRIPLES the price of Seafrog. That's just too tempting to ignore. If this housing is okay it'll permits me to go for the A7R III body."

For a fine, expensive camera like the Sony A7R III, it is was mine, I would buy a real housing, one made by Subal, Nauticam, Sea&Sea or Aquatica, to name some top makes.

Why? Because they are made of aluminum and do not deform with diving pressures and with time. They also accept fiber optic cables for the strobes. In contrast, a housing made of plastic is much more susceptible to deform under pressure, or from temperature changes such as one encounters during travel. A housing that only uses sync chords, but not fiber optic cables, is bad news as sync cords are prone to corrosion and failure, best avoided.

It is true that a plastic housing is less expensive than an aluminum one - cheaper and trouble prone is a better way to say it. If the housing or port cracks or deforms it will leak and you can kiss your camera, lens and housing electronics good bye.

The Sony 90 mm macro is indeed quite slow to focus in low light, but it's not too much of a hindrance in practice. I use DMF autofocus mode with back-button focus for macro in those conditions. Autofocus will typically get you close to the correct focus plane, then you can rock the camera back and forward and use focus peaking to ensure the eyes (or other features) of your subject are sharp.

I have an A7rIII, and I'd certainly agree with the comments above about optimising the port for the lens you'll be using. You'll have far less depth of field than with a smaller-sensor camera (I previously had m4/3), and the high resolution makes this rather obvious. I have to stop down to f/10 or more to get anywhere near acceptable corners with my 100 mm Zen port and Canon 8-15 mm lens.

I love the 42 mp (except the hours it can take to ingest images, and the need for an 8TB hard drive), but I'd lean towards the A7III if it'll allow you to get a Nauticam or comparable housing. I have no knowledge of the Seafrogs, but the aluminium housings tend to have improved ergonomics and last a lot longer. I subscribe to the "buy once, cry once" philosophy