Which small dome port to take with me on a very deep wreck dive

Hi team Wetpixel ;-)

I already went through all the posts on mini dome use cases and they all clear.

But, I want to toss in my specific use case and see what you would recommend.

I ask since some of these dives are difficult to do so I don't have many opportunities for try and test approach that I would normally do.

- I am going to take some wreck shots at about 60-100m depth.

- I will use new Nikon 8-15 fisheye on D850.

- As for shooting, no split shot opportunities. Also I don't really see value of corner sharpness on these dives so will compromise here. Instead, I will focus on framing the entire wreck with ambient light in blue, getting some flash lighted parts of wreck in the foreground while rest of the wreck and blue is in the background or really just some CFWA with details or fish and again parts of the wreck and blue in the background. 

- Large dome port was too bulky for me with rebreather, stages and rest of the dive kit so I took with me now only 4 inch mini dome and 7 inch glass dome 

What do you think will work better: 4 or 7 inch dome? Is there an obvious better choice?

My main use case is natural light ... or traces of it down there :-) if I have to choose one.

Thanks,

Marko

If you want small, go for the 4". I use that with the Nikkor 8-15 albeit on a D500. But it should be fine on the D850. Corner sharpness is good even if that's not important for you.

The advantage of the 4", other than the obvious small size, is the ability to be able to tuck strobes in close to the housing and light a close subject if you need to. But then if you are natural light shooting..... is there any/much natural light at 100m??

I regularly dive at those depths and, at least here in California, there isn't much natural light.

Even if there is some natural light where you are planning to dive, the colors will all be washed out and shades of blue at that depth without any artificial light so any CFWA shots won't highlight whatever is in the "close" range.

My guess is that without any artificial light, you will have to really boost ISO (resulting in grainy photos) and/or open up the aperture resulting in blurry corners (as you mention).

I usually dive with a Sony a6400, the 10-18 lens and the 7" dome port (along with my rebreather, multiple stages, reels, strobes, etc.). Sometimes I use the 16-50 "kit lens" and the WWL-C. 

Either way, I always bring artificial light.

- brett

I think it is a big mistake to use the 4". 

The 4" will give you really mushy (and obviously poor) corners. You are investing a significant amount of time and effort, not only in your gear, but in each dive. It seems to be a mistake to significant compromise the images you produce by using an optical system that is limited? 

With a full framer camera, I would look at 7" minimum with a fisheye, and this is especially true when you are forced to shoot wide open due to low light levels. Even with the 7", I find the corner distortion significantly distracting  at apertures of f/9 or so.