Is the sony a7r2 (w/Nauticam) worth the money? Any experiences w/this equipment?

[dfein 0]

I am currently looking to upgrade equipment. Will be doing photo/video 50/50 of the time. I was conidering the lumix gh4, but just read about the sony a7r2, which seems incredibly better for taking quality stills.

 

I am curious about peoples experience with the sony a7r2, regarding the whole process of use, from lenses, strobes, to dealing with the larger file size. I will be working for a dive shop, so will have a lot of file sharing via dropbox to do, so it might not be worth having a full frame mirrorless.

 

Lastly, mirrorless vs dslr pros and cons?

 

Thanks

[dr.rob 2]

What are you upgrading from? Are you happy/unhappy with the image quality of your current set-up?

 

IMHO, full-frame is overkill for underwater. The main advantage of full frame cameras is that they are better at gathering ambient light in low-light situations, but assuming you are using strobes, this is not really an advantage underwater. The image quality differences between FF, APS-C and m4/3 is really minimal for underwater shots, especially for macro. Before jumping into FF, think about costs, bulk and available lenses. If I was starting from scratch, I probably would go m4/3. If you look at the best underwater shots from m4/3 (i.e., Oly, GH4, etc), I don't think you will find a perceptible difference between those and the best UW shots taken with FF.

 

Mirrorless vs. DSLR is a very interesting and debatable question. Advantage of Mirrorless is: less expensive, less bulky, same image quality. Advantage of DSLR is better AF (although that advantage is fast disappearing, I think many of the best mirrorless cameras have more or less caught up). Another advantage of DSLR is better lens availability, but that advantage is also disappearing. Another advantage of DSLR is better battery life, assuming you are using mainly the optical viewfinder rather than live view. For me, the advantage of smaller form is more important than better battery life.

 

I would perhaps go out on a limb and say 2015 is the year that mirrorless caught up and surpassed DSLR, at least for underwater.

[dfein 0]

Thanks for your response. I will be working for a dive shop and will be selling the photos, and I would like to get gear that can work in low light as well as with a strobe. I have heard of problems with the gh4 performing adequate white balance, and am curious if anyone has experience with the a7r2 underwater, whether it performs on the level of say the 5dmark3. I have heard that the camera heats up while capturing 4k. I am hoping to hear some experiences with either the sony A7r2, or the sony A72 underwater. I would use the nauticam housing.

[akivisuals 1]

I can't say that I have much experience shooting any of these cameras underwater as I am a relatively new diver. That said, I've been shooting photo and video professionally since the late 1980's. I own the Sony A7rII and have owned several of the Sony mirrorless models including the A7, A7s, NEX-5, NEX-5n, NEX-7. Canon DSLRs have been my staple cameras since I bought my first DSLR in the 10D. I sold one of my 5D3's earlier this year to help finance the A7rII. For video I'm shooting a C100. I also have and use a GH3. All this to say that for stills work and much of my video work I'm moving on to Sony.

 

I love my C100 but Canon has been holding back technology that they've had for years on their prosumer/pro level cameras. They own the lion's share of the market and want to sell cameras so they don't release technology that they are sitting on. They release models very slowly and don't offer a ton of upgrades in performance because they don't want to cannibalize their pro division. Sony, on the other hand, has nothing to lose. They constantly push the envelope as far as technology because they want the market share that Canon owns. I've been phasing out my Canon gear except for some of my go to lenses for the C100 and switching to Sony.

 

The A7rII is a GREAT camera. It checks all the boxes on what you might want for stills and video. High res in stills, 4K in camera video, fast frame rates for video, great low light performance, options to go to full frame or Super35, in body 5-axis stabilization, ability of adapt all manner of lenses to the body, small size and light weight. The GH4 is a great buy and has very good performance but is just so-so in low light compared to the Sony mirrorless options. I agree with the sentiment that a m4/3 camera is perfectly fine for underwater use though. You might actually want some of that depth of field that you lose with a full frame body. Plus it's small and lightweight. I actually went out and bought an older Olympus E-PM1 and housing to cut my teeth on before investing several thousand into a Nauticam housing for my Sony bodies. I've shot my A7rII in a warm climate at 4K and had no problems with it overheating. That said, I didn't shoot long clips. If budget is an issue I would strongly consider the GH4. It does a lot of really good things at a 1/3rd of the price. Take this all with a grain of salt though since I have little experience taking this stuff underwater.

[tamas970 12]

I am on m4/3 (E-PL5, no better sensor has been released since) and being disappointed in the low-light performance (orange filter@5-10m) and migrating to Sony in the coming months (no trips until February, I have some time to collect the bits and pieces). I also want 4k video - for that the only really high quality choice is the a7rII/a7sII. Not sure if I'll start with the a7rII, might pick up a used a7II for 1/3 price and learn to handle FF - I can use the same housing for the a7rII. I agree w your point about withheld tech, c'mon, why can't a bloody FF, 3500$ Canon/Nikon body nowadays record 4k video??

For the OP: If it worth depends on your wallet and on the availability of alternative housings. In case Ike releases their version (communicated with them, they say it's not hopeless ) you have a fully functional system for ~1k$ cheaper.

The camera itself has the best available FF imho. Downsides are limited battery life and white balance issues latter is no problem for stills (shooting raw anyway...), for video I am not sure how to circumvent it/how prevalent it is once you set mwb.

I can't say that I have much experience shooting any of these cameras underwater as I am a relatively new diver. That said, I've been shooting photo and video professionally since the late 1980's. I own the Sony A7rII and have owned several of the Sony mirrorless models including the A7, A7s, NEX-5, NEX-5n, NEX-7. Canon DSLRs have been my staple cameras since I bought my first DSLR in the 10D. I sold one of my 5D3's earlier this year to help finance the A7rII. For video I'm shooting a C100. I also have and use a GH3. All this to say that for stills work and much of my video work I'm moving on to Sony.

 

I love my C100 but Canon has been holding back technology that they've had for years on their prosumer/pro level cameras. They own the lion's share of the market and want to sell cameras so they don't release technology that they are sitting on. They release models very slowly and don't offer a ton of upgrades in performance because they don't want to cannibalize their pro division. Sony, on the other hand, has nothing to lose. They constantly push the envelope as far as technology because they want the market share that Canon owns. I've been phasing out my Canon gear except for some of my go to lenses for the C100 and switching to Sony.

 

The A7rII is a GREAT camera. It checks all the boxes on what you might want for stills and video. High res in stills, 4K in camera video, fast frame rates for video, great low light performance, options to go to full frame or Super35, in body 5-axis stabilization, ability of adapt all manner of lenses to the body, small size and light weight. The GH4 is a great buy and has very good performance but is just so-so in low light compared to the Sony mirrorless options. I agree with the sentiment that a m4/3 camera is perfectly fine for underwater use though. You might actually want some of that depth of field that you lose with a full frame body. Plus it's small and lightweight. I actually went out and bought an older Olympus E-PM1 and housing to cut my teeth on before investing several thousand into a Nauticam housing for my Sony bodies. I've shot my A7rII in a warm climate at 4K and had no problems with it overheating. That said, I didn't shoot long clips. If budget is an issue I would strongly consider the GH4. It does a lot of really good things at a 1/3rd of the price. Take this all with a grain of salt though since I have little experience taking this stuff underwater.

Edited October 22, 2015 by tamas970

[dreifish 364]

What are you upgrading from? Are you happy/unhappy with the image quality of your current set-up?

 

IMHO, full-frame is overkill for underwater. The main advantage of full frame cameras is that they are better at gathering ambient light in low-light situations, but assuming you are using strobes, this is not really an advantage underwater. The image quality differences between FF, APS-C and m4/3 is really minimal for underwater shots, especially for macro. Before jumping into FF, think about costs, bulk and available lenses. If I was starting from scratch, I probably would go m4/3. If you look at the best underwater shots from m4/3 (i.e., Oly, GH4, etc), I don't think you will find a perceptible difference between those and the best UW shots taken with FF.

 

Mirrorless vs. DSLR is a very interesting and debatable question. Advantage of Mirrorless is: less expensive, less bulky, same image quality. Advantage of DSLR is better AF (although that advantage is fast disappearing, I think many of the best mirrorless cameras have more or less caught up). Another advantage of DSLR is better lens availability, but that advantage is also disappearing. Another advantage of DSLR is better battery life, assuming you are using mainly the optical viewfinder rather than live view. For me, the advantage of smaller form is more important than better battery life.

 

I would perhaps go out on a limb and say 2015 is the year that mirrorless caught up and surpassed DSLR, at least for underwater.

Having shot both a Nikon D800 full-frame system and a GH4 underwater, I think there are real differences between the two, both when it comes to image quality and ergonomics/usibility.

 

For macro shooting, the D800+105mm macro produces much more detailed files than the GH4 + olympus 60mm. And the tonality is more pleasing. For wide angle, the differences are a bit more subtle since you can shoot the GH4 at wider apertures than the full-frame camera, but I think they're still there, especially when it comes to dynamic range. This can be noticeable when you have large gradations in illumination in different areas of the picture (shooting portrait orientation on a wall dive, for example).

 

The biggest difference for me though is the autofocus system. The D800 3d tracking is sooo much faster and more accurate for focus & recompose work with moving subjects than any of the equivalent "lock-on" modes I've tried on the GH4 and the Olympus OM-1. Perhaps the new Sony A7RII comes closer--I'd be interested to hear from someone who has shot the A7RII and a Nikon full-frame underwater.

[tamas970 12]

Having shot both a Nikon D800 full-frame system and a GH4 underwater, I think there are real differences between the two, both when it comes to image quality and ergonomics/usibility.

 

For macro shooting, the D800+105mm macro produces much more detailed files than the GH4 + olympus 60mm. And the tonality is more pleasing. For wide angle, the differences are a bit more subtle since you can shoot the GH4 at wider apertures than the full-frame camera, but I think they're still there, especially when it comes to dynamic range. This can be noticeable when you have large gradations in illumination in different areas of the picture (shooting portrait orientation on a wall dive, for example).

 

The biggest difference for me though is the autofocus system. The D800 3d tracking is sooo much faster and more accurate for focus & recompose work with moving subjects than any of the equivalent "lock-on" modes I've tried on the GH4 and the Olympus OM-1. Perhaps the new Sony A7RII comes closer--I'd be interested to hear from someone who has shot the A7RII and a Nikon full-frame underwater.

True, full-frame should provide you much better detail&dynamic range than m4/3. However ports and optics are at least as important for the resolution as the sensor. Regarding AF: true, DSLR-s are leading here. However mirrorless is coming up tremendously.

 

After looking at several reviews and browsing through a big pile of forums I concluded that the A7sII should be the coming king of UW foto+videography.

4k video on the 7rII is crippled by the faulty binning algorithm when shooting full-frame. Super35 is usable, however that crops ~half the sensor.

As for stills, in most waters I dive, I doubt that the added resolution of the A7rII would materialize, probably I'd also need a perfectly focused nikonos lens for that too and someone, who filters all slit and sh&@t from the water...

 

OTOH, the 7S family is an absolute low-light winner, ISO 12800 is usable and provides a dynamic range you see at ISO 1600 in case of the OMDmk2... This means those filter assisted manta/whaleshark shots won't look washed/noisy anymore.

[dreifish 364]

True, full-frame should provide you much better detail&dynamic range than m4/3. However ports and optics are at least as important for the resolution as the sensor. Regarding AF: true, DSLR-s are leading here. However mirrorless is coming up tremendously.

 

 

After looking at several reviews and browsing through a big pile of forums I concluded that the A7sII should be the coming king of UW foto+videography.

4k video on the 7rII is crippled by the faulty binning algorithm when shooting full-frame. Super35 is usable, however that crops ~half the sensor.

As for stills, in most waters I dive, I doubt that the added resolution of the A7rII would materialize, probably I'd also need a perfectly focused nikonos lens for that too and someone, who filters all slit and sh&@t from the water...

 

OTOH, the 7S family is an absolute low-light winner, ISO 12800 is usable and provides a dynamic range you see at ISO 1600 in case of the OMDmk2... This means those filter assisted manta/whaleshark shots won't look washed/noisy anymore.

 

Full frame will require larger domes/port, obviously, especially for wide angle rectilinear lenses. The (size) difference between a 170/180mm dome and a 230mm one is very noticeable, and significant for travel.

 

That being said, assuming equal quality domes, the optics (e.g. lenses) on full frame have an inherent advantage because of the size and pixel density of the sensor. A bad lens on full frame will still resolve much more detail than a great lens on m4/3 or APSc. Even when the sensors have equal megapixels, because of refraction. Check out the DXOMark lens sharpness tests sometime -- the Nikon 105mm macro resolves 12 megapixels on detail on the APS-C d7100 sensor. The same lens, however, resolves 19 megapixels on the full frame D750 sensor. And both sensors are 24megapixel sensors. That's just physics at work. Boost the resolution (e.g. pixel density) of the sensor, and you get even more detail. Same lens on the D810 resolves 21 megapixels of detail (which shows that it's actually not such a great lense, since the best lenses on the D810 can resolve 30+ megapixels according to DXO).

 

For comparison, the olympus 60mm macro only resolves 10 megapixels on the Olympus EM-1. So going from micro4/3 to full frame gives you twice the resolution. Now, you may argue that the water between your port and the subject dissipates much of that advantage, but, in my own experience, having worked with both systems, you can still see a difference. Especially with macro.

 

As for the A7RII, I really want to like it -- I agree with you that on paper it looks like the perfect hybrid photo/video camera and I would love to upgrade to it from my GH4. However, for underwater use, I have two major concerns:

 

1. The white balance for ambient light underwater video. According to Backscatter's review, you need a red filter to properly white balance. And even with the red filter, the results to my eye look too purple and fake. Compare the wide angle footage in Backscatter's review with underwater 4k footage shot on the Canon 1DC -- the Canon white balance and colors are much more pleasing, in my opinion. Since I think the GH4 does underwater macro video (with lights) equally well to A7RII, and my main reason for upgrading would be better low light performance and colors for ambient light wide angle video, the A7RII's limited white balancing ability and questionable underwater colour science makes me hesitate. I'd like to see more underwater wide angle footage from the A7RII.

 

2. The focusing system underwater, especially focus tracking. As I mentioned, I absolutely love Nikon's 3D tracking in AF-C mode for shooting macro photos, and I always get frustrated with the GH4's autofocus system in similar situations (the tracking usually can't pick up a fish's eye, so you have to manually move focus points around). From what I can gather, the A7RII's autofocus tracking isn't as good/flexible/versitile as Nikon's implementation. And it doesn't work in low light (just like the GH4) meaning you need to use a focus light. Focus lights can be a significant disadvantage when working with skiddish creatures like mandarin fish.

 

All of which leaves me at a loss for what to do. I want to upgrade to an A7RII, but I think a Nikon D810 is still a better choice for photography. And for video, Canon has more pleasing colors underwater, which, IMO, makes a bigger difference than resolution for wide angle video. If you absolutely need a camera that can do both great underwater 4k video and photos, AND you shoot wide angle video, then the Canon 1DC might be a better choice than the A7RII, budget allowing.

 

If you just need macro video or underwater video where artificial lighting will dominate (e.g. inside caves, deep wrecks) the GH4 is probably a match for the A7RII on the video front since you can shoot at low ISOs.

Edited October 23, 2015 by dreifish

[kkfok 24]

If you need to shoot with ambient light I think Canon still has an edge on that, this is particularly true for video as really strong video lights are expensive and sometimes they drive away subjects underwater.

[ChrigelKarrer 52]

The quality, dynamic range and speed of a full frame camera - in my case the D800 - and high quality lenses is still far superior

to any non full frame camera and it gives you the option to do much bigger crops due the much higher pixels.

Unfortunately DSLR cameras are not good to do underwater video, so in this moment they are limited to best quality photography.

 

There are several treads regarding the use of the the Sony A7 underwater and it seems that there are some annoying limits like

overheating and troublesome white balance for example and i am not so sure if the low light capability is soooo useful under water

as the use of video lights is a must due the lack of colors at greater depths.

The low light capability can become handy shooting in very shallow water, fresh water or still using video lights doing night dives, caves or wrecks.

 

My buddy is considering to switch from a video camera to a hybrid, but his conclusion is that the A7r2 is not the way to go.

 

Chris

[tamas970 12]

 

Full frame will require larger domes/port, obviously, especially for wide angle rectilinear lenses. The (size) difference between a 170/180mm dome and a 230mm one is very noticeable, and significant for travel.

 

If I take this road, I'll obviously go for Nikonos lenses I know its MF, and I have to go back to where I started photography 25 years ago but the sharpness of the pictures I've seen from nikonos stuff

is beyond anything I've seen before. Some advanced aspheric wide converters like the WWL-1 might catch up, the classical dome solution is quite limited.

 

Regarding WB concerns: is that an issue if one uses a filter and sets the WB to a fixed value? (6k, or anything that suits the depth+water color) I am very much fan of filters.

 

Focusing: true, however DSLR-s are very poor on video, especially in my price range (<3k$). 1DC is definitely ruled OUT, I am not giving away such an amount of money for something that turns to

0.1$ scrap metal in 10-15 years.

 

If you need to shoot with ambient light I think Canon still has an edge on that, this is particularly true for video as really strong video lights are expensive and sometimes they drive away subjects underwater.

My lights are quite strong (2*100w halogen) and their color is a good match, but in tropical waters I have no chance against the sun:) (or at least the amount of blue it provides at 10m depth)

Need an upgrade in this department too, but LED technology is still in its infancy, high CRI+low temp sources just started to appear in the last year.

 

There are several treads regarding the use of the the Sony A7 underwater and it seems that there are some annoying limits like

overheating and troublesome white balance for example and i am not so sure if the low light capability is soooo useful under water

as the use of video lights is a must due the lack of colors at greater depths.

The low light capability can become handy shooting in very shallow water, fresh water or still using video lights doing night dives, caves or wrecks.

 

My buddy is considering to switch from a video camera to a hybrid, but his conclusion is that the A7r2 is not the way to go.

The A7 is stone age compared to the recent cameras, but true, the A7r2 has shortcomings I don't like either, first being the problematic

FF mode in 4k and the 8bit limited HDMI output. AF speed I cannot judge until I saw a camera in action, anyway if I go for Nikonos lenses,

AF becomes irrelevant.

Regarding low-light: dynamic range comes hand-in-hand with it. DR bears impact even on well-lit macros, where something white in the foreground

reflects a huge amount of light, with a lesser camera you have to choose: either you burn the white stuff (subject?!) or you loose some of the background.

 

I want to love the A7sII, but I can't. 12MP sounds little if tack-sharp optics are provided.

Edited October 23, 2015 by tamas970

[dreifish 364]

 

If I take this road, I'll obviously go for Nikonos lenses I know its MF, and I have to go back to where I started photography 25 years ago but the sharpness of the pictures I've seen from nikonos stuff

is beyond anything I've seen before. Some advanced aspheric wide converters like the WWL-1 might catch up, the classical dome solution is quite limited.

 

I'm not sure you want the Nikonos as your only option for wide angle. Might be fine for video, but for photos, autofocus is quite nice if trying to capture action. So is the ability to zoom, which you get with lenses like the 16-35mm. Besides which, corner sharpness (and dome size) is only really a concern with rectilinear lenses. Fisheyes are pretty sharp. I think being able to use the Canon 8-15mm would actually be a strong draw for the A7RII.

 

Regarding WB concerns: is that an issue if one uses a filter and sets the WB to a fixed value? (6k, or anything that suits the depth+water color) I am very much fan of filters.

 

 

Judge for yourself. Here's video taken with the A7RII and a red filter. Here's video taken with the 1DC without a filter. Personally, I think the colors of the water column on the A7RII still look bad -- too purple.

 

Focusing: true, however DSLR-s are very poor on video, especially in my price range (<3k$). 1DC is definitely ruled OUT, I am not giving away such an amount of money for something that turns to

0.1$ scrap metal in 10-15 years

 

The A7RII and its housing will also depreciate in value quite quickly. If anything, they will depreciate faster than the Canon, since Sony seems to be on pace to introduce a new model every year. Price wise, a 1DC can be had (used) for around $5000-5500. Housing probably around $4000. So you're looking at 3-4k more than you would pay for a (new) A7RII + aluminum housing. Lenses and domes should be roughly equal in price (notwithstanding nikonos lenses).

 

 

My lights are quite strong (2*100w halogen) and their color is a good match, but in tropical waters I have no chance against the sun:) (or at least the amount of blue it provides at 10m depth)

Need an upgrade in this department too, but LED technology is still in its infancy, high CRI+low temp sources just started to appear in the last year.

Yeah. Basically, for tropical wide angle, the most important aspect of video quality is the white balancing of the camera with ambient light. Or a camera that shoots raw video, but that's a whole different class in terms of price.

AF speed I cannot judge until I saw a camera in action, anyway if I go for Nikonos lenses, AF becomes irrelevant.

I think this may turn out to be very important, IF you shoot moving subjects. Autofocus performance can make a world of difference in terms of nailing the shot and what you can shoot.

Regarding low-light: dynamic range comes hand-in-hand with it. DR bears impact even on well-lit macros, where something white in the foreground

reflects a huge amount of light, with a lesser camera you have to choose: either you burn the white stuff (subject?!) or you loose some of the background.

 

Actually, DR is most important for ambient light wide angle. For macro, you're controlling the lighting. If your subject is very reflective, turn down your lights/strobes and slow down the shutter to bring in more ambient light for the background. I'm not sure I understand why you would need wide dynamic range in this circumstance -- unlike, for example, shooting a wide angle image where you have a sunburst in the picture. It also helps that for macro you can generally shoot at base ISO because of the artificial lighting.

[tamas970 12]

I'm not sure you want the Nikonos as your only option for wide angle. Might be fine for video, but for photos, autofocus is quite nice if trying to capture action. So is the ability to zoom, which you get with lenses like the 16-35mm. Besides which, corner sharpness (and dome size) is only really a concern with rectilinear lenses. Fisheyes are pretty sharp. I think being able to use the Canon 8-15mm would actually be a strong draw for the A7RII.

I'd certainly miss AF and probably need both systems (I can feel the pain in the back and the wallet already...). For nice walls, wrecks, schools of fish, stationary objects (even a whaleshark - however I never encountered one, I don't know how fast these behemots move...) nikonos would be ideal. Sharks, and especially playful dolphins, etc: fast AF...

 

You mentioned the large domes: absolutely true, I am still missing a contemporary solution to the problem. A correctly designed wide converter, such as the Nauticam WWL-1 could be an answer to that, however it is still very inactive area. Nikon abandoned the field with their last Nikonos camera, since then only the housing manufacturers and Inon are revisiting the old Rebikoff concept with more or less success...

 

BTW on m43, the inon h100 with a standard zoom provides more or less the same results as the pricey pana 7-14+dome combo. Has anyone tried something like this on full frame? I am looking for macro vs wide flexibility on the same dive.

Edited October 26, 2015 by tamas970

[Mark K 5]

I have been with my A7rII for a month and two. DP review has just published their review I believe A7rII is the closest thing to replace an FF underwater dSLR. If you can use A7RII properly and get used to its AF system, you can save a lot of weight while traveling. However, if weight saving is not a priority, a conventional dSLR like D810 or 5Ds may be more rewarding than this small camera.

[dreifish 364]

I have been with my A7rII for a month and two. DP review has just published their review I believe A7rII is the closest thing to replace an FF underwater dSLR. If you can use A7RII properly and get used to its AF system, you can save a lot of weight while traveling. However, if weight saving is not a priority, a conventional dSLR like D810 or 5Ds may be more rewarding than this small camera.

 

Have you experienced any particular letdowns with the A7RII, Mark? It sounds like you chose the system for weight saving reasons. Did you shoot a DSLR underwater before? If so, do you mind listing the advantages/disadvantages you've personally encountered?

[Basil 13]

There is no right answer -- there is just what works for you. Both the GH4 or the A7R II are very capable (full disclosure, I have a Sony and a Panasonic, but neither of those models). Other things being equal (which they rarely are), a larger sensor will give better low light performance, dynamic range, and resolution. Whether there is a meaningful difference between full frame (Sony A7 series), APS-C (Samsung NX-1), or Micro Four Thirds (Panasonic GH4 or GX8), and whether that difference is due to the sensor size, is a hotly debated point in the photo/video world. Some say that it does matter:

 

https://www.youtube.com/watch?v=DtDotqLx6nA

 

Others say no, it really doesn't:

http://dedpxl.com/crop-or-crap-math-or-moment/

 

Both of these are worthwhile videos -- you can actually agree with both. I think the rate of technological change is altering some underlying assumptions on this -- think of it this way -- the Panasonic GH4 has 12.8 stops of dynamic range, which outscores the Canon 5D Mark III, even though the latter has a full frame sensor. But the Canon is about 3 years older -- that is how the technology has advanced, across the board. In the end, "scores" on the internet are not important -- it's whether you have an image you love.

That said, I will affirm (since I have a Panasonic LX100, which is a compact camera) that doing 4k video is FANTASTIC. Even just downscaling the 4k video clips to HD, when you edit them, gives you really beautiful HD. Although DSLRs have advantages over mirrorless (particularly on autofocus, though that is starting to change), there really are no 4K options for DSLRs, unless you go for the Canon 1D C, which is older, hugely more expensive, and is lacking a lot of really nice video features (like focus peaking) that are standard in mirrorless or compact cameras. For doing 4K video, and having interchangeable lenses, and access to a housing, your options are the Panasonic GH4 or the GX8, the Sony A7R II or A7S II, or the Samsung NX1 (Ikelite just came out with a housing for it, but Samsung is rumored to be shutting down its camera manufacturing -- which is a shame because the NX1 is supposed to be a very capable camera). Fuji and Olympus both have 4K capable cameras coming, sometime next year.

Back to the point -- larger sensor perform better, but lenses are at least important to the quality of your image. You have to balance off total system cost (camera, lenses, housing, ports, lights, accessories), performance, and size. Choose wisely, since this is a several thousand dollar expenditure!

Consider this option -- rent a GH4 and some good lenses (say, the Panasonic 12-35mm pro zoom, and the 25mm F1.4 prime), and take it out and play with it for a few days. Shoot video, shoot stills, do it in a variety of situations (bright, dark, indoor, outdoor, on a tripod, handheld, etc...). Then rent the A7R II, with say the 24-70 F4 zoom, and the 55mm F1.8 prime, and do the same thing. Take a look at the pictures and the video clips -- which ones do you like better? Show some to non-photographer friends -- just see what an untrained eye thinks. Show some to photographers and videographers and get their opinions. Evaluate the user interface on each camera -- how fluid is your shooting experience -- can you easily access key settings, and will you be able to do so if that camera is underwater in a housing? Which camera is more fun? (That is actually the most important question!)

If desired, you can repeat with other models (the Panasonic GX8 -- newer model -- more biased towards stills, newer sensor, 4K video but not all the high end video options of the GH4) and the A7S II (fewer but bigger pixels -- greater low light sensitivity and more advanced video specs), etc.... Your options in cameras and lenses are going to grow over time.

There is no right answer, it's just what is right for you.

[Kogia 3]

One big difference I have found between DSLR and mirrorless is the viewfinder. If your shooting style is mostly point & shoot, it won't matter. But if you do much composing through the viewfinder you may find (as I have with the Sony a7r) that the little electronic viewfinder and LED can both be hard to work with, especially if the ambient light is high. I much prefer the optical viewfinder on an SLR.

[dreifish 364]

While I can see how the monitor might be difficult to work with in bright sunlight, Kogia, I don't think that's really true of electronic viewfinders, which generally come with an eye-cap to block out the ambient light. I've certainly never had any issues with composing on an electronic viewfinder in higher-end mirrorless cameras like the Sony NEX-7, Olympus EM-1 and Panasonic GH4. I can't imagine the A7R is any different, though I've never owned one, only played with one in a store.

 

If anything, I would say that electronic viewfinders provide a great advantage, because they show you an accurate representation of your exposure -- so you can tweak your settings /before/ taking the shot. They also allow you to check overexposure through live histograms and zebra patterns and to verify critical focus using 1-to-1 magnification and focus peaking. Find me an optical viewfinder that can do all that!

 

Moreover, the viewfinder in the A7R, A7RII, and most modern mirrorless cameras offer the same or greater magnification than a full frame DSLR like the Nikon D810 or Canon 5DIII-- not sure why you would call it "little". It's in fact higher magnification than the optical viewfinders in most (all?) crop-sensor DSLRs.

 

Now, you might still have a preference for optical viewfinders, and I'll concede that for shooting sports and wildlife on land where you are tracking motion, they may be a better choice. But I think their benefits are greatly reduced underwater where you aren't shooting fast action with telephoto lenses, whereas electronic viewfinders retain all their benefits.