Field Review: Nikon D750 in the Red Sea

With Nauticam NA-D750 housing

By Alex Mustard.

Autofocus

Read Nikon’s marketing blurb on the Nikon D750 and there are four features they are keen to promote. The new 24 MP sensor capturing the images, the EXPEED 4 processor that runs the show, the enhanced video options (boring) and the Multi-CAM 3500 II autofocus. It was the autofocus I was keenest to try as the promo prose promises next generation performance with the new grouped AF points introduced with the D4S and improved low light performance over even the D810.

The last Nikon camera I had that allowed us to use a moveable group of AF points was the Nikon D2X, and as I noted in my Wetpixel review of the Nikon D3, this was something I was frustrated to see dropped as I used it “about 80% of the time on the D2X”.

Other modes have filled the gap. I use AF-C Auto-Area for all my wide angle on my D4 and D7100 (because it just works) and I was so surprised that I actually had a single out of focus wide angle frame this year that I posted about it on Facebook! For fish portraits and most macro I use AF-C and 3D tracking, using the 3D tracking to follow subjects, to account for my own movements as I float in the water and for the recompose and shoot tracking technique I first extolled in the D3 review of September 2008. I use AF-C with single point for critical focus situations such as super macro or standard macro where the focal point of the subject (e.g. eye, rhinophore etc.) is well away from the middle of the frame. I use all three modes with thumb focus activation from time to time, but in the main I leave AF activation on the shutter release. All that said, I was excited to have grouped AF back and wanted to see how it would fit into the way I focus and shoot.

For wide angle shooting it is a useful mode, especially when taking a series of vertical reef scenics, as the AF group can be left in the lower third of the frame, where the foreground subject is likely to be, so ensuring precise focus for the optimum depth of field. However, I find that Auto-Area (with all 51 sensors active) is so trustworthy on the latest Nikons and automatically allows for quick changes in subject position, that I feel it is a superior option to grouped AF.

For macro shooting the grouped AF worked, but I found it slower than using single point (the fastest) or 3D tracking (the most versatile). I also found it less accurate than either of the other two modes. In the example of the lizardfish, below, I shot a number of shots on each mode and had far more out of focus on the eye when I placed the grouped points over the eye than when I used 3D tracking with the point over the eye.

A nice feature is that I didn’t have to reposition the focus point in the frame when switching between the modes, as the single point remains in the same part of the frame as the group was positioned. In conclusion, the grouped AF did not fulfil my anticipation and I didn’t discover an especially useful underwater application for it on this short trial with the camera. Hopefully more time with the system might bring up some uses.

I also wanted to test the low light focus capabilities of the AF and the Red Sea caverns of southern Egypt were ideal with many wide angle and macro subjects. I never dive with a focus light in the day in the Red Sea (I don’t like unnecessary camera clutter) and have shot in the caverns many times, so I have a good baseline of expectation of what AF systems can do. The D750 specs suggest it is better in low light than the D810, being sensitive down to -3EV (vs -2EV). Adam’s review revealed means the D810 can focus in the light of a full moon, so I guess the D750 needs only half a moon!

Shooting inside the caverns is a stern test for both the ISO performance (more on that on the next page) and the AF sensitivity of a camera. As I recommended to the group you need to consider the ISO, aperture and shutter speed you are happy to go to and then sacrifice a little on all three when necessary. It is also important to expose correctly if we want to open up all the detail from the RAW files in post processing, and it is easy to underexpose in the dark caves because they make the LCD appear brighter. Finally, there is the challenge of focusing in the dark. Many of the group found they needed to use thumb focus, locking the focus at the expected distance in a brighter part of the caverns.

The caverns are really dark in places, but I found last year that my D4 could always focus on wide angle scenery without the need to switch to back button focusing. The D750 also coped very well and I didn’t switch over to thumb focus at any point. It felt a little less sure-footed than my D4, but that might have been because I was less familiar with the camera or, more likely, the difference was caused by using a much smaller dome port on this trip. A small dome creates a virtual image compressed closer to the camera than a big dome. It therefore makes focusing more critical/difficult for the camera. The new Nauticam 140 dome is reviewed separately. Accounting for this, the D750’s low light AF was impressive.

I also shot the macro with the D750 in the caves, again without a focus light, and to raise the stakes I was shooting with a 2x AFS teleconverter on my 105mm lens. I found a nice sabre squirrelfish confident in its dark spot beneath an overhang in the cave. The camera did struggle more than I expected with this subject through the TC, but it ultimately produced pleasing portraits. I tried both grouped and single point AF and the latter was much more reliable, the former works best in lots of light and with a fast lens (and not a TC).

We also shot fast moving dolphins at dusk in Fury Shoal. Being so dark I had to open the aperture more than I wanted too and this made focus critical. The D750 coped very well with this challenge and I didn’t have to reject any photos for focus. Lots were deleted for other reasons.

The D750 boasts Nikon’s latest and best specced AF system, and it is very good, but throughout the week I felt it remains at least no better and at times inferior to my D4. I think the difference must be in the processing power behind the AF system, which is just simply more powerful in the flagship pro-models. Despite Nikon’s marketing claiming this is the update on the updated AF system in the D810 and D4S, they carefully word its capabilities “Providing the same autofocus features as you’ll find in Nikon’s flagship D4S!” The subtext in my mind is “same features, just not quite the same performance”.

In conclusion, the AF system in the D750 is one of the finest in any camera to ever go underwater. I think my negative comments, above, come more from the fact that marketing hype led me to believe that this would be a next generation experience, when I found it was probably ahead of the D800, but fails to match the D4. If Nikon marketing hadn’t insisted this was not the D610 successor, then I would have been comparing to the D610 and singing its praises for being a significant improvement on an already good system.

Autofocus speed allows us to get the shot, but when the action is fast and we’re not using strobes we also need high frame rates and capacious buffers. The D750 boasts a faster frame rate (6.5 vs 5 frames per sec) than the D810, which I was able to test with the spinner dolphins. The frame rate may be fast, but I think the advantage over the D810 is only marginal, with a subject like dolphins, as both cameras will run into the buffer with a some index finger exuberance. I can see a bird photographer noticing the difference between 6.5 and 5 fps when they have a single moment of action. But with a subject like dolphins, which will circle you for at least 5 to 10 seconds while you shoot away, the buffer is probably more important than the frame rate underwater. The D750 is a significant upgrade on the D610 in this area, but I don’t have direct experience to comment on the difference between the D750 and D810 buffers. But I think that DPReview’s comment that the increased frame rate of the D750 over the D800 (4 fps) might cause some to upgrade from D800 to D750 is unlikely to hold for underwater photographers, as frame rate is only really exploited underwater when shooting big animals without strobes.

Page 1. Introduction.
Page 2. The Nikon D750.
Page 3. The Nauticam NA-D750.
Page 4. Autofocus Performance.
Page 5. Sensor Performance and Conclusions.