ISO, image quality and shooting FX.

The D4 produces stunning images at just about every ISO setting and it is easy to get carried away by the performance of its sensor. But I believe this misses the point of the D4. This is definitely a photographer’s camera, much more than a measurebator pleaser. Where the D4 excels is in taking photos, capturing the moment almost irrespective of the prevailing light conditions. Pixel peeping controlled conditions tests of the D4 images, is like trying to evaluate a Ferrari 458 with only a rolling road (in the dark, without seeing the car, sitting inside or driving it). The D4 is so much more than its sensor.

Despite my dislike of pixel peeping, I am going to share some controlled conditions test shots from the D4, although I do feel I am betraying the ethos of this camera by doing it!

The main reason the D4 excels at low light shooting is it has big pixels, but Nikon have introduced design improvements too. The pixels are spaced at a pitch of 7.3 micrometres and use gap-less micro lenses, which according to Nikon mean that all available light is channeled to the sensor. On top of this the “quantum efficiency” of the sensor has been improved, for a more efficient conversion of light to electrical signal. The take home message of this techno babble is a sensor with improved signal to noise ratio and wide dynamic range at all ISO settings.

Below are a series of 100% crops of photos taken of a seahorse (model) in the pool, which you notice is particularly lifelike and is even turning away slightly from the camera! Thank you to Martin Edge for allowing me to drop in on one of his 1:1 teaching sessions in the UK to take them.

I shot 7 ISO values, 1 full stop apart: 100, 200, 400, 800, 1600, 3200. I see no point in showing intermediates between these values because the differences are already so small! I did not test higher ISO values partly because I did not expect ISO 3200 to be so good, but mainly because at ISO 3200 I was already on minimum power on the single Z240 strobe and at f/32. The situation has to be very dark for ISO 6400. The first image shows the entire frame, the red rectangle showing the position of the crop, and the second image shows 100% crops at the different ISOs.

I selected this crop to reveal noise. I shot with single strobe to generate some shadows as noise is always most obvious in shadows. The largest shadow area in the crop is around the back of the eye.

Note that these are RAW files just directly outputted from Lightroom. I have not applied any post processing. Better image quality could have been achieved with additional processing, especially using Nikon’s NX2 software or even the D4’s in built RAW converter, which is optimized to get the most out of the files. However, I feel it is more valuable to show unadjusted RAW files as most people will know how to quickly improve them in the software. The files also show some JPG noise caused by saving for web.

The tests show that noise is minimal throughout this range and the camera records excellent detail at a pixel level. Well lit areas and highlights show almost no noise even at ISO 3200 at pixel level, while noise is more obvious in shadow areas. That said noise levels remain low and could easily be removed entirely with noise reduction software.

Although I do not have the test shots in this series from higher ISO settings (6400 and 12800) I have made these tests on land (shooting orchids) and both show fairly linear increases in noise (in both shadows and midtones/highlights) from ISO 3200, but both are useable. In well-lit conditions I would think that ISO 6400 would still reproduce well across a double page spread and ISO 12800 would be good on a single page, such as a cover.

But here we run into one of the problems of pixel peeping. High ISO performance is always better under good lighting, the sort of conditions you see in studio tests, than it is under the real world conditions, the type of conditions when we want to use high ISO values. We want a camera that can reproduce this performance underwater. Furthermore, in underwater photography we tend to use high ISO for shooting in available light (as strobe lit shots are rarely light limited), and available light underwater has a strong colour cast (blue). Limited wavelengths make it harder for the sensor to perform and noise is amplified significantly when we make major colour corrections in post.

Iceland was an ideal location for shooting available light wide angle in low light. There are many fissure and canyon dives, which are filled with clear, cold spring water, but also very dark. The image below looks bright and tropical because we associated clear, blue water with those conditions. But it was actually taken in the early morning, under cloudy skies. It was snowing on the way to the dive. Despite using ISO 2500, I was only able to achieve a shutter speed of 1/60th.

The requirement to colour correct the image in the RAW converter has definitely increased the noise at the pixel level, particularly in shadows.

Measurebators obsess over noise at high ISO because it is the easiest to discern: show 100% crops and you can bore endlessly about it. Actually the area that the D4 files impress me most is their high dynamic range at high ISO settings. And this is probably more valuable to the underwater photographer too.

Throughout its ISO range the D4 files preserve excellent detail into both shadows and highlights, but it is at the higher ISO values that it seems particularly groundbreaking. In the same way that the previous generation of cameras (D3) got on top of noise to the point you didn’t really think about it, the current generation have nailed dynamic range.

Enough pixel peeping. There always seems too much focus on wanting to see another 100% crop at some high ISO, instead we really should ask “when will we really need that high ISO?”

For those that dive deep or in dark places (or early or late in the day) and like to shoot wide angle then high ISO performance is undoubtedly valuable. This is particularly true for subject matter that it is not possible to light with strobes (such as big creatures, large shipwrecks and scenery) that are just too large. But it can also be a great benefit for more normal wide angle allowing us to work at much more ‘normal’ shutter speeds to balance the light. For still life scenic images this is not particularly critical, but for moving subjects this can be a significant benefit.

One of the most obvious benefits I have seen from the increased high ISO noise performance of cameras in the last few years is a significant increase in the quality of temperate water wide angle photography. Being able to shoot ISO 400-800 has been a great benefit. Will another couple of stops be as revolutionary?

ISO can also benefit in bright conditions when photographing fast action. I think that every photographer comes back disappointed the first time they photograph wild dolphins. Dolphins swim fast and most photographers, who are used to shooting with flash, don’t use a fast enough shutter speed when chasing cetaceans. As a result most people’s first dolphin shots are blurred on the edges because of subject movement. The same is true of other action like baitballs on the sardine run and with sailfish. ISO is a big benefit here. Coincidentally, all of these are situations where high frames per second would also be beneficial.

It is easy to think that high ISO would be a benefit for everything, but this is misleading. Every camera I have ever used produces its best image quality at base ISO. The ISO kings are the ones where the loss in quality is minimal. High ISO has no benefit for CFWA reef photography or macro shooting, which are two of the most popular disciplines underwater, because in both cases our strobes easily illuminate everything. For those that dive only in clear, bright, warm waters you will rarely need to bump the ISO.

However, strong ISO performance opens up creative possibilities underwater, particularly making use of continuous lighting for both wide angle and macro. This could be particularly interesting for behavior sequences, where the D4 would also be able to take many frames per second. I’ve some shots in mind…

FX vs DX (again)

I’ve included this section because I keep getting emails about the FX vs DX debate and just as many asking “why does my 14-24mm have blurred corners underwater?” If you want to dig deeper into this, I’d also suggest watching my dome port talk from DEMA that shows many examples of the points I am making.

Nikon has released two FX cameras this year (D4 and D800) and if rumours are to be believed then they are not finished. Soon we may have a third new Nikon FX, cheaper than the D800 and probably somewhere between the two on resolution. Plus there will soon be great deals on secondhand D3 and D700 systems. It is a lot of temptation for those currently shooting DX Nikons, like the D200 or D300, to consider FX. The question is should you switch?

First, both DX and FX work underwater. Sometimes in discussing the differences we tend of overblow them. Shooting FX generally means we can’t cut corners. For wide angle we need good ports, port setups and lenses. And for macro we have to be more precise with focusing and how we put our images together. I regularly shoot DX and FX side by side and with macro I find that an imprecisely focused DX shot will be saved by the depth of field, while a FX shot will be cruelly exposed as being out of focus. Anyone who delivers the images regularly at full resolution to publishers or agents will know that the one thing you can’t save in Photoshop is out of focus, even slightly.

I personally believe that, in general, DX cameras make for better underwater cameras than FX ones. To explain I’ll compare them at three different lens ranges: fisheye, wide angle and macro. The areas that FX beats DX is offering high resolution and high ISO performance, but do you really need these gains? DX cameras are not bad in these departments, just not as good as FX.

For wide angle a main limitation is achieving good corner sharpness, because FX cameras offer less depth of field for any given lens angle of coverage (at the same aperture). This is particularly critical with non-fisheye wide angles and causes the blurred corners (because the camera is trying to focus on a curved plane of focus created by the dome when in water).

Fisheyes.

Fisheyes work well on DX and FX and are forgiving of port setups on both. The main limitation on FX is with mini-domes. Many DX users fear they will miss the 10-17mm, but actually they don’t that much. I have both FX and DX systems and when I swap back to the 10-17mm I find I see more of its optical flaws than I used to. On full frame the choice is Nikon 16mm and Sigma 15mm. The Sigma focuses closer, the Nikon is better shooting into the light (the Sigma is a flare monster). I have both and use both and still can’t decide which I prefer!

The DX options of 10.5mm and 10-17mm both work very well behind mini-domes (100mm/4”), which are great for travel and for CFWA/WAM. The 16mm does not focus close enough for such small domes. The 15mm does not fit in such small mini-domes unless you shave the lens shades. I prefer a 150mm/6” mini-dome with the 15mm, which means the shades can stay and it gives better corner sharpness, than a smaller dome, while at the same time being pretty small (certainly smaller than the front of a D4 housing).

Rectilinear wide angles cause the most corner sharpness problem with wide angle on FX. And many people choose to avoid them all together, shooting only fisheye and if they need a tighter lens, mounting a fisheye on a teleconverter. That latter solution is likely to negate the resolution advantages of 20MP+ sensors, although still might be useful for CFWA/WAM shots because of the unique perspective they offer.

The key to good rectilinear wide angle underwater is getting the right lens and putting it behind a quality dome port positionned the correct distance away from the lens. With the right advice from your dealer you should be straight into good images. People have problems when they try and cut corners or cobble together a make do solution. My preferred lens is the Nikon 16-35mm, which Ryan Canon was the first to suggest I try. I believe it performs significantly better behind a dome than either the 14-24mm or 17-35mm (both of which are probably better out of the water).

FX is great for macro, the shallow depth of field is well suited to more open aperture shots where the background is blurred and out of focus. Where it struggles against DX is when we want to achieve high magnifications. To achieve the same subject size in the frame on FX we need more lens (or to add a diopter, teleconverter or extension tube) and as a result end up with less depth of field. This is not an insurmountable problem, but if you go on a macro trip as the only FX shooter you will quickly realize how much harder you are working to get the same types of shots as everyone else seems to be snapping away. So open up your aperture and impress them with your FX bokeh!

All of Nikon’s FX cameras offer DX modes that output DX sized RAW files and shade the viewfinder to show only the DX section. So theoretically you can have the best of both worlds. The D4’s DX resolution is quite limiting, but with the D800 there is almost as much DX resolution as the D7000. Furthermore, use an FX camera in DX mode you get flash synch equivalent to 1/500th second and significantly better AF than the D7000. The only drawback is the viewfinder. When an FX camera’s viewfinder is reduced to DX size it becomes much smaller than the viewfinder of a DX camera, which is a drawback underwater.

Ultimately I think the best way to get the best of both FX and DX worlds with the D800 in macro is to shoot to crop, rather than switch to DX mode and crop at the time of shooting and have to use the small viewfinder. The exception will be those shooting for competitions that do not allow cropping in post).

I’ll finish this section by repeating what I said at the start. Both DX and FX work underwater. Sometimes in discussing the differences we tend of overblow them, so don’t panic. If you decide to go the FX route, just be aware of the differences and you’ll find them smaller than you expected.

Next: Autofocus and Shooting The D4.

(1) Introduction.
(2) Camera and housing overview: Part 1 D4 camera.
(3) Camera and housing overview: Part 2 NA-D4 housing.
(4) ISO, image quality and shooting FX.
(5) Autofocus and shooting experience (macro and wide, stills and video).
(6) Comparisons with other cameras and conclusion.