Monday, October 20, 2014

Nikon D810 vs D750 vs Df: High ISO Noise and Image Quality

Nikon D750

The D750 is Nikon's middle of the road  FX camera... it doesn't lack in key features in the way that the D610 does and it doesn't cost an exorbitant amount in the way that the D810 does. But does that make it a "just right" camera or an "average compromise"? Here's a short test of the camera at the cusp of acceptable image quality (tight detail shot at ISO 6400 and above) and how it fairs against the D810 (more resolution) and Df (cleaner image noise). Is there a "Nikon look"? Partly yes and partly no. Output across the different Nikons share certain similarities... good exposure control, crisp detail and wide dynamic range... but there are differences built into the default output of each model.

The following is an ad hoc comparison of the D810, D750 and Df on an "equal usage" basis. As you will see, there are some differences (mostly minor) in file output when these cameras are shot on the same setting. This is on top of the obvious differences in the number of pixels. All crops were taken from exposures at f/8 through the center frame using a Zeiss Distagon T* 2,8/21. This was the lens; in case you were wondering, it's awesome:


High ISO Quality at Native Image Size



The following is an ad hoc demonstration of each camera's JPEG output quality through the ISO range. Here is the test scene; the target is the pop refrigerators as shot through the center portion of the lens. In other words, the method was to project a small patch of tight detail onto each camera's image sensor. Thankfully, the availability of an extremely high quality wide-angle lens made this task easier given the jury-rig conditions of the test. Pay attention to the legibility of the soda bottles for detail retention (or lack thereof) as the ISO value rises, speckling in the broad colour patches for overall image noise, as well as the harshness of the reflections and shadows as dynamic range decreases. These samples are not directly comparable to similar samples found elsewhere in this blog because of variable ambient lighting conditions. Click on all images for 100% crop view.


Base ISO


Exposure plays an important part of image noise, and even though all three cameras were set up in the same way (f/8, centre-weighted metering, Picture Control at standard, high ISO noise reduction off), the actual exposure values that each camera produced were different. Notably, the Df exposes brighter (longer shutter speeds) than either of the D810 or the D750, which a producing equivalent exposures. This is also the same behaviour that the D610 seems to exhibit when compared to the D750 and D810. Part of the reason seems to be the higher resolution exposure meter used in the D750 and D810 versus that used in the D610 and Df; certainly, the exposure produced by the D750 seems to be the closest to what the naked eye would perceive. This behaviour manifests whether the Df is shot in spot metering mode or center-weighter metering mode. Here are the shutter speeds at base ISO: 

  • D810: 1/8s (ISO 64)
  • D750: 1/13s (ISO 100)
  • Df: 1/8s (ISO 100)

You can also see the cumulative effect to file size from adding 50% more pixels as you go up from the Df to the D810. Between the D810 and the D750 or the D750 and Df, the actual increase in linear resolution is just over 20%... that's enough to be visually distinct but not enough to be definitively overwhelming. However, you can see that the difference between the Df and the D810 is dramatic. The lack of an optical low-pass filter on the D810 gives it crisper looking edges and a bit more colour saturation, but the advantage is subtle. (At this magnification, each of the pop bottles are approximately 15 pixels wide.)


Another thing to note is that the default tone curve of the D810 seems to be more "conservative" than the D750. Though both cameras are using a similar exposure, the D810 at default settings seems biased towards protecting the highlights at the expense of shadow brightness. The D750 has a more natural-looking rendition, but its highlights are a tad bit bright... not quite harsh but certainly harder-looking bright patches than with the D810. Setting the D810 to a steeper tone curve (the "Vivid" setting) pushes the shadows down a bit further. Conversely, backing the tone curve of the Df off (the "Portrait" setting) doesn't reduce the brightness of that camera's rendition. For reference, here is what the samples look like when the Df exposure is equalized to the other two cameras (-0.67EV)

Base ISO

(Note: This is a very specific example of a large amount of high-contrast detail in a small viewing area, so the exposure differences between the cameras will likely not hold up under different shooting circumstances.)

ISO 6400


Here are the 100% crops from each camera at ISO 6400. Note that even though the D810 shows the most noise, the lack of the optical low-pass filter and greater resolution also means that it produces the most detailed image. (Note: as the anti-aliassing filtration is reduced and eventually removed, high ISO noise becomes more apparent as the AA filter is effectively a hardware version of the "blur" function used in image editing.) The Df is not directly comparable, as it is using a long shutter speed and producing a brighter exposure. Nevertheless, the innate cleanliness of the Df file rendition is apparent... as is the file size difference compared to the D750 and D810. The shutter speeds are:

  • D810 - 1/800s (ISO 6400)
  • D750 - 1/800s (ISO 6400)
  • Df - 1/500s (ISO 6400)

Even though there is a high degree of chroma noise in the D810 file, it is more than made up for by the increase in detail. Likewise, the Df file shows the least amount of fine detail, but it has the best edge and border retention of the three at this setting. Even though it is exposing 2/3 EV brighter, the hard-edge retention would hold at equivalent shutter speeds.

ISO 6400

Here are the shutter speeds for ISO Hi 1.0, which is the equivalent of ISO 25,600. Even though Nikon likes to advertise how high the ISO capability of the cameras are, the fact that they are labelled as boosted setting should tell you something about how Nikon's engineers feel about them. The respective shutter speeds are:

  • D810: 1/3200s
  • D750: 1/3200s
  • Df: 1/2000s

This is not a setting that you would want to use on any of the cameras with the exception of the Df, and even then output would benefit from a judicious amount of post-processing. This is truly the territory of the Df (and the D4s); the D810 is marred by chroma noise and the even though the D750 has a somewhat clean-looking appearance, the image noise mitigates its resolution advantage over the Df. (Again, the Df is exposing brighter at the same camera settings, but the overall subjective differences will be the same at the same shutter speeds.)  However, all is not perfect with the Df; note the colour shift.

ISO Hi.1.0 (aka, ISO 25,600)

D810 vs D750 at 24mp


Here is how the D750 compares to D810 images that have been down-sampled from 36mp to 24mp. These were taken at base ISO.

D810 vs D750 at 24mp

This is the reason why many consider the D800 and D810 the best cameras on the market in terms of image quality: they aren't just good because they can resolve 36 megapixels; when you downsample the files the D810 is also one of the best 24mpp or 16mp cameras on the market. Under these circumstances, the D750 produces excellent detail, but the re-sampled D810 file is crisper and has more colour saturation. Downsizing a file from a larger size to a smaller size reduces the resolution, but the extra information isn't exactly thrown away either, as it "fills-in" the missing data lost to the Bayer-pattern colour-filter array. You can, of course, sharpen the D750 to approximate the difference. The following sample uses unsharp mask at  80% strength at 0.5 pixel radius on the D750 sample:

With USM applied to D750 sample

Yes, in general terms, the removal of the anti-aliasing filter on the D810 is worth only a minor amount of sharpen in gross subjective terms, but the difference can't purely be made up in post-processing. Sharpening improves the course appearance of the image, but it can't match the intricate, low contrast or very tight detail that the higher resolution sensor is picking up.

(Note: Yes, the D810 is slightly smaller than the D750 sample. This is due to positioning constraints, as the D810 is a taller camera than either the D750 or Df, and as such, the lens mount is further up from the bottom of the camera.)

D810 vs D750 vs Df at 16mp


Here are the D810 and D750 at base ISO re-sampled to 16mp to match the Df. Again, when you consider how small this crop is compared to the total scene, this is an admirable amount of detail from all three cameras. However, you can see the differences in crispness and perceived detail as you move from the D810 to the D750.

At 16mp

Though it has the least resolution, the Df does have a subjective crispness to the look of it's images. This is partly because of the larger pixel well; bigger photodiodes means that each pixel "sees" the scene through a larger portion of the lens. The result is crisp-looking edges and borders even though the total resolution is lower. Not-coincidentally, this is why many people found the D700 to be a forgiving camera to use, and partly why some people find Fujifilm X-Trans files to be more sharp-looking than those from other APS-C cameras.

Concluding Thoughts


These are three extremely capable cameras that produce excellent output, but they are excellent in different ways. If outright image quality matters, the D810 is definitively the best camera of the three, but the difference isn't going to be justified by the price for most non-professionals. The Df is the most user-friendly of the bunch, as the 16mp resolution is more forgiving to hand-holding skills and lens. For many people, the Df will produce the most pleasing images of the three if file size and ultimate detail aren't an issue. Yes, it does have extraordinary clean-looking files, but that's only when you pixel-peep. If you compare images at the same viewing size, the D810 and D750 will have more detailed-looking files up to ISO 3200-6400. The D750 is the Goldilocks camera of the bunch. It's "just right".... less expensive than the other two and has a bit of the D810's outright resolving power with some of the cleanliness of the Df output.



With thanks to Broadway Camera

5 comments:

  1. The DF is holding up brilliantly despite its pixel disadvantage in both low iso and high iso tests in my opinion. Something special about the D4 sensor unless you need 15 stops of dynamic range and mega-size prints that is.

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  2. I agree - the Df files look wonderful in this comparison. I am quite surprised that the D810 isn't blowing it away with all it's extra resolution.

    Very impressive Df!

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  3. Did you find Raw files between the d810 and d750 to be similar with respect to high ISO noise, after down sampling? I'm curious because I'm seeing differing results among reviews. I have the d750 and know that the jpg files are cleaner but I'm wondering if this is only a jpg algorithm as the dpreview photos show similar noise levels for print raw files.

    Thanks

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    Replies
    1. There isn't really so much a break-even point as it is as "zone". First of all, all of the EXPEED4 cameras have visibly cleaner higher ISO rendering than the EXPEED3 generation, but it is primarily JPEG.

      Above ISO 6400 the D750 will look cleaner, but the downsampled D810 has an edge in edge definition and micro-contrast. The texture of the noise is going to be naturally different because the D810 is unfiltered, whereas the D750 is lightly AA-filtered.

      From what I can tell, the D800/D810 sensors seem to be built to a higher quality than the D610/D750 sensors, they seem to be slightly more efficient and have more base DR. In other words, if the D750 sensor was built like D810 but at 24mp, it might be better still.

      I like both cameras; the D750 is closer to reality for me, but there's never been an instance where I regretted the chance to use the D800 or the D810.

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  4. thank you so much for this post. After 2 years, I'm still wondering about those 3... (despite the DF for a second camera, or maybe the Fuji x-T2).

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