|Left: Nikon D750 Right: D7200|
DX versus FX, crop vs full frame: it's a question that's been on many shooter's minds since the dawn of the so-called "affordable" full frame era. It's a false dichotomy, really. There's no question that full frame is better but the dilemma for many is whether or the cost can be justified. If you are being paid to do photography, even if it's the odd weekend wedding gig, then the answer is easier to arrive at: go with full frame, because that is where most of the competition is already at.
For the non-professional shooter, Nikon has moved the goalposts since the D7100/D6100 era. The D7200 and the D750 are both extremely capable cameras, but the value proposition has been altered somewhat. The D600 (and D610) were designed to be extremely easily "step-up" solutions for DX users: they were more or less the same camera, but with upgraded sensors. Comparatively, the D750 is more when compared to the D7200.
- Comparatively slimmer body
- Group Area AF
- Higher resolution exposure meter
- Additional highlight priority spot metering
- Power aperture control during video and live view
Because of these additions, the gap in price between the two tiers has increased. Ordinarily, this would discourage some shoppers from looking at the more expensive option, but the situation is made less clear by the apparent lack of interest Nikon has given the serious DX market in recent years.
Note: You can see a comparison of the D7100 vs D610 here. Things have moved on since then; it's no longer as simple a deliniation between enthusiast DX and FX like it was before.
High(er) ISO Image Quality
Ostensibly, image quality is the reason to step up to full frame, so we'll go straight to the good stuff. Given that a full frame sensor is 2.33x larger in area than an APS-C sensor, this implies that the individual photo-diodes are approximately twice as big. Naturally, the larger pixels of the D750 FX sensor will make for cleaner high ISO images, but the implied difference (twice the area, twice the light gathering ability) implies that the difference is roughly one EV. In years past, this was a big deal, but given the prevalence of image-stabilized lenses and successive generations of sensor improvements, this is no longer the outright advantage that it seems to be. The difference of one stop from ISO 3200 over ISO 1600 is now a modest improvement in real-world performance if you are talking about ISO 6400 FX vs ISO 3200 DX when shot through a stabilized lens.
The following is an ad hoc demonstration of each camera's default JPEG output quality through a selected ISO range. 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.
|The test scene. The pop refrigerator is the ad hoc test target.|
Both cameras were shot at f/5.6 to make the exposure values easier to understand; in other words, the nominal exposure figures are comparable, but the depth of field isn't equalized between the two cameras. This isn't crucial, as the test target is some distance away and the the target is flat. To make things even easier, each D7200 sample is paired with a D750 sample that is shot at one ISO level higher. (Other settings: ADL off, high ISO NR off, default picture control.) Click on images for 100% crop view.
That's fairly close, isn't it? Except for the fact that they are one ISO step apart, both cameras produce similar, but not identical output. The D7200 holds its own, showing the crispness of not having an anti-aliasing filter. The D750's bigger photodiodes produce a lot of edge acuity even with the low-pass filter that is integrated into its sensor. If anything, the texture of the D750 image noise has a slightly finer grain, but that's about it. If you need the advantage of an extra stop in terms of image noise and dynamic range, the D750 has it.... but if you aren't pushing the camera to the utmost limits, then you aren't missing as much as you would think if you go with the D7200.
Where the differences do show up is in the extremes of shooting, either fairly dark locations or scenes with extremes of light. The qualitative advantages of the D750 are small, but they do add up. As a rule of thumb; if you are presented with a single picture, 90% of the time you will likely not be able to tell which camera it came from. If you are presented pictures from both cameras, you will likely be able to see the difference, but you may not be wowed by it.
The downside to the D7200 is the apparent lack of love that Nikon has been giving the DX system. This is an issue, but not a pertinent one. You can build a fairly high quality lens collection through careful selection on Nikon and third party lenses, with the only sore spot being the lack of quality primes for the often used 16mm and 24mm focal lengths. For outright quality, the lenses that are available for full frame are better than their crop-frame equivalents.
However, there is an advantage to the D7200 if reach is an importance. Paired with either the Sigma or Tamron 150-600mm lenses, the DX camera makes for a more effect bird photography camera than the D750. As a general rule of thumbs, things that are far away also tend to be quick-moving as well. In this regards, the D7200 AF system, even though it is missing the Group Area mode of the d750, is quite up to the task of long-range photography. Except for the Canon 7D Mark II, there isn't a crop frame camera that has as good an AF system as the D7200.
If full frame isn't an immediate possibility there is always the option of gradually accumulating full frame lenses for a possible switch in the future. This strategy is sound but does have its downsides. The crop factor alters the working distance of lenses when they are used on DX; the 24-70mm f/2.8 general-purpose zoom becomes something of a 35-105mm "portrait-zoom plus a bit of wide angle". In other words, what was once a lens that was generally good for walk-around purposes on FX becomes something that you may have to change from time to time. For some lenses the inconvenience factor will come into play and for others it won't, but you are generally better off having gear that is suited to your current needs rather than having non-suited gear in anticipation of a day that may or may not come.
Diffraction and Perceived Lens Sharpness
At typical viewing sizes, resolution loss due to diffraction will start creeping into D750 shots around f/11. However, with the D7200 and its tighter pixel pitch, the onset of diffraction limitation begins at f/8. Emphasis on the word "begin" as resolution doesn't drop off after the initial point of diffraction limitation... it's more a case that contrast begins to gradually decrease. What this means is that moiré is only a potential problem for the D7200 below f/8. Most people don't expect moiré to be a a big issue in everyday shooting, but it's likely that fashion photographers might have to deal with it (textiles and clothing) more so than others. Note that if you are a landscape aficionado the removal of the anti-aliasing filter isn't any help for small apertures and extended depth of field. Truth be told, as the megapixel counts have increased cameras have already already been using lighter filtration than cameras in the past. So diffraction-wise, the advantage goes to the D750; within it's aperture range you have a slightly wider latitude in depth of field before diffraction starts setting in.
Whatever advantages that the D7200 has in removing the low-pass filter are mitigated by the high pixel density of the sensor and the demands this places on the quality of the lenses being used. Even though full frame lenses are cheaper than DX lenses, the larger pixels of the D750 place "less of a burden" on the quality of the glass.
An Overlooked FX Lens Advantage
Another advantage of the FX over DX is that when both are set to produce the same depth of field, the FX camera will be using a lens one stop down. At close range, this is an advantage that is often over-looked. Imagine going for a trendy super-shallow depth of field shot with the D7200 and a 50mm f/1.4 lens. When shot wide open, fast primes have all sorts of optical flaws, though some would use the more flattery term "dreaminess" rather than "flawed." For the equivalent D750 image, an 85mm (because a 75mm doesn't exist) lens shot at f/2 would give the equivalent depth of field. The D750 image would be superior because stopped down, the FX lens would be operating in a more optimal portion of it's aperture range, meaning that even though both lenses would give similar looking out of focus backgrounds, the D750 and FX lens would be more contrasty and would suffer less from chromatic and spherical aberrations.
Because lens optical performance is a complex topic, the objective description of such is beyond the scope of this blog. Though there are many aspects to quantify (resolving power, field curvature, distortion, aberrations, etc.), a general sense of a lens’ character can be determined without resorting to lab testing. The following is one aspect; bokeh and apparent background blur with the subject at short distances. The following is the scene, a camera store with a busy background with the test target set approximately 2~3 feet in front of the camera. The D7200 is equipped with the AF-S 35mm f/1.8 G DX, whereas the the D750 has the AF-S 50mm f/1.8 G. Both are "normal" lenses; the 35mm DX will give a slightly higher amount of magnification than the 50mm under these conditions.
The crops are taken from the area just off to the left and back of the focus target, approximately seven feet behind the autofocus target.
Many things are going on here. Yes, the FX sensor of the D750 will give more background blur but the difference here is exaggerated by the harsher rendition that the 35mm DX gives in out of focus areas. You are going to get more foreground/background separation with full frame, but the difference will be subtle depending on your lens and focus distance. However, there is something that is visually nice about bokeh on a full frame camera compared to a crop frame camera; you can get more of the subject isolation at wider angles of view, and generally speaking, the higher quality of the FX lenses on FX bodies produces a softer quality to the blur. If we had replaced the 35mm DX with the more expensive and higher spec'd Sigma 30mm f/1.4 ART, the subjective difference between the two formats would be less pronounced.
For videography, the D750 is the better choice by virtue of it's power aperture function. The D750 and D810, unlike the lower-tier Nikon bodies, are able to articulate the lens aperture during live view and video. This feature is absent on the D7200 because it involves extra components to make it work. Nevermind the fact that this is a simple task for the likes of a mirrorless camera like the Sony A7, the stratification of lens functionality is a by-product of the continued evolution of the Nikon F mount over many, many years. Other tangible benefits of the D750 are the obvious inclusion of a tilt LCD display and the ability to shoot 60 fps video at the full field of view. The D7200 can manage 60 fps, but does so at a 1.3x crop factor.
The Hidden Cost of Depreciation
Based on previous dives into the U.S. used Nikon camera market, average depreciation in terms of asking prices for camera gear runs about 12-15% per calendar year. (The actual picture is much more complicated, as full frame cameras seem to depreciate more quickly in the early part of their lifecycle). Your mileage may vary depending on how well you take care of your camera, but market forces will inevitably bring down the value of all used equipment. If you take a D7200 and a D750 in 2015, roughly half of the value will be gone within 4-5 years. Even if both cameras depreciate at the same rate, you will lose $500 more with the D750... on just the camera, not even counting the lenses.
This brings up an important point about financing a camera hobby. The cameras themselves are now fairly mature in technology, so there is the temptation to think of any camera that you buy now as "the last camera that you will ever need". While that may true, the inevitable fact is that there will be something else to tempt us down the line. If you had bought a D700 back when many people felt that full frame was finally in grasp, you would have had a great camera. It's still a good camera, and if you don't shoot professionally or don't do large prints, there's no reason to stop using it. However, the D700 is only 12mp, doesn't do video, has no WiFi.....
Unlike the D7000/D7100 and D600/D610 generations, the D750 is not the direct step-up alternative to the D7200. The D600 and D610 are almost exact FX replicates of the DX cameras, making them "easy choices" for users that were considering one format or the other. The D750 is more of a stretch, as it is better in almost every way over the D7200 (additional AF mode, higher resolution exposure meter and additional highlight priority exposure mode, flip screen and better video options, etc). There is a logic to doing it this way; because all cameras are extremely capable now, it is not merely enough to differentiate on sensor quality alone. In order to justify the higher price point, the D750 doesn't just enhance the "prosumer" DX experience into full frame; it extends it into new areas of functionality.
One analogy that is used frequently on this blog still applies to these two cameras. Moving up to full frame is like moving into a richer neighbourhood. Even if you get a good deal on the house, you will incur more costs due to putting your kids through private school and the cost of fancy cars and keeping up with the Joneses. The camera is the first expense; the lenses, larger bags and sturdier tripods are expenses that will come later. In that sense, the opportunity cost of owning an expensive FX camera but not being able to afford a wide lens selection is like being house-rich but income-poor.
There's no easy way to answer which is best for any given person, because circumstances vary. Choosing between the two is likely a decision about wants rather than needs; if it were the latter the decision would be arrived at easier and sooner. This isn't necessarily a bad thing, as not all choices should be decided upon by cold hard logic. However, remember this point.... it's the job of all companies... camera or otherwise... to give you something that you will like but to make you desire that other shiny new thing that's just out of your reach....
With thanks to Broadway Camera