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[Note: this article does not contain actual images for comparisons, if that’s what you are searching for.]
Sony A7 / A7R are exciting cameras, but I’m still using my OM-D, and in no hurry to switch to it. This article discusses why, from the perspective of my shooting style – it may very likely be different from yours. I used Nikon film camera, Canon EOS digital, and Sony NEX-3 before switching to OM-D E-M5. I may consider switching back to Sony when a successor of A7R with improvements (IBIS at OM-D-level performance) that I require becomes a reality, but that’s not available now.
Image Quality – Sensor
Image quality is the number one factor to consider for camera equipment, so let me address this first. You get better image quality (lower noise and higher dynamic range) with a larger sensor at the same technological generation, that’s just physics, there’s nothing to argue with that. 35mm Full Frame (FF) inherently has a better image quality than m43, assuming both have lenses that do their respective sensors justice, and if you can accept the associated bulk and weight and can use a fast enough shutter speed to stabilize the shot. Likewise, medium format digital backs offer significantly better image than 35mm FF at base ISO. Do we get rid of the SLR and mirrorless cameras and switch to medium format just because medium format is “better”? No, medium format is not for everybody. The key here is getting a good trade-off between image quality and weight / bulk / convenience / cost, but what constitutes a good trade-off is different for everybody.
Image Quality – Image Stabilization
(Note: I am a pixel peeper. By ‘sharp’ I mean a photo looks sharp at 100% magnification level with a good edge acutance and without any double image at all.)
For me, I use a standard zoom lens most of the time, and more than half of my shots are indoors. Those who used OM-D knows that 5-axis in-body image stabilization (IBIS) works really well, and is more advanced than typical image stabilization offered by others. The 5-axis IBIS is indispensable to getting my indoor shots sharp at relatively low ISO.
At 36mp and without IBIS, it is harder to get pixel-level sharp photos from A7R hand-held without the very best techniques. I’ve seen friends with A7 and A7R take photos that are hand shaken. Actually not just my friends, even Pekka Potka wrote that some of his hand-held shots turning out to be shaken. Even dpreview reported the issue of A7R auto ISO logic and shutter speed selection, further increasing the problem. Although FE 55mm f/1.8 is extremely sharp, this awesome sharpness is hampered by the necessity of using higher ISO when you don’t have IBIS in A7 / A7R in low-light hand-held shooting.
Image Quality – Camera + Standard Zoom Lens
Sony knows that it is impractical to make a 24-70mm f/2.8 that is small enough to match the small body size of A7 / A7R. So it makes the FE 24-70mm f/4 instead of f/2.8. However, even after compromising the aperture, its edge performance is still not very good. To get a better image quality from a standard zoom lens, one has to use an adapter with the A-mount 24-70mm f/2.8 (or the Canon 24-70mm f/2.8 II). However, this clearly would not be well-balanced with the A7 / A7R for hand held shooting. So for the rest of this article, only the FE 24-70mm f/4 OSS would be considered to be the standard zoom lens for A7 / A7R. (The FE 28-70mm is clearly not as good as the FE 24-70mm, so forget about it.)
Like many m43 lenses, the Olympus 12-40mm f/2.8 PRO (offering the 24-70mm field of view in FF terms) is very sharp wide open. Although larger than most m43 lenses, it is still smaller than its FF counterparts and is well-balanced with OM-D camera body. (Mostly I need more DOF, not less, for my indoor shots, so such argument like “m43 f/2.8 lens is equivalent to f/5.6 lens on FF” is wrong for shutter speed considerations.)
At this moment I cannot find any direct image comparison of Olympus 12-40mm f/2.8 vs FE 24-70mm f/4. However, based on the various reviews I’ve seen and from my own experience of shooting with 12-40mm f/2.8, it seems likely that 12-40mm f/2.8 will offer comparatively sharper edge-to-edge image at f/4. Doing handheld shots with a standard zoom lens indoors, the inherent FF sensor advantage (2 stop or less) is nullified by 5-axis IBIS and the large aperture sharpness of m43 lenses.
Another thing to consider is the magnification, which is very important for my shooting style. Olympus 12-40mm f/2.8 offers 0.6x (physical 0.3x) FF-equivalent magnification, whereas the FE 24-70mm f/4 offers 0.2x magnification only.
Many people cite Depth-of-Field (DOF) control as an inherent advantage of FF compared to m43. I think this can be debated. A shallow DOF is great for subject isolation, but for other shots, a deeper DOF is preferable. Everybody knows that FF 85mm f/1.2 offers awesome shallow DOF, however, many professionals expressed their disagreement with portrait shots where only one eye is sharp while the other eye is outside DOF. So crazy shallow DOF is not universally appreciated. For close ups, you usually need more DOF, not less. So m43 wins in offering more DOF when you need it even with less available light, and FF wins in offering shallow DOF when you need it – but that’s only one stop for our standard zoom lens comparison between FE 24-70mm f/4 and the 12-40mm f/2.8 (offering f/5.6 DOF in FF terms).
(For those who seek shallow DOF with m43, there are lenses like Olympus 75mm f/1.8, Panasonic Leica 42.5mm f/1.2 and Olympus 45mm f/1.8. I believe these lenses get the job done sufficiently.)
I spent enough time with NEX-3 to know that its AF was not great and simply gave up at low light. When I tried out A7R with native FE 55mm f/1.8 lens, I’m surprised and really disappointed to find that its AF still lags behind OM-D so much, it looks like its AF has not significantly improved. (Since the newer Sony A6000 supposedly has very fast AF, perhaps we can look forward to the successor to A7 / A7R for AF improvement.)
Continuous Shooting Speed
I used to think I didn’t need the high continuous shooting speed. However, when the situation arises, you’ll be thankful that you have that speed to capture the exact moment you want. Obviously OM-D offers higher continuous shooting speed than A7 / A7R.
Again I used to think I didn’t need weather sealing, but I was wrong. Although I rarely need it, I did shoot in the rain and snow, and those shoots happened to be really important for me.
OM-D with 12-40mm f/2.8 is great for a camera + standard zoom lens combo. 😉
The reason is that the 12-40mm f/2.8 is a truly great lens. Coupled with the OM-D 5-axis IBIS, this is unbeatable in low-light handheld shooting. For daylight shooting with a standard zoom lens, you only get up to 2-stop image quality improvement from A7 / A7R by using very heavy and bulky lenses like the A-mount 24-70mm f/2.8. Replacing it with the lightweight FE 24-70mm f/4, you no longer have 2-stop image quality improvement when edge-to-edge sharpness is taken into account.