Thursday, May 29, 2014

Sony DSC-RX100 III: Effective Aperture Comparison

                                                                                        Sony USA

Depending on how you look at it, the combination of a large sensor and large aperture in a small camera body is either the Holy Grail of photography... or its the unicorn. The Sony DSC-RX100 III is probably the closest thing to that ideal, having a maximum aperture range of f/1.8-f/2.8. It's easy to be seduced by numbers; this is a fairly bright lens, but it is mated to a sub-DSLR/mirrorless sensor. As large as the 1" 20mp Sony sensor is for a small camera, how "fast" is the RX100M3 in terms of equivalent aperture and depth of field in comparison to the "real thing" (i.e, enthusiast-level APS-C cameras)?

(Full review is here)

Rather than to reinvent the wheel, let's first refer to DPReview's comparison chart. This diagram is helpful for comparing various compact cameras against one another, and as you can see the RX100M3 is only bested by the Canon G1 X Mark II when comparing the difference advanced compact cameras together. Do note the behavior of the Sony's lens over the focal length range: even though the specs are f/1.8-f/2.8, you only get the benefit of f/1.8 at the widest end of the lens; otherwise, RX100 III's lens behaves as if it is a constant aperture f/2.8 from 28-70mm equivalent. This isn't as fast as the specs would indicate, but it is better overall than almost all of the rest of the field when you take into account sensor size.

However  these cameras aren't directly comparable in one area: price. The RX100 cameras have always been expensive for their market segment when they are first introduced, and the Mark III is no exception. At a list price of just under $800 USD, there are a number of mirrorless cameras that could be had for the same money. Most mirrorless cameras are larger and heavier than the RX100 cameras, but the ones that aren't significantly so are in Sony's own lineup: the A5000 and the A6000, when you pair these bodies with the E 16-50mm f/3.5-5.6 OSS PZ pancake kit lens. Yes, it's not the same type of camera, and they generally appeal to two different types of shooters, but the the size and weight difference between the two aren't insurmountable. The A6000 lists at the same price as the RX100M3, and the A5000 is even less expensive. 

Here is the difference between the RX100 III and the A6000 with kit lens in terms of equivalent aperture when compared to an APS-C sensor. What does "effective" aperture mean? It's easiest to think of it as either measure of the amount of background blur that the camera/lens combination can develop under equivalent conditions, or as a comparison of the safe hand-held shutter speeds.

Camera Diagonal Crop Factor Effective Max Wide Aperture Effective Max Long Aperture

Sony RX100M3 0.56 3.2 5.0
Panasonic GM1 0.77 4.6 7.3
Canon G1X Mark II 0.83 2.4 4.7
Sony A6000 1.00 3.5 5.6

The winner here is the Canon G1X Mark II by virtue of having the brightest lens paired with the second largest sensor. The RX100 III is actually a tad bit brighter than the Sony A6000 equipped with the kit lens, but not by enough to make a meaningful difference. There is something that must be noted, however, and that is that depictions of equivalent apertures between difference cameras assumes that the sensor efficiency is the same between each camera, which is rarely true. Also being ignored is the subjective visual impact of the number of pixels. The G1X Mark II suffers in this area; even though it has the best effective aperture, it has the lowest pixel count of all the cameras. That's not the only area where it lags as well: a more complete picture develops when you look at the measure dynamic ranges of the sensors (via DxO Mark

Camera DXO Landscape (Dynamic Range, EV)

Sony RX100M3 12.4
Panasonic GM1 11.7
Canon G1X Mark II 10.8
Sony A6000 13.7
Note 1: RX100M3 score taken from RX100M2, same sensor
Note 2: Sony A6000 score unavailable at time of writing. Average of Pentax K3 and Nikon D5300.
                                                                                                                                                  via DxO Mark

Not surprisingly, the largest sensor also has the largest dynamic range. What is surprising is that the RX100 III's sensor, though smaller and more pixel dense than the Panasonic GM1's m4/3 sensor, scores higher on DxO's dynamic range tests. This is due in part to the fact that the RX100M2/M3 sensor utilizes backside illumination to make up for the smaller pixel wells. To be fair to the Canon, DxO's methodology notoriously does not favour the way Canon sensor's work. (How bad is it? The T3i scores 11.5EV.) The composite DxO mark puts a fair weight on low ISO dynamic range, in which the Canon sensor's have typically lagged and suffered (rightly/wrong).

In terms of visual impact, how useful is the RX100 III's faster lens? Shallow depth of field (DOF)is typically only feasible at longer apertures... think portrait shooting. Here is the total DOF (in front and behind point of focus) for the above cameras when photographing a subject at 10 feet with the camera at 70mm equivalent and maximum aperture, assuming 'typical' viewing size and distance. The GM1 is calculated at 60mm, the maximum for its kit lens. Just for kicks, the D7100 with the 17-55mm f/2.8 and the 85mm f/1.8 are thrown in. (85mm being slightly longer than the rest):

Camera Total DOF (in feet) at max aperture/longest focal length, at 10 feet

Sony RX100M3 1.23
Panasonic GM1 1.89
Canon G1X Mark II 0.97
Sony A6000 1.38

Nikon D7100, 17-55mm f/2.8 0.69
Nikon D7100, 85mm f/1.8 0.29

The take home message? If you want nice bokeh, a compact take-anywhere camera is not the tool, no matter how leading-edge it is. All of the cameras, save for the DSLR with the f/2.8 zoom or f/1.8 portrait lens will produce a wide zone of acceptable focus under portrait conditions. This is common sense for the Sony A6000, as even a little bit of experience will show that a kit f/3.5-5.6 DSLR/mirrorless lens only produces a modicum of subject isolation. What's remarkable about the RX100M3 is how similar it is to the DSLR under these conditions.

Concluding Thoughts

Sony RX100 III or the  A6000 kit? It's a tougher choice than it seems. The lure of the small size of the RX100 form factor is tough to ignore, but the interchangeable lens options of the E-mount make the A6000 more practical. When the first generation RX100 was introduced, there was a lot of noise about how it was a "DSLR in a compact body." That was pure hyperbole: though it was vastly superior to any other compact camera available for its time, it was not a DSLR replacement.

Skip forward two generations and adding upgrades to both the lens and the sensor, the hype comes closer to reality. The RX100 III in terms of bokeh and dynamic range behaves a lot like an entry-level DSLR or mirrorless camera... no exaggeration this time. From a technical standpoint, that is quite an achievement, but bear in mind that the cost of the RX100M3 is significantly more than the entry-level DSLR/mirrorless that it is ostensibly replacing.


  1. excellent comparison !I think your blog should be more popular as it provides really good reviews.
    Would look forward for real world samples once M3 comes to market. If we look at sample pics of Rx10 which has same F2.8 , there is decent amount of bookeh in portraits. I expects similar results with M3.

    1. Thanks very much for the compliment. That's an interesting way of looking at it; if you known what the RX10 looks like wide open at 70mm, then you have an idea of what the M3 will do... although, to be fair, I suspect that the RX10 will be a wee bit sharper compared to the M3... one is in the middle of the zoom range, and the other will be at the extreme.

  2. Excellent review. Really, it's very well written. Thanks.

  3. I've been using an RX100 M3 since it came out and love it. It is so good, and so capable, that it makes choosing my next system camera difficult because I already have so much capability in my pocket.

    Good info in your review, I especially liked the APS-C DOF comparisons. Very useful to measure (generally) what each camera brings to the table.

    1. I've warned a lot of DSLR people that if they get the RX100M3 as their second camera, they'll end up using more than their first. Also seeing young families that would have otherwise saved up for a DSLR going for the RX100m3. Same price point, different tradeoffs

  4. That is a very interesting way of comparison "effective" aperture !
    Too often reviewers focus heavily on ISO performance and noise but
    fail to take into account how fast (wide open) the lens is capable of across the board of its zoom range allowing for lower ISO usability ( not to mention bokeh) hence better IQ obviously with respect to sensor size as well

    I would really like a review on the Canon G7X as well, thanks Douglas. Breath of fresh

    1. Was able to do that too. Same concept but different execution. The GX 7 is the value-oriented choice, in some ways better, but side-by-side the Sony is the more premium product in terms of build quality and features.

  5. Sorry for earlier post I notice you have posted that comparison review and I in fact also commented on it too

  6. Excellent article. Exactly what I was looking for

  7. Just like someone else said, this is exactly what I was looking for.

    I've been eyeing the RX100m3 for a bit, primarily as a vlogging camera that can get shallower DoF (and superior image quality) than the point-and-shoot that I've had for the last few years (A Samsung WB250F, with 14MP - 1/2.3" BSI-CMOS Sensor). Then I just saw a local shop had the A5100 for a bit cheaper and the A6000 for about the same price. Obviously I could spend more on lenses for the Alpha cameras and get amazing results, but this is already more than I want to spend. So what I needed to know is what kind of DoF I can expect with the RX100m3 compared to the Alpha cameras with the standard 16-50 lenses.

    Looks like the RX100m3 is still what I'm after!


    1. You can see the visual differences here: