Trying to get my head around shallow DOF abilities of RX100M2 vs G1X Mk II vs RX100M3

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2eyesee
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Trying to get my head around shallow DOF abilities of RX100M2 vs G1X Mk II vs RX100M3
6 months ago

I have an RX100M2, and it’s great but I am starting to long for the ability to create shallow depth of field portraits.

The Canon G1X Mark II and its larger sensor will obviously do better here. Then there is the soon to be announced RX100M3 with its rumoured f/2.8 lens at 70mm. I've been trying to get a handle on how these all compare – even with an A6000 with a kit lens (larger sensor but slower lens).

So with the help of an Android app, and Circle of Confusion values from DOF Master, I’ve made some calculations based on an example to compare them all. Please bear with me if I’ve got any of this wrong – the reason I post on these forums is to improve my knowledge (which is pretty basic) so I’m happy to be corrected.

I’ve taken my RX100M2 with distance to subject of 2m, focal length of 100mm equivalent (37mm actual) as a basis for this comparison. To maintain the same framing of the subject, different focal lengths require a change in the distance to the subject. So an RX100M3 at 70mm will have to be closer, a G1X Mark II at 120mm will have to be further back. I got some rather interesting results (assuming my calculations are correct!):

RX100M2
Focal length: 100mm equivalent, 37mm actual
Aperture: f/4.9
Distance to subject: 2m
Depth of field: 31cm

Focal length: 70mm equivalent, 26mm actual
Aperture: f/4.0
Distance to subject: 1.4m
Depth of field: 26cm

RX100M3
Focal length: 70mm equivalent, 26mm actual
Aperture: f/2.8
Distance to subject: 1.4m
Depth of field: 18cm

G1X Mark II
Focal length: 120mm equivalent, 62.5mm actual
Aperture: f/3.9
Distance to subject: 2.4m
Depth of field: 18cm

Focal length: 70mm equivalent, 36mm actual
Aperture: f/3.5
Distance to subject: 1.4m
Depth of field: 17cm

A6000 + Kit lens
Focal length: 75mm equivalent, 50mm actual
Aperture: f/5.6
Distance to subject: 1.5m
Depth of field: 20cm

A6000 + 50mm f/1.8
Focal length: 75mm equivalent, 50mm actual
Aperture: f/1.8
Distance to subject: 1.5m
Depth of field: 6cm

What I conclude form all this is that both the RX100M3 and G1X Mark II will provide a noticeably shallower depth of field over my RX100M2. But neither are much better than an A6000 with kit lens – they are all in the 17-20cm DOF range in this example.

It’s only when you put a fast prime on a big sensor that you get seriously shallow depth of field – the A6000 with 50mm f/1.8 gets down to 6cm DOF in this example. So I may better off just getting an A6000 with kit lens, which will give me the opportunity to put a fast prime like this on it.

In trying to improve my understanding of DOF, I found this article an interesting read. It pointed out that if you change the focal length while changing distance to subject to maintain framing of the subject, if your aperture doesn’t change, your DOF remains the same.

So with an RX10, all the following produce the same depth of field:

  • 50mm f/2.8 and 2m from subject 
  • 100mm f/2.8 and 4m from subject
  • 200mm f/2.8 and 8m from subject

One thing that does change though is the degree of blur in the out of focus areas, and maybe this aesthetic is one thing I’m missing from all the above calculations. So while on an RX10 50mm, f/2.8, 2m from subject will have the same DOF as 200mm, f/2.8, 8m from subject, the 200mm shot will have a more blurred background which would produce better subject isolation.

Another interesting thing to note is that the RX100 and RX100M2 will produce shallower DOF at 70mm and f/4.0 than 100mm and f/4.9 (as long as you are changing your distance to subject to maintain the same framing).

Sorry for the long rant, but with so many different systems now on the market I was just trying to get my head around how they compared with respect to their ability to produce shallow depth of field. I welcome any comments, corrections or additional information.

Sony a6000 Sony Cyber-shot DSC-RX10 Sony RX100 Sony RX100 II
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