Shallow Depth of Field

I know this is a can of worms but as a relative newbie I still don't understand how sensor size affect DOF. If I use my Legacy Olympus 50mm/f1.8 on my GF2 I can get very shallow DOF, but as my Lumix lenses only go down to f3.5 I don't get the same effect with them, but that makes sense as the aperture is much smaller. Yet using my X10 at f2.0 the effect is not so evident so I guess there must be something else at play

I have tried reading up on this but if anyone can direct me to a good website that explains it I would be very grateful.

:confused: from Scotland


Hall of Famer
Nov 12, 2010
If I'm wrong, I hope someone will correct me, but here's what I understand about it:

Each object that's hit by light, reflects that light in all directions. Your camera lens captures some of that light, but it contains rays which were sent out at slightly different directions (the light hitting the right hand side of the lens must have been reflected off the subject in a slightly different direction than the light hitting the left hand side of the lens). The lens bends the light rays back to a single point, right at the sensor, which is then in focus.

Out of focus (OOF) areas of the photo occur when the rays of light from a place closer to, or further from the subject, hit the outer edge of the lens at a different angle compared to those rays of lights that are reflected off the subject. Because the lens bends light in a single way, rays coming in at a different angle will not come together (be focused) at the sensor, but slightly before or after it. At the sensor, these rays of lights will cover a larger area, causing the unsharpness.

The DOF is therefore caused by the 2 factors which determine the angle at which rays of light arrive at the sensor: the distance to the subject (closer by = steeper angles = shallower DOF) and the physical size (diameter) of the diaphragm / aperture (larger diaphragm = steeper angles = shallower DOF).

Bigger sensors don't necessarily have shallower DOF, but to get the same field of view, they need larger lenses (the X10 only requires a ~6mm lens to get the same 28mm equivalent field of view as a 14mm lens on m4/3). Since the f-number of your aperture is calculated as "focal length in mm divided by physical aperture diameter in mm", an X10's 6mm lens at f2 has a physical aperture size of 6/2 = 3mm, whereas an m4/3's 14mm lens at f2 would have a physical aperture size of 14/2=7mm. Therefore, despite the fact that they have the same 28mm-equivalent field of view, the M4/3's real aperture is more than twice as large = steeper angles for the rays of light falling on the sensor = shallower DOF.

Making the effect you're seeing even stronger, the 50mm f1.8 lens has a 27,7mm aperture, which is about 10 times as large as your X10's at 6mm / f2.

sorry it turned out to be such a long read!:eek:
Jan 31, 2011
Newcastle, Australia
It has an almost painted look to it. Of course one of the coolest things about the larger sensors CSCs is that you no longer even need a big DSLR to do it.
Indeed... and this is why in all likelihood, I will sell off my K-5 and WR lenses, and get another K-r. That will also give me some cash to buy other things. Another lens? Another camera? The new Samsung Galaxy Note? LOL. Can we spell G.A.S., children?
Jan 31, 2011
Newcastle, Australia
sorry it turned out to be such a long read!:eek:
You were probably right, but I have no clue. All I know is that to get a realtively shallow DoF with a compact, I need the subject to be a long way separate from the background, and I could never get a shot like that of this grevillea with a compact. The whole flower would be in focus, and some of the background as well. And I would never get bokeh like that either.


Hall of Famer
Dec 24, 2010
Brisbane, Australia
Not necessarily. Any larger sensor CSC (Sony NEX, Samsung NX, Ricoh GXR, Micro 4/3) has the capability to achieve the same shallow depth-of-field as a DSLR, assuming the system has the range of lenses available to give you that look of course.


Jan 2, 2011
Indeed ... an example from an Olympus E-P2 with a long zoom at a smallsh aperture ...

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bluebell by _loupe, on Flickr

E-P2, 70-300ED, 1/2000s, f/7.1, 272mm, ISO400

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