Is the DOF difference between M4/3 and full-frame really 2 stops?

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hookgrip

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I've heard from many sources that the DOF difference between MFT and APS-C was 1 stop, and the difference between MFT and FF was 2 stops.

However, I saw these comparison shots on DPR recently, and now I'm not so sure if it's "just" 2 stops anymore.

At least to my eyes, it looks like the Zeiss @ f/2.8 produces more background blur than the PL25 @ f/1.4. It looks like the Zeiss stopped down to ~f/3.2 or f/3.5 would give a similar level of blur compared to the PL25 wide open at f/1.4.

It there really more than a 2-stop difference in DOF between MFT and full-frame?

Zeiss 50mm @ f/2.8 on Sony A7r:
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PL25 @ f/1.4 on GX7:
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Dramaturg

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I think here you are comparing bokeh, not DOF. To compare DOF you'd have to take a picture of a ruler or some kind of DOF meter. As for the bokeh (or the way lens renders OOF and blurs the background) - two 50mm lenses on FF will have different bokeh. Perhaps that is the case?
 

MAubrey

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If there is a difference (I don't really see one), then it's a difference in how the lenses renders out of focus areas and how that can affect the background blur.

But background blur and depth of field are not the same thing. In truth, in terms of the areal difference in sensor size (864 square mm vs. 225 square mm), the difference is actually less than two stops. It's more like 1 2/3s stops. The diagonal crop is 2x, that's what matters for angle of view. The vertical crop is actually 2.08 and the horizontal crop is 1.85.
 

Bif

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In the applied sense, DOF (whether shallow or deep) is a visual thing. Dependent on sensor size, lens focal length, lens aperture, working distance from the lens to the subject, and distance from the subject to background elements.

Yes it is mathematically quantifiable, but for the creative image maker why bother and get bogged down with the math side of it. Choose a lens with focal length appropriate for what you want to "see", and set it up visually. I personally don't care about maybe being able to get shallower DOF with FF, I take the camera I have, select the lens, and manage the distance factors to give me what I want. Been doing that for almost 5 decades with 120 roll film (Blads), 35mm film, APS-C sensor cameras, and now m4/3.
 

Ulfric M Douglas

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I've heard from many sources that the DOF difference between MFT and APS-C was 1 stop, and the difference between MFT and FF was 2 stops.

However, I saw these comparison shots on DPR recently, and now I'm not so sure if it's "just" 2 stops anymore.
(Blimey, you been digging through really OLD threads!)
You can use the same lens on both formats,
with m4/3rds (and old 4/3rds) you get half the horizontal framing of 35mm (full-frame)
which means that for the same horizontal framing of any scene the focal length of a m4/3rds lens is half that of a 35mm lens.
The focal length of a lens has a greater effect on focus/blurring than the aperture of a lens.

Once you introduce different lenses at different apertures the concept of "how many stops" becomes inexact,
as if the F-stops of lenses weren't inexact enough!
 

rogergu

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My understanding is they should have same DOF at the same "physical" focal Length, so if you compare pans 25mm f1.4 with something 25mm full frame lens, they should have the same background blur effect. However, you need to crop the full frame picture as 43 is cropped on the sensor.

If you agree what I said above, then the question is actually to compare a 25mm lens with 50mm lens. Of course that will be different. The longer focal length the shorter DOF at the same aperture.

In the reality, due to the fact that the 43 is cropped, so to get the same view, you need to keep longer distance from the object than the full frame. That changes the "relative" DOF on the image, so there is no obsolute direct comparison I think.

You can try to compare oly 45mm with your full frame setup and see how much difference that would be.
 

rogergu

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BTW, that is why I feel oly 75mm is a better choice than 42.5mm for portrait if the distance is not a problem.
 

Amin Sabet

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I've heard from many sources that the DOF difference between MFT and APS-C was 1 stop, and the difference between MFT and FF was 2 stops.
It's closer to 0.7 stops between MFT and APS-C and 1.3 stops between APS-C and FF.

Sent from my LG-VS980 using Mu-43 mobile app
 

hookgrip

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It's closer to 0.7 stops between MFT and APS-C and 1.3 stops between APS-C and FF.

Sent from my LG-VS980 using Mu-43 mobile app
That does help clarify, though in the examples I've seen it looks like even more than 2 stops difference between MFT and FF.
 

flash

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He said the diff between APSC and FF is 1.3 stops, not the diff between m43 and FF.

DOF is an illusion, not empirically measurable. A few reasons that DOF might appear different.

1. The rated apertures of the lenses may not be exactly as advertised.

2. Slightly different focal point.

3. Different lens design leads to different fall off characteristics.

4. Focal lengths not exactly as advertised.

There are several others. But you get the idea. A half stop is within the "tolerances" of what you might expect to see.

Gordon
 

hookgrip

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Here's another comparison I found. Again, it seems like the FF image at f/5.6 has more background blur than the MFT image at f/2.8.

5D2, 200mm, f/5.6:
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GH3, 100mm, f/2.8:
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BeyondTheLines

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I think you're splitting hairs here. I see slightly more magnification with the first shot and as others have pointed out, other small differences can be attributed to many things
 

spatulaboy

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Wow you are really really splitting hairs here. There is almost no difference in that flower pic. People should sit back and enjoy the whole picture instead of staring at what's in the blurry bits.
 

Serhan

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As Gordon said different lenses might have different bokeh/blur characteristics and also the actual t stops of the lenses are mostly greater then the f stops, eg 25mm 1.4 has T1.7, 35-200 2.8 has T3.1, 42.5 1.2 has T1.6, etc. More about T stops:
http://en.wikipedia.org/wiki/F-number
T-stop

A T-stop (for Transmission-stops) is an f-number adjusted to account for light transmission efficiency (transmittance). A lens with a T-stop of N projects an image of the same brightness as an ideal lens with 100% transmittance and an f-number of N. For example, an f/2.0 lens with transmittance of 75% has a T-stop of 2.3. Since real lenses have transmittances of less than 100%, a lens's T-stop is always greater than its f-number.[6]

Lens transmittances of 60%–90% are typical,[7] so T-stops are sometimes used instead of f-numbers to more accurately determine exposure, particularly when using external light meters.[8] T-stops are often used in cinematography, where many images are seen in rapid succession and even small changes in exposure will be noticeable. Cinema camera lenses are typically calibrated in T-stops instead of F-numbers. In still photography, without the need for rigorous consistency of all lenses and cameras used, slight differences in exposure are less important.
 

Klorenzo

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Here's another comparison I found. Again, it seems like the FF image at f/5.6 has more background blur than the MFT image at f/2.8.
Has was already told DOF and blur are different things. Dof stops as soon as something is just a little blurry instead here you are looking to how much blurry things are outside of the focus area. Dof is about distance, blur is about picture area.

You can check blur difference here (in the flower example there should be NO difference, the two lines overlap)

http://howmuchblur.com/#compare-2x-100mm-f2.8-and-1x-200mm-f5.6-on-a-0.9m-wide-subject
http://www.dpreview.com/articles/6091822765/background-blur-and-its-relationship-to-sensor-size

and dof here

http://www.cambridgeincolour.com/tutorials/dof-calculator.htm

In your example the framing is not the same (the Canon is closer, I can see less leafs on the flower and in the background) so this could be one reason. Another, as already told, could be the different rendering of the out of focus parts.
 
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