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Will a Nikon D80 + 50mm f/1.8D and a Lumix LX5 set both at an aperture of f/2.0 (50mm @ f/2.0 for D80 and 24mm @ f/2.0 for LX5) have the same bokeh ouput? I plan to get the LX5 as a second camera, and I love "bokeh-ish" shots, so I'd like to know your thoughts.

I don't know if the distance between where I am and where the subject is will matter (i.e. I have to be closer to the subject with 24mm to get a similar framing as with the pic I take with 50mm), but I do know that the degree of "out-of-focus" of the background will depend on the distance between the subject and the background. Again, I don't know if this is relevant to the question or not...just thinking out loud. :D

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An important question (raised by @Nick Miners' answer below) is whether by "same bokeh" you are referring to the quality of the out of focus area (see What is bokeh, exactly?) or simply the depth of field? –  mattdm Feb 1 '12 at 17:49
    
I have an LX5 and, in my experience at least, the only time you ever get a nicely blurred background is when shooting something really close in macro mode, so if you want a camera which produces nice background blur, you'll probably have to look elsewhere :-( –  mdresser Feb 18 '12 at 21:29
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5 Answers 5

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No. The sensor size plays a major part in bokeh. Sensor dimensions of your dSLR are about 3 times bigger than sensor of the compact, so a photo taken with compact's 5.1mm f/2 will look similar to one taken at 16mm f/6.3 using APS-C sensor. Also, the shorter focal length will reduce bokeh effect, because wider angle of view means more background has to fit into same image space and therefore each background object will be projected smaller (more dot-like, i.e. sharper).

Here's a quick comparison of two photos with similar subject, both at f/2, first taken with a compact camera (at its widest focal length) and second with a dSLR (58mm lens):

compact at f/2 dSLR at f/2

The angle of view will be similar near the longer end of the LX5 lens, where maximum available aperture is f/3.3; to see how its bokeh would look like, set your 50mm on D80 to f/10.

Here's a quick comparison of two photos with similar subject and similar angle of view, first taken with a compact camera (at its longest focal length) at f/3.2, second taken with a dSLR (58mm lens at f/11):

compact at f/3.2 dSLR at f/11

To get bokeh effect on a compact camera, you have to pay up for a large sensor, such as in Fuji X100 or Sigma DP2. And even then, the effect will be weaker, because the angle of view of those cameras is wider than your 50mm on a dSLR. Or, you could rely on some alternative techniques to get good background separation.

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@dpollitt I used Windows built-in calculator to calculate crop factor difference and multiplied the f-number with it, as explained in Matt Grum's answer to another question. –  Imre Feb 1 '12 at 16:08
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I'd argue it's not the sensor size but the focal length of the lens that affects the bokeh. The sensor size dictates the use of shorter focal lengths generally, but it does not have a direct effect. Bokeh is purely a function of the lens. –  Nick Miners Feb 1 '12 at 20:46
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@Nick purely optically, yes; but given a fixed framing of subject (as in this question), using same focal length on different sensor sizes will affect your distance from subject, and the resulting bokeh will be different due to different perspective. With this restriction of similar framing, sensor size becomes the dictating variable for focal length to choose. –  Imre Feb 1 '12 at 21:06
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I agree w/nick, this answer is misleading. The bokeh at a given aperture (which is what this question is asking) will be the same. You should indicate up front in the answer that you're taking distance into account. –  Shizam Feb 24 '12 at 17:59
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@Shizam the desire for similar framing is already expressed in the question. Anyhow, added images to illustrate my point. –  Imre Feb 25 '12 at 23:23
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Subject distance does matter in producing bokeh. Think of it this way: there is a subject, and another object that is 1m farther from it. If the subject itself is 1m from the camera, the other object is twice as far away. But if the subject is 10m from camera, the other object is 11m, only 10% further from the subject. If the subject is at near-infinity (like sun/moon)) then the "near object" would be practically on the same distance. This is why once we focus on a star, other stars that are light years further from them stay in focus.

The two cameras you mentioned will have different subject distances if you want to compose the picture the same way i.e. to cover the same area of frame, as effective focal length of a lens varies greatly with sensor size. DSLRs have much larger sensors compared to prosumers and point and shoot cameras. (The size ratio of the sensor to the standard 35mm sensor is called the crop factor of the sensor) In effect, they will have different bokeh.

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f/2 is f/2 is f/2. That's the ratio of the focal length divided by the aperture, which is basically a measure of the light that is coming into the camera.

Bokeh is simply the Japanese word for "blur". What we call bokeh is just the parts of the photos that are outside the Circle of Confusion. Some people (such as this guy) will have you believe that bokeh is the quality of the blur and not the out-of-focus areas themselves. It's generally held that the more blades in the diaphragm (it sets the aperture), the better (more pleasing) the quality of the bokeh produced by that lens.

Consider this: a shot on 35mm film with a 50mm lens set at f/2 and 2m distance of a very large painted grey wall that is perfectly illuminated has constant brightness across the film. The center of the film is no less dark than the outer edges. The circle of confusion doesn't change at all. The lens doesn't care that you've put it on a Leica III (Model F) loaded with 35mm Tri-X or if you've put it on an Epson R-1D (which has a "crop factor" of 1.6 due to its sensor size). The only thing that will change is the real-world area of the image (e.g. the entire car vs. just the passenger doors when shot from the side) when identical settings and vantage points are used.

All the numbers on a camera with regards to focal length and f-stop are typically given in 35mm equivalents, thus a f/2 aperture with the zoom set at 50mm focal distance on a pocket camera is going to be the same as a f/2 aperture on a Leica Summitar mounted on a Leica and will give you the same out of focus area just less total area photographed, due to the reduced size of the imager.

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Hi andrew, the depth of field is different when using the equivalent focal length and same fstop on a compact, compared to a full frame. The panasonic lx5 at 50mm equivalent field of view (actual 10.6mm focal length), focussing at 3m, at f2.8 has a depth of field of 3.5m. the leica m9, using a 50mm lens at 2.8, has a depth of field of just 0.6m. I have used the lx5 lens spec from dpreview, and the calculator at dofmaster.com I understand your point, but the comparison with equivalent field of view is more practical comparison in real world situations. –  rapscalli Feb 1 '12 at 18:50
    
In your last paragraph, you mean 50mm real focal length, right? So something like 280mm 35mm effective on a typical small-sensor point-and-shoot superzoom. –  mattdm Feb 1 '12 at 23:02
    
Ah @rapscalli, but when you go for the same field of view you have changed the focal length used, so of course you're changing DOF. –  Andrew Beals Feb 2 '12 at 1:57
    
If you're going to demand the exact same photo and then compare numbers, that's another thing entirely. When you're speaking of the bokeh, you have objects in focus, and the rest of the frame really only matters in that it frames the in-focus items nicely. –  Andrew Beals Feb 2 '12 at 2:01
    
@mattdm I'm speaking of 35mm equivalent and in the Leica/Epson case, the focal distance (50mm) is exactly the same. You either have a sensor (which is smaller than a standard 24x36mm frame) or you have an actual piece of film. DOF is the same, you just get a cropped photo from the smaller sensor. I understand what DOFmaster is trying to sell and how they're borking the numbers. –  Andrew Beals Feb 2 '12 at 2:06
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There is no objective measurement of bokeh as such, it is very much an aesthetic quality that can't really be quanitified. However, it is generally considered to be 'better' when the following apply:

  1. The depth of field is very shallow
  2. The aperture of the lens is as close to a perfect circle as possible

Depth of field is a function of aperture, but it is actually directly related to the absolute size of the aperture, not just its relation to the focal length, which is what the f-number refers to. The two lenses you specify will have an aperture diameter of 25mm in the case of the 50mm lens, and 12mm in the 24mm lens, meaning the depth of field is greater in the 24mm lens.

By these measurements, the 50mm lens, with its larger physical aperture, is more likely to provide 'better' bokeh, on the assumption that both lenses, when wide open, will have perfectly circular apertures.

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The LX5 has 5.1-19.2mm lens, which is 24mm equivalent in wider end. Thus, the maximum physical aperture is only 2.55mm (5.8mm in tele end). –  Imre Feb 1 '12 at 18:03
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No, a compact and DSLR won't product the same bokeh. All of the answers given thus far are entirely correct, however there is a more fundamental reason they create different results: bokeh is the result of the number of aperture diaphragm blades and the optical formula used to create the lens. In other words, two different lenses will have different bokeh -- that's all there is to it.

Now, two different lenses could produce very pleasing bokeh, and could even produce very similar bokeh. But remember that the bokeh is first a result of the lens you use and it's easy to tell that the results are most likely to be different.

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While you have an interesting alternate viewpoint, I think the focus of the question is on the amount of bokeh, which is influenced solely by the diameter of the physical aperture. –  Nayuki Minase Feb 27 '12 at 7:32
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