Bokeh

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I use a digital compact and therefore, due to sensor size/focal length, have a very limited ability to blur the background.

I use Photoshop's "Gaussian Blur" a lot when I want to separate a subject from a background.  It's quite effective.

Difficult to do with video though.

[rogerzilla]

Gaussian blur is also quite different to real OOF blur.  There is software that can simulate the latter reasonably well.

[Tewdric]

Leica 75mm f1.4 blur is hard to beat..



Taken with my old M6, which I miss very much..

[rogerzilla]

I would say "go and buy an M3, they're only £500 from a dealer and much nicer than an M6" but then I realised they only have 50/90/135 framelines.

The ultimate Leica bokeh is supposed to come from the pre-aspherical 35mm Summicron, but that's a bit weird; a 35mm has sufficient DOF that you rarely get anything far enough OOF to benefit.

[Ivo]

The ultimate Leica bokeh is supposed to come from the pre-aspherical 35mm Summicron, but that's a bit weird; a 35mm has sufficient DOF that you rarely get anything far enough OOF to benefit.

Does it?



Ok, an 1.4/85 gives you more room to play with (Samyang in my case)

[Charlotte]

Taken last night, wide open with my lovely Nikon 17-55mm f/2.8:

[Biggsy]

Bad bokeh (Leitz Summicron collapsible 5cm at f/2.8 )

I would be interested to see a comparison of good and bad bokeh with precisely the same scene and DOF - with a difficult background like in the above.

I'm not yet absolutely convinced that that unpleasant appearance of the blurred twigs/leaves is all down to bad bokeh.  Seeing an example of good bokeh (with a different lens) with a different scene isn't enough even when it features a similar subject.  Subtle differences in the subject can make a large difference to the appearance in the photos, not to mention differences of distances and DOF as well.

[Riggers]

Advanced Bokeh:

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Shouldn't that be Trueman, you're just not focussing on this are you?

[tonycollinet]

The ultimate Leica bokeh is supposed to come from the pre-aspherical 35mm Summicron, but that's a bit weird; a 35mm has sufficient DOF that you rarely get anything far enough OOF to benefit.

Interestingly any focal length lens has the same DOF with the same aperture and the same SUBJECT magnification. That is if you take a picture with a 35mm and a 60mm lens so that the subject fills the same area of the frame (35mm lens will be at 1/2 the distance of the 60mm), and at the same aperture, then the DOF will be the same.

However, the background on the 60mm image will look softer, because the narrower field of view effectively expands half the amount of background to fill the frame - and hence also expands the blurred area of background making it look less "busy"

[rogerzilla]

This is true, but the perspective of a wide angle lens tends to preclude certain subjects close-up to get the equivalent image size (e.g. full-face portraits) so in practice you do see greater DOF.

[Ivo]

How do you explain the differences between my 35mm and 85mm shot on the previous page? The aperture of the 35mm was 2.4, of the 85mm was 3.2. The DOF of the 85 is clearly a lot thinner, despite the longer distance to the subject.
A longer lens will allways have a shallower DOF then a wider lens. Even when you crop the photo of the wider lens. Of course aperture shouldn't be too different.

[rogerzilla]

There was a series of photos in the "A" level standard text which showed this quite clearly.  You can stand 3 metres away with a 35mm lens or 9 metres away with a 105mm lens and still get the same subject size with everything in focus at (say) f/8.  The actual DOF from the subject to infinity is the same; it just seems as if the 105mm has less depth of field because everything is further away.

In your 35mm/85mm shots, the subject's head fills more of the frame in the 85mm shot; possibly 50% more.

[tonycollinet]

In your 35mm/85mm shots, the subject's head fills more of the frame in the 85mm shot; possibly 50% more.

This - although by my measurement 40% more which will result in shallower dof.

It's worth pointing out, that the "same DOF rule" also only applies when the subject distance is relatively small compared with the hyperfocal distance.

[chris]

Canon 100-400 zoom @ 400mm f8.0.

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16mm Sony lens with +3 dioptre filter. f11 1/160

[iakobski]

The ultimate Leica bokeh is supposed to come from the pre-aspherical 35mm Summicron, but that's a bit weird; a 35mm has sufficient DOF that you rarely get anything far enough OOF to benefit.

Interestingly any focal length lens has the same DOF with the same aperture and the same SUBJECT magnification. That is if you take a picture with a 35mm and a 60mm lens so that the subject fills the same area of the frame (35mm lens will be at 1/2 the distance of the 60mm), and at the same aperture, then the DOF will be the same.

However, the background on the 60mm image will look softer, because the narrower field of view effectively expands half the amount of background to fill the frame - and hence also expands the blurred area of background making it look less "busy"

That's what you'd think, logically, but in fact, no it doesn't work like that. The wider angle lens has greater DOF.

This was the first lesson at college, elventy years ago: they gave us a load of 5" x 4" sheet film, a bunch of lenses and some big white cubes. Get the same size object on the film, measure depth of field with a tape measure.

[rogerzilla]

DOF is independent of focal length as long as the subject distance is considerably shorter than the hyperfocal distance (i.e. the background is blurred).

[Pingu]

[Charlotte]

Reminds me of this:

[tonycollinet]

The ultimate Leica bokeh is supposed to come from the pre-aspherical 35mm Summicron, but that's a bit weird; a 35mm has sufficient DOF that you rarely get anything far enough OOF to benefit.

Interestingly any focal length lens has the same DOF with the same aperture and the same SUBJECT magnification. That is if you take a picture with a 35mm and a 60mm lens so that the subject fills the same area of the frame (35mm lens will be at 1/2 the distance of the 60mm), and at the same aperture, then the DOF will be the same.

However, the background on the 60mm image will look softer, because the narrower field of view effectively expands half the amount of background to fill the frame - and hence also expands the blurred area of background making it look less "busy"

That's what you'd think, logically, but in fact, no it doesn't work like that.

Yes it does - here is an explanation better than anything I can conjure up....
Depth of field

Or if you like - bang in the figures to practically any DOF calculator you care to find.

[Exit Stage Left]

The ultimate Leica bokeh is supposed to come from the pre-aspherical 35mm Summicron, but that's a bit weird; a 35mm has sufficient DOF that you rarely get anything far enough OOF to benefit.

Interestingly any focal length lens has the same DOF with the same aperture and the same SUBJECT magnification. That is if you take a picture with a 35mm and a 60mm lens so that the subject fills the same area of the frame (35mm lens will be at 1/2 the distance of the 60mm), and at the same aperture, then the DOF will be the same.

However, the background on the 60mm image will look softer, because the narrower field of view effectively expands half the amount of background to fill the frame - and hence also expands the blurred area of background making it look less "busy"

That's what you'd think, logically, but in fact, no it doesn't work like that.

Yes it does - here is an explanation better than anything I can conjure up....
Depth of field

Or if you like - bang in the figures to practically any DOF calculator you care to find.

All you need to know about depth of field is that it depends on the physical size of the objective lens. If you look at an f2.8 telephoto lens, it has a big piece of glass at the front. An f2.8 wide angle lens looks like a pinhole by comparison. That is because the wide angle lens is gathering light from a broader area, so needs less glass to get that same value of light.
As the size of the film or sensor increases it needs more light, to acheive the same f value. So the objective lens has to increase in size. It's not the f number that changes DOF but the diameter of the objective lens. This is why the cost of cameras and lenses rises exponentially as the format size increases, everything becomes more critical in terms of focusing and exposure due to the size of the glass required, which costs more to get right, and is easier to get wrong, all the way up to the Hubble telescope.
The bigger the piece of glass on the front, the shallower the depth of field with it wide open.

[AndyK]

As the size of the film or sensor increases it needs more light, to acheive the same f value. So the objective lens has to increase in size.

Not true. My 6x6 Rollei TLRs have smaller lenses than my 35mm rangefinders.

[Exit Stage Left]

As the size of the film or sensor increases it needs more light, to acheive the same f value. So the objective lens has to increase in size.

Not true. My 6x6 Rollei TLRs have smaller lenses than my 35mm rangefinders.

The objective lens will be pretty much the same size for a 50mm f 2 lens, or any value, regardless of format. On the rangefinders that is a standard lens, on the TLR that is a wide angle. I just took a look at the only TLR I have, a Lubitel 66 and the lens on that is a f4.5 75mm and it has an objective about the same size as the f2.8 50mm lens from a FED, and therefore the same DOF properties fully open.

[AndyK]

As the size of the film or sensor increases it needs more light, to acheive the same f value. So the objective lens has to increase in size.

Not true. My 6x6 Rollei TLRs have smaller lenses than my 35mm rangefinders.

The objective lens will be pretty much the same size for a 50mm f 2 lens, or any value, regardless of format. On the rangefinders that is a standard lens, on the TLR that is a wide angle. I just took a look at the only TLR I have, a Lubitel 66 and the lens on that is a f4.5 75mm and it has an objective about the same size as the f2.8 50mm lens from a FED, and therefore the same DOF properties fully open.

Yes, I know this, my point was the lenses are physically smaller. The physical size of the lens has nothing to do with DoF. The reason the focal length changes is to increase or decrease the circle of confusion to obtain the correct coverage for the size of format.

It is the focal length combined with the F-stop that determines the DoF, not the size of the lens.