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Author Topic: What lens delivers the strongest background blur?  (Read 6626 times)

BozillaNZ

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Re: What lens delivers the strongest background blur?
« Reply #15 on: July 16, 2013, 06:33:39 AM »
One such example of this phenomenon is an 85/1.2 versus a 300/2.8 lens.  When both are shot around 1:10 magnification (which is near MFD for both real-world implementations), the former is predicted to have about 2x the blur circle diameter up to about 1 foot behind the subject, decreasing until the two have equal blur at about 11-12 feet behind the subject, after which the 300/2.8 will dominate.  What is happening is that a faster f-number will increase the blur at distances close to the subject, but a longer focal length will increase the blur of very distant objects because of perspective.

You are exactly right, this is the level of understanding regards to DoF and background blur that most of the newcomers find hard to grasp.

Larger entrance pupil gives shallower DoF, while longer focal length (tighter angle of view) gives more distance background blur.

It is those two factors together, along with subject/background distance relationship determine the lens's ability to "blur the background"

When you are comparing a fast wide angle with a slow telephoto, it becomes complicated since you can't flat out say which one is better at blurring background, it depends on how far the background is to say which one is better!
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Re: What lens delivers the strongest background blur?
« Reply #15 on: July 16, 2013, 06:33:39 AM »

neuroanatomist

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Re: What lens delivers the strongest background blur?
« Reply #16 on: July 16, 2013, 06:41:49 AM »
It is those two factors together, along with subject/background distance relationship determine the lens's ability to "blur the background"

When you are comparing a fast wide angle with a slow telephoto, it becomes complicated since you can't flat out say which one is better at blurring background, it depends on how far the background is to say which one is better!

Correct.

While the plotted data are useful, our backgrounds are not often infinitely far away (or far enough to be treated as such).

For anyone who's interested, Bob Atkins wrote a calculator for background blur that accounts for lens properties (as in the plot above) as well as subject distance and foreground/background distances.

http://www.bobatkins.com/photography/technical/bokeh_background_blur.html
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Re: What lens delivers the strongest background blur?
« Reply #17 on: July 16, 2013, 06:44:13 AM »
Just let me guess...
200/1.8? :)

200mm f/1.8 would score a value of 3.1 which means 5th place ( behind 500 f4 but better than 300 f2.8 ).

Good luck with that. The error of this comparison is in the "given magnification".
In reality, for background blur, I'd pick 35/1.4 over 500/4 any day of the week :)

P.S. You forgot 1200/5.6 ;).
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photonius

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Re: What lens delivers the strongest background blur?
« Reply #18 on: July 16, 2013, 06:53:21 AM »
These numbers are simply invalid in the case you mentioned where MM is about 1:10 BECAUSE it is near MFD as you mentioned.

You would see from the content of my previous post that what is more interesting to many photographers who wish to get more background blur is that such blur is achieved for objects not infinitely far away from the subject in focus, and as a result, a list of entrance pupil diameters is an oversimplification that can mislead people as to which lenses perform in the way they might want.

Quote
Also there is no = in the equation but a =~ which means approximately. The formula would be exactly correct at infinity as you said but it is exact enough for most of the focal range but NOT for the region near MFD. So in my opinion there's nothing really to "clarify" here.

That is not correct; you are confusing focus distance with subject-background distance.  The model for points at infinity is not a function of focus distance or subject magnification, which are uniquely determined by a fixed magnification.  It is a function of the separation between the subject in focus and the background object.  This is something that holds true even if the lens is not focused near MFD, and conversely, your approximation is GOOD if you focused at MFD but the background is at infinity.

And in my opinion, my use of the word "clarify" is intended in the sense of assisting others with their understanding of the phenomenon of background blur.  If you don't want to acknowledge that, that's fine by me--I will let others decide for themselves whether what I have written is meaningful or useful for them.

Yes, I concur, an important aspect is how much another (background) object is blurred with respect to the object in focus.
The "holding tank" has a number of graphs that show how the circle of confusion changes in diameter (degree of out of focus blur) behind and in front of the plane of focus for different focal lengths:
http://www.zen20934.zen.co.uk/photography/dof/dof.htm

For people who don't want to be bothered with formulas, here is a simulator, that can simulate the DOF with objects at different distances (I did not check if the results are actually accurate):
http://kingfisher.in.coocan.jp/boke2/bokekeisan2e.html


BozillaNZ

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Re: What lens delivers the strongest background blur?
« Reply #19 on: July 16, 2013, 06:54:15 AM »
I'd like to share a photo shot by a pal on another forum:

He used 200mm f2 to do this shot: tell me if any shorter lens can ever achieve this effect:

hint: subject distance: 17.6m



35 1.4? pfff, not even close

Contrary to popular belief, in order to get most background blur (isolation), you shoot head/shoulder with wide angle (35), half body with medium (50/85) and full body with telephoto (>200), not the other way around.

Wide for full body, tele for close up just gives you flat and boring snap shots.
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Re: What lens delivers the strongest background blur?
« Reply #20 on: July 16, 2013, 07:31:02 AM »


I wasn't talking about the quality of the blur, but its strength.


Yup. I did get that. Just making the point that it isn't the whole picture.  Wide open bokeh from some lenses is just horrible.


This is already considered by using the same magnification for all the lenses which means the focus distance for a 50mm will be much closer than that of a 600mm lens to retain the same magnification (exactly as you would use them in the field).


But the point of a lens like the 50mm is that it can do much greater magnification, up to 1:2, and so that messes with the perspective and blur even further.  I'm making the general point that the tools you have compared are so different that this one criteria is no way to pick a lens.  I'm not saying it's a worthless comparison, just that there are about a dozen other parameters to consider before I would get to this point.  You wouldn't use a 50mm macro for distant wildlife in the same way as you wouldn't automatically use a 600mm for portraiture.

To use the old adage, it's like comparing an apple with a tractor.

Actually I was comparing Canon prime lenses to Canon prime lenses.


Ok a tractor to a lamborghini then. Other than for this theoretical test (done using maths rather than with any consideration of hands on, actual experience of individual lenses) these lenses are designed for tasks so far apart that you might as well be comparing an apple with a tractor.  Your theory is seriously skewed and weighted as you cannot possibly be using something like a 50mm macro in the way that it was designed to perform best and is the way most folk will use it.


To go back to the point about the aperture shape, will this affect the maths at all?  Is the area of the diaphragm pupil exactly the same on a 200mm f2.8 lens with six blades as on one with nine?

Maximum blur is always achieved wide open - so in general there are no aperture blades.

In general.  Might want to check some of your zooms.  For example my 17-40 used to shift aperture slightly as you zoomed, as did my ancient 28-70 f3.5-5.6 II.  Again, how useful is this test in real life when with most of these lenses folk will probably shoot with the iris closed a stop or two.  For example I own the 100 f2.0.  Great fast lens.  Hopeless wide open because of chromatic abberations that are gone by f2.8.  So blur reduced and an iris shape introduced when the lens is set to be practically used.

It's interesting in a stats way, but I wouldn't pick a lens based on it.

+1
[/quote]

Glad we agree on that at least.

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Re: What lens delivers the strongest background blur?
« Reply #21 on: July 16, 2013, 07:34:20 AM »
I'd like to share a photo shot by a pal on another forum:

He used 200mm f2 to do this shot: tell me if any shorter lens can ever achieve this effect:

hint: subject distance: 17.6m



35 1.4? pfff, not even close

Well, my vote is for 200/1.8 (first page). What I meant with 35/1.4 is that 500/4 is very impractical for what we are discussing here.

Quote
Contrary to popular belief, in order to get most background blur (isolation), you shoot head/shoulder with wide angle (35), half body with medium (50/85) and full body with telephoto (>200), not the other way around.

Wide for full body, tele for close up just gives you flat and boring snap shots.

Yes, I agree :).

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Re: What lens delivers the strongest background blur?
« Reply #21 on: July 16, 2013, 07:34:20 AM »

GMCPhotographics

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Re: What lens delivers the strongest background blur?
« Reply #22 on: July 16, 2013, 07:53:18 AM »
I'd like to share a photo shot by a pal on another forum:

He used 200mm f2 to do this shot: tell me if any shorter lens can ever achieve this effect:

hint: subject distance: 17.6m



35 1.4? pfff, not even close

Contrary to popular belief, in order to get most background blur (isolation), you shoot head/shoulder with wide angle (35), half body with medium (50/85) and full body with telephoto (>200), not the other way around.

Wide for full body, tele for close up just gives you flat and boring snap shots.

The OP asked a very general question. With your very nice posted image, taken with a 200mm lens, another focal length prime will not create an identical image. The background blur can be less or more depending on the working distance, focal length, aperture and subject distance from the background. If you hinge on a 200mm then the only way to create a simular isolation is to go closer with a wider lens or further back with a longer lens. If one goes wider, then a larger aperture will be needed to create a clean background.
A 35mm f1.4 and 85mm f1.2 are both perfectly capable of doing this, although the 35mm is better suited to "head and shoulders" portraits and not "head and toes" portraits. The wider lens will be a lot closer and cause a different look to the 200mm image. There will be a different look from the amount of compression difference between the 200mm and 35mm, but that's an entirely different subject. 

I regularly use a 35mm f1.4 and 85mm f1.2 for my professional wedding work and it's very very easy to melt the background, but tricky to get a precise point of focus. That said, my 24-70L is very good at melting backgrounds too. At 70mm @ f2.8 it's min focus distance is very close and more than capable of making clean backgrounds.

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Re: What lens delivers the strongest background blur?
« Reply #23 on: July 16, 2013, 07:57:00 AM »
I'd like to share a photo shot by a pal on another forum:

He used 200mm f2 to do this shot: tell me if any shorter lens can ever achieve this effect:

hint: subject distance: 17.6m



35 1.4? pfff, not even close

Contrary to popular belief, in order to get most background blur (isolation), you shoot head/shoulder with wide angle (35), half body with medium (50/85) and full body with telephoto (>200), not the other way around.

Wide for full body, tele for close up just gives you flat and boring snap shots.

One other thing to bear in mind when shooting head 'n shoulder portraits with 35mm is to keep out of slapping distance when you show the model the pictures.

With regard to the wonderful 200 f2, its ability of the focus point to be pin sharp at f2 adds to the differential between in and out of focus, and this exaggerates the effect. The 50 f1.4 on the other hand is very soft, and this spoils the differential between in and out of focus.

BozillaNZ

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Re: What lens delivers the strongest background blur?
« Reply #24 on: July 16, 2013, 08:02:47 AM »
The OP asked a very general question. With your very nice posted image, taken with a 200mm lens, another focal length prime will not create an identical image. The background blur can be less or more depending on the working distance, focal length, aperture and subject distance from the background. If you hinge on a 200mm then the only way to create a simular isolation is to go closer with a wider lens or further back with a longer lens. If one goes wider, then a larger aperture will be needed to create a clean background.
A 35mm f1.4 and 85mm f1.2 are both perfectly capable of doing this, although the 35mm is better suited to "head and shoulders" portraits and not "head and toes" portraits. The wider lens will be a lot closer and cause a different look to the 200mm image. There will be a different look from the amount of compression difference between the 200mm and 35mm, but that's an entirely different subject. 

I regularly use a 35mm f1.4 and 85mm f1.2 for my professional wedding work and it's very very easy to melt the background, but tricky to get a precise point of focus. That said, my 24-70L is very good at melting backgrounds too. At 70mm @ f2.8 it's min focus distance is very close and more than capable of making clean backgrounds.

That's some nice input. However if you try to take full body portrait using 35 1.4, it cannot achieve the same amount of background blur as a 200mm lens, because background compression plays a big factor on achieving this effect.

I don't deny the ability for 35 1.4 to achieve background blur, but it won't do much at this size of a subject. What I'm trying to get to is wide angle is good at blurring background when shooting small things close up, while telephone is good at blurring background when shooting big things (relatively) far away. So the chart in topic doesn't really tell you the whole picture.
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J.R.

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Re: What lens delivers the strongest background blur?
« Reply #25 on: July 16, 2013, 09:17:25 AM »
Shame the 50 f1.4 is unacceptable at 1.4.  :(

 ??? How did you arrive at this conclusion?


Just from practical experience. I've always found it disappointing in the centre of the frame wide open when compared with other, admitably more expensive lenses. It just doesn't 'sing' until around f2.2.

So with regard to the OP's data, the curve might be more exaggerated if critical quality at max aperture were to bs applied; but of course that's subjective.

I still think the data is interesting: my half joking comment about the 85 f1.2 / 200 f2.8 was half serious !

OK. I couldn't understand your comment in context of information in the original post.  :)
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surapon

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Re: What lens delivers the strongest background blur?
« Reply #26 on: August 11, 2013, 09:39:03 AM »
Well, Dear Friends
I love  the Background Blur of my Canon FE 85 mm. F/ 1.2 L MK II = The First one, The Second Choice = Sigma 50 mm. F/ 1.4, And The Third one = Canon EF 20-200 F/ 2.8 L IS USM at 200mm at F= 2.8.
Just my 2 Cents Opinion.
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PS. All these Photos   at. F= 1.2 by Canon 85 mm. F/ 1.2 L MK II
« Last Edit: August 11, 2013, 09:41:53 AM by surapon »

surapon

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Re: What lens delivers the strongest background blur?
« Reply #27 on: August 11, 2013, 10:09:41 AM »
Dear Friends.
This Photo = Canon EF 70-200  at 200 mm. F/ 2.8, about 8 meters from the subject.
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Re: What lens delivers the strongest background blur?
« Reply #27 on: August 11, 2013, 10:09:41 AM »

surapon

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Re: What lens delivers the strongest background blur?
« Reply #28 on: August 11, 2013, 10:18:20 AM »
These Photos from Sigma 50 mm. F/ 1.4 Lens
Enjoy.
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surapon

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Re: What lens delivers the strongest background blur?
« Reply #29 on: August 11, 2013, 10:19:21 AM »
These Photos from Sigma 50 mm. F/ 1.4 Lens
Enjoy.
Surapon

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Re: What lens delivers the strongest background blur?
« Reply #29 on: August 11, 2013, 10:19:21 AM »