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03-11-2020, 04:44 AM - 1 Like   #16
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QuoteOriginally posted by Serkevan Quote
I understood Biz was talking about the amount of blur more than its quality.

Quality, of course, is a completely different matter.
Bokeh isn't defined in a way that cares about the amount. It is literally defined as the quality not as a quantity.

https://www.google.com/url?sa=t&source=web&rct=j&url=https://en.m.wikipedia....lup8en2ymCy6Ve

03-11-2020, 04:49 AM - 1 Like   #17
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QuoteOriginally posted by Serkevan Quote
I understood Biz was talking about the amount of blur more than its quality.
Then he should not have used the term "bokeh" in the title of the thread.

Bokeh is not quantifiable. By definition.
03-11-2020, 04:54 AM   #18
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QuoteOriginally posted by Sandy Hancock Quote
Then he should not have used the term "bokeh" in the title of the thread.
what shoud have I used ? blur ?
03-11-2020, 04:55 AM   #19
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QuoteOriginally posted by biz-engineer Quote
what shoud have I used ? blur ?
Depth of field perhaps?

03-11-2020, 04:57 AM   #20
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QuoteOriginally posted by UncleVanya Quote
Depth of field perhaps?
Ahrrr. Depth of field is not the same as background blur. A 50mm lens on FF can produce the same depth of field as a 150mm lens on a 4x5 format camera, although the two images of the same subject respectively taken with each system would look completely different. So in the past I read here in this forum and in other places that the amount of background blur was related to lens aperture size, everything else being equal.
03-11-2020, 05:00 AM - 1 Like   #21
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QuoteOriginally posted by biz-engineer Quote
Ahrrr. Depth of field is not the same as background blur. A 50mm lens on FF can produce the same depth of field as a 150mm lens on a 4x5 format camera, although the two images of the same subject respectively taken with each system would look completely different.
A fair point. I'm not sure what to call this but I'm certain it isn't bokeh as normally defined and discussed.
03-11-2020, 05:06 AM - 1 Like   #22
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QuoteOriginally posted by biz-engineer Quote
Sure. Now if I use my 100 macro to make a brenizer (bokeh pano), I can produce more melted background compared to doing the brenizer with my 70-200 f2.8, although the 70-200 appeared at first to be a better choice for a brenizer..
For the same subject-to-camera and same background-to-camera distance, the 70-200mm lens - shot at 100mm (assuming it actually is 100mm, allowing for focus breathing) - and the 100mm prime will both produce the same depth of field - the same level of blur - when shot on the same camera, at the same aperture, and reproduced at the same dimensions on the same media. The quality or "character" of the bokeh may differ, though. Whichever lens produces the smoothest-looking bokeh (which, in this example, has nothing to do with depth of field) might be the better choice for your "melted" background, but that's going to be subjective...


Last edited by BigMackCam; 03-11-2020 at 05:21 AM.
03-11-2020, 05:08 AM   #23
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QuoteOriginally posted by UncleVanya Quote
A fair point. I'm not sure what to call this but I'm certain it isn't bokeh as normally defined and discussed.
Both you and Sandy are correct - and that's why I talked about amount of "blur" and not amount of bokeh. Biz's thread's title is in that regard incorrect, but the body of the post, mentioning "amount of blur" is using the better term.

---------- Post added 03-11-20 at 05:12 AM ----------

QuoteOriginally posted by BigMackCam Quote
For the same subject-to-camera and background-to-camera distance, the 70-200mm lens - shot at 100mm (assuming it actually is 100mm, allowing for focus breathing) - and the 100mm prime will both produce the same depth of field when shot on the same camera, at the same aperture. The quality or "character" of the bokeh may differ, though. Whichever lens produces the smoothest-looking bokeh (which, in this example, has nothing to do with depth of field) might be the better choice for your "melted" background, but that's going to be subjective...
The only way to test the amount of blur here (otherwise the visual aspects of bokeh will confound it) would be to force a specular highlight ("bokeh ball") from a point-like light source near the center of the frame. In this test, the diameter of the ball should be the same (admitting some slight inaccuracies because, of course, nothing is ever dead accurate. We are still talking about an art with imperfect* optics).

*And that's, at least partially, the beauty of it all, innit?

Last edited by Serkevan; 03-11-2020 at 05:13 AM.
03-11-2020, 05:15 AM - 1 Like   #24
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QuoteOriginally posted by BigMackCam Quote
For the same subject-to-camera and same background-to-camera distance, the 70-200mm lens - shot at 100mm (assuming it actually is 100mm, allowing for focus breathing) - and the 100mm prime will both produce the same depth of field - the same level of blur - when shot on the same camera, at the same aperture. The quality or "character" of the bokeh may differ, though. Whichever lens produces the smoothest-looking bokeh (which, in this example, has nothing to do with depth of field) might be the better choice for your "melted" background, but that's going to be subjective...
And then there is the ever popular weird bokeh. In the end it comes down to out of focus stuff that looks kinda cool within the context of the photo. Alexandra Bochkareva's Meet Me in the Forest

03-11-2020, 06:02 AM - 2 Likes   #25
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QuoteOriginally posted by biz-engineer Quote
A while back, it was said that lens bokeh amount (blur) is a function of aperture diameter, or focal length divided by minimum f number.

Examples:

50mm @ f/1.4 => 50/1.4 = 35.7
100mm @ f/2.8 => 100/2.8 = 35.7
135mm @ f/2 => 135/2 = 67.5
70-200 2.8 zoom @ 200 f/2.8 => 71.43

Looking at those numbers, it looks like the 70-200 f2.8 zoom should be able to produce more blur than the 100 macro lens. But while using the D-FA 100 macro, I was able to produce a lot of background blur when getting close to subject. I realized the focal-length / aperture ratio might give a wrong estimate for lens blur ability. Minimum focus distance should be included but how?
The diameter of the bokeh is defined by the physical diameter of the aperture and the differences in the magnifications of the in-focus and out-of-focus subjects.

If the out-of-focus subject is at infinity (m_out = 0 as in the case of distant city lights), then the diameter of the bokeh on the sensor is just the magnification of in-focus subject times the focal length times the numerical aperture (m_in * F *A).

Lenses with closer minimum focus distance tend to have higher maximum magnifications which would give them stronger bokeh effects (assuming the in-focus subject is at maximum magnification). The DFA 70-200 2.8 goes to m = 0.13 (@120 cm MFD) meaning that a distant point of light would be a 9.3mm diameter bokeh ball. The 100/2.8 macro goes to m = 1 meaning that a distant point of light would be a 35.7mm diameter bokeh ball.
03-11-2020, 06:17 AM - 1 Like   #26
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Back to the original title "Lens Bokeh Ability"

I am a retired Accountant and no longer have any interest in figures or facts or Autopsies of subjects; just doing & trying with what I got.
And what I got is a HD 55-300 lens that has the best Bokeh of all my lenses and I have a FA 77Ltd (One of the best Low Light lens ever as well as the other stuff it can do).
Back to the HD 55-300. The graduation of bokeh between Fore (partial) & Aft in the first photo is amazing turning subject in the scene into 3D . The first & second photos background bokeh is a perfect mat for the subject - definitive yet soft.
The 3rd photo is just because the FA 77mm is not just a Portrait lens.
The Exif is attached for the #'s people.

Last edited by pentaxic; 03-12-2020 at 08:10 PM.
03-11-2020, 06:26 AM - 2 Likes   #27
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This is absolutely the best article I have read regarding this subject.
https://lenspire.zeiss.com/photo/app/uploads/2018/04/Article-Bokeh-2010-EN.pdf
03-11-2020, 07:31 AM   #28
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QuoteOriginally posted by Oldbayrunner Quote
This is absolutely the best article I have read regarding this subject.
https://lenspire.zeiss.com/photo/app/uploads/2018/04/Article-Bokeh-2010-EN.pdf
Clicked on the link and it did not work. ??
03-11-2020, 07:42 AM   #29
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i use this. Online Depth of Field Calculator
03-11-2020, 07:42 AM   #30
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QuoteOriginally posted by kernos Quote
Clicked on the link and it did not work. ??
It's working fine for me
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