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09-21-2010, 10:02 PM   #16
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QuoteOriginally posted by violini Quote

Bokeh or bocca is due to the defect of a lens system which is unable to focus all the 3-dimensional objects unto a 2-dimensional plane.

Just a small but important correction. Bokeh is caused by physical laws, not a defect.
This may not seem like it is important, but it needs to be corrected because that above statement is flat out wrong, and absurd to anyone who has taken a whit of time to educate themselves about optics.

09-22-2010, 05:09 AM   #17
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May I ask why did you buy a DSLR (or two DSLRs for the record) if you want point&shoot style "infinite focus" pictures?

I mean if I want to transfer 40' containers regularly then I don't buy a Porsche 911 and ask how could I transfer 40' containers with it... I rather buy a container lorry for this job.
09-22-2010, 07:24 AM   #18
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QuoteOriginally posted by violini Quote
brofkand, thanks for the link about hyperfocal distance.

The lens in the eye is a soft lens; the muscle can change the focal length instantly. That's why we can see objects near and afar.
That's true, but, especially in low light (just like a camera), the iris in your eye is wide open. It is possible to focus your eye on a close object, while mentally concentrating on another, far-away object, which will be out of focus. In your example, you are simply changing focus, which a camera lens can do, as well, albeit perhaps not as quickly.

The human eye can't focus a 3D object onto a 2D surface, either. The retina of your eye is two-dimensional, although it is not a plane. In order to focus on objects at different distances, the lens in the eye, as you point out, changes focal length (rather than focal distance) rapidly, but it is still true that not all 3D objects in your field of view are in focus simulataneously.

Try Adam's experiment in a dimly lit room and then again, outside in bright sunlight. Remember, do not allow your eye to change focus. Keep it focused on your finger in both cases, but mentally concentrate on the background. You should find that, outside, the background will be more in-focus than indoors.

To say that the human eye doesn't have bokeh (a term I personally hate) is hogwash.

And, in a camera lens, bokeh is not the result of a "flaw" in the lens. It is a fact of physics. To say it is a flaw implies that a really high-quality lens could achieve more DOF at the same aperture than a poor lens. That is simply not true. A good lens can have a more PLEASING bokeh than a cheap lens, but DOF is a mathematical function of the focal length, aperture and focus distance.

Just shoot at the smallest aperture you can, to achieve the greatest DOF. Of course, then, you risk diffraction. Again, diffraction isn't really a result of a flaw or defect, either. It happens because different light wavelengths bend differently as they pass the edge of the iris. This, too, is a fact of physics.

And, Rawhead, a pinhole is a lens, if you accept the definition of lens to be a device that focuses light. It is not a GLASS lens, but it still accomplishes the same function.

Last edited by noblepa; 09-22-2010 at 07:33 AM.
09-22-2010, 07:46 AM   #19
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QuoteOriginally posted by Lowell Goudge Quote
What about a fish eye lens?
That was my thought Lowell, My 8mm fisheye at F16 or above is certainly "Bokehless"

NaCl( it's interesting trying to focus it at that fStop)H2O

09-22-2010, 07:54 AM   #20
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Thanks Paul, nice explanation. As to the name "bokeh" I agree. My sister, who speaks and writes fluent Japanese says that "bokeh" is also Japanese slang for jet lag.

NaCl(a fact I find highly amusing)H2O
09-22-2010, 08:34 AM   #21
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QuoteOriginally posted by NaClH2O Quote
Thanks Paul, nice explanation. As to the name "bokeh" I agree. My sister, who speaks and writes fluent Japanese says that "bokeh" is also Japanese slang for jet lag.

NaCl(a fact I find highly amusing)H2O
LOL

The word "Bokeh" sounds like it should be used to to describe the gooey stuff that collects in the corner of your eyes.

When I'm badly Jet lagged my eyes suffer from intermittent vignetting:ugh: or in the extreme case totally leaving the lens caps on. :ugh:
09-22-2010, 12:35 PM   #22
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QuoteOriginally posted by violini Quote
I just bought K-x and K-7, both 2nd-hand. I am looking for a "bokehless" lens, i.e., a lens which has "infinite" depth of field. I would like to hear from the experienced photographers which Pentax lens approaches this ideal.

Bokeh or bocca is due to the defect of a lens system which is unable to focus all the 3-dimensional objects unto a 2-dimensional plane. Many photographers use this defect to isolate the subject from the background. Fortunately, human eyes do not have bokeh. Why can't they make camera lenses like human eyes?

My dog's eyes are like those "Limited" camera lenses with good bokeh; he could not see the rabbit 7' away in the grass, but he could smell it. The dog will see it until the rabbit starts to move.
Are you trolling?
09-22-2010, 04:43 PM   #23
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Generally the wider the focal length the wider the hyperfocal distance. The best I've ever used is the DA 15mm Limited. Very limited bending and a DOF from your feet (literally) to infinity at f-11 or so. I've never seen any lens that didn't suffer diffraction at f-22. They all reach a point of limited returns, but the 15mm can go to about f-16 without noticable diffraction. Even as Limiteds go, this is a very special lens.

09-22-2010, 06:43 PM   #24
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violini:

The focal length of the eye does not change, it is fixed. Remember, a lens's focal length is determined when it is focused at infinity. For a healthy eye (not far or near sighted) it is about 17mm. As the eye changes, this can change slightly, so here we are talking short term (day to day) not long term. What changes is the focus, it is the ULTIMATE auto focus! Current systems still cannot come close.

In the camera, to focus we move the lens element closer or further from the image plane. Since the lens in the human eye cannot move, the muscles squeeze the Sclera ( the back part of the eye's sphere) making the eye longer or shorter (mostly longer) to focus on objects closer than infinity.

Check out the following resources:

Geniet: Focal length and acuity of the human eye
The Human Eye
The Eye and Its Parts

And true, the human eye does have bokeh, but it also has great depth of field and the focus is so fast, by the time you try to look at the out of focus area, your eye has focused! When you reach about 40 or 50 years old, and try to focus on something close, like when you read, the bokeh becomes easier to perceive!

Regards, DA

Last edited by BigDave; 09-22-2010 at 06:49 PM. Reason: addition
09-22-2010, 07:04 PM   #25
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I think bokeh is so appealing because it sort of matches the DOF of the human mind. It's not just about how the eye focuses, but how the mind interprets the scene. When you look at your child's face, that's all you see. You concentrate upon it. That's what creamy bokeh does.
On the other end of the spectrum, I think a good landscape lens sees better than the human mind, because it records detail evenly, while the human eye must look around, concentrating here and there and there, to take it all in.
09-22-2010, 07:39 PM   #26
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QuoteOriginally posted by BigDave Quote
violini:

The focal length of the eye does not change, it is fixed. Remember, a lens's focal length is determined when it is focused at infinity. For a healthy eye (not far or near sighted) it is about 17mm. As the eye changes, this can change slightly, so here we are talking short term (day to day) not long term. What changes is the focus, it is the ULTIMATE auto focus! Current systems still cannot come close.

In the camera, to focus we move the lens element closer or further from the image plane. Since the lens in the human eye cannot move, the muscles squeeze the Sclera ( the back part of the eye's sphere) making the eye longer or shorter (mostly longer) to focus on objects closer than infinity.

Check out the following resources:

Geniet: Focal length and acuity of the human eye
The Human Eye
The Eye and Its Parts

And true, the human eye does have bokeh, but it also has great depth of field and the focus is so fast, by the time you try to look at the out of focus area, your eye has focused! When you reach about 40 or 50 years old, and try to focus on something close, like when you read, the bokeh becomes easier to perceive!

Regards, DA
I'm not an opthomologist, but I beg to differ. The human eye lens DOES change focal length. In fact, in the second link you offered, the author writes (see the section titled "Accomodation"): "You can change the focal length of your eye by using the muscles of your eye to change the curvature of the lens. "

In a camera, the focal length is fixed (let's limit ourselves to simple primes). We focus the lens by moving it nearer or further from the image (sensor or film) plane. When the object is at infinity (or at least very far away), the lens to sensor distance is equal to the focal length. In fact, that's the definition of FL. To focus on something closer, we move the lens away from the sensor.

In the human eye, the distance from the retina to the lens is fixed. The lens doesn't move toward/away from the retina. How then, do we focus on objects at different distances? By changing the focal length.

It doesn't take very much. Using the figure of 17mm given in several articles I found, and the ones you quoted, I calculated that, to focus on an object 1/2 meter away, the focal length must decrease to about 16.4mm. A 16.4mm lens that is 17mm from the sensor (retina), will be focused at an object closer than infinity.

BTW, the formula I used is: 1/id + 1/od = 1/F, where

id - the image distance (from lens to sensor/retina)

od - the object distance (from lens to object)

F - focal length.

Note that, as od gets larger and approaches infinity, the second term gets smaller and smaller and approaches zero. Therefore, we end up with 1/id = 1/F, or id = F, meaning that, when focused at infinity, the lens to sensor distance is equal to the FL. When id equals od, we have 1/id + 1/id = 1/F, or id = 2F. Anyone who's into macro photography knows that if you add 50mm of extension to a 50mm lens, you get 1:1 images and the object is 100mm from the lens.

And, you're right about the age thing. I'm 59 and I tried the experiment of focusing on my finger, held a foot in front of my face. Without my glasses, I simply couldn't do it.
09-23-2010, 02:30 AM   #27
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QuoteOriginally posted by noblepa Quote
And, in a camera lens, bokeh is not the result of a "flaw" in the lens. It is a fact of physics. To say it is a flaw implies that a really high-quality lens could achieve more DOF at the same aperture than a poor lens. That is simply not true. A good lens can have a more PLEASING bokeh than a cheap lens, but DOF is a mathematical function of the focal length, aperture and focus distance.
... and resolution. With infinite resolution (which my cameras don't have ) there would be zero DOF. The actual DOF depends on the pixel density in the sensor (and that of the printer or screen, if it's limiting) because you can't see a difference between the in-focus and the slightly-out-of-focus areas of the image if the pixel raster cannot differentiate between them.

And then there is the resolution of the spectator's eye: Depending on the viewing distance, there is an "acceptable circle of confusion" -- we won't see any degree of sharpness smaller than that. For analog photography where there is no fixed pixel pitch, the DOF table calculations are based on this.

Many compact cameras don't show a pleasant bokeh also because the IQ is lacking: the resolution is not fine enough to show a smooth transition from "sharp" to "blurred". And this can't be cured by more MP's alone...
09-23-2010, 06:17 AM   #28
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QuoteOriginally posted by Pentaxosaurus Quote
... and resolution. With infinite resolution (which my cameras don't have ) there would be zero DOF. The actual DOF depends on the pixel density in the sensor (and that of the printer or screen, if it's limiting) because you can't see a difference between the in-focus and the slightly-out-of-focus areas of the image if the pixel raster cannot differentiate between them.

And then there is the resolution of the spectator's eye: Depending on the viewing distance, there is an "acceptable circle of confusion" -- we won't see any degree of sharpness smaller than that. For analog photography where there is no fixed pixel pitch, the DOF table calculations are based on this.

Many compact cameras don't show a pleasant bokeh also because the IQ is lacking: the resolution is not fine enough to show a smooth transition from "sharp" to "blurred". And this can't be cured by more MP's alone...
High enough resolution is there in many modern compact camera sensors, but another limiting factor on top of your previous point is that their tiny lenses simply don't have the ability to open up to big apertures required to render big defocused blobs. By my estimation, f/2.8 on a P&S lens can sometimes be the equivalent of f/11 on a 135-format lens.

My eyes are short-sighted to -10 dioptres. I have no trouble rendering wonderful bokeh - I simply take my spectacles off! Problem is, it's all blurred beyond a few inches.
It could be said I have natural macro lenses...
09-23-2010, 06:43 AM   #29
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easy, use your kit lens at 18mm, f22, voila! DIE bokeh, DIE!
09-23-2010, 10:28 AM   #30
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I owned a Canon G11 before moving on to Pentax K-7. I've seen so many sample photos on the Internet taken with over thousand dollars lenses; these photos with partly sharp, partly blurred objects are really disturbing to me.
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