Mark Dubovoy's essay

[Antisthenes]

And it would be of great help if the two of you would act in a civil manner, use your own names rather than some pseudonym (as most of us do because of a general request last year), and provide some evidence of your scientific background.

A "great help" for whom ?
I happen to be, in real life, in a professional position such that having my name traceable to some random Internet forum would be against my own, and many other people's interests.

I also have the relevant degrees in science and professional experience thst qualify me to give me a reasoned opinion on the topic at hand.

That background also makes me immediately recognize the vacuous factoids and "logic" proferred by some people, who presume that they are sufficiently kowledgeable to dismiss DxO's and Mark Dubovoy's quite competent observations.  The presumption of such people can elicit, as you've seen, a fairly critical reaction from myself.

Should you think that you have a sufficient professional qualification to contest or disprove even a single one of the elements in my exposition, please be my guest.

[pegelli]

Maybe this discussion might get somewhere if you provided some data and evidence versus your current attitude of "I know it all and you guys don't"


Maybe this discussion might get somewhere if some people actually had experience with film-based photography and knew that with film, the diameter of an OOF disc is directly proportional to the lens' aperture.

Check, I do

Maybe this discussion might get somewhere if some people had a sufficient intellect to understand that when a digital sensor delivers an OOF disc whose diameter is less than what you'd get on film, that this necessarily implies that light rays are being lost — i.e. not recorded by the photosites.

Do you have any other evidence than the pictures on photozone.de to substantiate your claim that the oof disk at f1.2 on the 5DMkII is smaller than it would be on film? Because I don't think those pictures prove that.

[Antisthenes]

Do you actually read the information on the pages you're linking to ?

Yes. However, the part you seem to have difficulty with is that the rear element of the 85mm f/1.2 restricts (or is of equal size from the perspective of the sensor) the exiting cone of light. While not at the actual exit pupil distance, it would virtually act as a rear aperture if it wasn't dimensioned exactly right (that's why it's so large).

The part you seem to have difficulty with is that the half-angle of the light cone emitted by a lens is determined essentially by its aperture — i.e. the particular f-number setting of that lens, which isn't necessarily the lens' full open aperture.

If you don't believe me, let me quote from the very web page to which you provided the link:

"Indeed, at infinity focus the apical angle of the light cone that impinges upon the film is the same for all lenses at the same F-number"


The diameter of the rearmost element can restrict the light cone's apical angle, but does not determine it.

Furthermore, the position of that last element does not define the distance between the imaging plane and the exit pupil.

An accurate determination of the exit pupil position is required for your chief ray tilt angle calculations to have any semblance of reality.

As an example, a lens that is "telecentric" on the image side is one that has its exit pupil at a large, possibly infinite distance from the image plane.

In such a case, it is obvious that the tilt angle of the chief rays — which, from the sensor's point of view, emanate from the exit pupil — will exhibit almost no variation across the sensor's entire diagonal.
With your simplistic approach, you'd probably assign an entirely fictitious position to the exit pupil, resulting in a totally incorrect chief ray tilt angle behavior model.

To repeat, your strange fixation that the distance or diameter of the lens' last element are somehow relevant pieces of information to determine the exit pupil — a.k.a. virtual aperture — position as well as chief ray tilt angles is totally misguided, and your calculations are therefore meaningless.

[Antisthenes]

Do you have any other evidence than the pictures on photozone.de to substantiate your claim that the oof disk at f1.2 on the 5DMkII is smaller than it would be on film? Because I don't think those pictures prove that.

Will you please first provide some evidence that you've bothered to read and understand the contents of my posts — e.g. these sentences:

A simple way to assess the critical incidence angle — that is, the acceptance angle — above which the rays cannot be recorded anymore is thus to measure the diameter of the out of focus disc formed by a point source.

[..]

With some digital sensor designs, acceptance angles can be quite limited.  At some point, the linear relationship between the lens aperture and the OOF disc diameter recorded on the picture must then break down, as the tilted marginal rays cannot reach the photodiodes anymore.


Given that anybody with an APS or full-size DSLR and a f/1.2 or f/1.4 lens can verify that, even with the lens wide open, an OOF point lioght source appears at the center of the image as a perfect circle [blah]

That "anybody" in the above sentence also includes you, pegelli.

[pegelli]

Will you please first provide some evidence that you've bothered to read and understand the contents of my posts — e.g. these sentences:


That "anybody" in the above sentence also includes you, pegelli.

I do read and understand everything you write, it's no more than a qualitative description of what you are failing to quantify. I conclude from your remarks that the answer to my question is "no", which means your whole evidence is on shaky ground.

[Antisthenes]

I do read and understand everything you write, it's no more than a qualitative description of what you are failing to quantify. I conclude from your remarks that the answer to my question is "no", which means your whole evidence is on shaky ground.

Nope.  You think you understand, but the noetic reality is quite different.

You don't seem to be the sharpest tool in the drawer, so let me try to put you on the right track.

Me:
"If you were to hold an apple some distance above the ground, and let it go, it would fall towards the ground.  Anybody with an apple can verify that"

You:
"can you provide across the Internet some evidence that the apple would, as you assert, fall ?"

Me:
"well, anybody with access to an apple could verify it for himself if he/she bothered to read the description of that (trivial to perform) experiment'"

You:
"Your description is purely qualitative, and I conclude that you cannot provide, across the Internet, evidence that the apple would fall.  I won't bother to perform the experiment myself, and I conclude that your evidence is on shaky ground"

Me:
 

[b_z]

I refuse to use my real name on internet, sorry for that.

As for the background check, I'm still a student, in one of the best French scientific schools. Namely the Ecole Normale Superieure de Lyon, where I had Cedric Villani (one of this year Fields medalist) as a teacher and tutor. Obviously I'm not in an English major, but mathematics major and physic minor.

Pegelli, you're fighting against windmills.

[Antisthenes]

As for the background check, I'm still a student, in one of the best French scientific schools.

A good English word to describe your ilk is sophomoric

Obviously I'm not in an English major, but mathematics major and physic minor.

Tidbit: Besides my science background (my thesis advisor was a Nobel laureate, BTW), I happen to have a French minor, and judging by your prose, my French happens to be miles above your English skills...

[PierreVandevenne]

 Antisthenes said...

You don't seem to be the sharpest tool in the drawer, so let me try to put you on the right track.

Cough, cough, cough.

A good English word to describe your ilk is sophomoric

Hmmmm...

Tidbit: Besides my science background (my thesis advisor was a Nobel laureate, BTW), I happen to have a French minor, and judging by your prose, my French happens to be miles above your English skills...

Yeah, sure. Unsubstantiated ad hominem attacks.

Once more (parce que je pense que le franc n'est pas tombe...), I believe this is a place where real people, using their real names, enjoy disagreeing in a respectful way, a skill you have obviously not mastered.

[Antisthenes]

Once more (parce que je pense que le franc n'est pas tombe...), I believe this is a place where real people, using their real names, enjoy disagreeing in a respectful way, a skill you have obviously not mastered.

Should you think that you have a sufficient professional qualification to contest or disprove even a single one of the technical elements in my exposition, please be my guest.

Being respectful to others, in my book, includes refraining as much as possible from proffering ill-informed, ignorant opinions and judgments about a technical topic that demonstrate nothing more than the vacuity and presumption of the person behind them.

The problem with such people is that they are so ignorant that:

1) they don't even realize their ignorance about some particular technical topic

2) they can't recognize or appreciate the application of real knowledge.

In particular, a sure sign on photography-oriented forums identifying these conceited types is their criticism and summary judgment of some DxO-related methodology, even though they don't have a shred of an inkling of the qualification to really understand the issue at hand.

I have no connection with DxO whatsoever, other than being an occasional visitor of their site.
Still, I think I know enough about some domains germane to DxO's activities, including applied mathematics, physics and engineering to realize that the odds of some random bloke being right about some arcane technical topic, and DxO wrong, is vanishingly small.

DxO is of course not special, as the same thing can be said for any number of domains, including camera design, IT, law, economy, marketing, history, music, foreign relations, literature etc.

The day conceited ignoramuses become intelligent enough to appreciate the negligible odds of they having a better insight about a particular topic than the people, groups or companies that have cultivated real, specialized knowledge, ability and experience is the day this kind of tedious thread will disappear from the Internet.

Meanwhile, in technical, fact- and science-based topics, I don't think it's an entirely bad thing for some people to occasionally come across a person who doesn't tolerate fools gladly, and makes them realize the value of restraint and of thinking twice about whether their background really equips them to issue informed opinions and judgments.

[PierreVandevenne]

Posted by: Antisthenes 
Should you think that you have a sufficient professional qualification to contest or disprove even a single one of the technical elements in my exposition, please be my guest.

Tempting.

Posted by: Antisthenes
Considering the typical price, size and weight differentials between a f/1.2 and a f/1.4 lens, the fact that — when used on a DSLR like the Canon 5D2 — the effective speed of an f/1.2 lens, as well as its DoF and bokeh might be equivalent only to that of a f/1.5 lens is a quite relevant observation on a photo forum.

This is what you call a relevant fact. I happen to have a bunch of lense and can easily check if your facts are grounded in reality.

So here we go.



Can you spot the image that was shot at 1.2 on a Canon 5D MK II and can you spot the one that was shot at 1.6?

Any difference in depth of field and/or bokeh? Yeah, I though so.

Any photographer who has shot eyes at 1.2 and eyes at 1.6 knows what your reality is worth.

BTW, I shot this at 3200 iso, in poor lighting, because what can be seen is that the 1.2 image is noisier, which seems to indicate that the automatic gain boost that has already been observed has an impact on the quality of the image in extreme conditions (it can be measured on more normal exposures, but is not as obvious).

So that's it: a clear statement of fact in one of your messages doesn't appear to be connected with the real world.

While I don't rebreathe as many Nobel blessed oxygen molecules as you do, you'll easily understand I cast a doubtful eye on your digressions after that divergence.

PS: and yes, I found the text "knowing E we know everything" particularly well suited to the occasion. <G>

[pegelli]

You don't seem to be the sharpest tool in the drawer

You mean "sharp" as in 'con-artist', yep, there you outdo me but I have no problem with you being very proud of that.

Btw, interesting dissertation on the apple, your first doctorate was under Newton I guess?

Why don't you go here or here and add to your impressive scientific qualifications. Who knows, next time you might be two or three times as right as you are now.

 

[Christoph C. Feldhaim]

To whom it may concern:
The increasing ad hominem attacks in this thread start making reading it increasingly unpleasant ...
Please stop it.

<°)(((o><

[Bart_van_der_Wolf]

To whom it may concern:
The increasing ad hominem attacks in this thread start making reading it increasingly unpleasant ...

I agree.

And therefore, in an attempt to further the discussion in a more constructive direction, I've modified my initial diagram on the assumption that the Pupil Magnification effects at near infinity focus should not play a role. Hence I've attempted to determine the position of the exit pupil a bit more accurately as shown in the updated diagram:

Interestingly, the maximum angle of incidence has reduced from my more pessimistic diagam earlier. So the question becomes even more to the point; How hard is it for a microlens to cope with that? It would be nice to have some answers on that, rather than attempts to side track the discussion.

In fact, I think another issue may be more prominent, and potentially the reason why manufacturers attempt to compensate for such a small loss in the first place, and I've not seen it addressed before if I'm not mistaken:
The effect of reflecting light from the sensor's IR filter / cover-glass. While the protective layer is usually anti-reflection coated, it does still reflect a certain amount of light, and the coating introduces a color cast for more oblique rays of incident light.

Cheers,
Bart

[BJL]

So the question becomes even more to the point; How hard is it for a microlens to cope with that? It would be nice to have some answers on that, rather than attempts to side track the discussion.

Here is some data for green light at the center of the field for one Kodak sensor with micro-lenses, the 31MP 44x33 with 6.8 micron pixels used in the H3D-31 etc. See figure 6, page 15:
http://www.kodak.com/global/plugins/acrobat/en/business/ISS/datasheet/fullframe/KAF-31600LongSpec.pdf
It seems that at 27º, the sensitivity is off by a factor of 0.7: a loss of 30% or about 1/2 stop.

For comparison, in another Kodak sensor with the same 6.8 micron pixel design but no microlenses (the 48x36mm 39MP KAF-39000) the loss is only about 10% at 27º and increases to 30% only at 40º: see figure 8, page 15 of
http://www.kodak.com/global/plugins/acrobat/en/business/ISS/datasheet/fullframe/KAF-39000LongSpec.pdf

In fact, I think another issue may be more prominent, and potentially the reason why manufacturers attempt to compensate for such a small loss in the first place, and I've not seen it addressed before if I'm not mistaken:
The effect of reflecting light from the sensor's IR filter / cover-glass.

An interesting thought: the split between reflection and transmission increases as the angle of incidence increases, so that could also be a factor. But I suspect it is a smaller factor than the micro-lens effect: a table on page 28 of the above document suggests that cover glass reflection is less than 2%. Even if that is for the best case of perpendicular incidence, refection losses at 27º seem unlikely to be near the above 30% figure. I suppose that with some reasonable assumptions on the refractive index of the cover glass, one could compute the reflection/transmission fractions as a function of incident angle from basic optics formulas, but I am too lazy to look that stuff up.

[sandymc]

Here is some data for green light at the center of the field for one Kodak sensor with micro-lenses, the 31MP 44x33 with 6.8 micron pixels used in the H3D-31 etc. See figure 6, page 15:
http://www.kodak.com/global/plugins/acrobat/en/business/ISS/datasheet/fullframe/KAF-31600LongSpec.pdf
It seems that at 27º, the sensitivity is off by a factor of 0.7: a loss of 30% or about 1/2 stop.

For comparison, in another Kodak sensor with the same 6.8 micron pixel design but no microlenses (the 48x36mm 39MP KAF-39000) the loss is only about 10% at 27º and increases to 30% only at 40º: see figure 8, page 15 of
http://www.kodak.com/global/plugins/acrobat/en/business/ISS/datasheet/fullframe/KAF-39000LongSpec.pdf

Kodak wrote up their experiences with those sensors, and specifically addressed addressed the microlens question. The article is here (warning: highly technical): http://wwwcafr.kodak.com/global/plugins/acrobat/en/business/ISS/supportdocs/31Mp_and_39Mp_Full-Frame_CCD_paper.pdf

There's also a less technical Dalsa article here: http://www.dalsa.com/public/dc/documents/Image_Sensor_Architecture_Whitepaper_Digital_Cinema_00218-00_03-70.pdf

If you access to SPIE, there's also the Catryse/Liu/El Gamal article "QE Reduction due to Pixel Vigneting in CMOS Image Sensors"; I don't have a download location for that.

Long and the short of it - microlens efficiency depends on a LOT of things

Sandy

[Bart_van_der_Wolf]

Here is some data for green light at the center of the field for one Kodak sensor with micro-lenses, the 31MP 44x33 with 6.8 micron pixels used in the H3D-31 etc. See figure 6, page 15:
http://www.kodak.com/global/plugins/acrobat/en/business/ISS/datasheet/fullframe/KAF-31600LongSpec.pdf
It seems that at 27º, the sensitivity is off by a factor of 0.7: a loss of 30% or about 1/2 stop.

Thanks for that document. BTW, 70% is 1/3rd of a stop loss if I'm not mistaken. However, the way I interpret that figure 6 on page 15 is that they're talking about full diagonal performance. In the center of the sensor array (where the DxO measurements are taken) there is no significant loss. That means that any automatic correction in gain will lead to relative overexposure in the center. I know we're talking about a small correction, but then why bother at all and confuse matters? Afterall, it's a minor correction compared to the vignetting and light fall-off (some 1.8 stops on a 5D2 at f/1.2)! The distance to the corner of a 24x36mm sensor is onlly 21.6 mm, so the angle of the center rays hit the sensor at an angle of some 20 degrees (if my estimate of the exit pupil position is correct).

I would agree that such a (gain, or exposure) correction is best left to the photographer. Some photographers do know what they're doing, and don't shoot on P-mode only (some even bracket to optimize output  ).

For comparison, in another Kodak sensor with the same 6.8 micron pixel design but no microlenses (the 48x36mm 39MP KAF-39000) the loss is only about 10% at 27º and increases to 30% only at 40º: see figure 8, page 15 of
http://www.kodak.com/global/plugins/acrobat/en/business/ISS/datasheet/fullframe/KAF-39000LongSpec.pdf

Which demonstrates that different designs (this one doesn't have the surrounding buffer and light shielded pixels around each sensel) achieve different results. There are too many design differences to only attribute it to the microlenses.

An interesting thought: the split between reflection and transmission increases as the angle of incidence increases, so that could also be a factor. But I suspect it is a smaller factor than the micro-lens effect: a table on page 28 of the above document suggests that cover glass reflection is less than 2%. Even if that is for the best case of perpendicular incidence, refection losses at 27º seem unlikely to be near the above 30% figure.

It's hard to say how much of an effect the individual components contribute to the resulting cumulative effect graphs without comparing with a coverglass-less version.

Cheers,
Bart

[pegelli]

To whom it may concern:
The increasing ad hominem attacks in this thread start making reading it increasingly unpleasant ...
Please stop it.

<°)(((o><

Christoph, you're right and I'm sorry. But after so many personal attacks and insults to several members (incl. myself) it felt good just to vent back. Won't happen again if this remains a respectful technical discussion.

Let me try to make up to you and the other respectful forum members by adding another technical observation. If you look at the diameter ratio of the out of focus circles at the different apertures on photozone.de my conclusion is that even if you assume these are from an infinitely small point light source the lens at f1.2 has an out of focus circle that would correspond with an ~f1.4 image (so already better than the f1.5 that was claimed). Since the out of focus highlight is probably not infinitely small   (but a diameter of maybe something like 10-15% of the out of focus circle) the ratio of the circles of confusion points more to something like between ~f1.2 and ~f1.3. So it seems the magnitude and impact is much smaller as some want us to believe, if at all there. Obviously these are estimations based on hand measurement of out of focus circles that were not in the middle of the frame, so it's probably best to wait with definite conclusions until the additional DxO measurements as promised in Mark Dubovoy's article are available. However my calculations are in line with Pierre Vandevenne's test as well as BartvanderWolf's updated diagram, so I'm looking forward to see more from DxO in the future and get to the bottom of this issue.    

[PierreVandevenne]

Just to summarize the findings so far, from a practical point of view

- there is indeed a "hidden" gain (ISO) boost at wide apertures, 1.2 and to a lesser extent at 1.4. This is both measurable and visible in some conditions such as low light and high ISO for 1.2.

as far as photography is concerned, using 1.2 and 3200 ISO is rarely a creative choice. If you do it, you need to do it and can live with somewhat suboptimal quality.

- the 1.2 lenses are not as good wide open as they are stopped down. But that's hardly unexpected...

- bokeh and dof appear to behave as expected. Used in the conditions, 1.2 does provide a shallower DoF than 1.4, 1.6 and obviosuly 1.8. The Canon 85mm 1.8 and the 50mm 1.4 are excellent deals from a price/quality point of view, but not to the point that they perform identically to their higher priced siblings.

[BJL]

Thanks for that document. BTW, 70% is 1/3rd of a stop loss if I'm not mistaken. However, the way I interpret that figure 6 on page 15 is that they're talking about full diagonal performance.

A few comments.

1. Stops are a logarithmic/power scale, so 70% is half a stop (as 50% is one stop). A one stop decrease in illumination is a factor of 1/2 in light, so a half stop increase is the square root of that, or sqrt(0.5) or about 0.7.

2. The caption says that these are measurements at the center of the sensor:
"Normalized Angle QE at the center of the sensor under green LED illumination."
With low f-stops, there is a reduced sensitivity to light at the outside edges of the broad light cone everywhere, though the problem gets worse towards the edges. So correcting for the part of the sensitivity loss experienced everywhere including at the center while leaving the additional off-center effect to lost-processing correction makes sense.

3. It has been said in a great many places that micro-lenses, in the usual designs, decrease the acceptance angle, and that this is the dominant reason that MF sensors almost never have micro-lenses, despite the penalty in low-light performance from omitting them. Those other design differences you an Kodak mention, like the narrower "windows", are there purely for the sake of the use of micro-lenses, being necessitated by the micro-lenses, to avoid cross talk (light entering through one CFA but then getting counted in a neighboring photosite). This cross-talk is worse with microlenses (though also present without) because some light gets bent even more off-perpendicular by the microlenses. This is discussed nicely in the papers that sandymc mentions above (thanks sandymc!)

But to put it simply: Kokak acknowledges the problems cuased by the worse off-perpendicular sensitivity of its sensors with microlenses (uses strategies like off-set microlesnes to mitigate the effect), and so if Kodak could reduce this disadvantage of it sensors with microlenses by changing other details like the masking to be more like in its sensors without micro-lenses, surely Kodak would do it! Any worsening of off-perpendicular sensitivity in can only be explained as something necessitated by the design needed when micro-lenses are present.

I could dig up a Dalsa reference on microlenses reducing acceptance angle if you want: Dalsa has a new approach where the microlenses are far closer to the wells, which essentially eliminates the off-perpendicular" disadvantage. Or to paraphrase what Kodak says about its sensors without microlenses, the effect is about equal in magnitude to the cos^4 effect in play with any sensor, including film. So the effect is far worse than "cos^4" with Kodak's microlensed sensors!