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Archive 2011 · Sony NEX-C3 first impressions

  
 
Ajay C
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p.3 #1 · p.3 #1 · Sony NEX-C3 first impressions


denoir wrote:
Ajay, I was referring to the diodes in the CFA that filter the light by wavelength. I assumed that they are diodes tuned to a wavelength anyway but I suppose it could be any type of semiconductor filter where the band gap is tuned to the desired wavelength. I perhaps used the term "photosite" incorrectly - I was referring to the whole thing, CFA filter included - not just the diode that measures light intensity and that comes after the filter.



There are no diodes in the CFA. CFA is the filter. And conventional silicon (CMOS) responds to visible spectrum. There are other semiconductor compounds (III-V) which respond to broader spectra but there are no such applications in commercial photography. Without the CFA, all photo diodes / pixels respond to light in the same way. So, the "tuning" is done by the CFA.


Shifting the CFA at the edges, would that really work? Wouldn't it mess up tele lenses that produce much smaller ray angles? Wouldn't we end up with the reverse situation with tele lenses producing color shifts? I know the M9's Kodak sensor uses that technique but it doesn't work all that well and I always assumed that they pushed it as far as they dared without sabotaging the output for normal and wide lenses.

Yes, it works rather effectively. When the CFA is shifted, it is not completely optimized for extreme ray angles. It just mitigates color cross talk for high ray angles. The formula used for shifting can be optimized for a "certain" range of ray angles.

Actually, looking at what you posted NEX-C3 might be a better sensor in terms of color cross talk than the M9 sensor (assuming NEX-C3 is not doing the correction in software).

They can't do it by software as different lenses produce different color casts and the C3 doesn't know which lens you've mounted when you are not using one of their lenses.


I never said anything about lenses . There are some hardware "tricks" which can detect color cross talk in the RAW data.


To a previous post by uhoh7, the sensor assembly, for most practical reasons is hermetically sealed. There are some layers of plastic / glass (IR cut, AA and other stuff) on the sensor. Even eye glass cleaning wipes will work. Don't put big scratches on top of the glass.



Jul 28, 2011 at 04:10 AM
AhamB
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p.3 #2 · p.3 #2 · Sony NEX-C3 first impressions


Ajay C wrote:
I never said anything about lenses . There are some hardware "tricks" which can detect color cross talk in the RAW data.


That's obviously not the method that the M9 uses (color shift mitigation is done based on lens coding).

The lack of color shift of the ZM18 on the NEX-3C is suprising, btw.



Jul 28, 2011 at 04:59 AM
denoir
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p.3 #3 · p.3 #3 · Sony NEX-C3 first impressions


Ajay C wrote:
There are no diodes in the CFA. CFA is the filter. And conventional silicon (CMOS) responds to visible spectrum. There are other semiconductor compounds (III-V) which respond to broader spectra but there are no such applications in commercial photography. Without the CFA, all photo diodes / pixels respond to light in the same way. So, the "tuning" is done by the CFA.


I know the photodiodes in the sensor are monochromatic but I assumed there was some form of semiconductor device doing the color filtering in the CFA. When I think about it however it wouldn't make sense as you are not interested in getting an electrical response to a wavelength at that point - you are just doing band pass filterering. So the CFA consists of tiny monochromators - i.e the filtering process is purely optical?

I don't think then that the CFA is the cause of the color shift. As you can see in the images above there is a clear asymmetry to it. You've got a red shift in one part of the image and a cyan shift in another. I could accept that you'd get a single color cast towards the edges if one of the filters (red for instance) was more sensitive to light coming at an oblique angle, but I can't see how on earth you'd get a global asymmetry to it.

At best I can see how you'd get a loss of definition towards the edges as light that was supposed to be captured by one photodiode leaks to the neigbour.


Yes, it works rather effectively. When the CFA is shifted, it is not completely optimized for extreme ray angles. It just mitigates color cross talk for high ray angles. The formula used for shifting can be optimized for a "certain" range of ray angles.


I really don't see how cross talk could account for the color shift. Not any type actually. The CFA induced one would affect things symmetrically. I don't see how the electrical crosstalk in the semiconductor could produce the effect either (i.e flow through the space between the well and the substrate). It has however been very long since I knew the semiconductor stuff adequately so I may have missed something completely.

I have however yet to come across an explanation for the asymmetry in the color shift.


I never said anything about lenses . There are some hardware "tricks" which can detect color cross talk in the RAW data.


Perhaps, but those tricks did apparently not work for the M9 or the older NEX cameras or color shift would have not been a problem in the first place...



Jul 28, 2011 at 05:36 AM
LightShow
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p.3 #4 · p.3 #4 · Sony NEX-C3 first impressions


I imagine DXO and/or DPR and/or Imaging Resource will get to the bottom of it all.

If the issue(a big if) is the light passing through the filter at high angle causing the light to separate into it's component colors, I wonder if it could be a coating that helps direct light at high angels towards the sensor, kind of like a reverse prism, or a thinner filter may help. just thinking out loud....



Jul 28, 2011 at 06:45 AM
denoir
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p.3 #5 · p.3 #5 · Sony NEX-C3 first impressions


Morfeus wrote:
I kind of read some excitement between the lines and some surprise, Luka. Am I wrong?


Heinz, the surprise is the lack of color shift, and I must admit it was a pleasant one.

I'm always excited about new gear as it usually encourages me to go out and shoot, but I can't say that it is more than that when it comes to this particular camera. It's nice, great value for money but there's no getting away from the fact that it's a live view only crop camera. There's really not much I can do with it that I can't do better with other gear that I already have.

Still, it doesn't change the fact that new toys are fun


LightShow wrote:
I imagine DXO and/or DPR and/or Imaging Resource will get to the bottom of it all.


Oh, I seriously doubt it unless Sony expressly tells them. Our best hope for an explanation here is Ajay who actually works with CMOS sensor design.



Jul 28, 2011 at 08:36 AM
Morfeus
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p.3 #6 · p.3 #6 · Sony NEX-C3 first impressions


Well, I just meant to say that I think it is surprisingly good for what it is (crop) and the price, Luka. Off course it is not a Leica.


Jul 28, 2011 at 10:08 AM
FlyPenFly
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p.3 #7 · p.3 #7 · Sony NEX-C3 first impressions


Great fun review, enjoyed reading it. I can't wait to see what the NEX7 brings.


Jul 28, 2011 at 10:14 AM
denoir
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p.3 #8 · p.3 #8 · Sony NEX-C3 first impressions


Morfeus wrote:
Well, I just meant to say that I think it is surprisingly good for what it is (crop) and the price, Luka. Off course it is not a Leica.


It's fantastic value for money, I agree. And as I said a comparison to the M9 is essentially ridiculous given the price difference between the two. However as I've chosen the NEX-C3 to be a backup camera, I have to make the comparison for myself and I might as well share the results. In absolute terms I think the C3 is a very good camera. I'll do some comparisons to the Canon 7D when I'm done with the M9 comparisons and I would not be surprised if the C3 came ahead.




Jul 28, 2011 at 10:16 AM
denoir
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p.3 #9 · p.3 #9 · Sony NEX-C3 first impressions


FlyPenFly wrote:
Great fun review, enjoyed reading it. I can't wait to see what the NEX7 brings.


Thanks. I'm sure the NEX7 will be quite good. I am a bit skeptical about the supposed 24 megapixel if the sensor is still ASP-C sized though. I've done some comparisons of the C3 to the M9 (I'll post the results soon) and my initial impression is that the 16 megapixel of the C3 is already pushing the boundaries of the useful.



Jul 28, 2011 at 10:20 AM
AhamB
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p.3 #10 · p.3 #10 · Sony NEX-C3 first impressions


LightShow wrote:
I imagine DXO and/or DPR and/or Imaging Resource will get to the bottom of it all


I kinda doubt that, since color shift most likely hasn't been an issue with the OEM lenses and I don't think those 3 that you mention do anything with adapting manual focus lenses in their tests.



Jul 28, 2011 at 10:25 AM
Ajay C
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p.3 #11 · p.3 #11 · Sony NEX-C3 first impressions


denoir wrote:
I know the photodiodes in the sensor are monochromatic but I assumed there was some form of semiconductor device doing the color filtering in the CFA. When I think about it however it wouldn't make sense as you are not interested in getting an electrical response to a wavelength at that point - you are just doing band pass filterering. So the CFA consists of tiny monochromators - i.e the filtering process is purely optical?


Correct, it is purely optical. All that CFA does is filter the light into one primary color (depending on the color of the cfa) - band pass + some attenuation. Loosely speaking, it is like sticking a red / blue / green filter in front of your lens.

I don't think then that the CFA is the cause of the color shift. As you can see in the images above there is a clear asymmetry to it. You've got a red shift in one part of the image and a cyan shift in another. I could accept that you'd get a single color cast towards the edges if one of the filters (red for instance) was more sensitive to light coming at an oblique angle, but I can't see how on earth you'd get a global asymmetry to it.

No CFA by itself will not cause color shift. Different hues are common. There is math to it but I'll try to explain in simple terms. For instance, take a pixel quad (2x2 - [Green, Red] and [Blue, Green] in the next row), and imagine white light rays coming in perfectly normal. CFA filters the light, and the corresponding pixels get excited, and produce an electrical response. i.e. all channels respond the same way and when pixel data is demosaiced, it is a perfect white response (assuming white balancing was done). Now imagine, light rays coming in at an oblique angle and the micro-lenses dead center on top of the pixel. All of a sudden, all the light that should be gathered by the pixels is - a. not going into the pixel (attenuated), b. some of it reflected around and goes into other neighboring pixels. If you read (a) and (b) carefully, the pixel response has changed and also the neighboring pixels are responding differently. Depending on the angle (and the side) at which light rays hit the pixel, different intensity of light can leak into neighboring pixels, and hence elicit different response. When this neighboring pixel data is used for further processing, and the same color gains (white balancing) are applied, it is not pure white but colored, and depends on which pixel (or a combination) had the best response to these light rays. The key to asymmetrical color shifts is the angle of the light rays itself. Hence the idea behind the shifted micro lenses is to reduce this "mischanneling" of the light at the edges of the optical array.

Not directly pertinent here, but take a look (search for spectral response) at a spectral response / QE curves of sensors. The long tail of a primary color also affects the other two colors. This would also cause color crosstalk and engineers try to reduce this response. i.e. make a better band pass filter.




Yes, it works rather effectively. When the CFA is shifted, it is not completely optimized for extreme ray angles. It just mitigates color cross talk for high ray angles. The formula used for shifting can be optimized for a "certain" range of ray angles.


Sorry my bad, i meant the micro-lenses, not the CFA. CFA is not shifted as the pixel centers remain the same through out the array.

I really don't see how cross talk could account for the color shift. Not any type actually. The CFA induced one would affect things symmetrically. I don't see how the electrical crosstalk in the semiconductor could produce the effect either (i.e flow through the space between the well and the substrate). It has however been very long since I knew the semiconductor stuff adequately so I may have missed something completely.

It is nothing to do with electrical cross talk on the IC.

I have however yet to come across an explanation for the asymmetry in the color shift.

Read above.



Perhaps, but those tricks did apparently not work for the M9 or the older NEX cameras or color shift would have not been a problem in the first place...


I am not surprised. Micro-lens shifting is relatively new for APS-C sized (and bigger pixel) sensors. Smaller pixels (like cell phone camera sensors) have much worse of a problem because of color crosstalk. The new NEX sensor could be using shifted micro-lenses, while the older one did not. Or perhaps that they just used a newer microlens architecture with the older pixel technology. Anyone's guess. This DPR / DXOmark can figure, unequivocally

Edited on Jul 28, 2011 at 10:30 AM · View previous versions



Jul 28, 2011 at 10:27 AM
joe88
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p.3 #12 · p.3 #12 · Sony NEX-C3 first impressions


Luka, can you post some sample shots with the 28Cron and 35Lux when you have some time? Thanks!


Jul 28, 2011 at 10:28 AM
douglasf13
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p.3 #13 · p.3 #13 · Sony NEX-C3 first impressions


Thanks for the test shots, Luka. Btw, did you focus the lens to infinity in those shots?


Jul 28, 2011 at 10:37 AM
denoir
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p.3 #14 · p.3 #14 · Sony NEX-C3 first impressions


Ajay C wrote:
No CFA by itself will not cause color shift. Different hues are common. There is math to it but I'll try to explain in simple terms. For instance, take a pixel quad (2x2 - [Green, Red] and [Blue, Green] in the next row), and imagine white light rays coming in perfectly normal. CFA filters the light, and the corresponding pixels get excited, and produce an electrical response. i.e. all channels respond the same way and when pixel data is demosaiced, it is a perfect white response (assuming white balancing was done). Now imagine, light rays coming in at an
...Show more

Thanks Ajay, but I still don't see how a global left/right asymmetry could arise. The angle hitting a microlens/photosite/pixel on the extreme left side will be exactly the same as one symmetrically on the extreme right side. So why is there a red hue on the left side and cyan hue on the right side?

joe88 wrote:
Luka, can you post some sample shots with the 28Cron and 35Lux when you have some time? Thanks!


Sure.


douglasf13 wrote:
Thanks for the test shots, Luka. Btw, did you focus the lens to infinity in those shots?


Yep, infinity focus in all cases.

Edited on Jul 28, 2011 at 10:42 AM · View previous versions



Jul 28, 2011 at 10:40 AM
AhamB
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p.3 #15 · p.3 #15 · Sony NEX-C3 first impressions


denoir wrote:
Thanks Ajay, but I still don't see how a global left/right asymmetry could arise. The angle hitting a microlens/photosite/pixel on the extreme left side will be exactly the same as one symmetrically on the extreme right side. So why is there a red hue on the left side and cyan hue on the right side?


I guess the color shift is asymmetric because the angle of incidence onto the RGBG quadruplets of the Bayer array varies across the whole sensor. The RGBG subpixel arrangement is the same all over the sensor, but depending on the direction the light is coming from, the light leakage must affect different subpixels. Makes sense?

Edited on Jul 28, 2011 at 11:05 AM · View previous versions



Jul 28, 2011 at 11:00 AM
denoir
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p.3 #16 · p.3 #16 · Sony NEX-C3 first impressions


Alright, time for some test results. As the NEX-C3 is supposed to serve as my backup camera for an M9, the comparisons are with an M9.


The lens used in all tests was the Zeiss 25/2.8 Biogon ZM. It holds the distinction of being the lens with highest recorded resolving power (400 lp/mm, MTF10) so it outresolves any existing sensor - a full frame sensor of over 500 megapixel would be required to make full use of the resolution of the lens.

Resolution

Full image M9:

http://peltarion.eu/img/comp/nex-m9/B_m9_full.jpg

Full image C3:
http://peltarion.eu/img/comp/nex-m9/B_c3_full.jpg


100% crops, center frame:
http://peltarion.eu/img/comp/nex-m9/B_crops.jpg

What would happen if we reduced the C3 image size to match the M9 FOV? I.e could you use the C3 as the equivalent of a tele converter, or are you better off just cropping an M9 file:

http://peltarion.eu/img/comp/nex-m9/B_crops_ds.jpg

Close, but no cigar. The C3 image was reduced to an 8 megapixel image to match the field of view and it isn't quite there. So perhaps 16 megapixel is a bit of an overkill, at least as far as resolution goes.


Latitude

Dynamic range in digital cameras is a complex issue that to a large degree will depend on the RAW development. So a more useful thing and more simple thing to look at is the latitude - i.e how much can you push or pull the exposure. The test scene is the same as above but I took one shot that was 2 stops over exposed and one that was 2 stops under exposed with each camera. The idea is to see how good it is at recovery.


Shadows

The M9 is quite good at recovering shadows and my hopes were that the C3 with its newer sensors could match it.


Full image M9:
http://peltarion.eu/img/comp/nex-m9/C_m9_full.jpg

Full image C3:
http://peltarion.eu/img/comp/nex-m9/C_c3_full.jpg


I then pushed the exposure two stops in the RAW developers. Here's a before/after shot of a dark region (~40% crops)

M9:

http://peltarion.eu/img/comp/nex-m9/c_m9.jpg

C3:
http://peltarion.eu/img/comp/nex-m9/c_c3.jpg

Quite good results. It looks like the C3 is a match for the M9 in that respect.

Highlights

I had very high hopes for the C3 for this. The M9 is terrible at recovering highlights. Given that my 5DII is quite good at it, I was expecting a lot for a more modern CMOS sensor.

M9:
http://peltarion.eu/img/comp/nex-m9/d_m9.jpg

C3:
http://peltarion.eu/img/comp/nex-m9/D_c3.jpg


I then pulled the exposure two stops in the RAW developers.

M9:
http://peltarion.eu/img/comp/nex-m9/D_m9_pull.jpg

C3:
http://peltarion.eu/img/comp/nex-m9/d_c3_pull.jpg

That was surprising and disappointing. Given that the M9 is not particularly good at this I had expected the C3 to be a lot better. It looks that like with the M9 one has to expose to preserve the highlights when shooting the C3, but even more so.



Jul 28, 2011 at 11:02 AM
denoir
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p.3 #17 · p.3 #17 · Sony NEX-C3 first impressions


AhamB wrote:
I guess the color shift is asymmetric because the angle of incidence onto the RGBG quadruplets of the Bayer array is different in each quadrant of the sensor. Some of the subpixels will be attenuated more and some will be excited more due to the light leakage caused by the obliquely incident light. The RGBG subpixel arrangement is the same all over the sensor, but depending on the direction the light is coming from, the light leakage must affect different subpixels. Makes sense?


The quadruplets are in series GRGBGRGBGRGBGRGBGRGBGRGB

So light hitting from the left side has the following possible transitions if it contaminates the neighboring pixel

R->G
G->B, G-R
B->G

and from the right side


R->G
G->R, G->B
B->G

So it's the same.

Edit: Corrected the transitions above.

Edited on Jul 28, 2011 at 11:25 AM · View previous versions



Jul 28, 2011 at 11:09 AM
douglasf13
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p.3 #18 · p.3 #18 · Sony NEX-C3 first impressions


Judging by the buildings, it looks to me like the nex was exposed more in the first place, in that last test.


Jul 28, 2011 at 11:13 AM
denoir
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p.3 #19 · p.3 #19 · Sony NEX-C3 first impressions


The M9 shot was exposed by a 1/3rd stop more in that shot if one goes by exposure values. There's a difference in dynamic range between the cameras and you have to remember that the different RAW developer do their bit on the "plain" image.


Jul 28, 2011 at 11:16 AM
JimBuchanan
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p.3 #20 · p.3 #20 · Sony NEX-C3 first impressions


denoir wrote:
Thanks Ajay, but I still don't see how a global left/right asymmetry could arise. The angle hitting a microlens/photosite/pixel on the extreme left side will be exactly the same as one symmetrically on the extreme right side. So why is there a red hue on the left side and cyan hue on the right side?


This is a most interesting thread. Thanks, Luka, for the work. I look forward to seeing test shots all processed by the same RAW converter, ie LR.

As far as the asymmetry of color shift, noted above, I thought I read an explaination that the Bayer array is not symetrical. Aside from the ratio of GRB being 2:1:1, the left side of a representative grid will have a different number of red than blue.

Note: Sorry for not keeping up with the posts, but I think I am on the same track as AhamB, in this regard.



Jul 28, 2011 at 11:26 AM
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